Vapor Barrier, Insulation foam board under slab diy Garage build EP 9
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- Опубліковано 7 лют 2025
- Laying down under slab plastic vapor barrier and ridgid foam insulation board to insulate the concrete monolithoc slab. You need a good vapor barrier to keep moisture from coming up through your concrete slab. In a cold climate like mine a good ridgid foam is needed to keep from having a lot of heat loss into the ground. I checked into under slab closed cell spray foam instead of going this route but it was a lot more expensive.
Make sure to have a good laser transit to keep track of your elevations as you go. If you have to rent it a number of times it may be worth just buying one, it was for me. I'm really happy with the accuracy of the one I have and will link it below.
amzn.to/3ddiXPc here is the Topcon laser transit level that I use for all this building prep. Super accurate and easy to use. I love mine. If you have to rent it a number of times anyways I think it’s worth just buying one.
amzn.to/3HbLi3r here you can check out similar plate compactors. 
This is a new series on my diy 32 x 56 garage - shop build. I want to show you how to start building a garage or shop from the very start of just having a empty lot. Watch for future videos on this build.
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I hope this video helped you. Thanks for watching.
#vaporbarrier #underslabprep #insulationboard #rigidinsulation #concreteslab #monoslab #garagebuild #shopbuild #buildityourself #diy - Навчання та стиль
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That was incredibly informative! Great series!
Thank you so much Tim! I’ll try to cover more as I go. Thanks
Awesome job, thanks for bringing us along
Thank you! Thanks for being here.
Nice project and video. I'm planning a similar building in coastal Maine. Unlike yours, I'm designing the frost protection for the unheated condition, even though it will have an apartment that can be intermittently heated. I'm using 30psi 3" XPS boards that go in a continuous plane under the footings and 49" out. The gravel mound inside the footings is on top of the foam. I'll add vertical insulation after the slab is poured, going about a foot up the walls to complete the thermal envelope. I'm skipping the radiant heat - just heat pumps (40% paid by Maine, 30% USA).
Thank you. Sounds like you got a good plan. Good luck with everything!
There is a reason to use the expensive under slab insulation. It is made to withstand the weight of the cement with a 25 psi rating. The less expensive foam board can compress over time and cause cracks in the concrete which can cause leaks in your pex heating tubing.
Better to use the right product instead of cutting corners to save a few $$$
Yes it’s good to use foam that rated for under concrete use for sure. The ones I used was sold by a Logix Icf dealer and is rated for under concrete slab. 👍
You mentioned insulation outside the slab, are you putting in horizontal insulation around the building kind like a skirt? That will help keep the ground hotter so you waste less heat to the ground when the heating is on, and it will help raise the frost-line dramatically as well! 👍
Yes I’m insulating around the whole perimeter and also outside the building. Doing a frost protected mono slab. For my climate it needs to be 16” on the edge and 32” out sloping away from the building. Thanks
If the floor drains go to day light, the P-trap may be unnecessary.
They might be yes, I just wanted to make sure there’s no issues. So far I’m happy with it no issues.
My foundation contractor said he lays board first then vapor barrier, then rebar/mesh to avoid concrete getting under the insulation board and cause floating.
I’ve heard someone else mention that. I’ve never had any issues doing it this way but you can do whatever you think is best. My concrete guy didn’t have any issues with doing it this way. Maybe it depends if they use a pump truck since it’s coming straight down or if they just use the chute of the truck cuz it would come out sideways more.
I was wondering the same. I asked my buddy who does concrete for a living and he said that you have to tape the Foam board seams. "Iceberging" can still happen with the moisture barrier over the foam boards, it can still get in between the foam boards and separate it. I guess, taping the edges is the trick?
@@adrianv3916 yep, we ended up using the hitz Halter insulation board. Taped up seamed and sides. It also comes pre-treated with termite repellent.
The vapour barrier has to be on the warm side , found out through the inspector seem to be different answers .
@@kdcustomwoodworking Yes, the vapor barrier should be on the top of the insulation so any condensation can drain to the soil. If you put the vapor barrier on the cold side like this guy, the foam could be be sitting in water (degrades the R-value) indefinitely.
looking forward to more episodes as you near the finish line. Question.....will your mono-slab have any re-bar or wire mesh reinforcement?
Thanks for being here! Yea I’ll do rebar.
Do you have to take the wood box out after pour or can those boxes be left in? Is it important to do that or is that just your own preference? Thanks.
You can just leave them if you want. They can be removed when you do the tub drain if you need the room. I took mine out afterwards.
Not too much extra cost put it down first put your styrofoam down put another layer on top of the styrofoam and go from there
Yes you could. 👍
Welp. You want to put down the foam first then the plastic to prevent the foam from floating if the concrete should sleep under it. Or. Plastic Foam Plastic is an option but overkill.
Yeah, I’ve had other people say that. I put it in nice and tight, so no issues at all. That’s how all the concrete people do it around here so maybe it’s a preference thing.
My concrete buddy does it this way but he tapes off all the seams between the foam boards, to prevent "Iceberging".
Did you also put foam insulation at the bottom of the footing? I see it alongside the wall but wasn't sure if you placed it at footing floor. Great video by the way
Thank you. No I did not put it under the footing because of potential settling issues. I did the outside perimeter and also 32 inches out sloped away from the building for frost protection. That’s what my area requires.
I really enjoyed your video. Nice job I was wondering if the interphone pulled off when you went to go strip your forms or if it stayed in place
I meant the two inch foam stay in place when you strip the forms
Yes it stayed in place. I’ll show that more coming up. Thanks.
Nice
Thank you!
Pretty sure the vapor barrier is supposed to go on TOP of the insulation... directly under the slab.
Not really sure that would make a difference whether is on top or under as long as there’s a moisture barrier. I’ve always seen it done this way
From what I have read, the reason for placing the vapor barrier above the insulation is that when pouring cement, any gaps in the insulation can cause the cement to seep underneath and lift the insulation.
@rc1112006 yeah I suppose I could see that if it’s not placed tightly. Mine overall went together really nice and if there was any corners that were messed up where there was small voids or cutting around pipes, etc. I just spray foamed around those to make everything nice and tight
NO
Iam 72 yrs old. I've been using a Sawzall blade and visegripes for yrs.. maybe I should have used youtube b4 we had youtube???? Nothing new here??? Amen
Haha good for you! I’ve never seen anyone else doing that. 😁
Need to put foams in the footing as well otherwise by note insulating the footing you defeat the purpose of the whole project.
I don’t want to for the weight of the building sitting on it, I’m insulating the perimeter 32” out from the building for frost protection.
ua-cam.com/video/EuYv4Fk6ZDI/v-deo.htmlsi=UC-UVCDaVCTIniX_ I show that more in this video.
What thickness and r value was your foam board??
It’s 2 1/2” thick. I think the dealer for it said R12-15 somewhere in there.
An important mistake made was the 6 mil should go on top of the foam.
Why not stop the moisture below it?
To prevent iceberging, if cement gets under the foam it can push up and cause problems
Do you happen to remember what the cost per sheet was for the foam. I have been checking out logix website but can't find the product you used.
Ok. No issues with mine at all and it wasn’t pumped nicely straight down, it was poured and raked in. I laid it nice and tight. It was made by beaver brand I think but came from a logic dealer. Not sure if they’re necessarily together though.
Oh the cost, I think it was 35 a sheet. This was a few years ago that I purchased it though.