Insulation required for frost protected shallow foundation
Insulation required for frost protected shallow foundation
(OP)
Hi Folks,
I am designing a foundation for a unheated storage unit. I am planning to use a slab on grade system with thickened edge. My question is
1. should we provide a continuous insulation layer under the entire slab or should we insulate only at the edge of the wall and extende it out a few feet? The document i am referring to design the insulation calls out for a continuous layer of insulation beneath the slab. However, I have not seen that in regular building practice. Have any of you provided continous insulation beneath the entire slab?
2. Is there any web site which has information on specifying the insulation ?
I have attached the document which I used to design the insulation for your reference.
Thanks all
I am designing a foundation for a unheated storage unit. I am planning to use a slab on grade system with thickened edge. My question is
1. should we provide a continuous insulation layer under the entire slab or should we insulate only at the edge of the wall and extende it out a few feet? The document i am referring to design the insulation calls out for a continuous layer of insulation beneath the slab. However, I have not seen that in regular building practice. Have any of you provided continous insulation beneath the entire slab?
2. Is there any web site which has information on specifying the insulation ?
I have attached the document which I used to design the insulation for your reference.
Thanks all






RE: Insulation required for frost protected shallow foundation
From personal experience, if you have a soil that is anywhere near being frost susceptible, I would insulate. I watched the center of my new garage floor the first winter heave upwards of 2-3". The outer perimeter of the slab near the frost walls did not heave..needless to say I now have a severely cracked and uneven floor.
RE: Insulation required for frost protected shallow foundation
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Insulation required for frost protected shallow foundation
I have never personally seen the middle of a floor heave.
Was this a completely detached garage in a very cold area?
Just curious.
RE: Insulation required for frost protected shallow foundation
RE: Insulation required for frost protected shallow foundation
All this was during the summer, mind you.
The day after my trusted concrete finisher poured the floor, but before he got there to cut it(he poured it very late in the day) the floor had already cracked pretty badly. I was very P%$$ed off and wanted to blame him for not cutting it immediately, but the cracks were more severe than T&S cracks.
The outside show now signs of settlement and I thought confined sand would be a good base.
To this day I cannot think of what would cause the cracks other than settlement.
I have since "routed out" the cracks with an angle grinder and filled them with a flexible Sikadur product. The cracks are now nice and dirty like the floor and aren't nearly as bad looking.
Sorry for the thread hi-jacking.
RE: Insulation required for frost protected shallow foundation
Like you, the floor failure was and still is very frustrating. I guess nothing a few thousnad dollars won't fix.
Struct6, insulation is a lot cheaper!
RE: Insulation required for frost protected shallow foundation
I really don't think the sand could have settled enough and quickly enough to cause my problem. I also can see the chalk line on the wall the finisher used and the floor hasn't settled. I also tamped the sand/fill in, in lifts.
Old school guys have been telling me for years and years that "confined sand is a great base"
Maybe it was junk concrete?
RE: Insulation required for frost protected shallow foundation
RE: Insulation required for frost protected shallow foundation
Even "good" concrete will crack with a poor base.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Insulation required for frost protected shallow foundation
RE: Insulation required for frost protected shallow foundation
I guess I am fully aware that good concrete (And I am just talking a basic mix done properly) will crack on a bad base but I thought I had a good base.
The reason I suggested the "junk" concrete was the batch plant the finisher liked to use was notorious sending out 10 yd trucks with 8.5 - 9 yards on them and more than once I saw contractors tearing out two day old driveways after using these fools.
I guess what I was getting at is, can a mix be so bad that a 3/16" crack shows up in one day?
RE: Insulation required for frost protected shallow foundation
Did you see the placement? I am wondering if they placed a 10" slump! Was the weather dry and windy?
8.5 yards of concrete plus another 1.5 yards of water and we have 10 yards of concrete for ToadJones' garage! It only cost us 8.5 yards worth and we get to pocket the rest!
You got to love the craftspeople we have today!!!
RE: Insulation required for frost protected shallow foundation
I am actually still P!$$3d about it
I worked for years building houses and this one was of the worst I have seen, ON MY OWN HOUSE.
The funny part is, the guy is a great "finisher"...the floor looks like glass where ever it isnt cracked
Also, the cracks have never gotten any worse.
They are now filled perfectly smooth with a super flexible Sikadur product.
I still think it was a concrete issue.
RE: Insulation required for frost protected shallow foundation
RE: Insulation required for frost protected shallow foundation
I'm going with the 30" slump you suggested
RE: Insulation required for frost protected shallow foundation
Is it possible the movement you have was caused by swelling of the clay soil? Water can migrate upward by capillary action. The sand around the outside would not be susceptible to swelling.
BA
RE: Insulation required for frost protected shallow foundation
RE: Insulation required for frost protected shallow foundation
BA
RE: Insulation required for frost protected shallow foundation
The driver probably added water onsite in excess of at added at the batch plant, adding to the shrinkage seen.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Insulation required for frost protected shallow foundation
I agree 100%
RE: Insulation required for frost protected shallow foundation
Turn-down slab foundations are commonly used in Scandinavian countries .
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Every one of them spacifies vertical, and outer horizontal wing insulation. As long as you have an adequate amount of compacted structural backfill, you should be fine.