How to Create a Truly Insulated Slab
HTML-код
- Опубликовано: 29 сен 2024
- 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.
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.
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.
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.
Thermal Nosebleed
The reason the granite counter top "feels" colder than the wooden cutting board is that human sense "heat flow" and not temperature. Our brains attach a "preceived" temperature to that heat flow rate that our skin detects. You also fail to discuss the thermal mass of the insulated concrete and how high mass materials stabilize temperature. Insulating the concrete make a lot of sense but some of your understanding is not correct.
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
So the reason to not add in brick is for us that would mean bringing in another trade. Second, the reference of it being a lot of weight on that exterior wall, the residential building is actually very little weight in the grand scheme of buildings. They are actually very light. We think of them as heavy because we cannot pick them up but our foundations think of them as very light.
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.
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.
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.
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?
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.
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.
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.
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.
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.
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.
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?
His footers are presumably below the frost line. You are probably thinking of a frost-protected shallow foundation.
Jake,
I just watched your video and had a few questions. I’m a homeowner in Ohio, adding a covered screened in patio to my home. The base will be concrete 14x18. The contractor wants to do 1” blue Dow insulation foam board in the concrete pad. 3-4” gravel base and 4” concrete. I’ve never heard of using the blue Dow. Is this a common acceptable practice that I should not be concerned about? Please help.
If the space is just a patio, and it isnt going to be conditioned I wouldn’t spend any money on insulation. What are you insulating against? If the space is to be conditioned I would make the arguement that the insulation the contractor is putting forward (which I believe is XPS) is only R-5 and doesnt meet code in your market. Therefore the matter should be addressed from the code perspective of what does the IRC 2021 say is required.
I’m not sure what you mean by conditioned? He’s saying the 1” blue Dow rigid foam board insulation helps with the movement from ground heave freezing and thawing etc.
What I mean is if the room will be inside or outside? Conditioned like heated and cooled. If the space is not going to be conditioned and always outside, Ive never heard that arguement of using insulation to limit movement before. I can’t say I would understand how that layer would make any sense, that would be a question for an engineer I guess, I would hate to simply say your contractor is incorrect without having all of the information at hand.
#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.
Ummmm how is the slab connected to the exterior concrete wall?? if it is not well I will not get into the problems that will happen LOL 🙂
It isnt connected. I would love to hear how you disagree with our engineer though.
@@jake.bruton.aarow.building Engineers are just that engineers!! They design something and never go back years later to see that the crap designed on paper does not work?? Who are you going to call? LOL You would think there would be a ledge for the slab to sit on or at least j hooks from the stem wall to the slab? Something to mesh the two together? If you do not any settlement that happens with these two separations will be disastrous!! Drywall cracking/windows breaking the list is long. You will learn that in time about engineers 🙂
@@jake.bruton.aarow.building i think the confusion comes from the fact that you are now using a 4" footing and it isn't below frost depth. You get away with this on a monolithic slab as the entire structure is one piece. But this just appears to be a shallow stemwall.
"that concrete is exposed due to code"- why do you say due to code. Why not provide the reason why the code is such. That would be more informative.
He probably doesn’t know why exactly it’s the code. Code books are written by engineering committees and then adopted by local municipalities for whatever region they live in. Builders don’t have to know why the codes are, just what the codes are. My assumption is 6” of exposed concrete above the dirt is probably what’s required to keep the siding away from the ground and prevent rot, or moisture trying to wick its way in to the framing. In my area it’s 8” from dirt
Sorry for not catching this to reply sooner. Obviously we can’t catch all information in every video even when we try. The code is written this was for two main reasons. One, is as stated above, to prevent non-cementous type manterials from being in contact with the ground. Two, is to provide an inspection path for bugs like termites. If you have 6” of exposed foundation the you have bare concrete on which a visual inspection can take place and you can see them making a path from soil up to your building. If the cladding went all the way to soil they could migrate in secret.
@@jake.bruton.aarow.building thank you for the reply. Learned something new about the bug inspection area
@@jake.bruton.aarow.buildingwow thats good info. Thanks!
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.
How does this differ from frost protected shallow foundations? I would like to have one of those on my next 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?
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.
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.
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.
Heated floor
do it out of icf...
Great explanation
ty
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.
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
What holds the slab to the foundation? Couldn’t they separate?
Gravity holds the two together.