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md2lgyk 07-30-2012 10:18 AM

Insulating a Garage
 
We have a detached 12x30 premanufactured garage (one of those Amish buildings). I am in the middle of turning 240 sq. ft. of it into an art studio for my wife. There will be no water or sewer, but it will be insulated and have heat, lights, air conditioning, and even a small wood stove.

We built our own house, so this project isn't a big deal. But I'm not sure how to handle the ceiling insulation. The roof is built using 2x4 trusses, which she wants to leave open to give a cathedal ceiling look. That means I have only a 3-1/2 inch cavity for insulation.

What is the best way to maximize the R-value in this situation?? I'm thinking rigid foam board, but that's pretty expensive. So is spray foam. Any other options?? She doesn't expect to be using the studio much during the winter (we live in Eastern WV) but wants to at least be able to keep it above freezing to protect her paints and other supplies.

Windows on Wash 07-30-2012 11:03 AM

Rigid is going to be your best bet for R-Value per inch and cost effectiveness.

Is the current roof vented in any capacity?

The rigid foam will require, if you are going to go code, a thermal barrier between it and the space.

Even if you used SPF, I would but a layer of rigid up just so that you don't need to trash the foam if the roof ever need a piece of plywood to come off.

md2lgyk 07-30-2012 11:27 AM

Great, thanks for the info. Since the walls and floor are nearly finished, spray foam is pretty much out of the question. It was just a thought early on.

Not sure what you mean about the thermal barrier. I intend to finish the ceiling with tongue & groove pine or maybe beadboard, so the insulation will be covered. Is there something else I need to do?

The roof is not currently vented at all, nor do I plan to vent it. Will that cause problems, considering this space will be only occasionally occupied and not lived in? I don't see how I could vent it anyway - putting in baffles would take away much of the already-limited insulation space.

Windows on Wash 07-30-2012 01:40 PM

Rigid board then and fur out the bottom chords of the trusses and cover them as well to break the thermal bridge.

The T&G qualifies as the thermal barrier.

md2lgyk 07-31-2012 09:48 AM

Great, thanks.


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