The finer details of frost protected shallow foundations
SpyingOnMyKeystrokes
| Posted in General Questions on
2 questions for the experts:
1) Does a Frost Protected Shallow Foundation require extra enlarged width of horizontal insulation at inward corners as is required for exterior corners?
2) For unheated patios, etc., a layer of 6″ gravel (or non-frost permeable soil) is recommended below horizontal insulation, and required to, “drain to daylight or dry well.”
Is there a standard means to do this? Could a designer use a perforated series of pipes at bottom of gravel layer that meet and drain to daylight, kind of like a reverse septic system?
Thanks for input!
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Replies
AK, inside corners do not need extra insulation. Outside corners see cold air from two directions so they need extra protection.
I'm not sure what you are asking with the patio question, but I think the answer you're looking for is to use 4" perforated pipe--the same stuff used for foundation perimeter drainage, either rigid smooth-wall PVC or flexible corrugated pipe.
Michael, thanks for your reply. Yes that's what I was looking for. Attached is a detail that represents the condition I am looking to provide drainage for, as is prescribed for the gravel base beneath the horizontal insulation for unheated building. I'm hoping a patio slab (actually a driveway in my case) can be insulated in the same way shown in the detail.
To clarify my drainage question (#2 above):
Can the 6" gravel layer be sloped at the bottom towards one corner and reliably drain a large gravel area beneath insulation, or is some type of 4" perforated pipe grid required to move water to a drain? I'm considering some heavy spring melt conditions, as an example. It seems there would always be the possibility water would find it's way into the gravel base beneath the insulation.