Why Put Spray foam Insulation Under Slab?
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- Опубликовано: 4 мар 2020
- Rigid insulation is used under concrete floors when there is in-floor heating, and sometimes now even when there is not. However, closed cell medium densty spray foam is quickly becoming the perferred choice for the insulating part. Here are 4 reasons why....
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+1 .. Damn,,, as a long time subscriber and Spray Jones advocate .... Sure wish there was a professional, knowledgeable Foam contractor in the metro Denver, Colorado area ... Effective application is sooo key! ..
Great tutorial "Spray Foam" instruction video's .... Thank You !!
incredible and informative always .. and the applications blow my mind. Your channel is a HUGE gift.
Hi Mike - Great video. Please can you tell me if the wooden wall battens should stop before/above the floor level so you can spray under them, so there is a continuous layer of foam. So the wood is not touching the un sprayed cold floor? Thanks.
In U.K. we have to put the floor slab over compacted road stone. Insulation goes above the slab under the floor screed.
Alternatively we use concrete T beams with aerated concrete blocks. Spray foam over that would still need the screed.
Thanks!
I'm already committed to doing 3" CCSF on walls & ceilings. I'm also looking at doing this subgrade. 2# vs 3# if same price? ( The contractor has enough 3# left over from another job. ) thx
How about putting 2 inches of rigid foam down and then spray foam on top for the seams and connections?
I am in climate zone 5 needing R30 under the slab are you able to achieve that, 1900 square-foot floor base footprint approximately what would that cost I'm in North Carolina likely out of your area just looking for an understanding
This is a structural floor. A cardboard void form is used to space the slab off the ground and 100% onto the piles. The OSB is used to strengthen what we walk on. The cardboard void form is meant to crush, rot and fall away. For more info on this system: voidform.com/products/surevoid/surevoid-product-line/slabvoid-2/#:~:text=SlabVoid%C2%AE%20is%20a%20corrugated,the%20placement%20of%20liquid%20concrete.
awesome! brand new concrete slab for a future home, in northern california. would you recommend insulating the bottom of them concrete? no basements or walls. im thinking of doing the forms 6" deep and add some type of gravel and foam insulating then pouring the concrete. any thoughts?
Always.
So I'm playing with the idea of spray foam over a triangular type locking drain rock, over bare earth, then the concrete slab right over the top. Is this a configuration that you've seen or would additional air/vapor barriers be required? As far as I can tell and going by your video, the foam performs all those functions at the same time.... Thanks for the video, very interesting
The foam does perform those vapour barrier functions. Just research which product and see that they have some reports confirm this. We do.
Hey mike, I know this is an old video but have a question/idea here and wondering your thoughts. Spraying under a slab here, talking the subgrade under the foam. I know pee rock surface is ideal to spray on but many people prep with gravel or fill sand which can then be harder to spray on. Would rolling out and stapling down soil stabilization poly geotextile matt over the sad and spraying on that be a bad idea? Just trying to think of the best idea on how to deal with spraying of those light materials and then when compacted, blow out when being sprayed direct to
Yes that method is a pain. The fabric needs to be pinned down with A LOT of spikes. If you cannot secure it the foam lift it right off the ground. Hence why gravel, crushed rock is best.
I have an older mobile home that needs new skirting and a vapor barrier beneath it. I'm thinking of the spray foam under it and to use ICF blocks for the perimeter skirting with spray foam inside the blocks instead of concrete as the blocks do not support any weight of the mobile home. Do you think this could be done ?
Waste of materials.
Plywood skirt finished how you want it to look on the outside and then SPF on the inside for the insulation.
Thanks for posting, do you not need to put a Damp proof membrane polythene sheet under the foam?
You don't use plastic with plastic. We R it!
This looks great.
So what If I wanted to spray a basement floor in preparation for finishing. Is that possible.
I know if I build a house I’ll for sure use this technique
I like the way you think...but will this eliminate the poly barrier?
Yes. It is plastic
Beautiful work! Curious on who specified osb to be placed on the ground and what purpose it serves. Even with a vapor barrior on ground surface and osb placed on top moisture is going to find its way in and rot that "horizontal mulch". Thanks for sharing
This is a structural floor. The slab rests on piles NOT the ground. What you see is cardboard void form then covered with OSB so that we can walk on the void form safer. The OSB is only there for the time to spray - just like the cardboard void form is. No one cares about it after that.
