Installs Foundation Protection
Chapter A9 – Installs Foundation Protection
Prerequisite Knowledge:
Topic 1 – Draining Tile, Waterproofing, and Damp-Proofing
Overview
The first line of defense against water infiltration through a foundation and basement floor is maintaining a proper grade around a house and using downspouts to mitigate the water away. A slope of 1:12 is recommended to encourage rainwater to flow away from a building along the topsoil. However, even with this slope, water is still able to seep into the ground and it can exert incredible forces on the foundation and basement floor. These forces are known as hydrostatic pressure. To counteract these forces and prevent structural failure and water infiltration, most buildings use both drain tile and waterproofing.
Drain Tile
Drain tile is a perforated pipe that is 4-6” (100-150 mm) in diameter that is placed around the footing of a building. It collects any rainwater that runs down the foundation wall which then drains into a sump pit. It is placed with bottom of the tile in line with the bottom of the footing on undisturbed or compacted soil. It should maintain a slope of 1/8” per foot (10 mm per meter) towards the sump pit. To prevent silt from clogging the drain tile, it is installed covered with a fabric sock and covered with at least 6” (150 mm) of clean crushed rock.
While some jurisdictions allow the tile to drain directly into the sewer, it is more common for the drain tile to slope towards a sump pit. The sump pit is typically fitted with a pump that disposes of the accumulated water directly into the sewer system. See figure 1 below for a typical drain tile setup.
Damp-Proofing
Damp-proofing is required on a foundation “where the exterior finished ground level is at a higher elevation than the ground level inside the foundation walls”. It is required on both the interior and exterior surfaces of foundation walls and any slab-on-grade other than in garages. It is the second and most effective line of defense against dampness and moisture infiltrating through the foundation.
Exterior Damp-Proofing
Prior to applying damp-proofing, the foundation walls need to be free of honeycombing. Any voids, if present, should be filled by parging. The surface should also be clean, dry, and free of any projections. All tie holes and cracks should be filled with the proper caulking or plastic cement. Damp-proofing is applied by brushing or spraying on a heavy coat of bituminous (asphalt) material. Often a second coat is applied after 12-24 hours. The damp-proofing material should be allowed to cure for 24 hours before backfilling takes place, otherwise the material may be scraped off.
Interior Damp-Proofing
Interior damp-proofing is required where insulated and finished wood framed walls are applied along the interior perimeter of a foundation. The damp-proofing is typically a sheet of polyethylene which is applied directly to the concrete wall up to the height of the exterior grade (see figu