How to Create a Truly Insulated Slab

Unless you have felt an uninsulated slab in the winter you probably don't understand the lack of comfort that cold feet actually offers. However, in this week's video Jake walks you through the simplest way to uncouple that concrete slab from the ground (temperature) below.

[larion]

Here in Northern Europe we make many slabs with even more insulation. First 12 inches of Macadam under the whole slab, that is compressed well. This will drain and be the capillary break layer. The macadam is carefully adjusted with laser level. Then you lay out the border/edge beams for the slab. These are made by aproximately 4 inches of eps insulation and only a thin glassfiber board on the outside. The beam is 16 inches high. On the inside of the beam 12 inches of eps insulation then fills out the whole slab except next to the edge. Most of the slab will then be 4 inches of concrete on top of 12 inches eps insulation. But next to the edge there will be 12 inches thick (and 12 inches wide) concrete beams. With 2-4 inches of eps insulation on the outside.

[garyjennings]

Would really like to see a sectional drawing of how the wall sits on the curb and vertical foam. I assume you are using 2x6 wall framing. 4” curb plus 1.5” foam to match the plate?

[Kakalacki]

I am surprised that it is not a code requirement in Missouri for there to be insulation in a slab foundation. In PA we are required to have either 2 or 4 ft of continuous insulation from the top of the slab, depending on the climate zone you are in. The insulation can be either verticle or horizontal or a combination of both.

[liberaljoe]

Isn't the standard the Frost Protected Shallow Foundation (FPSF) where the insulation goes on the outside of the foundation along with a horizontal insulation extending out X inches depending on your Air Freezing Index? Just a thought.

[patty]

What prevents frosty from taking the edges? A frost protected shallow foundation, insulates the entirety of the slab so the frost doesn’t get under the edges.

[paulcanel]

So your stud wall (2x6 5.5” wide) sits partially on top of the 4” curb wall and partially on top of a piece of insulation board correct?

[charliewright]

How do you finish the 1 1/2 rigid foam insulation on the stem wall/curb? I plan to pour slab on grade with hydronic heat and will have R14 under the slab spray foam or rigid. I will also have rigid foam on the stem wall interior and exterior. Do you bevel 45 degrees the rigid foam on the interior? I plan to use 2 inches on the exterior too and I’m wondering a good detail on how to finish? Thank you, Charlie

[KAMMEDIALLC]

Is there any risk of upheaval or subsidence with the interior slab being uncoupled from the perimeter footing?

[frankrizzo]

Thank you for the video. I think this is a great idea to do to all homes. I wish you took it one step further and installed radiant heat into that slab before it was poured. It would have been more efficient than any other type of heat you can put in that home. Even still, what you did is 100% better than what is usually done.

[doug]

Great idea, I've always wondered what slab on grade didn't have this. What's the additional cost of adding the foam as a thermal break?

[Syncrogreg]

Do you use 2x4 or 2x6 for the framing? Feel like 2x6 would come more inside to overlap the foam at flooring

[ioda]

Makes a lot of sense. I don't understand why this isn't standard, especially for northern climates.

[Syncrogreg]

So you pour footers first then insulate and pour slab last?

[badawesome]

How does this differ from frost protected shallow foundations? I would like to have one of those on my next house.

[Chris-pjos]

That blue foam against your pre-poured exterior "stem wall" will also serve as an expansion joint I would think as well? Am I to understand that this slab has no radiant heat pipes installed inside it as well?

[ronwyl]

Going to be building a garden room, and for a quick question...
why don't you edge the slab with a small brick wall?lot

Seems me that you are exposing the edge of the concrete to the elements, plus the weight of the walls on the edge must be quite a lot

[davidniquot]

We got more advanced syustem here in europe ... the whole slab is inside a foam jacket... wall included. Only a small part of the heat is exiting from the slab ... more exit from walls and even more from the roof. There is a need for continuous insulation around the house.

[steelyspielbergo]

I learned about insulated raft slabs after becoming interested in building science. Yet I don't see them being used very often by anyone, including the "building science types".

[franklinmade]

Hi Jake, How do you handle the slab insulation at the door openings?

[rangerdoc]

If you're adding a thermal break, then it's no longer a monolithic slab, but rather a perimeter foundation & inner floating slab?
Edit: Nevermind. I watched again & see where you poured traditional stemwall below frost depth.