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Foundations · Below GradeICF Basement Waterproofing:
ICF Basement Waterproofing:
Keep It Dry Without Melting the Foam
A concrete wall is not a waterproof wall, ICF or not. Water gets in at joints, ties and holes, pushed by wet soil and high groundwater. The good news: an ICF basement done right is one of the driest basements you can build. The bad news: the wrong product will dissolve your foam.
The Short Answer
Waterproof an ICF basement with a membrane made for ICF (peel-and-stick or a foam-safe liquid), a dimple or drainage board over it, weeping tile at the footing in clean stone, and clean, compacted backfill graded away from the house. Never use solvent-based asphalt products on EPS foam. Seal every penetration, protect the foam above grade, and give the sump somewhere sensible to send the water.
Where Water Gets In
- At the joint between the footing and the wall.
- Through form ties and any small voids in the concrete.
- Around pipes, sleeves and window wells.
- Over the top of the waterproofing, at the grade line.
- Up through the slab when the groundwater is high and there is no drainage.
The Layers That Keep It Dry
- Footing joint. A keyway or waterstop and a membrane lapped down over the footing.
- Membrane. Peel-and-stick sheet or a liquid membrane approved by the ICF and membrane manufacturers for EPS foam.
- Drainage board. Dimple board or a drainage mat that protects the membrane and lets water fall to the weeping tile.
- Weeping tile. Perforated pipe with filter sock beside the footing, surrounded by clear stone, draining to a sump or daylight.
- Backfill. Clean granular material placed in layers, not a load of clay chunks and boulders dumped against the wall.
- Grading. Ground sloped away from the house, with downspouts carried well clear.
Building on a Wet Lot?
High water tables near the bay are common. Send us your lot details and we will plan the foundation and drainage before the first block goes down.
Products to Avoid
This one melts foam
Solvent-based asphalt dampproofing, some primers and some construction adhesives dissolve EPS. If the label mentions solvents, petroleum distillates or toluene, keep it off the foam. Check that the product says it is compatible with expanded polystyrene.
Also avoid plain spray-on dampproofing as your only protection on a finished basement. Dampproofing slows moisture; it does not stop water under pressure.
Site, Grading and Groundwater
Sandy lots near Wasaga Beach and Tiny drain fast but can have a high water table. Clay lots around Barrie hold water against the wall. Rock lots on the Canadian Shield send water sideways along the rock. The fix differs:
Sand
Check the seasonal water table. Raise the house if needed rather than fight it with pumps.
Clay
Good drainage board, granular backfill and a reliable sump with a backup.
Rock
Plan drainage along the rock face and under the slab. Blasting changes the water paths.
Our ICF lot grading guide covers the outside of the house in more detail.
The Grade Line
Carry the membrane a few inches above finished grade and cover the exposed foam with a parge coat, protection board or metal flashing up to the siding. That strip of foam is what weed trimmers love most.
Get a Real Number for Your Project
Send us your plans or a rough sketch. We price the ICF work from real wall areas, not guesses, and tell you straight if ICF is not the right fit.
Questions We Get
How do you waterproof an ICF basement?+
Use a membrane made for ICF over the foam, a dimple or drainage board over that, weeping tile in clear stone at the footing, clean backfill and good grading away from the house.
Can you use tar on ICF?+
Not solvent-based asphalt products. They dissolve the EPS foam. Use a membrane or liquid product that is labelled as compatible with expanded polystyrene.
Is an ICF basement drier than a poured basement?+
Usually, because the wall is insulated and stays warm, so you do not get condensation on cold concrete. It still needs proper waterproofing and drainage.
Do ICF basements need a sump pump?+
Most Ontario basements need a sump or a gravity drain to daylight for the weeping tile. Whether you need a pump depends on the lot, the water table and where the water can go.