Replies

1. 
   hasbeen | Jul 25, 2003 03:35am | #1

   Are you planning to heat the garage?  Will you have south windows that could give you some solar gain?

   Any jackass can kick down a barn, but it takes a carpenter to build one.

1. 
   pccb | Jul 25, 2003 04:01am | #2

   hey hasbeen.

     Yes it will be heated. but i am wondering if the 32" i.c.f. stem wall will keep the slab from having a frost heave. thanks pedro

1. 
   hasbeen | Jul 25, 2003 05:33am | #3

   My thought would be that it would help a little, but I wouldn't do it UNLESS I was going to heat the garage full time to room temp all winter.  Then I'd probably go ahead and do it, if I could afford it at the time.

   I wasn't thinking about frost heave, just heating.  Any jackass can kick down a barn, but it takes a carpenter to build one.

2. 
   hasbeen | Jul 25, 2003 05:36am | #4

   Cold climate means different things to different people.  I've lived in the Arizona desert and the mtns of western Montana.  Is your garage inspected?  If you really live in a very cold climate 32" sounds a bit shallow for the footer.  Not insulating the slab would tend to keep the soil under the garage a bit warmer...

   Any jackass can kick down a barn, but it takes a carpenter to build one.

3. 
   Nivek | Jul 28, 2003 12:59am | #5

   How cold is your climate? Here up north we have to co a minimum of 48" with our footing to get below the frost line. If 32" is sufficient in your area you will not have to worry about frost heave. Insulating the floor would be good for radiant floor heating to stop the heat from going into the ground instead of through the concrete. You may however consider placing styrofoam to your fondation wall to stop the cold from coming through the concrete fondation and getting under your floor.

   Kev

4. 
   DennisS | Jul 28, 2003 08:28am | #6

   Pedro -

   It may be too late if you've already graded your base, but I'd advise putting a 6" lift of pea gravel under the slab for a capillary break and 2" of polyiso foam (of similar)insulation. The insulation isn't all that expensive in the long run, contributes to a consistent slab thickness and provides a good base for the rebar chairs during placement of the concrete.

   If you intend to furr and finish the interior of the garage, I like to extend the insulation up the inside of the perimeter walls to the thickness of the slab as well to reduce the edge loss.

   ...........

   Dennis in Bellevue WA

   [email protected]

1. 
   dtown | Jul 28, 2003 07:42pm | #7

   What would be the difference in using 1.5" rigid versus 2"?  I know the r-value changes but aren't we just looking for a thermal break here of sorts?  The heat will be transfered mostly through conduction.  I am in a similar situatino and am trying to decide between 1.5" Owens Corning Foamular 150, 2" of the same product, 1.5" and 2" of the Dow Blue Board, and plain old EPS white board.  I have concerns with the compressive force rating on the EPS being only 10 psi along with it's absorption.  THe absorption should be a big deal under the slab with a vapor barrier below but the perimeter is more of a concern.  Anyone else out there with knowledge or recommendations?

1. 
   joeh | Jul 28, 2003 08:40pm | #8

   DTown, beadboard type XI is rated at 25 pounds per square inch, type II is 15. I believe for a garage slab type II is adequate and the cost is less than half of the extruded boards.

   Joe H

2. 
   Gabe | Jul 29, 2003 12:44am | #9

   The real downside to using beadboard where moisture is expected is that it's permeable and will not only absorb water but will deteriorate over time if cycled.

   Gabe

   You may find this little site helpful https://www2.srp.gov/homeenergymanager/advisor/foaminsul.html

   Just be careful how you interpret the information contained.

1. 
   xMikeSmith | Jul 29, 2003 01:28am | #10

   dennis... bead board comes in different compressive strengths.. if i was putting it under a slab i would buy 2.0 lb/cf instead of the normal 1.0 lb/cf

   also.. a loot of swedish studies have shown that there is no measureable absorption of water in EPS.. so that myth has been debunked AS FAR AS I'M CONCERNED..

    others may choose to disagreen.. but my thoughts have changed about EPS vs. poly-iso over the last few years.. time was we would use only blue board, pink board or green board , but they are overrated  and in a lot of conditions cannot perform as well as EPS..

    now this is just my own humble opinion.. so take it for what it's worth...

