Foundation and damp glossary
48 terms in plain English, with the words used in the US, Canada, the UK and Australia. Each definition links to the guide that explains it in depth, and our engineer-written foundation and moisture answers start from the homepage.
Same thing, different words
Searching from outside the US? These are the names each country uses for the same part of the house.
| US | UK | CA | AU |
|---|---|---|---|
| Expansive soil | Shrinkable clay | Expansive soil | Reactive soil |
| Crawl space | Underfloor void | Crawl space | Subfloor |
| Footing drain, drain tile | Land drain | Weeping tile | Ag pipe, agricultural drain |
| Pier and beam house | Suspended timber floor | Pier and beam house | House on stumps |
| Basement waterproofing | Tanking | Basement waterproofing | Waterproofing, tanking |
| Mold | Mould | Mold | Mould |
| Vapor barrier | Vapour barrier | Vapour barrier | Vapour barrier |
A
- AS 2870Used in: Australia.
- The Australian Standard for residential slabs and footings. It classifies sites by how reactive the soil is and grades wall damage into categories from negligible to very severe.Read the guide
B
- Backwater valveUsed in: Canada, US.
- A one-way valve fitted to a home's sewer line that closes when sewage flows backward, so a city sewer backup cannot flood the basement.Also called Backflow valveRead the guide
- Bowing wallUsed in: all countries.
- A basement wall that has been pushed inward by soil and water pressure, usually bulging most near mid-height. Bowing often appears with a horizontal crack.Read the guide
- BRE Digest 251Used in: UK.
- UK guidance from the Building Research Establishment that grades visible damage to walls from Category 0 (negligible) to Category 5 (very severe), mainly by crack width and how hard the repair is.Read the guide
C
- Carbon fiber strapsUsed in: all countries.
- High-strength strips bonded to a basement wall with epoxy to stop it bowing further. They stabilize a wall but do not push it back into place.Also called Carbon fibre strapsRead the guide
- Cove jointUsed in: all countries.
- The seam where a basement wall meets the floor slab. Because the two are poured separately, it is one of the most common places for water to enter.Read the guide
- Crawl spaceUsed in: US, Canada.
- A shallow, unfinished space between the ground and the first floor of a house, usually 18 inches to a few feet high, that gives access to plumbing, wiring and ducts.Read the guide
- Crawl space encapsulationUsed in: US, Canada.
- Sealing a crawl space with a heavy liner over the ground and walls, closing the vents, and controlling humidity, usually with a dehumidifier.Read the guide
- CuppingUsed in: all countries.
- Wood floorboards whose edges sit higher than their centers, usually because moisture is reaching the underside of the boards.Read the guide
D
- Damp-proof courseUsed in: UK, Australia.
- A horizontal barrier built into a masonry wall near ground level that stops moisture from the ground rising up the wall.Also called DPCRead the guide
- Damp-proof membraneUsed in: UK, Australia.
- A waterproof sheet laid under a concrete floor slab to stop ground moisture coming up through the floor.Also called DPMRead the guide
- DehumidifierUsed in: all countries.
- A machine that removes water vapor from the air. In basements and sealed crawl spaces it keeps relative humidity low enough to limit mold and wood rot.Read the guide
- Dew pointUsed in: all countries.
- The temperature at which air holds all the moisture it can. When a surface is colder than the dew point, water condenses on it.Read the guide
- Differential settlementUsed in: all countries.
- When one part of a foundation sinks more than another. The difference, not the settling itself, is what usually cracks walls and floors.Read the guide
E
- EfflorescenceUsed in: all countries.
- White, powdery salt deposits on concrete or masonry, left behind when water moves through the material and evaporates at the surface.Read the guide
- Epoxy injectionUsed in: all countries.
- Filling a foundation crack with epoxy resin under pressure. It bonds the concrete back together and seals the crack, and is used when a structural repair is needed.Read the guide
- Expansive soilUsed in: US, Canada.
- Clay soil that swells when it gets wet and shrinks when it dries. The repeated movement can lift, drop and crack foundations.Also called Expansive clay; reactive soil (Australia); shrinkable clay (UK)Read the guide
F
- FootingUsed in: all countries.
- The widened concrete base at the bottom of a foundation wall or pier that spreads the weight of the house into the soil.Read the guide
- French drainUsed in: US, Canada.
- A trench filled with gravel and a perforated pipe that collects groundwater and carries it away, either outside the house or under the basement floor.Read the guide
- Frost heaveUsed in: US, Canada.
- Upward movement of the ground when water in the soil freezes and expands. It can lift shallow footings, slabs and steps.Read the guide
H
- HeaveUsed in: all countries.
- Upward movement of a foundation, usually caused by clay soil swelling, frost, or soil recovering after a tree is removed.Read the guide
- Helical pierUsed in: US, Canada.
