Civil Engineering Glossary: Terms Property Owners Ask About

1

100-year flood (base flood): The 100-year flood, or base flood, is the flood with a 1% chance of being equaled or exceeded in any year. Over a 30-year mortgage that is about a 26% chance of at least one such flood.See also: Base flood elevation (BFE), Return period (design storm), Special Flood Hazard Area

8

811 (call before you dig): 811 is the national number to request free marking of underground utility lines before digging. Most states require a call at least two to three business days before excavation, and the locators mark lines with colored paint and flags.See also: Subsurface utility engineering (SUE)

A

AASHTO: AASHTO, the American Association of State Highway and Transportation Officials, publishes the standards used for roads and bridges in the US, including the Green Book for geometric design and the LRFD Bridge Design Specifications. State DOTs and many cities base their street standards on AASHTO.See also: Superelevation, Sight distance
ACI 318: ACI 318 is the American Concrete Institute's Building Code Requirements for Structural Concrete. It governs the design and detailing of concrete members, including strength, reinforcement, cover and durability, and is adopted by the IBC.See also: IBC (International Building Code), Concrete cover, Rebar
ADA (Americans with Disabilities Act): The ADA is the federal civil rights law that requires public accommodations and public facilities to be accessible. For site work, the 2010 ADA Standards limit slopes on accessible routes (5% running slope, 2% cross slope), ramps (8.33%) and accessible parking, and require curb ramps with detectable warnings.See also: Accessible route, Curb ramp, Cross slope
ALTA/NSPS survey: An ALTA/NSPS Land Title Survey is a detailed boundary survey prepared to national standards for commercial real estate transactions. It shows boundaries, easements, improvements, access and other items tied to the title commitment, and lenders and title insurers often require it.See also: Boundary survey, Easement, Professional land surveyor
ASCE 7: ASCE 7, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, is the American Society of Civil Engineers standard that defines the dead, live, snow, wind, flood and earthquake loads a structure must be designed for. The IBC adopts it by reference.See also: IBC (International Building Code), Live load, Dead load, Wind load, Seismic design category
Accessible route: An accessible route is a continuous path that a person in a wheelchair can use to reach a building entrance from parking, sidewalks and transit stops. Under the ADA Standards it has a running slope of no more than 1:20 (5%) unless built as a ramp, and a cross slope of no more than 1:48 (about 2%).See also: ADA (Americans with Disabilities Act), Curb ramp, Cross slope
Aggregate base: Aggregate base is a compacted layer of graded crushed stone placed under pavement or slabs to spread loads and provide drainage. State DOT specifications define gradations such as dense-graded aggregate base.See also: Pavement section, Subgrade
Air entrainment: Air-entrained concrete contains billions of microscopic air bubbles, created by an admixture, that give freezing water room to expand. It is required for exterior concrete exposed to freeze-thaw cycles and deicing salts.See also: Concrete mix design
Anchor bolt: An anchor bolt is a bolt cast into or installed in concrete to attach a sill plate, column base plate or equipment to the foundation. Size, spacing and embedment are specified on the structural drawings.See also: Hold-down, Uplift
As-built drawings: As-built drawings (record drawings) show how a project was actually built, including changes made in the field and the final locations and elevations of utilities. Many agencies require surveyed as-builts before accepting public improvements or releasing bonds.See also: Construction documents, Invert elevation
Asphalt pavement: Asphalt pavement (hot mix asphalt, or flexible pavement) is aggregate bound with asphalt binder, placed and compacted hot in one or more lifts. It is cheaper initially than concrete and is the most common US road surface.See also: Pavement section, Concrete pavement, Aggregate base
Atterberg limits: Atterberg limits are lab tests that measure the water contents at which a fine-grained soil changes behavior: the liquid limit, where it starts to flow, and the plastic limit, where it becomes moldable. They are used to classify clays and silts and predict swelling.See also: USCS (Unified Soil Classification System), Expansive soil

B

BMP (best management practice): A best management practice is a measure used to prevent or reduce stormwater pollution, either structural (ponds, silt fence, inlet filters) or non-structural (street sweeping, good housekeeping). Permits and SWPPPs list the BMPs required on a site.See also: SWPPP (stormwater pollution prevention plan), Erosion and sediment control, Green infrastructure
Backflow preventer: A backflow preventer is a valve assembly that stops water from flowing backward from a property into the public water system, protecting it from contamination. Irrigation, fire sprinkler and commercial services usually require one, with annual testing.See also: Water main
Base flood elevation (BFE): The base flood elevation is the elevation the 1% annual chance flood is expected to reach, shown on FEMA maps for zones such as AE. It is the starting point for setting minimum floor elevations in flood zones.See also: Zone AE, Freeboard, Elevation certificate
Beam: A beam is a horizontal member that carries loads across an opening by bending, transferring them to columns or walls. Common beams are wood joists and headers, steel wide-flange beams and reinforced concrete beams.See also: Deflection
Bearing capacity: Bearing capacity is the ability of soil to support the pressure from a foundation without failing in shear. Engineers design with an allowable bearing pressure, which applies a safety factor and also limits settlement.See also: Presumptive bearing value, Settlement, Spread footing
Benchmark: A benchmark is a fixed point with a known, recorded elevation used as the reference for a survey or for construction staking. Projects state which vertical datum the benchmark is based on, usually NAVD 88.See also: Topographic survey, Construction staking
Berm: A berm is a raised mound or ridge of earth. Berms are used to direct stormwater, form the sides of a pond, screen views or reduce noise.See also: Swale, Detention pond
Bioretention (rain garden): Bioretention is a planted depression with engineered soil that captures runoff, filters it through plants and soil, and either infiltrates it or discharges it through an underdrain. A residential rain garden is a small version.See also: Bioswale, Green infrastructure, Underdrain
Bioswale: A bioswale is a swale designed to treat stormwater, with plants and engineered soil that filter pollutants and allow infiltration. It is a common green infrastructure practice.See also: Swale, Green infrastructure, BMP (best management practice)
Boundary survey: A boundary survey locates and marks a property's corners and lines based on the deed, plats and field evidence. It shows improvements near the lines and any encroachments, and it is often needed before building close to a setback.See also: Professional land surveyor, Property line, Encroachment
Building permit: A building permit is the approval a local building department issues before construction begins, confirming the plans meet the adopted building code. Permits are followed by inspections at set stages, and the work is closed out with a final inspection or certificate of occupancy.See also: Certificate of occupancy, IBC (International Building Code)

