Under Slab Insulation Techniques

[OldNeons]

This is not another debate of the merits of under slab insulation
I know I'm doing it - 1.5" Pink Board.

My garage is 28x42 - 3 car semi-attached with living space above. I'm curious what techniques you all have found best/most efficient for foam at the edges. I have 8" trench block and 3 courses of 6" block on top of that all the way around. Wondering the best way to try to isolate the slab from the cold exterior walls. I have 2" foam around inside of trench block for about half of the garage - and 2" foam around outside of trench block on other half (long story - don't ask....). I want the slab to rest on the 2" ledge (difference between 6 and 8" block) I have around inside of foundation - but would like to insulate it. Thought about putting 24" tall 1/2" pink board on the interior foundation walls and then putting FRP all the way around 4' up to facilitate washing the garage out? Also thought about putting 1/2" foam on top of the 2" ledge as I don't think I want 1.5" foam on top of my ledge under the slab as I want a solid bearing point for the slab on the foundation.

Also, do you recommend poly vapor barrier when using foam?

Techniques for foam at Garage Door Openings (3) and Passage Door Opening (2)?

I don't plan this to be a working garage - just daily driver parking for my wife, kids and I. That said there is finished space above, so I want to keep it at say 45-50 in the winter. I'm thinking a couple small propane fired radiant heaters should do the trick? Tell me I'm ok not putting radiant in the slab? I don't want to regret it later that I didn't put the Pex in - LOL. I plan to live here another 30 years.....

Thanks for the input!

 

[BuffettFan]

http://www.insulationsolutions.com/index.htm

These folks are based in East Peoria, Il and are experts at under slab insulation.

Personally, I would install the pex, even if you don't plan to heat the slab. You sure can't do it after the fact and who knows what use you may have for the space over the course of 30 years!.

 

[OldNeons]

Thanks Buffett - I know that area well - went to school in Champaign many years ago....
I appreciate the referral - I'll check them out. As for Pex, I'm having a hard time not doing it - but you have to draw the line somewhere. I am DEFINITELY heating the floor in my shop when I build it. The garage in question is attached to the house and therefore I just don't ever see it being anything more than daily driver parking. I don't really have a utility room or any place for the boiler/manifolds etc in the garage. I was really hoping to get by good insulation (6" walls), insulated garage doors, and the radiant heaters to keep things comfortable without installing an in floor system???? If I planned to work in this garage there would be no discussion - it would be in the floor....

 

[slimcake]

spray foam! When i ran the numbers it was the same $ to install the sheets as it was to spray foam it. Twice the product in the spray foam!

 

[OldNeons]

Never thought of spray foam - what type of foam did you use - and how thick? Cost? thanks

 

[wssix99]

I have 2" foam around inside of trench block for about half of the garage - and 2" foam around outside of trench block on other half (long story - don't ask....).

If you don't have a continuous layer of insulation around one side, it defeats the purpose. If you stop on one side and then continue on the other, then you'll have a pathway for heat to get out. (Just like leaving your door open during the winter.) Something is better than nothing, but having this break will greatly undermine the efficiency of what you are investing in.

I want the slab to rest on the 2" ledge (difference between 6 and 8" block) I have around inside of foundation

This will be problematic for your floating slab and could lead to stressing and cracking. The slab should be free and isolated from the structure. You can kill two birds with one stone here - just use 2" of foam to isolate the slab from the wall. When the slab cures, use a heat knife to cut the foam out a little bit and then install a 2" slab gasket on top for a nice finish. See posts 8 and 12 here: https://www.garagejournal.com/forum/showthread.php?t=369472&highlight=slab+gasket

Techniques for foam at Garage Door Openings (3) and Passage Door Opening (2)?

See the link above for a good discussion on these points. ^

I'm thinking a couple small propane fired radiant heaters should do the trick? Tell me I'm ok not putting radiant in the slab?

Propane heaters are not legal in this application. Code doesn't allow you to have those propane tanks in a structure with living space.

Heat is heat and any heater will do. If you don't care about the comfort of radiant heat, then you can just put in whatever heater is most economical for you. You could do an oil, natural gas, propane heater, etc. (If you do a propane heater, you'd need a permanent tank installed outside the structure.)