@@andreycham4797 Congrats on being blocked.
@@SprayJones this why I like your page! Cheers!
@@SprayJones termites sure do duh... plus lower areas flood seen that too...couple feet easily..plus foam would hold moisture..super rot pest conditions..
@@petero2693 its suppose to rot away
What happens when that OSB rots with ground moisture? Won’t that cause a void? I have seen one of your other vids where you sprayed gravel. That made more sense to me.
Termites too..yes wood will rot ..ever hear of a sump pump..did you ever put wood into wet damp soil...??
Totally..lot of my homes had water sump pumps..might be dry now but things change.. basements can and do flood..its a given..power outage failed pumps is a flood.. seen it all too often
It is a structural floor. It is designed to have a void.
@@SprayJones so the OSB is below grade, but suspended above the grade with a vapor barrier separation? Ground moisture will still rise beneath it if it is not uncoupled from the earth.
@@musicteacherbuilder There is a cardboard void form to take up the space between the dirt and slab. OSB was installed just to walk on. The foam is the vapour barrier and insulation. It is installed where conventional products would be. The cardboard is supposed to rot and crush and fall away. They do not want ground heaving and pushing the slab up.
In minute 1:40, are there cables?
I use FastFoot forming products (a great Canadian company) for my footers. Do you know if this spray foam can be used to insulate around the outside of the footers since it would be applied over their fiber reinforced HDPE fabric. Just wondering if it would stick (or if it matters once covered by dirt).
Thanks
I do not know. Would have to learn about that product first.
Could you comment on closed cell spray foam being used to spray wood boiler water pipes underground to better insulate pre insulated pipes.
Most of the underground pipes in the market are 4 inch pipe with supply and return tubing inside with injected closed cell , problem is the pipes inside only have 1 inch closed cell at weakest for the entire run.
My thoughts are 6 to 10 mill plastic underneath then 2 inch rigid foam underneath with 4 inch overlap on both sides .
Then spray 3 inches closed cell around pipes, then wrap 6mil minimum plastic around then bury with fill .
What would be your thoughts ,
Thank you sir
Put the water pipes inside 4" weeping tile. Place on 2" rigid insulation, spray 2 inches of closed cell SPF over the top. Repeat until done. No extra poly. Beware if they lay in high water table spots. Extra waterproofing steps will need to be taken for the foam.
If they are pre-insulated, add another 2 inches. Closed cell underneath is correct. Skip the extra poly. Make sure not sitting in high water table spot, if they do, extra liquid applied water-proofer will be needed over the SPF.
They claim that only a degree or two is lost with the 12$ a foot precast. Keep ur run as short as possible. I put the precast in a 2” oc foam box. If ur boiler is like mine I’m wasting more heat than I need. I just keep r going depending on the temp.
How thick do you generally spray under slabs like that?
2 inches
I am sprayiing 2" closed cell foam on my 4300 sq foot slab within my new home. I am following all your great recommendations. However, my spray contractor is telling my GC to put plastic down between the sand within my envelope before he sprays for the slab. I have some footers for load bearing walls. Spray contractor says he needs the plastic for adhesion of the foam, but I see a problem when they start pouring the concrete. Meaning the footers will pull on the contour that has formed within the footers and split the spray foam and cause it to crack and create a void before the slab is poured. In my view we should cover the sand base of the slab with gravel. Fill the footers with concrete then come in with the foam for a continuous floor of closed cell (kind of like a shower pan) and then pour the slab on the foam. Am I missing something hear? Is my thinking incorrect? Or can they do it as planned with plastic over the sand base, spray the floor, walls of the load bearing footers and base, then come in and pour? Thanks for all the info, you have been a great help in helping me build a solid well sealed home! Thank You.
You cannot spray to a loose substrate. Sand is No good. Poly is no good. In both cases the foam will lift off of the substrates. We spray to rushed rock or road base gravel. Things MUST be dry.
If the foam cups away it will break when the weigh comes on it.
You are correct in your assessments.
@@SprayJones Update, my contractor and I had a discussion on this after your reply. We retooled the whole process. It put us a week behind, but now its on point. Crushed rock and we even went as far to tamp the rock down, laser pointed to make sure we were even across the slab. 2" of closed cell will be installed on Monday. Then the slab will be poured. Thanks again for all the great advice!
👍👍
Does spray foam keeps pipes from freezing under the cement slab
It can.
Not bad man... not bad at all..