C

CBR (California Bearing Ratio): The California Bearing Ratio is a test that compares a soil's resistance to penetration with that of a standard crushed rock. It is used to rate subgrade and base strength for pavement design; soft clays may be below 5, good crushed stone 80 or more.See also: Subgrade, Pavement section
CMU (concrete masonry unit): A concrete masonry unit is a precast concrete block, commonly 8 by 8 by 16 inches nominal. Reinforced CMU walls have vertical rebar in grouted cells and are used for foundations, retaining walls and commercial buildings.See also: Rebar, Retaining wall
Catch basin: A catch basin is a storm drain inlet with a grate or curb opening that collects surface water from streets and parking lots. Many include a sump below the outlet pipe to trap sediment and debris.See also: Storm drain, Storm inlet
Certificate of occupancy: A certificate of occupancy (CO) is the document a building department issues when a building has passed final inspections and may legally be occupied. Lenders and buyers often require it, and utilities may not be permanently connected without it.See also: Building permit
Change order: A change order is a written amendment to a construction contract that changes the scope, price or schedule. Unforeseen site conditions, design changes and owner requests are common causes.See also: RFI (request for information), Differing site conditions
Civil drawings: Civil drawings, or civil plans, are the sheets in a construction set that cover site work: demolition, grading, drainage, utilities, paving, erosion control and details. They are prepared and sealed by a civil engineer.See also: Site plan, Grading plan, Utility plan
Clearing and grubbing: Clearing and grubbing is removing trees, brush, stumps, roots and debris from a site before grading. Grubbing specifically means pulling out stumps and roots so organic material is not left under fill or pavement.See also: Topsoil stripping, Earthwork
Compaction: Compaction is densifying soil with rollers, plates or tampers to increase strength and reduce settlement. Specifications usually require fill to reach a percentage, such as 95%, of the maximum dry density from a Proctor test, placed in thin lifts near optimum moisture.See also: Proctor test, Field density test, Engineered fill
Concrete compressive strength (f'c): Specified compressive strength, written f'c, is the strength in psi that concrete must reach, normally at 28 days. Residential concrete is often 2,500 to 3,000 psi, while structural and exterior work commonly uses 4,000 psi or more.See also: Concrete cylinder test, Concrete mix design
Concrete cover: Concrete cover is the thickness of concrete between the outside surface and the nearest reinforcing steel. ACI 318 requires 3 inches where concrete is cast against soil, 1-1/2 to 2 inches for formed surfaces exposed to weather or earth, and 3/4 inch for interior slabs and walls with #11 bars and smaller.See also: Rebar, ACI 318
Concrete cylinder test: Cylinder tests check concrete strength. Technicians cast samples from the truck into cylinders, cure them, and break them in a lab at set ages (often 7 and 28 days) to confirm they meet the specified f'c.See also: Concrete compressive strength (f'c), Slump, Special inspection
Concrete mix design: A mix design is the recipe for a concrete mix, giving the amounts of cement, supplementary materials, water, aggregates and admixtures to meet the specified strength, slump, air content and durability. It is submitted by the ready-mix supplier for the engineer's review.See also: Water-cement ratio, Concrete compressive strength (f'c), Slump
Concrete pavement: Concrete (rigid) pavement is a portland cement concrete slab, jointed or continuously reinforced, used for highways, heavy truck areas and dumpster pads. It costs more up front than asphalt but lasts longer under heavy loads.See also: Asphalt pavement, Control joint
Construction documents: Construction documents are the final drawings and specifications used to permit, bid and build a project. They are more detailed than schematic or design development plans and must be complete enough for a contractor to price and build from.See also: As-built drawings
Construction staking: Construction staking is the surveyor's work of setting stakes and marks in the field that show contractors where to build and to what elevation, for example building corners, curb lines, pipe locations and grades.See also: Benchmark
Contour line: A contour line on a map connects points of equal elevation. Lines close together mean steep ground; lines far apart mean flat ground. Grading plans show existing contours dashed and proposed contours solid.See also: Topographic survey, Grading plan, Spot elevation
Control joint: A control (contraction) joint is a groove cut or tooled into a slab so that the cracks concrete naturally develops as it shrinks form in a straight line at the joint. Spacing is commonly 2 to 3 times the slab thickness in inches, expressed in feet (for example 8 to 12 feet for a 4 inch slab).See also: Slab on grade
Cross slope: Cross slope is the slope across a road or sidewalk perpendicular to the direction of travel, which drains water off the surface. Roads typically use about 1.5% to 2%, and ADA accessible routes are limited to 1:48 (about 2%).See also: Superelevation, ADA (Americans with Disabilities Act)
Culvert: A culvert is a pipe or box structure that carries a stream or drainage ditch under a road, driveway or embankment. It must be sized for the design flood so water does not overtop the road or back up onto adjacent property.See also: Headwall, Invert elevation, Riprap
Curb and gutter: Curb and gutter is the concrete edge of a street that combines a raised curb with a gutter pan. It defines the roadway edge, protects the sidewalk area and channels stormwater.See also: Gutter, Curb ramp
Curb ramp: A curb ramp is the short sloped section that connects a sidewalk to the street at a crossing. ADA rules limit its slope to 1:12 (8.33%) and require detectable warning surfaces, the bumpy tactile panels, at the street edge.See also: ADA (Americans with Disabilities Act), Accessible route
Curve number (CN): The curve number is a parameter in the NRCS (formerly SCS) runoff method that reflects land use and hydrologic soil group. Higher numbers (up to 98 for pavement) mean more runoff.See also: Hydrograph
Cut and fill: Cut is soil removed to lower the ground; fill is soil placed to raise it. Engineers try to balance cut and fill on a site so soil does not have to be hauled in or out, which saves money.See also: Earthwork, Grading plan, Engineered fill

D

Dead load: Dead load is the permanent weight of the structure itself and fixed items, such as framing, floors, roofing, walls and permanent equipment.See also: Live load, ASCE 7, Load path
Dedication: Dedication is the transfer of land or improvements from a private owner to a public agency, for example dedicating right-of-way for a street widening or a new road built in a subdivision. It is usually done on a plat or by a recorded deed.See also: Right-of-way, Plat, Public improvements
Deep foundation: A deep foundation carries loads through weak upper soil to stronger soil or rock, using driven piles, drilled shafts (caissons), auger-cast piles or helical piles. It is used where shallow footings would settle too much or lack capacity.See also: Helical pier, Foundation, Ground improvement
Deflection: Deflection is how much a beam, joist or slab sags under load. Codes limit deflection (for example span/360 for floors under live load) to prevent bouncy floors and cracked finishes, even when the member is strong enough.See also: Beam, Live load
Detention pond: A detention pond (dry pond) temporarily stores stormwater during a storm and releases it slowly through a control structure, so downstream flows do not increase. It is normally dry between storms.See also: Retention pond, Detention vs retention, Outlet control structure
Detention vs retention: Detention holds stormwater temporarily and releases it at a controlled rate, so the facility drains dry. Retention keeps water permanently, either as a wet pond or by infiltrating it into the ground, and does not release the stored volume downstream. Local codes sometimes use the terms differently, so check the definitions in the drainage manual.See also: Detention pond, Retention pond, Infiltration
Dewatering: Dewatering is lowering groundwater or removing water from an excavation so work can proceed in the dry, using sumps, well points or deep wells. Discharge of the pumped water may need a permit.See also: Groundwater table, Shoring
Differential settlement: Differential settlement is uneven settlement between different parts of a structure. It causes cracked walls and slabs, sticking doors and sloping floors, and is a common cause of foundation repair.See also: Settlement, Underpinning
Differing site conditions: Differing site conditions are physical conditions found during construction that differ materially from what the contract documents indicated or what would normally be expected, such as rock, groundwater or buried debris. Many contracts allow extra time and cost for them, which is one reason soil borings are done before bidding.See also: Change order, Geotechnical report, Soil boring
Drainage easement: A drainage easement reserves a strip of land for stormwater to flow or for a pipe, swale or pond, and often gives the city a right to access it. Owners typically cannot fill, fence or build in it in a way that blocks the flow.See also: Easement, Swale, Detention pond
Driveway permit: A driveway permit (curb cut permit or access permit) authorizes a new or modified connection from private property to a public road. The agency reviews location, width, spacing from intersections, sight distance and drainage.See also: Encroachment permit, Sight triangle, Right-of-way