 

[slimcake]

Never thought of spray foam - what type of foam did you use - and how thick? Cost? thanks

It was 1.5 inches thick closed cell foam. Cost me like $1.50 a sq ft. By the time I had the guys lay the foam panels and tape em it was a wash. With the spray there is no void places and probably the best vapor barrier there is!

 

[wssix99]

It was 1.5 inches thick closed cell foam. Cost me like $1.50 a sq ft. By the time I had the guys lay the foam panels and tape em it was a wash. With the spray there is no void places and probably the best vapor barrier there is!

You are talking about insulating your walls, right? (Not under your slab.)

 

[slimcake]

You are talking about insulating your walls, right? (Not under your slab.)

Yes and no. I did the whole house in spray foam insulation. Under the basement and the garage slab is 1.5 inches of closed cell spray foam insulation as well. Don't know why anyone would do it any other way!!

 

[wssix99]

Under the basement and the garage slab is 1.5 inches of closed cell spray foam insulation as well. Don't know why anyone would do it any other way!!

Sorry to be the bearer of bad news. Regular foam board is much more resilient to long term compression loads/stresses. If you compare "compressive creep" ratings for the materials, you'll see that the foam board compresses much less under higher loads over a longer period of time.

Leaving extra "pads" for lifts also can create high stress areas in the slab, (depending on their location, positioning of saw cut joints, the slabs reinforcing layout, etc.) leading to cracks under/around the lift posts. This also compromises the slab insulation. (The lift base plates are designed in such a way that "footers" are not needed, which is why the lift instructions call for simple plain slabs.)

 

[slimcake]

Sorry to be the bearer of bad news. Regular foam board is much more resilient to long term compression loads/stresses. If you compare "compressive creep" ratings for the materials, you'll see that the foam board compresses much less under higher loads over a longer period of time.

Leaving extra "pads" for lifts also can create high stress areas in the slab, (depending on their location, positioning of saw cut joints, the slabs reinforcing layout, etc.) leading to cracks under/around the lift posts. This also compromises the slab insulation. (The lift base plates are designed in such a way that "footers" are not needed, which is why the lift instructions call for simple plain slabs.)

Well alright mister smarty pants. Ur saying that 4x8 sheets of foam on top of rocks will be better than closed cell foam? Huh. I guess u should study up. Closed cell is like pouring concrete on top of those rocks. Open cell maybe but closed cell?? Come on man...

Sent from my Moto Z (2) using Tapatalk

 

[poppinjohnnies]

Check my build link below. I used 2". This will be the first winter for it. No moisture sweat to date.
Buffettfan: You have another Parrothead here, dude!

 

[wssix99]

Well alright mister smarty pants. Ur saying that 4x8 sheets of foam on top of rocks will be better than closed cell foam?

Yes, it will perform better. Over time, your spray foam will compress more and you will loose insulation value, relative to if you had used insulation board.

I'm not trying to be "smart," and I'm not going to call you any names. I'm giving you a reference to where you can look up the properties of these materials so you can understand why everyone else isn't doing this, which is what your question was.

Huh. I guess u should study up.

I don't understand why others should study up when they follow the professional norms, understand how this works, and read the instructions before they use a material. Here are some technical documents for foam board that discuss the compressive strengths they are designed for. There are also footnotes that describe the creep characteristics of the material. I would be very interested to see if you have any similar documentation for spray foam that gives installers assurance that the product has been similarly tested or is similarly resilient.

http://commercial.owenscorning.com/assets/0/144/172/174/c273fe0e-e0c8-4bb2-9ed3-6e3ba390a12c.pdf
http://msdssearch.dow.com/Published...foam/pdfs/noreg/179-02548.pdf&fromPage=GetDoc

Closed cell is like pouring concrete on top of those rocks.

So is drywall. You can put a sheet of drywall flat on the floor and walk around on it, just fine. However, if you do this over time - it will develop ruts. (This is a similar phenomena.)

Epoxy has similar issues also and only special epoxies can be used overhead or under sustained tension because of it. (Even though epoxy seems rock solid, it slowly flows like a liquid and will fail under sustained stress.) http://www.nytimes.com/2007/07/11/us/11bigdig.html

 

[willymakeit]

Foam blocks are used under roads and other civil projects for fast fill. Same reason sheets or blocks are used under slabs.