- A steel shaft with screw-like plates that is turned into the ground until it reaches firm soil, then connected to the foundation to support it.Also called Helical pile; screw pileRead the guide
- Horizontal crackUsed in: all countries.
- A crack running roughly level along a basement wall. It usually means the soil outside is pushing the wall inward, and it should be checked by an engineer.Read the guide
- Hydrostatic pressureUsed in: all countries.
- The pressure of groundwater pushing against basement walls and floors. It rises when the soil around the house is saturated.Read the guide
J
- JoistUsed in: all countries.
- One of the parallel horizontal beams that support a floor. In a crawl space or basement ceiling, the joists are usually visible.Read the guide
M
- MudjackingUsed in: US.
- Raising a sunken concrete slab by pumping a cement-based slurry underneath it through drilled holes.Also called SlabjackingRead the guide
P
- Penetrating dampUsed in: UK.
- Moisture that gets through a wall from outside, usually rain driven through cracks, failed pointing or blocked gutters.Read the guide
- Pier and beam foundationUsed in: US.
- A foundation in which the house sits on beams supported by short piers, leaving a crawl space underneath.Also called Post and beamRead the guide
- PolyjackingUsed in: US.
- Raising a sunken concrete slab by injecting expanding polyurethane foam underneath it. The foam is lighter than mudjacking slurry and sets quickly.Also called Foam jackingRead the guide
- Polyurethane injectionUsed in: all countries.
- Filling a leaking crack with polyurethane that expands into a flexible seal. It stops water but does not restore structural strength.Read the guide
- Push pierUsed in: US, Canada.
- A steel pipe pier driven down to firm soil or bedrock with hydraulic jacks, using the weight of the house as resistance.Also called Resistance pierRead the guide
R
- Reactive soilUsed in: Australia.
- The Australian term for clay soil that swells and shrinks with moisture. AS 2870 classes sites from slightly to extremely reactive.Also called Expansive soil (US)Read the guide
- ReblockingUsed in: Australia.
- Replacing or re-leveling the stumps or blocks that support a raised house. In parts of Australia, notably Victoria, it is used to mean the same as restumping.Read the guide
- Relative humidityUsed in: all countries.
- How much water vapor the air holds compared with the most it could hold at that temperature, shown as a percentage. Keeping it below about 60% limits mold growth.Also called RHRead the guide
- RestumpingUsed in: Australia.
- Replacing the stumps, the short posts that hold a raised timber house off the ground, when they have rotted, sunk or moved.Read the guide
- Rising dampUsed in: UK.
- Ground moisture drawn up through masonry walls by capillary action, usually where a damp-proof course is missing or has failed.Read the guide
S
- SettlementUsed in: all countries.
- Downward movement of a foundation as the soil beneath it compresses. Small, even settlement is normal in the first years after building.Also called SettlingRead the guide
- Sill plateUsed in: US, Canada.
- The lowest horizontal timber of a house frame, bolted to the top of the foundation wall. Moisture from a damp crawl space can rot it.Also called MudsillRead the guide
- SisteringUsed in: all countries.
- Fastening a new joist alongside a weak, cracked or sagging one so the two carry the load together.Read the guide
- Slab-on-gradeUsed in: US, Canada.
- A foundation where the concrete floor is poured directly on the ground, with no basement or crawl space underneath.Also called Slab foundationRead the guide
- Stair-step crackUsed in: all countries.
- A crack that follows the mortar joints in brick or block in a stepped pattern, often a sign of uneven settlement.Read the guide
- SubsidenceUsed in: UK, Australia.
- Downward movement of the ground under a building, often caused by clay shrinking in dry weather, tree roots or leaking drains. In the UK it is a specific insurance term.Read the guide
- Sump pumpUsed in: US, Canada.
- A pump in a pit at the lowest point of a basement or crawl space that switches on automatically to remove water collected by the drains.Read the guide
U
- UnderpinningUsed in: all countries.
- Strengthening an existing foundation by extending it deeper or wider, or by supporting it on piers, so it rests on firmer soil.Read the guide
V
- Vapor barrierUsed in: US, Canada.
- A sheet, usually polyethylene, that slows moisture moving from the ground or a wall into the air. In crawl spaces it covers the soil.Also called Vapour barrier; vapor retarderRead the guide
W
- Wall anchorUsed in: US, Canada.
- A steel plate inside a bowing basement wall, connected by a rod to an anchor buried in the soil outside, that holds the wall and can gradually pull it back.Read the guide
- Water tableUsed in: all countries.
- The level below which the ground is saturated with water. A high water table raises pressure on basement floors and walls.Read the guide
- Weeping tileUsed in: Canada.
- The Canadian name for the perforated drain pipe laid around a house's footings to carry groundwater away from the foundation.Also called Footing drain or drain tile (US)Read the guide
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