E

Earthwork: Earthwork is the excavation, hauling, placement and compaction of soil and rock on a construction site. It is usually priced by the cubic yard, and quantities are calculated by comparing existing and proposed surfaces.See also: Cut and fill, Compaction
Easement: An easement is a legal right to use part of someone else's property for a specific purpose, such as a utility line, drainage channel or shared driveway. The owner keeps title, but generally cannot build in a way that blocks the easement holder's use. Easements are recorded with the deed or plat and show up in a title search.See also: Right-of-way, Utility easement, Drainage easement, Plat
Elevation certificate: A FEMA Elevation Certificate is a form completed by a surveyor or engineer that documents a building's flood zone and key elevations, such as the lowest floor, compared with the base flood elevation. It is used to rate flood insurance and prove compliance.See also: Base flood elevation (BFE), LOMA and LOMR
Encroachment: An encroachment is a structure or improvement that extends across a property line, setback or easement, such as a fence, driveway or building corner on a neighbor's land. A boundary survey is the usual way to find one.See also: Boundary survey, Property line, Easement
Encroachment permit: An encroachment permit (also called a right-of-way or street opening permit) authorizes private work in a public right-of-way, such as a driveway apron, utility connection or sidewalk replacement. The agency sets requirements for traffic control, restoration and inspection.See also: Right-of-way, Traffic control plan
Engineer of record: The engineer of record is the licensed engineer who sealed the design documents for a project and is responsible for that design. Questions, changes and substitutions that affect the design go back to this engineer for review.See also: PE stamp, RFI (request for information)
Engineer's letter: An engineer's letter is a sealed letter in which a licensed engineer documents an observation or opinion, for example that a foundation repair was completed per design, that existing framing can carry a new load, or that damage is or is not structural. Lenders, buyers and building departments often request one.See also: PE stamp, Structural inspection
Engineered fill: Engineered (structural) fill is soil of approved type placed in controlled lifts and compacted and tested under the observation of a geotechnical engineer, so it can support foundations or pavement. Undocumented fill has no such record and is usually removed or evaluated.See also: Compaction, Cut and fill
Entitlements: Entitlements are the land use approvals needed before a property can be developed for a specific purpose, such as rezoning, subdivision approval, site plan approval and variances. Securing entitlements often comes before construction permits.See also: Zoning, Subdivision, Site plan
Erosion and sediment control: Erosion control keeps soil in place (mulch, seeding, blankets), and sediment control traps soil that has already eroded (silt fence, sediment basins, inlet protection). Both are required on disturbed construction sites.See also: Silt fence, Stabilized construction entrance, SWPPP (stormwater pollution prevention plan), Hydroseeding
Expansive soil: Expansive soils are clays that swell when wet and shrink when dry, lifting and cracking slabs, foundations and pavements. Treatment includes removal and replacement, moisture control, lime stabilization and foundations designed for the movement.See also: Atterberg limits, Post-tensioning

F

FEMA flood zone: FEMA flood zones are areas mapped on Flood Insurance Rate Maps by flood risk. Zones beginning with A or V are Special Flood Hazard Areas, the 1% annual chance floodplain, where federally backed mortgages require flood insurance and local floodplain rules apply. Zone X is outside that area.See also: FIRM (Flood Insurance Rate Map), Zone AE, Special Flood Hazard Area
FIRM (Flood Insurance Rate Map): A Flood Insurance Rate Map is FEMA's official map of flood zones and base flood elevations for a community. Current maps are available on the FEMA Flood Map Service Center.See also: FEMA flood zone, Base flood elevation (BFE), LOMA and LOMR
Field density test: A field density test checks whether placed fill has reached the specified compaction, usually with a nuclear density gauge or sand cone. Results are reported as a percentage of the Proctor maximum dry density.See also: Compaction, Proctor test, Special inspection
Finished floor elevation (FFE): Finished floor elevation is the design elevation of the top of a building's ground floor. It is set so the floor is above surrounding grade and, in flood zones, at or above the required flood elevation.See also: Grading plan, Base flood elevation (BFE), Freeboard
Finished grade: Finished grade is the final ground surface elevation after all grading, topsoil and paving are complete. Codes generally require finished grade to slope away from a building foundation.See also: Grading plan, Positive drainage, Subgrade
Fire flow: Fire flow is the amount of water, in gallons per minute at a residual pressure of 20 psi, that must be available for firefighting at a site. The fire code sets the required flow by building size and construction type, and a hydrant flow test confirms what the system delivers.See also: Water main
Floodway: The regulatory floodway is the channel and adjacent land that must be kept free of obstructions so the base flood can pass without raising flood heights more than a set amount. Development in a floodway generally requires a no-rise certification from an engineer.See also: No-rise certification, Special Flood Hazard Area
Foundation: A foundation is the part of a structure that transfers its loads into the ground. Shallow foundations (footings and slabs) bear near the surface; deep foundations (piles, piers and drilled shafts) carry loads down to stronger soil or rock.See also: Spread footing, Deep foundation, Bearing capacity
Foundation drain: A foundation drain, or footing drain, is a perforated pipe placed beside the footing and surrounded by gravel to collect groundwater and relieve water pressure against basement walls. It discharges to daylight, a storm drain or a sump pump.See also: French drain, Foundation waterproofing
Foundation waterproofing: Foundation waterproofing is a membrane or coating on the outside of basement walls that prevents water penetration under hydrostatic pressure. Dampproofing is a lighter coating that resists only soil moisture; codes require waterproofing where a high water table exists.See also: Foundation drain, Hydrostatic pressure
Freeboard: Freeboard is an added margin of height above a required flood level, such as one or two feet above the base flood elevation for a building floor, or the height of a pond embankment above its maximum water level.See also: Base flood elevation (BFE), Finished floor elevation (FFE)
French drain: A French drain is a trench filled with gravel, usually with a perforated pipe at the bottom, that collects groundwater or surface water and carries it away. It is used to relieve wet yards and to drain water from behind walls and around foundations.See also: Underdrain, Geotextile, Foundation drain
Frost depth: Frost depth is how deep the ground freezes in winter at a location. Footings are placed below it so freezing and frost heave do not lift them; the required depth is set by the local building department and ranges from a few inches in the South to several feet in the northern states.See also: Spread footing

