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Waterproofing system for an underpinned building

Waterproofing system for an underpinned building

Waterproofing system for an underpinned building


I have a building that its 1st floor slab will be demolished and then 8 feet of soil will be excavated so that the building will have a cellar level. Issue is that the existing footings are rubble (not water-resistant obviously) and these rubble footings will be the new cellar foundation walls. The rubble footings will also be underpinned with concrete to reach the desired cellar elevation.

Is there a way to waterproof the walls? Or should I just accept that they will allow water seepage no matter what and then mitigate that by having the Owner install a french drain system? So basically will tell him to leave a gap between cellar slab and foundation wall so that seeped water will flow down to the perimeter drain and ultimately to the sump pump.

RE: Waterproofing system for an underpinned building

I'll do exactly the way you mentioned, and with a positive floor slope towards sump pit.

RE: Waterproofing system for an underpinned building

Since you are excavating for the basement, extend the excavation and cast the walls with formwork, not against bare earth. Remove the forms and provide an appropriate waterproofing. My recommendation is a coal tar waterproofing such as Bitumastic 50 with at least two plies of scrim to bridge shrinkage cracks in the concrete. Don't forget to require a water stop to be cast in place between the walls and the floor slab.

RE: Waterproofing system for an underpinned building

Don't forget that exterior drainage (rain, roof eaves, etc) next to the house is the most likely source of water from above. Proper sloping of exterior can make a major difference. Gutters are a great help in that regard.

RE: Waterproofing system for an underpinned building

Building below the ground water table requires waterproofing, which is described in most building codes.

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