   GABE has installed more cf of foam insualtion on one project that i will in my entire life... and his site was a very informative site.. however.. field tests of EPS buried  and underwater have shown that it does NOT absorb water...

    to restate:

   EPS is not permeable

   EPS is available in different densities

   EPS can be manufactured with borates to prevent vermin infestation.. none of the poly-iso's are so treated..

   EPS costs about half of what the same R-value of poly-iso...

   in short.. in your case i would spec 2" EPS at a density of 2.0 lb/cf

   Mike Smith   Rhode Island : Design / Build / Repair / Restore

   Edited 7/28/2003 6:34:04 PM ET by Mike Smith

1. 
   BillHartmann | Jul 29, 2003 02:06am | #11

   Mike

   I have seen EPS absorb water and LOTS OF IT.

   It was used as floation.

   I suspect that it was very low density product that had lots of space between the beads. Wrong product for the application.

   But I would not be concerned with a higher density product installed over a gravel bed.

2. 
   Gabe | Jul 29, 2003 03:20am | #13

   But I would not be concerned with a higher density product installed over a gravel bed.

   Gravel bed ain't the determining factor as much as the water table. One of the reasons for placing the VB directly underneath the concrete.

   As much as gravel is a great drainage media it is an equally great media for water to gather after a good rain.

   Underneath your slab, the gravel will conduct just as much water and any other saturated media and permeate through your slab.

   Mike, I don't base my comments on having installed a whole mess of foam insulation, I based it on the buildings that I have demolished to make way for the new ones. Buildings that had one form of bead board or another that has totally disintegrated during cycling and had a zero R factor.

   Insulation is not the place to save a buck today because that initial saving will cost you bucks forever after.

   Gabe

3. 
   DennisS | Jul 29, 2003 02:12am | #12

   Mike -

   I should probably not push polyiso in the manner it obviously appears, .... it's really more of a knee jerk option to use it here in our area (the Pacific NorthWest) where we, I at least, always spec at least a 6" lift of 3/8" pea gravel as a capillary break. Moisture migration isn't an issue with my slabs since I do everything I can to eliminate ground water under the slab in the first place. Expanded Polystyrene is probably every bit as good as Polyiso. I use rigid insulation as much to provide a consistent substrate for the slab as for anything. So from now on I'll just refer to it as "rigid" insulation. Most all these types of insulation perform quite well with respect to one another.

   Thanks for the information and pointing out my error.

   ...........

   Dennis in Bellevue WA

   [email protected]

4. 
   maggie2142 | Jul 29, 2003 03:57am | #14

   "if i was putting it under

   a slab i would buy 2.0 lb/cf instead of the normal 1.0 lb/cf"

   Mike,

   Would you use the 2 lb/cf density due to its greater compressive strength when in place under the slab (25 PSI vs 10 PSI), or because it is easier to handle and install without breaking and less likely to get damaged when the concrete is placed?

5. 
   xMikeSmith | Jul 29, 2003 04:14am | #15

   for the 2d reason.. and for that reason i would only use 2" no matter what foam we were installing under concrete..

    at times in the past we have used 1"  and even 1.5"... both always wound up with broken edges during the pour.. the 2"  ( especially with 1" of sand broadcast over it )always survived intact..

   the other nice thing about the 1" of sand is if your are using a poly vapor barrier, the sand anchors it and protects it and helps to quiet the concrete sub with his complaints about the "bleed water not having anyplace to go"  (??????)...

   Gabe:  i think there is EPS and eps.. but the tests i saw convinced me that my past thoughts about EPS in general , were wrong.. and i was missing the boat on using a good product... so i started looking for reputable mfr's.. so far I'm satisfied with anyone who manufactures under the franchise of "R-Control"

   http://www.r-control.com/ Mike Smith   Rhode Island : Design / Build / Repair / Restore

6. 
   Gabe | Jul 29, 2003 04:58am | #16

   I don't know about that product Mike............it's endorsed by Bob Villa. :)

   Well old buddy, if there were only one that did it all, there would be only one  product on the market.

   One kind of car, one kind of truck and holy crapp only one kind of fishing rod.....

   Thank the stars above that we have choices to argue over...

   Gabe

7. 
   xMikeSmith | Jul 29, 2003 05:36am | #17

   yeah.. i almost choked when i saw bob's smiling face.... .. but.. how's it go ?  the friend of our friend is our friend

   or somtin like datMike Smith   Rhode Island : Design / Build / Repair / Restore