G

Geogrid: A geogrid is a plastic grid with large openings that interlocks with soil or aggregate to reinforce it. It is used in retaining walls, steep slopes and under pavement base on weak subgrade.See also: Geotextile, MSE wall, Segmental retaining wall
Geotechnical report: A geotechnical report (soils report) is a geotechnical engineer's investigation of subsurface conditions at a site, based on borings, test pits and lab tests. It recommends foundation types, allowable bearing pressure, pavement sections, earthwork and drainage requirements.See also: Soil boring, Bearing capacity, Presumptive bearing value
Geotextile: A geotextile is a permeable synthetic fabric, woven or nonwoven, placed in soil to separate layers, filter water, add reinforcement or protect against erosion. Examples include filter fabric around drains and separation fabric under gravel roads.See also: Geogrid, Silt fence, French drain, Riprap
Grading permit: A grading permit authorizes earthwork such as cutting, filling and reshaping land. Most jurisdictions require one above a threshold volume (often 50 to 100 cubic yards) or for work near slopes, drainage paths or property lines, and usually require an engineered grading plan.See also: Grading plan, Cut and fill, Erosion and sediment control
Grading plan: A grading plan shows how the land surface will be reshaped, using proposed contours and spot elevations, so that water drains away from buildings and off the site in a controlled way. It also shows slopes, retaining walls, finished floor elevations and erosion control.See also: Contour line, Spot elevation, Finished floor elevation (FFE), Positive drainage
Green infrastructure: Green infrastructure uses vegetation, soil and natural processes to manage stormwater close to where it falls, through practices such as rain gardens, bioswales, green roofs and permeable pavement. It is also called low impact development (LID).See also: Bioretention (rain garden), Bioswale, Permeable pavement, BMP (best management practice)
Ground improvement: Ground improvement is treating weak soil in place so it can support a structure, using methods such as rammed aggregate piers, stone columns, deep soil mixing, dynamic compaction, wick drains or grouting. It can be cheaper than deep foundations.See also: Liquefaction, Deep foundation
Groundwater table: The groundwater table is the level below which soil is saturated. A high water table affects excavation (dewatering), basements, infiltration practices and foundation design, and it can vary by season.See also: Dewatering, Soil boring
Gutter: A street gutter is the paved channel along the edge of a road, usually formed with the curb as curb and gutter, that carries runoff to storm inlets.See also: Storm inlet, Curb and gutter

H

Headwall: A headwall is a concrete or masonry wall built at the end of a culvert or pipe outlet to hold back the embankment, protect the pipe end and reduce erosion. Wingwalls often extend from it at an angle.See also: Culvert, Riprap, Outfall
Helical pier: A helical pier (helical pile) is a steel shaft with screw-shaped plates that is twisted into the ground with hydraulic equipment. The installation torque indicates capacity. Helical piers are popular for underpinning, additions and sites with limited access.See also: Underpinning, Deep foundation
Hold-down: A hold-down is a steel connector that anchors the end of a shear wall to the foundation or the floor below so the wall cannot overturn under lateral loads.See also: Shear wall, Uplift, Anchor bolt
Hydrograph: A hydrograph is a graph of flow rate over time at a point during a storm. Detention design compares the pre-development and post-development hydrographs and routes the post-development hydrograph through the pond.See also: Detention pond
Hydroseeding: Hydroseeding is spraying a slurry of seed, mulch, fertilizer and tackifier onto bare soil to establish vegetation quickly. It is a common way to stabilize slopes after grading.See also: Erosion and sediment control
Hydrostatic pressure: Hydrostatic pressure is water pressure, which increases about 62.4 psf for each foot of depth. Water trapped behind a basement or retaining wall can more than double the load on it, which is why walls need drainage.See also: Lateral earth pressure, Foundation drain

I

IBC (International Building Code): The International Building Code is the model building code published by the International Code Council and adopted, often with local amendments, by nearly every US state or city for commercial and multifamily buildings. It covers structural design, fire safety, egress, accessibility and foundations, and it references standards such as ASCE 7 and ACI 318.See also: IRC (International Residential Code), ASCE 7, ACI 318
IDF curve: An intensity-duration-frequency curve shows how rainfall intensity varies with storm duration for different return periods at a location. Engineers in the US typically take values from NOAA Atlas 14 or local manuals.See also: Rational method, Return period (design storm)
IRC (International Residential Code): The International Residential Code covers one- and two-family dwellings and townhouses up to three stories. It contains prescriptive tables (footing sizes, span tables, bracing) so many houses can be built without a full engineered design, but conditions outside those tables need an engineer.See also: IBC (International Building Code)
Impervious surface: An impervious surface is one that water cannot soak through, such as roofs, pavement, concrete and compacted gravel. Many stormwater rules are triggered by the amount of new or replaced impervious area, and some cities charge stormwater fees based on it.See also: Lot coverage, Runoff coefficient, Stormwater management
Infiltration: Infiltration is water soaking into the ground. Stormwater designs use infiltration trenches, basins and permeable pavement where soils drain well, which requires infiltration testing to confirm the rate.See also: Percolation test, Permeable pavement, Detention vs retention
Invert elevation: The invert elevation is the elevation of the inside bottom of a pipe, channel or culvert. Sewer and storm plans list inverts at each manhole or structure to set the slope so water flows by gravity.See also: Manhole, Pipe slope, As-built drawings

