Waterproofing (Building)
Systems that stop liquid water from entering a building or structure.
Quick Answer
Building waterproofing is a system of membranes, coatings, and drainage that prevents liquid water from passing into a structure. Below grade it protects foundations, basements, and tunnels against groundwater and hydrostatic pressure. Above grade it covers decks, plazas, and walls. It differs from dampproofing, which only resists moisture, not pressurized water.
The Full Picture
Water is the most common cause of building damage. Waterproofing provides a continuous barrier, usually a membrane or coating, that blocks liquid water, paired with drainage that carries water away. Whether a barrier counts as waterproofing or only dampproofing depends on whether it resists water under pressure.
Below grade, waterproofing is installed against foundation walls, under slabs, and around elevator pits and tunnels. Common approaches include sheet membranes, fluid-applied membranes, bentonite clay panels, and crystalline admixtures or coatings in the concrete. Drainage boards, footing drains, and sump systems relieve hydrostatic pressure so the membrane does not carry all of the load.
Above grade, waterproofing protects plaza decks, balconies, green roofs, parking structures, and wet rooms such as showers. These assemblies often sit under pavers, topping slabs, or planting and are hard to reach after installation, so water testing, such as flood tests, is commonly done before covering them.
Application method affects both cost and risk. Sheet membranes arrive with controlled thickness but need careful lapping, while fluid-applied systems conform to complex shapes but depend on applied thickness. In every case, terminations, penetrations, and joints are where leaks start, so details and inspection carry more weight than the product name.
Real Examples
Common Misconceptions
People assume: Dampproofing and waterproofing are interchangeable.
Actually: Dampproofing, often a sprayed or rolled coating, resists soil moisture. Waterproofing is designed to resist water under hydrostatic pressure and is specified more rigorously.
People assume: Waterproofing is only a below-grade concern.
Actually: Plazas, balconies, terraces, and wet rooms all need waterproofing, and these above-grade areas are often covered up and hard to repair.
Frequently Asked Questions
What is the difference between waterproofing and dampproofing?
Dampproofing resists moisture and vapor from soil but is not intended to resist water under pressure. Waterproofing is designed to hold back liquid water, including hydrostatic pressure from groundwater.
What materials are used for building waterproofing?
Common options are sheet membranes, fluid-applied membranes, bentonite systems, cementitious or crystalline products, and hot-applied rubberized asphalt.
Where does waterproofing most often fail?
At seams, terminations, penetrations, joints, and transitions between systems, rather than in the field of the membrane. Poor surface preparation and damage during backfill are also common causes.
Is waterproofing tested after installation?
Often. Horizontal assemblies are commonly flood tested, and manufacturers or specifiers may require inspection and testing before the membrane is covered.