Insulating concrete floor. How to prepare to lay down foam board

In this video I describe how to prep your surface for foam board. Please note, I am NOT a professional concrete or insulation person, I am just showing how I am going about it in hopes to give tips to anyone looking to do this on a DIY level. Enjoy!
EDIT: I ended up "modding" my homemade dirt screed. I cut the edge at a 45 degree angle to make a cutting edge. This ended up making the screed much more aggressive and pulled much more dirt. It was almost to much, and I would make the edge wider next time. However it worked much faster, just had to be careful not to pull to much material and go to deep.

[@RickDugan-hillbillyhunter]

Hi. Good video. I had the experience here in Kentucky. $10000 to install pex and foam in my garage floor. Doing my own. Your video is very helpful. Please keep them coming!

[@petemiller519]

Good tip! Thanks. One thing, poly should go on top of the insulation instead of the bottom, to prevent the insulation sheets from floating up into the concrete since concrete can get in-between the foamboard and the poly. The poly is actually a moisture barrier in a slab application, not a vapor barrier.

[@barelystablefarm7151]

Thanks! I stapled the PEX directly to the foam board, so without peppering it with holes I installed the barrier underneath. I was told for it to be done this way by my concrete contractor. Thanks for your comment & happy Easter!

[@petemiller519]

@@barelystablefarm7151 I might not have watched the whole video. I was not aware you're doing PEX. My bad. Cheers from Canada.

[@kellyinfanger9192]

Excellent primer on getting the sand level. I'll bet you got better workmanship than you would have gotten after paying thousands to a contractor. I think the plastic vapor barrier is redundant. The foam is a pretty good vapor barrier, but I live in a dry area. Maybe put all but a couple of inches of sand down, lay the plastic with edges folded and taped up the walls, then screed out the last 2 inches of sand, and finish the rest just like you did in the video.

[@deanbirks]

Vapor barrier should go on top of the foam board not underneath. That way it prevents any cement getting underneath the foam board.

[@vmatin1]

In cold climates shouldn’t we put it underneath as well?

[@EXCELSIOR_INC]

Use 2 layers of 1" overlapping the seams to cover the cracks to prevent thermal bridging , if you're not going to use tongue and groove Cost the same $$ 00:56 vapour barrier goes down on top of the styrofoam and must be sealed water tight to prevent iceberging, meaning the water from the concrete will lift the styrofoam when you pour the concrete

[@barelystablefarm7151]

I directly stapled the pex to the foam. As directed by my floor guy, he said to install the barrier underneath otherwise it would be peppered with holes from the staples and essentially useless.

[@Boogle912]

4inches of cement weights 4,000 lbs over a 4x8foam board. Any air gaps you start with, won’t exist after 4,000 lbs of cement is poured over it.

[@barelystablefarm7151]

Maybe so, but I'm not willing to take any chances with any air gaps (I drive heavy machinery on this) and really is the way it -should- be done. It isn't that hard to level the surface at a consistent grade. The purpose of this video was to show a simple tool that any shmuck like myself can fabricate to make it super easy. Thank you for the comment!

[@Josh-ux6zz]

String lines are underrated

[@rollandelliott]

I have some 60psi rated insulation board that I want to lay down and instead of using cement on top I want to use foam tile backer board and then put tile on top of that. I am hoping code approves this method. What do you think? Cement is such a pain to work with. and only load will be people walking over it.

[@barelystablefarm7151]

I have heard of it done before. It's my understanding you cannot put tile directly on the foam and a backer board must be used (which you plan to do). The only thing I'm not sure about is PSI requirements, though you are using 60PSI board and would think it would be sufficient. Call the Codes dept or send an email and tell them your intentions. Obviously different locations may have different codes. Good luck with the project!!

[@m89hu]

Smart!!

[@MikeOrazzi]

Good tips. That stuff isn't cheap. The R10 is close to $62 a sheet.

[@barelystablefarm7151]

Wow you're right! I just checked and it's 60.48/sheet in my area. I think I paid 35/sheet when I did the floor and I thought that was expensive because it had gone up then too. Unbelievable! Thanks for watching!

[@Thelastmistake]

What is the strength of that insulation? I am about to do the same but no concrete over .Just 2 3/4 osb boards floating over the insulation

[@barelystablefarm7151]

The rigid foam I used is 25 psf strength (XPS), plenty for under concrete applications. For your application under OSB I'd use 40 or even 60 psf insulation. Owens Corning is a popular brand. Hope this helps!

[@steveedlund7357]

Good tips. How do you insulate the garage door opening between the slab and the approach?

[@barelystablefarm7151]

I insulated the outside of the foundation wall from the footing to just slightly below grade at the door approach. I did this across the entire gable end at the doors, but not the rest of the building since it's already insulated on the inside walls. Hope this helps.

[@steveedlund7357]

@@barelystablefarm7151 Thank you for the reply. Is there any way of creating a thermal break between the concrete approach and the garage slab that you might know of? My garage will be attached so it has a frost footing but the cold approach will be against the warm slab.

[@DarkSeid881]

Good tips. Can i install laminate after foam isolation? Will it be right?

[@barelystablefarm7151]

I have heard some installing plywood over the foam and then laminate on top so it has a good base. Some say to contact the manufacture and ask. Thanks for watching!

[@shannonelliott6116]

I understand vapor barriers in concrete floors...i understand insulating under a radiant floor heating system. Why insulate a concrete floor if it is not heated??

[@barelystablefarm7151]

It is still important to do because the cold ground acts as a heat sink. No matter how you heat the building it will be more efficient by creating a thermal break between the concrete and the ground. In some locations this (insulating the concrete) is also required by code.

[@shannonelliott6116]

@@barelystablefarm7151 I've never witnessed it being done, just curious. Thanks for the reply.

[@angetodac]

professionals are not going to do it better

[@Lotan-in8og]

oh look they’re building like they did in the 1940s. They’ve not seen we’re in the 21st century.

[@barelystablefarm7151]

What exactly is 1940?

[@Lotan-in8og]

@@barelystablefarm7151 What ever you’re trying to build its not from the 21st century!

[@roiad876]

Man, if you know some super advanced building technique please share

[@Lotan-in8og]

@@roiad876 Industrialised Lean BIM building system. Zero energy, sustainable, LCA 150 years plus, 12 weeks for a house 145m2, $90/m2. That’s how you build in the 21st century!!