L

LOMA and LOMR: A Letter of Map Amendment (LOMA) is FEMA's official ruling that a property or structure on natural ground is above the base flood elevation and therefore outside the SFHA. A Letter of Map Revision (LOMR) changes the map itself based on new data, and a LOMR-F covers areas raised by fill.See also: FIRM (Flood Insurance Rate Map), Elevation certificate
Lateral earth pressure: Lateral earth pressure is the sideways push of soil against a wall. It is often expressed as an equivalent fluid pressure in pounds per cubic foot, and it increases with depth, surcharge and poor drainage behind the wall.See also: Retaining wall, Surcharge, Hydrostatic pressure
Legal description: A legal description is the written description of a parcel's boundaries used in deeds, such as a lot and block reference to a recorded plat or a metes and bounds description of bearings and distances.See also: Plat, Property line
Level of service (LOS): Level of service is a letter grade from A (free flow) to F (breakdown) that describes traffic operations at an intersection or road segment, based on delay or density per the Highway Capacity Manual. Many agencies require development to keep intersections at LOS D or better.See also: TIA (traffic impact analysis)
Lift station: A lift station (pump station) is a wet well with pumps that raises wastewater from a low area up to a gravity sewer or into a pressurized force main.See also: Sanitary sewer
Liquefaction: Liquefaction happens when loose, saturated sand or silt loses strength and behaves like a liquid during earthquake shaking. It can cause buildings to tilt or sink and ground to spread. Seismic site studies evaluate liquefaction potential in susceptible areas.See also: Seismic design category, Site class, Ground improvement
Live load: Live load is the weight of people, furniture and movable items that a floor or roof must carry. ASCE 7 sets minimum uniform live loads by occupancy, for example 40 psf for residential living areas and 50 psf for offices.See also: Dead load, ASCE 7, Snow load
Load path: The load path is the route loads take from where they are applied, through roof, floor, beams, columns and walls, down to the foundation and into the soil. Every link and connection along it must be strong enough.See also: Dead load, Shear wall, Foundation
Load-bearing wall: A load-bearing wall supports weight from floors or the roof above, as opposed to a partition wall that carries only itself. Removing or opening a bearing wall requires a beam and posts sized by an engineer or code tables.See also: Beam, Load path
Lot coverage: Lot coverage is the percentage of a lot covered by buildings, or in some codes by all impervious surfaces. Zoning ordinances cap it to limit density and stormwater runoff.See also: Zoning, Impervious surface
Lot line adjustment: A lot line adjustment moves a property line between adjacent parcels without creating new lots. It typically needs a survey and local approval, and is simpler than a subdivision.See also: Plat, Property line, Boundary survey

M

MS4: An MS4 is a municipal separate storm sewer system, the network of public storm drains owned by a city, county or state. MS4 permits require the owner to control pollution entering the system, which is why local stormwater rules exist.See also: Storm drain, NPDES permit
MSE wall: A mechanically stabilized earth (MSE) wall uses layers of reinforcement, such as geogrid or steel strips, placed in compacted backfill to create a reinforced soil mass, with a facing of blocks or panels. MSE walls are common for highway and commercial grade changes.See also: Retaining wall, Geogrid, Segmental retaining wall
Manhole: A manhole is a vertical access structure, usually precast concrete, placed on a sewer or storm drain at changes in direction, slope or size and at regular spacing so the line can be inspected and cleaned.See also: Invert elevation, Sanitary sewer, Catch basin
Manning's n: Manning's n is the roughness coefficient in Manning's equation, which engineers use to calculate flow in pipes and open channels. Smooth plastic pipe is about 0.010 to 0.013, concrete pipe about 0.013, and grassy or natural channels much higher.See also: Pipe slope, Culvert

N

NOI (notice of intent): A notice of intent is the form filed with EPA or the state to obtain coverage under the construction stormwater general permit before land disturbance begins. A notice of termination (NOT) ends coverage once the site is stabilized.See also: NPDES permit, SWPPP (stormwater pollution prevention plan)
NPDES permit: The National Pollutant Discharge Elimination System is the Clean Water Act permit program for discharges to US waters. Construction sites disturbing one acre or more must be covered under the EPA or state construction general permit.See also: SWPPP (stormwater pollution prevention plan), NOI (notice of intent), MS4
No-rise certification: A no-rise certification is an engineer's hydraulic analysis showing that a proposed project in a regulatory floodway will not increase base flood elevations. Communities require it before permitting floodway development.See also: Floodway

O

OSHA soil types: OSHA classifies soil for excavation safety as stable rock, Type A, Type B or Type C, with Type C the least stable. The type sets the maximum allowable slope for trench walls: 3/4:1 for Type A, 1:1 for Type B and 1-1/2:1 for Type C.See also: Shoring, Trench box
Outfall: An outfall is the point where a storm drain or pipe discharges into a stream, ditch, pond or other receiving water. Outfalls usually need energy dissipation such as riprap to prevent erosion.See also: Riprap, Headwall, MS4
Outlet control structure: An outlet control structure is the box, riser or weir at a pond's outlet with orifices and weirs sized to release water at the allowed rates for different storms. It also includes an emergency overflow for storms larger than the design storm.See also: Detention pond

P

PE stamp: A PE stamp (or seal) is the mark a licensed Professional Engineer places on drawings, calculations or reports to show they were prepared under that engineer's responsible charge. Building departments and other agencies usually require stamped plans for structural, grading, drainage and utility work. The stamp is only valid in states where the engineer holds a license.See also: Professional Engineer (PE), Construction documents, Building permit
Parking stall dimensions: Parking stall size is set by local zoning; a typical standard stall is about 9 by 18 feet with 24 foot two-way aisles for 90 degree parking. ADA requires accessible spaces at least 8 feet wide with an adjacent access aisle.See also: ADA (Americans with Disabilities Act), Site plan
Pavement section: The pavement section is the layered build-up of a road or parking lot, typically surface course, base and subbase over compacted subgrade, with thicknesses designed for the traffic and soil strength.See also: Asphalt pavement, Aggregate base, Subgrade, CBR (California Bearing Ratio)
Percolation test: A percolation (perc) test measures how fast water drains into soil in a test hole, usually in minutes per inch. It is used to size septic drain fields and infiltration practices.See also: Infiltration, Septic system
Performance bond: A performance bond is a guarantee, issued by a surety company, that a contractor or developer will complete work as required. Municipalities often require bonds for public improvements such as streets and utilities in a subdivision before recording the plat.See also: Subdivision, Plat, Public improvements
Permeable pavement: Permeable pavement (pervious concrete, porous asphalt or permeable pavers) lets rain pass through the surface into a stone reservoir below, where it is stored and soaks in or drains away. It can reduce or eliminate a site's detention needs.See also: Infiltration, Impervious surface, Green infrastructure
Phase I environmental site assessment: A Phase I ESA is a records review, site visit and interviews, done under ASTM E1527, to identify potential contamination (recognized environmental conditions) before buying commercial property. A Phase II involves sampling soil or groundwater if the Phase I finds concerns.See also: Wetlands
Pipe slope: Pipe slope is the drop in invert elevation per length of pipe, usually stated in percent or feet per foot. Gravity sewers need a minimum slope to keep flow fast enough to carry solids. Plumbing codes set the minimum by pipe size (the IPC allows 1/8 inch per foot for 3 to 6 inch building drains and requires 1/4 inch per foot for smaller ones), and utilities set their own minimums for public mains.See also: Invert elevation, Sanitary sewer
Plat: A plat is a recorded map that divides land into lots, blocks, streets and easements, prepared by a licensed land surveyor and approved by the local government. Once recorded, it becomes the legal reference for those lot descriptions.See also: Subdivision, Lot line adjustment, Easement, Professional land surveyor
Positive drainage: Positive drainage means the ground slopes so water flows away from buildings and does not pond. The IRC requires grade to fall at least 6 inches within the first 10 feet from a foundation where possible (a 5% slope), with alternatives such as swales where lot lines are closer.See also: Grading plan, Swale, Finished grade
Post-tensioning: Post-tensioning is a method of reinforcing concrete with high-strength steel tendons in sheathing that are pulled tight with hydraulic jacks after the concrete hardens. It is common for residential slabs on expansive soil and for parking garages and thin floor slabs. Post-tensioned slabs must never be cut or cored without locating the tendons.See also: Slab on grade, Rebar, Expansive soil
Presumptive bearing value: Presumptive bearing values are conservative allowable soil pressures listed in the building code (IBC Table 1806.2) by soil type, such as 1,500 psf for clay and silt. They can be used where the building official does not require a soils report.See also: Bearing capacity, Geotechnical report, USCS (Unified Soil Classification System)
Proctor test: The Proctor test is a lab test that compacts soil at different moisture contents to find its maximum dry density and optimum moisture content. The Standard Proctor (ASTM D698) and Modified Proctor (ASTM D1557, more compactive effort) are the two versions.See also: Compaction, Field density test
Professional Engineer (PE): A Professional Engineer is an engineer licensed by a state board after earning an accredited degree, passing the FE exam, gaining about four years of supervised experience and passing the PE exam. Only a PE can offer engineering services to the public and seal engineering documents in that state.See also: PE stamp, Engineer of record
Professional land surveyor: A professional land surveyor (PLS) is licensed by the state to establish property boundaries, prepare plats and set monuments. Civil engineers rely on surveyors for boundary and topographic data, and in most states only a licensed surveyor can certify a boundary.See also: Boundary survey, Topographic survey, Plat
Proof roll: A proof roll is driving a loaded dump truck or heavy roller over a subgrade while an inspector watches for rutting or pumping. Soft areas that deflect are undercut or stabilized before base is placed.See also: Subgrade
Property line: A property line is the legal boundary of a parcel as described in its deed or plat. Fences and curbs are not reliable indicators; only a licensed surveyor can locate the line on the ground.See also: Boundary survey, Setback, Encroachment
Public improvements: Public improvements are the streets, sidewalks, curbs, water mains, sewers and storm drains a developer builds and then dedicates to a city or utility. They must be built to the agency's standards and are inspected and accepted before the agency takes over maintenance.See also: Dedication, Performance bond, Right-of-way

