Rigid insulation placed under continuous concrete footings?
Rigid insulation placed under continuous concrete footings?
(OP)
I have a client (homeowner) who wants to insulate under the slab on grade and wants to continue the insulation down under the continuous concrete footings (turned down footings 12" embed. The location of the project is in the west and there is not frost depth it is a one story wood frame. The slab is going to be heated (reason for insulation). Any advice or recommendations from the cold weather structural engineers since this is a first for me and not our typical construction method and does not appear normal practice of running the insulation under the footings.






RE: Rigid insulation placed under continuous concrete footings?
Moreover, I would never do that for settlement reasons.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Rigid insulation placed under continuous concrete footings?
RE: Rigid insulation placed under continuous concrete footings?
You may be right, but rigid foam has been used under footings for a long time. It does not seem to result in problems. What are your objections?
BA
RE: Rigid insulation placed under continuous concrete footings?
We used to put foam under sidewalks and slabs at times depending on where they were.
When we did home strip footings, I'd hand cut the last three or four inches of ground before forming the strip. Maybe I'm insane, but I wanted to feel every bit of bearing soil.
RE: Rigid insulation placed under continuous concrete footings?
RE: Rigid insulation placed under continuous concrete footings?
I have seen slab houses with ice cold floors around the perimeter from this!
Of course this makes having a good solid, dry base of paramount importance for the interior slab. I have also seen interior slabs move from heave.
But, it doesnt sound like you have temperatures that cold.
RE: Rigid insulation placed under continuous concrete footings?
RE: Rigid insulation placed under continuous concrete footings?
RE: Rigid insulation placed under continuous concrete footings?
RE: Rigid insulation placed under continuous concrete footings?
RE: Rigid insulation placed under continuous concrete footings?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Rigid insulation placed under continuous concrete footings?
This makes the slab floating at the wall with the possibility of local settlement, but that can be controlled with proper compaction.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Rigid insulation placed under continuous concrete footings?
RE: Rigid insulation placed under continuous concrete footings?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Rigid insulation placed under continuous concrete footings?
RE: Rigid insulation placed under continuous concrete footings?
Dik
RE: Rigid insulation placed under continuous concrete footings?
Anyone have any other ideas of how to distribute the footing pressures out across more of the insulation area without increasing the footing?
RE: Rigid insulation placed under continuous concrete footings?
Keep in mind the rated capacities of Rigid insulation are usually at 10% compression. I use this stuff in a vacuum press in my woodworking hobby, and trust me, 10% compression is true.
If you consider something like HI 40 or greater, you best discuss the cost realities with the client before preparing any drawings. I have had many a discussion with clients about the cost of HI 40 to 100.
Brad
RE: Rigid insulation placed under continuous concrete footings?
I'm still not sure I see the point. Granted, heat transfer was my worst subject, but I don't see how it would significantly reduce heat loss. How deep is the footing?
"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928
RE: Rigid insulation placed under continuous concrete footings?
Go deeper.
RE: Rigid insulation placed under continuous concrete footings?
My experience is that most install insulation under the slab and inside face of the wall. Most are actaully extending the wall insulation from the footing all the way to the top of the concrete wall. This also creates a thermal break between the slab and wall.
RE: Rigid insulation placed under continuous concrete footings?
But if you're using 25psi rigid foam, that's 3600psf. Assuming that's an allowable load, that exceeds the performance of many soils we encounter around here... I don't see how 'disastrous settlement' could occur - although it might be smart to consider how the product breaks down over its service life. If you're providing 2" or 4" and over 50yrs it breaks down and is crushed to a small fraction of its original thickness then I suppose you would have disastrous settlement, albeit relatively even throughout the structure...
The only issue I see with a floating slab with a 1/2" fiberboard joint for thermal break is seeing the 1/2" fiberboard joint. Doesn't bother me if it's caulked cleanly, especially in a basement.