Will foundation insulation inside cause foundation failure in Maine?
Yikes! An entry at InspectAPedia.com (“Building and Environmental Inspection, Testing, Diagnosis, Repair”) discusses foundation failures happening after insulating the inside walls of existing foundations – particularly in very cold climates with wet clay soil. Yikes. We’re in Maine (pretty darn cold in winter) and our soil is dense wet clay. We plan to insulate the inside of our poured-concrete foundation walls (circa 1936) with spray foam, 3″ at the top, 2″ down to floor. We’ll be pouring a concrete floor too, to replace the moist gravel floor, and insulate (1″ or so) under that.
Will our foundation wall fail if we insulate? Argh!
Also, we want to create a little “root cellar” room against a concrete corner, and insulate around that so the inside will be cool. Seems that has also led to buckled foundation walls.
What’s the consensus out there?
Here’s the reference from InspectAPedia: http://www.inspectapedia.com/Energy/Buckled_Foundation_Insulation.htm#InsulationRole
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Replies
Excellent question. Any chance you can excavate the clay soil away from your walls and replace with drain rock and drain tile? You'd have the chance to waterproof the concrete at the same time. Have you talked to local builders or engineers to see how this is typically handled in your area?
That article referred to block foundations, which are much more susceptible to frost and soil expansion. Poured concrete is more resistant to lateral movement, particularly if it was reinforced with steel.
Saturated clay can be expansive, and soils with a minimum of 5% silt are frost-active. If you have clay soils, you should first take measures to divert groundwater and roof runoff away from the foundation with gutters and downspouts, good grading and uphill swales.
Then you should be fine insulating your basement.
Anita,
Will all due respect to InspectAPedia, the information on the page you linked to is based on an old Solar Age article by my friend Steve Bliss. The article dates back 24 years, to January 1986.
I agree with Robert. These cases are really about saturated soil; the insulation played only a very limited role, if any, in these failures. (Evidently, the article is talking about unreinforced concrete-block basement walls in very damp soil.)
Consider the foundations of barns or sheds: these are unheated buildings, without any escaping heat from the building to warm the soil around them. Yet their foundations do not fail at a higher rate than the foundations of heated homes. Just because a foundation is cold, doesn't mean it will fail.