R

RFI (request for information): An RFI is a formal question from the contractor to the design team asking for clarification of the drawings or specifications. The written answer becomes part of the project record and may lead to a change order.See also: Change order, Submittal
Rational method: The rational method estimates peak runoff from a small drainage area with Q = CiA, where C is the runoff coefficient, i is rainfall intensity and A is area. It is simple and widely used for sizing inlets and pipes on small sites.See also: Runoff coefficient, Time of concentration, IDF curve
Rebar: Rebar (reinforcing bar) is ribbed steel bar placed in concrete to carry tension, because concrete is strong in compression but weak in tension. US bars are numbered by diameter in eighths of an inch, so a #5 bar is 5/8 inch.See also: Concrete cover, Welded wire reinforcement, ACI 318
Retaining wall: A retaining wall holds back soil where the ground changes elevation. Walls over about 4 feet tall (measured from the bottom of the footing), or walls supporting a surcharge such as a driveway or building, generally require a permit and an engineered design.See also: MSE wall, Segmental retaining wall, Lateral earth pressure, Surcharge
Retention pond: A retention pond (wet pond) holds a permanent pool of water and stores additional runoff above it during storms. The permanent pool lets sediment settle and improves water quality.See also: Detention pond, Detention vs retention
Return period (design storm): A return period, such as the 100-year storm, describes a storm with a 1 in 100 (1%) chance of being equaled or exceeded in any given year. It does not mean the storm happens only once a century.See also: IDF curve, 100-year flood (base flood)
Right-of-way: A right-of-way (ROW) is land, or a right over land, reserved for a public road, sidewalk, utility or railroad. The street right-of-way is usually wider than the pavement and includes the area for sidewalks and utilities, and work within it needs a permit from the owning agency.See also: Easement, Dedication, Encroachment permit
Riprap: Riprap is a layer of large, angular rock placed to protect soil from erosion by flowing water, at pipe outlets, channel banks, shorelines and bridge abutments. It is sized for the flow velocity and usually placed over a geotextile or gravel filter.See also: Outfall, Geotextile, Erosion and sediment control
Runoff coefficient: The runoff coefficient (C) is the fraction of rainfall that becomes runoff in the rational method, from about 0.05 for flat sandy lawns to 0.95 for roofs and pavement.See also: Rational method, Impervious surface