Is 2" under the slab good for Raydon Gas?
Of course.
Quick question, Mike... can you do spray foam OVER radiant heat? Or is this a bad idea?
Yes... but I need to know more about what you mean.
@@SprayJones to be more precise, I'm building a container home on Aslan. We included traditional insulation in the slab. However, plan to use closed cell spray foam in the walls and floor. In the floor, we are also doing a radiant heating system. The general contractor was installing the radiant heating before the spray foam which seems wrong based on your videos, chance of fire and the fact it seems the spray foam would prevent uts effectiveness.
My question is:
1. Would you use spray foam for the bottom later then
2. Put in the radiant heating and use traditional insulation or spray foam again?
Thank in advance!!!
How do these costs compare with rigid foam insulation? Is it alot more expensive or comparable?
Right now we are very competitive for normal applications.
Have you put spray foam under footings? Would a rating of 30 psi be enough to support a footing?
No it would not. Do not proceed with that.
@@SprayJones Thank you.
Would spray foam work on top of a crawl space concrete slab instead of a plastic crawl space liner? (crawl space encapsulation)
The slab was poured without vapor barrier underneath and is mildly porous in one spot (capillary action only no puddling of water)
Other parts of the slab have patches of efflorescence.
It would seem the spray foam would insulate and seal where a crawlspace liner would seal only.
Please watch "spray foam in contact with ground".
@@SprayJones So Yes, it does meet approval for vapor permeability. Yes, you mentioned it does meet approval to be sprayed in contact with the dirt/rock. I can assume a retrofit on an existing concrete slab would then be no different. Other than clean and dry would there need to be any other preparation of the slab prior to spraying?
Would a home DIY kit work or is it only the WALLTITE brand that meets approval? (west coast Canada)
@@Zewestcoaster In Canada you need a pro. CCMC certified product installed by a licensed contractor.
@@SprayJones To answer the question why: I was quoted $17,000 to encapsulate the crawlspace under a 1600sq foot rancher to prevent water vapor from migrating through the slab. If spray foam will accomplish the same job (or better than laying plastic on the slab) for around the same cost or less AND provide the added benefit of insulating from the cold, it's worth investigating.
The only concern would be having the capillary action of the water pushing the spray foam away from the slab (like it does with epoxy type paints) edit: the second concern would be the requirement for a fire barrier over the spray foam if laid on the floor of a 4 foot crawl space.
@@Zewestcoaster OK...hydrostatic pressure will not be able to push the foam up. Provided it was installed correctly.
Thermal barriers are not needed in a CS in Canada provided that they are under 5'10" in height and have no mechanical equipment in them. ie water heater or furnace.
Get someone in your area that knows code and has the engineering to back up what they are doing and you should be fine.
Could you staple floor heat pipe to this foam?
Yes. They sell plastic barbs to hold the pipe in place when using any kind of foam product.
@@SprayJones do you think the PEX should be elevated off the insulation and suspended into the slab as opposed to being at the bottom?
@@bpdp379 I do not care. That is up to the in-floor people.
I will say this.... the closer to the top the easier it is to punch something into the lines from above.... FYI.
@@SprayJones have you seen a preference on their end? I can see it’d be simpler to just lay it on the foam, but my layman senses say the tubing is more effective in the center of the slab. But now that I say that I suppose the slab is getting heated throughout and shouldn’t matter?
@@bpdp379 ... a little research on floor heating will tell you it's more efficient to have pipes within 2 inches of the surface. Pipes under 6 inches of concrete do not heat well. If you are worried about pipe damage you should plan ahead and map out areas to avoid while installing the pipe. (equipment areas and wall plates) Also, pipe locations can be found afterward using by using an IR camera to find the warm spots in the floor.
What happens to the void left by the rotted osb?
Nothing. They want a void. Do you understand what a structural floor is? There is a space under it of 6 - 8 inches so that the ground cannot push up against it and heave it. All weight is on the piles.
@@SprayJones thank you for this clarification. I was also confused about this concept
I have never seen a “structural floor” put this close to the ground , and when it was installed as a pour, the “forms” were designed to be removed. And there was a LOT more rebar than what I saw in this video. So I too was thinking this was a mistake on the homeowners part. But that aside, my thoughts are that;
I hope there is a plastic barrier under the wood, down against the dirt.
When it rots away, I hope that this doesn’t become a haven for carpenter ants or termites as this looks like prime breeding grounds.
