How to Create a Truly Insulated Slab
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- Опубліковано 4 лют 2022
- 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.
Very well spoken and presented.
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.
Could you send me more information on your method? Or tell me where I can obtain it.
The reason I ask is because the definition of Macadam in the USA in “ broken stone of even size used in successively compacted layers for surfacing roads and paths, and typically bound with tar or bitumen” so I want to understand your details.
Great explanation
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.
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.
I plan on leaving the foundation one piece but using radiant floor heating.
Modern building need to be built without any thermal bridges. Slab edge detail like helps to reduce thermal bridging and should be standard. In fact not only should be standard but the foam thickness should be increased to achieve higher u-values suitable for the climate. This is standard when building towards Passivhaus standards.
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.
This meets code because it is fully continuous.
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".
Any builder that isn't using such a basic insulation technique is not a building science based builder, that's obvious. I don't care what they call themselves.
Makes a lot of sense. I don't understand why this isn't standard, especially for northern climates.
Cost. Always the number 1 factor. Plus, there’s no one with high incentive to make this the standard.
Unless some deep pocket give some to make this the standard.
As always.
But either way i feel that this is not for everyone as it drives the cost up quite a bit.
its pretty similar to standard in UK but we use better insulation
This is not even good as a standard... look what we do in Europe... it's far better.
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.
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?
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How does this differ from frost protected shallow foundations? I would like to have one of those on my next house.
Your insulation design is a good idea but it only provides thermal separation from the outside concrete. If you had hydronic tubes to also heat the slab and your thermostat was set on 76, the slab would be 78 or higher. The example you used of granite counter tops was a good analogy. Imagine the comfort of heated floors.
Agreed. The challenge in climate zone 4 is that many days we heat overnight and then need some cooling in the afternoon. A heated slab changes very slowly and we need heating and cooling that are more responsive. Slab heat is very comfortable though. Sometimes it works well.
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.
The parameter of the slab must have insulation. There needs to be a 4 ft slope from the slab with ridged foam for frost!
I’m not sure what section of the code you are finding this in. Can you provide the code?
Is there any risk of upheaval or subsidence with the interior slab being uncoupled from the perimeter footing?
... also is the concrete not too heavy or the foam board underneath? It won't compress it at all?
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?
No radiant system. I would bet the engineering would not allow us to call the foam an expansion joint because it has a decent PSI rating.
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
We dont bevel our insulation because that little section of slab is kind of compromised. We just size it to work with the wall size. Our wall is a Zip R-6 with a 2x6 and 1/2” drywall this allows for a fairly thick wall that works well this concrete assembly.
they're using XPS for insulation. However, is it possible to use EPS of some density?
Absolutely. Most times now we use type 9 EPS or GPS.
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?
Yes. Think of is as a 2x4 wall is rated to hold the exterior of the building up and we are using the 2x4 part of the 2x6 assembly. Does that make sense? We end up with about 1” of the 2x6 floating over the foam assembly.
Hi Jake, How do you handle the slab insulation at the door openings?
The wall is thick enough that it covers and we order a jamb thick enough to work with the wall.
@@jake.bruton.aarow.building ok great. Maybe it’s just not visible in the video at the door opening. The concrete may have just discolored the edge of the foam if it continues across that door opening.
#1: so that foam is not under the entire slab? #2: How do I know if I can just trench and not build forms? Is it just a judgment call?
Has to be under entire slab. That's the whole thing.
What we see here is basic minimum anyway. This would not be allowed in Europe as insufficient though.
Take a piece of rebar, push into the ground. How deep it can go easily or at all will give you a quick estimate of how well the soil compaction is. Not all land is good to build on.
Heated floor
Thermal Nosebleed
What holds the slab to the foundation? Couldn’t they separate?
Gravity holds the two together.
do it out of icf...
Jake, I think you're mixing up emissivity with thermal conductivity in the context you're using. Different surfaces feel like different temperatures to human skin (which is basically a calorimeter) because the thermal conductivity of different materials.
I will have to look into that. Thank you for saying something.
If you are adding foam why not 6 or 10 inches
You absolutley could. For climate zone 4a this is suffcient.
Cost vs benefit trade off. 2in foam is usually more than $1/sqft and if you double the thickness you double the price. In addition, you need to allow room for that foam so more excavation or higher and thicker stem walls which both add cost. Everything affects everything else