S

SWPPP (stormwater pollution prevention plan): A SWPPP is the plan required under the Clean Water Act NPDES construction general permit for sites that disturb one acre or more (or are part of a larger common plan). It describes the erosion and sediment controls, inspections and housekeeping practices that keep sediment and pollutants out of storm drains.See also: NPDES permit, NOI (notice of intent), Erosion and sediment control, BMP (best management practice)
Sanitary sewer: A sanitary sewer carries wastewater from toilets, sinks and drains to a treatment plant. It mostly flows by gravity in sloped pipes with manholes, with lift stations where gravity is not possible.See also: Lift station, Manhole, Storm drain, Sewer lateral
Section 404 permit: A Section 404 permit from the US Army Corps of Engineers is required to discharge dredged or fill material into waters of the United States, including many wetlands and streams. Small projects may qualify for a nationwide permit; others need an individual permit.See also: Wetlands
Segmental retaining wall: A segmental retaining wall is built from interlocking concrete blocks stacked without mortar. Short walls rely on the block weight; taller walls add layers of geogrid reinforcement into the backfill and are designed by an engineer.See also: Retaining wall, MSE wall, Geogrid
Seismic design category: The seismic design category (A to F) rates the earthquake design requirements for a building based on the site's ground motion, its soil site class and the building's risk category. Higher categories require more detailing and limit some structural systems.See also: Site class, ASCE 7, Shear wall
Septic system: A septic system treats household wastewater on site where there is no public sewer, using a septic tank and a drain field (soil absorption field). Its design depends on soil percolation and the depth to groundwater and rock, and is permitted by the local health department.See also: Percolation test, Sanitary sewer
Setback: A setback is the minimum distance zoning requires between a building and a property line, street or other feature. Front, side and rear setbacks vary by zoning district, and some features like decks or eaves may have separate rules.See also: Zoning, Variance, Property line
Settlement: Settlement is the downward movement of a foundation as the soil below compresses under load. Uniform settlement is usually tolerable; differential settlement, where parts of a building settle different amounts, causes cracking.See also: Differential settlement, Bearing capacity
Sewer lateral: A sewer lateral is the private pipe connecting a building's plumbing to the public sewer main. In many cities the owner is responsible for the lateral all the way to the main, including the part under the street.See also: Sanitary sewer
Shear wall: A shear wall is a wall designed to resist lateral forces from wind and earthquakes by acting as a deep vertical beam. In wood buildings they are typically sheathed with plywood or OSB with specified nailing and hold-downs; in larger buildings they are concrete or masonry.See also: Hold-down, Seismic design category, Wind load
Shoring: Shoring is temporary support for the sides of an excavation, such as trench boxes, sheet piling, soldier piles and lagging, or hydraulic shores. OSHA requires a protective system for trenches 5 feet deep or more unless in stable rock, and an engineered design for excavations deeper than 20 feet.See also: Trench box, OSHA soil types, Dewatering
Sight distance: Sight distance is how far a driver can see the road ahead. Stopping sight distance must allow a driver to perceive a hazard and stop, and intersection sight distance must let drivers see oncoming traffic before pulling out. Landscaping, fences and signs near driveways are restricted to keep sight triangles clear.See also: Sight triangle, Vertical curve
Sight triangle: A sight triangle is the area at a corner or driveway that must be kept clear of obstructions above a set height so drivers can see each other. Local codes define its dimensions.See also: Sight distance, Driveway permit
Silt fence: Silt fence is a temporary barrier of geotextile fabric on stakes, trenched into the ground along the downhill side of a disturbed area, that slows runoff and lets sediment settle out.See also: Erosion and sediment control, Geotextile
Site class: Site class is a rating of the soil and rock profile from A (hard rock) to F (soils needing special study) that adjusts earthquake ground motions. It is determined from the average shear wave velocity or blow counts in the top 100 feet.See also: Seismic design category, Liquefaction
Site plan: A site plan is a scaled drawing of a property that shows existing and proposed buildings, driveways, parking, utilities, grading, drainage and landscaping. Most commercial projects and many residential ones need an approved site plan before permits.See also: Grading plan, Civil drawings, Zoning
Slab on grade: A slab on grade is a concrete floor placed directly on prepared ground, typically over compacted base and a vapor retarder. It can be a simple floor slab or a monolithic slab with thickened edges that act as footings.See also: Post-tensioning, Vapor retarder, Control joint
Slump: Slump is a field test of concrete consistency: a cone of fresh concrete is lifted and the drop in height is measured in inches. Specifications set a slump range, and a high slump from added water is a warning sign.See also: Water-cement ratio, Concrete cylinder test
Snow load: Snow load is the weight of snow a roof must support, based on the mapped ground snow load for the location and adjusted for roof slope, exposure and drifting. Drifts against higher roofs and parapets are a common cause of roof collapses.See also: Live load, ASCE 7
Soil boring: A soil boring is a hole drilled to sample and log the soil and rock below a site, often with Standard Penetration Tests at intervals. Boring logs record soil types, groundwater depth and test results.See also: Geotechnical report
Special Flood Hazard Area: A Special Flood Hazard Area (SFHA) is land that FEMA maps as subject to the 1% annual chance flood, shown as zones A, AE, AH, AO, V and VE. Construction in an SFHA must meet local floodplain management rules.See also: FEMA flood zone, 100-year flood (base flood)
Special inspection: Special inspection is third-party inspection and testing the IBC requires for critical work such as structural concrete, reinforcing steel, high-strength bolting, welding and engineered fill. It is in addition to the building department's own inspections and is performed by qualified inspectors hired by the owner.See also: IBC (International Building Code), Field density test, Concrete cylinder test
Spot elevation: A spot elevation is a single elevation called out at a specific point on a plan, such as a building corner, top of curb or pavement high point. Grading plans use them where contours alone are not precise enough.See also: Grading plan, Contour line
Spread footing: A spread footing is a widened concrete pad or strip under a column or wall that spreads the load over enough soil area to keep the pressure within the soil's allowable bearing value. It must extend below the local frost depth in cold climates.See also: Foundation, Frost depth, Bearing capacity
Stabilized construction entrance: A stabilized construction entrance is a pad of coarse stone, often over geotextile, at a site exit that knocks mud off truck tires before vehicles reach the public street.See also: Erosion and sediment control, SWPPP (stormwater pollution prevention plan)
Storm drain: A storm drain is the system of inlets, pipes and outfalls that carries rainwater away from streets and sites. In most US cities it is separate from the sanitary sewer and discharges without treatment to streams, so pollutants must be kept out.See also: Storm inlet, Catch basin, MS4, Sanitary sewer
Storm inlet: A storm inlet is the opening, such as a grate in a gutter or a curb opening, where surface runoff enters the underground storm drain system. Inlets are spaced so water spreading into the travel lane stays within allowed limits.See also: Catch basin, Storm drain, Gutter
Stormwater management: Stormwater management is the planning and design of measures that control the amount, speed and quality of rainwater runoff from developed land. Local rules typically require new development to limit peak runoff to pre-development rates and to treat a water quality volume.See also: Detention pond, BMP (best management practice), SWPPP (stormwater pollution prevention plan), Stormwater management plan
Stormwater management plan: A stormwater management plan (or drainage report) is the engineer's analysis showing how a project will meet local runoff and water quality requirements. It includes drainage area maps, runoff calculations, pipe and pond sizing, and maintenance requirements.See also: Stormwater management, Rational method, Hydrograph
Structural inspection: A structural inspection is an engineer's evaluation of the condition of a building's structure, such as the foundation, framing and walls, often after cracking, settlement, storm damage or before a purchase. The result is a report with findings and repair recommendations.See also: Differential settlement, Engineer's letter
Subdivision: A subdivision is the division of a parcel into two or more lots for sale or development. It requires local approval, a recorded plat, and usually public improvements such as streets, utilities and drainage designed by a civil engineer.See also: Plat, Entitlements, Public improvements
Subgrade: Subgrade is the prepared native soil or fill directly beneath a pavement or slab structure. Its strength, often measured by CBR or resilient modulus, drives pavement thickness design.See also: CBR (California Bearing Ratio), Aggregate base, Proof roll, Pavement section
Submittal: A submittal is information a contractor sends for the design team's review before ordering or installing a product, such as shop drawings, product data, mix designs and samples. The engineer reviews it for general conformance with the design.See also: Concrete mix design, RFI (request for information)
Substantial improvement: Under floodplain rules, a substantial improvement is a repair, addition or remodel costing 50% or more of the building's market value. It triggers the requirement to bring the whole building into compliance, usually by elevating it.See also: Special Flood Hazard Area, Base flood elevation (BFE)
Subsurface utility engineering (SUE): Subsurface utility engineering locates and maps existing underground utilities to defined quality levels (ASCE 38), from records research up to exposing lines with vacuum excavation (potholing). It reduces conflicts and surprises during design and construction.See also: 811 (call before you dig), Utility plan
Superelevation: Superelevation is the banking of a road on a curve, tilting the pavement toward the inside of the curve so vehicles can take the curve safely at speed. AASHTO limits maximum superelevation, commonly to 4% to 8% depending on climate and setting.See also: Cross slope
Surcharge: A surcharge is an additional load on the ground surface near a wall, excavation or footing, such as a vehicle, stockpile, building or sloping backfill. It increases the pressure on retaining walls and trench sides and must be included in design.See also: Retaining wall, Lateral earth pressure
Swale: A swale is a shallow, broad, vegetated channel that carries stormwater. Swales slow runoff and let some of it soak in, and are often used along property lines and roadsides instead of pipes.See also: Bioswale, Berm, Drainage easement, Positive drainage

