insulation under slab and subgrade?

[socapots]

Anyone ever build a slab on grade with the insulation like in the picture ?

I always thought the insulation was between the concrete and the compacted layer.

This is the site i bit it from.
http://www.cmhc-schl.gc.ca/publications/en/rh-pr/tech/2000-127E.html

 

[dirttracker18]

Mine and any others I have seen are on top of the compacted gravel. Not sure if you could get a go compact with the insulation underneath.

 

[Radix2]

Mine and any others I have seen are on top of the compacted gravel. Not sure if you could get a go compact with the insulation underneath.

I think you will get a better total compaction. When you compact gravel then set foam on top, there are all sorts of voids under the foam from loose stones, dips, etc. using this method, you would compress the foam better and have less voids vs having just the concrete pour and walking around to settle the foam...that's my theory.

I think the FPSF specs show this method since it is easier to do when you have a perimeter foundation vs cutting the foam and wrapping to keep it on top.

 

[joe--h]

Insulation goes on top of the fill. EPS type II is what you need. It's treated with borates so bugs don't eat it.

 

[tdkkart]

The extra layer of compacted sand in this case is there simply for thermal mass, which of course you would want to be on top of your insulation.

Thermal mass makes sense in some applications such as solar where you have a large emount of "free" heat available only at certain times. Heats up when the heat supply is available, then gives off heat when it's not. Stores and gives off alot of heat.

However, when you have a large thermal mass that has given up all it's heat, it takes a lot of energy to re-charge that mass.

It's 6 of 1. 1/2 dozen of the other.

The rest of the of the drawing looks pretty standard.

 

[rancherbill]

I always thought the insulation was between the concrete and the compacted layer.

It is on a flat slab with integrated footer. It would be a nightmare to try to do the foam the other way.

 

[buddyboy]

sand is an insulator,

any moisture in the sand could act as a thermal mass, but the sand would act as an insulator.

 

[Bondo]

Ayuh,..... I don't like how they got that 2x6 sill plate cantilevered out over the 2" of foam,....

It's a floatin' slab, with the buildin', built on a lip 'round the edge,....
Even with the wing foam along side, I doubt it would hold up in the frost We see 'round here,...

 

[socapots]

Ayuh,..... I don't like how they got that 2x6 sill plate cantilevered out over the 2" of foam,....

It's a floatin' slab, with the buildin', built on a lip 'round the edge,....
Even with the wing foam along side, I doubt it would hold up in the frost We see 'round here,...

Lol. Never even thought about that part. And now that i look at it. A piece of pressure treated plywood from in the ground, up under the siding.

Makes sense to have more thermal mass i guess. But i doubt any one does any heat by solar up here. Days get pretty short in the winters.

Having said that I've often wondered how well it would work for non inhabited out buildings.

 

[jnkpile]

Mine and any others I have seen are on top of the compacted gravel. Not sure if you could get a go compact with the insulation underneath.

The insulation is on top of the compacted gravel.
The insulation on the outside of the slab and the wing extending out from the building are essential to protect from frost heaving and it works very well. Personally I used 4"R20.
The 2x6 wall overhangs to avoid creating a drip edge. This can be allowed on a single story dwelling. This is a design for a temp controlled dwelling and not an unheated outbuilding.

 

[yeldogt]

This is a common building in Scandinavia -- The sand is so you have a solid fill ... it is the best/cheapest way to fill the void to save on concrete.

The 2x hanging over the footing works because these tend to be smaller building -- not some four story McMansion.

The wings have to be there -- the system works because it uses/ traps the heat of the earth to keep the foundation and the ground under it from freezing.

The problem with doing this in the US -- is getting an inspector to approve it. I wanted to do this about 5 years ago .. and I could not get it approved.

 

[rancherbill]

All that is structurally needed for a wall, whether single or 2 story, is a 2x4 wall. The 2x6 is specified for the insulation space.

It is overhanging to provide a smooth exterior so foam can be put against the concrete wall.

 

[rburke65]

Right or wrong, I had my compacted base, vapor barrier, insulation, wire mesh, pex tubing, and then placed the concrete. Good luck!

 

[boobag]

do people really build on a slab in freezing climates??

 

[BeachBoy]

Ayuh,..... I don't like how they got that 2x6 sill plate cantilevered out over the 2" of foam,....

It's a floatin' slab, with the buildin', built on a lip 'round the edge,....
Even with the wing foam along side, I doubt it would hold up in the frost We see 'round here,...

Unless you live in Russia or Alaska, your "round here" is milder than Canada and Scandinavia where this method is used.

 

[BeachBoy]

do people really build on a slab in freezing climates??

Yes they do.

I have pictures of this type of foundation being poured in VT at the Canadian border.

 

[rancherbill]

do people really build on a slab in freezing climates??

Sure!

The pic is from CMHC which is the Canada Mortgage and Housing Corporation. They are sort of like Fanniemae or freddymac, they guarantee mortgages.

These are minimum standards for Northern, Native or Rural housing. It is VERY expensive to build in some of these areas. You've seen Ice Road Truckers and there are lots of communities of 100 or 200 people who only can get stuff in the winter. There are no Home Depots in those areas, you plan and order in the summer, get it delivered in the winter and build in the spring. If you are short of nails you are screwed!!! They would have to be flown in.

Somebody has done the calcs and this is a valid design.

 

[rburke65]

I can't express enough how irritating are those flashing faces! Who knows.....maybe it's just me....