UnderSlab Minimum

Rich L.

Insulation isn't cheap but neither is energy. And the sad part of that statement is that we probably won't ever see energy this cheap again. Invest in the building envelope as you go. If it were me I would (and did) put 2" under and around the slab and a minimum of R19 in the side walls. Min of R38 in the ceiling, more is better. Insulation is a one time expense but the utilities to condition your building are ongoing. The tighter you make the structure now, the more you'll save down the road.

Rich L

m whooley

UnderSlab Minimum

Hello Wallies! Hoping for some feedback from all of the experience here:

I'm putting up a 1000 sqft post-frame garage (pole barn) and will be roughing in the radiant slab. Thinking of 1.5" XPS under slab and perimeter. Location is E Central PA, and wondering if 1.5" is really enough. The building is for storage and part time shop, expecting to keep the temp normally around 50(?).

Thanks much, appreciate any feedback!

GLENN_14

linier ft per sq ft

The answer lies mostly in the construction of the polebarn. If you plan on insulating it well then 12" on centers works well. Remember to insulate under the slab if you want to keep the long term operating cost down. Also you need edge insulation along the point where the slab meets the wall. The space should be quite comfortable for work and you can expect to use quite a bit less fuel to accomplish this level of comfort.

m whooley

Thank you Glenn,

The plan is to use at least R-10 on the walls/ceiling to start, and the slab will have the 1.5" XPS underneath and around the slab edge.

Unknown

bump up to 2" on the vertical edges, at least; that's an area of severe loss.

The rest, I'd prefer 2", but 1.5" isn't bad.

R10 for walls/ceiling is NOT adequate in your climate however. bump it up there for sure. Insulation is the gift that just keeps on giving, and energy is not getting any cheaper.

GLENN_14

rob is also correct

You want as much insulation as you possibly can get. it will never go away and will always help in keeping the bills down. you should also consider using some type of freeze protection (glychol) in the system as you will not be "living" in the space....

kpc_10

I like the insulation advise....

but my opinion is stay away from the glycol....I hate the stuff. Causes nothing but problems. If the slab and barn are well insulated the system could very well hold above freezing temps for several days. kpc

m whooley

Thanks gents -
Definitely agree that the perimeters should be 2" and will do that for sure. As much as I dislike glycol (used to work with it in medium pressure hydraulic systems - 3000 psi) my thinking is it's probably the best insurance against a freeze, especially in the edges of a slab-on-grade.

'Nother one - Seems that blueboard is the standard for underslab, but are there any issues with 25 psi foil faced polyiso instead? I think it has even lower absorption numbers than the blueboard.

m whooley

Thank you gents -
Definitely agree that the perimeters should be 2" and will do that for sure. As much as I dislike glycol (used to work with it in medium pressure hydraulic systems - 3000 psi) my thinking is it's probably the best insurance against a freeze, especially in the edges of a slab-on-grade. But I do not like the stuff.

'Nother one - Seems that blueboard is the standard for underslab, but are there any issues with 25 psi foil faced polyiso instead? I think it has even lower absorption numbers than the blueboard.

GLENN_14

INSULATION

BLUEBOARD WORKS WELL BUT IT DEPEND ON SLAB THICKNESS. YOU CAN USE ALTERNATE MATERIALS BUT THE SLAB THICKNESS MUST BE KNOWN. JUST STAY AWAY FROM BUBBLE FOIL INSULATION WHICH HAS A SORDED HISTORY WITH SLAB POURS.

Tom Manton

Isocyanurate

foam is open cell, not sutable for ground contact or damp location. Moisture entering foam conducts heat rendering insulation useless.

kpc_11

ants also...

love the taste...