T

TIA (traffic impact analysis): A traffic impact analysis (or study) estimates the trips a development will generate, adds them to existing traffic and evaluates the effect on nearby roads and intersections. It identifies improvements such as turn lanes or signals that the developer may have to build or fund.See also: Level of service (LOS)
Tap fee: A tap fee (connection or capacity fee) is the charge a utility collects to connect a new building to its water or sewer system. It can be a significant development cost, so it is worth checking early.See also: Water main, Sanitary sewer
Time of concentration: Time of concentration is the time it takes runoff to travel from the hydraulically farthest point of a drainage area to the point of interest. It sets the storm duration used to pick rainfall intensity in the rational method.See also: Rational method, IDF curve
Topographic survey: A topographic survey maps the ground surface with elevations, contours, trees, structures, utilities and other features. It is the base map a civil engineer designs on.See also: Contour line, Benchmark, Grading plan
Topsoil stripping: Stripping is removing the top layer of organic soil before building, because topsoil compresses and decays and is unsuitable under structures and pavement. It is often stockpiled and reused for landscaping.See also: Clearing and grubbing, Subgrade
Traffic control plan: A traffic control plan (maintenance of traffic plan) shows the signs, cones, barricades, flaggers and lane closures used to keep traffic and workers safe during construction in or next to a road. Plans follow MUTCD Part 6 and agency standards.See also: Encroachment permit
Trench box: A trench box (trench shield) is a steel or aluminum structure placed in a trench to protect workers from cave-ins. It does not hold the soil back like shoring; it protects workers inside it.See also: Shoring, OSHA soil types
Truss: A truss is a framework of members arranged in triangles that acts like a deep beam. Most US houses use prefabricated wood roof trusses designed by the manufacturer's engineer, and trusses must not be cut or altered without that engineer's repair design.See also: Beam

U

USCS (Unified Soil Classification System): The Unified Soil Classification System, ASTM D2487, groups soils by grain size and plasticity using two-letter symbols such as GW (well-graded gravel), SM (silty sand), CL (lean clay) and CH (fat clay). Building codes and geotechnical reports use these symbols.See also: Atterberg limits, Presumptive bearing value
Underdrain: An underdrain is a perforated pipe in a gravel bed placed below pavement, a sports field or a stormwater facility to remove water that seeps down through the soil.See also: French drain, Bioretention (rain garden)
Underground detention: Underground detention stores stormwater in buried pipes, vaults or chambers, freeing the surface for parking or buildings. It costs more than a pond but saves land on tight sites.See also: Detention pond, Stormwater management
Underpinning: Underpinning is strengthening or deepening an existing foundation, for example with steel push piers, helical piers or concrete extensions, to stop settlement or support new loads.See also: Differential settlement, Helical pier, Deep foundation
Uplift: Uplift is an upward force that tends to lift part of a structure, such as wind suction on a roof or overturning of a shear wall. Hurricane ties, hold-downs and anchor bolts resist it.See also: Wind load, Hold-down, Anchor bolt
Utility easement: A utility easement gives a utility company or city the right to install, access and maintain lines such as power, water, sewer or gas across private property. Structures, trees and sometimes fences are restricted within it.See also: Easement, Right-of-way
Utility plan: A utility plan shows the location, size, material and elevations of water, sewer, storm, gas, electric and telecommunications lines for a project, and how they connect to public systems.See also: Civil drawings, Invert elevation, Tap fee

V

Vapor retarder: A vapor retarder is a plastic sheet, typically 10 or 15 mil, placed under a slab on grade to limit moisture rising from the ground, which protects flooring and reduces mold risk.See also: Slab on grade
Variance: A variance is permission from a local zoning board to depart from a zoning requirement, such as a setback or height limit, because of a hardship unique to the property. It usually requires a public hearing.See also: Zoning, Setback
Vertical curve: A vertical curve is a parabolic transition between two grades on a road profile, either a crest over a hill or a sag in a dip. Its length is set so drivers can see far enough to stop and, for sags, so headlights reach far enough.See also: Sight distance

W

Water main: A water main is a public pressurized pipe that distributes drinking water, typically 6 to 12 inches in neighborhoods, made of ductile iron or PVC. Services, hydrants and fire lines connect to it.See also: Fire flow, Backflow preventer, Tap fee
Water-cement ratio: The water-cement ratio (w/c, or w/cm with other cementitious materials) is the weight of water divided by the weight of cement in a mix. Lower ratios give stronger, more durable concrete; adding water at the site to improve workability raises the ratio and weakens it.See also: Concrete mix design, Slump
Watershed: A watershed (drainage area or catchment) is all the land that drains to a single point, such as a culvert, pond or stream. Engineers delineate it from topography to compute runoff.See also: Topographic survey, Rational method
Welded wire reinforcement: Welded wire reinforcement (wire mesh) is a grid of steel wires welded at the intersections, supplied in sheets or rolls, and used in slabs and walls. A designation such as 6x6 W2.9xW2.9 gives the wire spacing in inches and wire size.See also: Rebar, Slab on grade
Wetlands: Wetlands are areas saturated with water often enough to support water-tolerant vegetation and develop wetland soils. Filling or disturbing wetlands and other waters of the US can require a Section 404 permit from the Army Corps of Engineers and state approvals, and a wetland delineation maps their boundaries.See also: Section 404 permit, Phase I environmental site assessment
Wide-flange beam: A wide-flange beam (W-shape) is the common I-shaped hot-rolled steel beam. It is named by nominal depth and weight per foot, so a W12x26 is about 12 inches deep and weighs 26 pounds per foot.See also: Beam
Wind load: Wind load is the pressure and suction wind places on a building, based on the mapped design wind speed, exposure category and building shape. It controls the design of roof connections, walls and lateral bracing in many areas.See also: ASCE 7, Shear wall, Uplift

Z

Zone AE: Zone AE is a FEMA Special Flood Hazard Area where a detailed study has set base flood elevations. New and substantially improved buildings must have the lowest floor at or above the base flood elevation plus any local freeboard.See also: Base flood elevation (BFE), FEMA flood zone, Freeboard
Zone VE: Zone VE is a coastal high hazard area subject to the 1% annual chance flood plus waves 3 feet or higher. Buildings must be elevated on open foundations such as piles, with the bottom of the lowest horizontal structural member at or above the base flood elevation.See also: Zone AE, Base flood elevation (BFE)
Zoning: Zoning is the local law that divides land into districts and controls what uses are allowed and how big buildings can be. It sets rules such as setbacks, height limits, lot coverage, density and parking that a site plan must meet.See also: Setback, Variance, Lot coverage, Site plan

Civil engineering glossary

1

8

A

B

C

D

E

F

G

H

I

L

M

N

O

P

R

S

T

U

V

W

Z

Have a project? Get a free quote.