Where I live this would be a problem
Would you ever recommend putting plastic down over earth, spraying that with foam, and then pouring over that? Seems like a good way to make an effective heat berm. Especially if you have permafrost.
Edit:
Just looked, you are a lot further north than I am. So you probably won’t have the same concerns.
But I am amazed that in your roofing (other vid) you only have 30r required. In my area we are required 49r
@@jgren4048 To be polite you are unaware of these methods which are sound and have specific reasons why they are done this way in our area. If you want to see more on foam to ground go watch that video in the line up. It is the second most recent. In the Second half I address spraying onto loose films and membranes.
So what's happening now with ants tunneling and insurance companies?
I'm starting to see a issue with ants, reaching the roof pan
Confused by the video. Spraying over OSB type subflooring(sandwiched with foam under it?) at ground level then putting concrete floor on top of that?
Structural floor. Has cardboard void form between ground and slab; slab rests on the piles. OSB is to firm up for walking on nothing more.
@@SprayJones So there is carboard and osb sandwiched between the foam and the ground? Does that get removed afterwards? Is there a crawlspace underneath? Seems like those things would rot being trapped so close to the ground.
@@JereHOTmiah The goal is to not have the ground touching the slab. All weight is on the piles. So a form is installed merely for the purpose of closing the gap between the earth and where the slab begins. It is only there for the pour. After you want it to rot, fall away or crush. No one can remove it, it is behind a 6 inch slab. Ground heave is a real issue here, so structural floors are the only sure way to not have cracking and slab lift.
@@SprayJones I googled some pictures and see how it works now. I have never seen that before. Thanks for explaining!
What happens when it cracks? Not airtight, radon tight, vapor tight anymore. 30 psi strength is great, but concrete is 4000 psi, and it cracks.
What happens to poly? Does it tear, get punctured, tape lets go, seems not sealed?
What happens to foam board under slab? What does it do when the ground moves?
Play where can I get this spray foam
Hire a Canadian Contractor.
Whats the typical cost of spraying 2” for under concrete?
Don't give out costs.
More than a new car lol
@@danbedard290 RC car... :)
I just had a trailer sprayed, and the guy did 2" for $2 / sq ft
@@chrisclark7992 That's horrible.
In my country, code is 12 inches of EPS foam board insulation under the slab, that would be a lot of spraying😵
I am birthing an idea that will smash codes if we do it correct.
It is time to fight back against stupidity.
Went over and talked to a guy that was working on a Habitat for Humanity home. Ask him what insulation was to be installed. R-19 fiberglas. I tried to explain to him about foam and the fiberglass is only an R-4. He says this house is 30% better than code and so tight even with house wrap. No Zip system. U-factor 27 windows. R-3, maybe R-4. So I asked about under slab foam. None. Helps in winter, but not in summer he said. Stack effect. Too bad. I tried.
Ya Ya... baffle with BS.
30% over code, so 30% more on paper to what is on paper..pure white paper values nothing more. Like selling MPG on cars...
House wraps are not air tight, they are a drainage plane. Air barrier is internal, it has to be, +600% more air leakage with drywall installed than not.
I have heard all of these before and then they are baffled when we spray less "r value" and blow their doors off for consumption.
@@SprayJones I even told him the cost savings on your heating and cooling would make up for the increased house payment. Besides being more comfortable. Warmer in the winter, cooler in the summer. I've looked up the R-value in windows for the total R-value in your wall assembly. We should be looking at windows like the European tilt turn .R-7, R-8. Airtight. My windows at home are double hung R-3. They leak. Poor seals.
@@michaelleuth7557 Bless your heart, we have all been there at one time. Many do not want to see it. They think they already have it. In 17 years of selling foam I only will spend time with the 30% that are on the fence and will listen, and you can tell when they are listening.
What about 1" under a heated driveway?
Colder temps 100% outside
As you wish..
@@SprayJones so U see no issues?
@@maurymoynihan5245 Well on the limited info I have no... 1 inch is insulation, watch the video on "is 1 inch enough".
In 25 year storms 3 feet of basement water is well normal..
That OSB under the slab will be a termite breeding ground.
Can you come to Ohio
Sure. Can DHS let us in to spray? I like the USA and would gladly come. MAGA
@@SprayJones idk
I need a crawlspace job done there's little room to work
There's only ever ONE reason to not use spray foam.
Thanks for watching.