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Author	Comments
Kyle & Son Posted: Aug 26, 2012 09:35 AM	Closed Cell Under Slab I'm spraying 2" of CC foam directly on the gravel before the concrete comes for a heated garage slab. Does anyone have an estimate of how much more foam I will need to add for spraying on the #2 stone under the slab? Thanks, Kyle
mason Posted: Aug 27, 2012 05:27 PM	Assuming the gravel is dry. The surface profile would add about 30% to the overall sq footage. The first one inch of foam would require about 30% more. Then spray the 2nd inch calculating about 15% extra. Use as cool a temperature setting as possible on your first pass (making sure you have a good mix). This allows the foam to settle into the cracks between the gravel, making a smoother profile for your next lift.
jimcoler I have over 10 years of experience specifying and installing open and closed cell spray foam. I've sold my business but I'm still selling for the new owners and consulting on large and custom specific jobs. I've expanded my knowledge into t Posted: Aug 28, 2012 09:59 PM	I have to say that you don't need much insulation under the slab. We done a lot of radiant floor heating up here in the north and put only an R-2.9 under the entire slab which acts as a vapor barrier, thermal barrier and radon retarder. It's made specifically for under concrete floors and radiant heating situations. When you think about it, the room is only about 65F and the ground under the slab is about 50F, so you don't have much of a temperature spread, so not much insulation is needed. I know codes say you need an R-10 or higher in some areas, but where did this come from? It came from the blue board companies pushing their product because it's R-10 for a 2" thick piece of foam board and this is the easiest for them to manufacture and handle!!! This didn't come from actual studies or real live cases! I know because I've seen it work in many cases! We have customers claiming 50% or higher energy savings by using this system and foaming the rest of the house!!!! So, how much of that R-10 is going to gain you anything when the first R-2 covers the majority of heat loss??
John Shockney Posted: Aug 29, 2012 01:45 PM	One school of thought when it comes to radiant floors is to insulate the sides of the slab down below the frost line and in 4-8 feet in under the slab, leaving the center un-insulated to then use the thermal mass of the earth underneath to store heat. This can help keep the water from freezing during power outages. Airpro
paul rogers Posted: Sep 02, 2012 11:54 AM	My thinking is close to air pro. Spray 2-3" to outside footing. All the way down 42". The thermal mass inside footing of the building is going to provide enough heat to prevent frozen water pipes. I have already heard of stories where 6 summer cottages in Northern Michigan lost power for 10 days at near zero temps. These cottages were on the same road near lake Michigan 5 had frozen pipes and water damage. The lone foamed cottage was 40-42 degrees inside and that was with out the footings being sprayed with closed cell. No damage to the foamed cottage as it never got below freezing. I am told that the ground 5 foot down is something like 52-53 degrees, whether it's Texas or North Dakota. So could not spraying the area below the cement floor be even better for holding heat in the winter?
maurice richter Posted: Sep 02, 2012 07:41 PM	Look up Frost Protected Shallow Foundation or Frost Protected Slab. You might be surprised how thin the insulation needs to be and how deep it does not have to go. Since my home is already a shallow foundation (built prior to 1900), I plan to add insulation outside the foundation like FPSF idea.

Author

Comments

Kyle & Son

Posted: Aug 26, 2012 09:35 AM

Closed Cell Under Slab

I'm spraying 2" of CC foam directly on the gravel before the concrete comes for a heated garage slab. Does anyone have an estimate of how much more foam I will need to add for spraying on the #2 stone under the slab?
Thanks, Kyle

mason

Posted: Aug 27, 2012 05:27 PM

Assuming the gravel is dry. The surface profile would add about 30% to the overall sq footage. The first one inch of foam would require about 30% more. Then spray the 2nd inch calculating about 15% extra. Use as cool a temperature setting as possible on your first pass (making sure you have a good mix). This allows the foam to settle into the cracks between the gravel, making a smoother profile for your next lift.

jimcoler

I have over 10 years of experience specifying and installing open and closed cell spray foam. I've sold my business but I'm still selling for the new owners and consulting on large and custom specific jobs.

I've expanded my knowledge into t

Posted: Aug 28, 2012 09:59 PM

I have to say that you don't need much insulation under the slab. We done a lot of radiant floor heating up here in the north and put only an R-2.9 under the entire slab which acts as a vapor barrier, thermal barrier and radon retarder. It's made specifically for under concrete floors and radiant heating situations. When you think about it, the room is only about 65F and the ground under the slab is about 50F, so you don't have much of a temperature spread, so not much insulation is needed. I know codes say you need an R-10 or higher in some areas, but where did this come from? It came from the blue board companies pushing their product because it's R-10 for a 2" thick piece of foam board and this is the easiest for them to manufacture and handle!!! This didn't come from actual studies or real live cases! I know because I've seen it work in many cases! We have customers claiming 50% or higher energy savings by using this system and foaming the rest of the house!!!! So, how much of that R-10 is going to gain you anything when the first R-2 covers the majority of heat loss??

John Shockney

Posted: Aug 29, 2012 01:45 PM

One school of thought when it comes to radiant floors is to insulate the sides of the slab down below the frost line and in 4-8 feet in under the slab, leaving the center un-insulated to then use the thermal mass of the earth underneath to store heat. This can help keep the water from freezing during power outages.

Airpro

paul rogers

Posted: Sep 02, 2012 11:54 AM

My thinking is close to air pro. Spray 2-3" to outside footing. All the way down 42". The thermal mass inside footing of the building is going to provide enough heat to prevent frozen water pipes. I have already heard of stories where 6 summer cottages in Northern Michigan lost power for 10 days at near zero temps. These cottages were on the same road near lake Michigan
5 had frozen pipes and water damage. The lone foamed cottage was 40-42 degrees inside and that was with out the footings being sprayed with closed cell. No damage to the foamed cottage as it never got below freezing.
I am told that the ground 5 foot down is something like 52-53 degrees, whether it's Texas or North Dakota. So could not spraying the area below the cement floor be even better for holding heat in the winter?

maurice richter

Posted: Sep 02, 2012 07:41 PM

Look up Frost Protected Shallow Foundation or Frost Protected Slab. You might be surprised how thin the insulation needs to be and how deep it does not have to go. Since my home is already a shallow foundation (built prior to 1900), I plan to add insulation outside the foundation like FPSF idea.

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