Proper wall insulation question.

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edselsouth1

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Exterior walls in an upstairs living space over a garage. Vinyl siding exterior, 1/2" green foam board, 7/16" OSB, are the layers from exterior inward. What would be the proper insulation for the 2x4 walls? Can't afford spray foam. Would like to use Roxul, but our big box stores claim it is unavailable here (north Alabama). Interior wall surfaces will be 1/2" drywall. Should standard insulation be faced or unfaced? Thanks for your replies.
 
Just because the big box stores don't sell it...doesn't mean you can't buy it. I'm not saying it is the right choice, but don't let some business major with no hands-on experience make that decision.
 
I can purchase Roxul by driving to locations in north Georgia, and s.e. Tenn. Guess unavailability is an Alabama thing.
Do you have an opinion as to the insulation I should be using in this application, if not Roxul? Using Roxul is not written in stone, but it is an alternative to what is available here. Pros and cons in this application? Thanks.
 
Fiberglass will work fine. what ever you use it will come in thickness for 2x4 or 2x6. And for walls with studs at 16" OC and 24" OC.
We use plastic sheeting for vapour barrier and only stores like Home depot carries the paper back, it dosn't add anything IMO. Not sure it is normal to need it where you are.
Sloped ceiling under roof is a whole different ball game.
 
slownsteady said:
Just because the big box stores don't sell it...doesn't mean you can't buy it. I'm not saying it is the right choice, but don't let some business major with no hands-on experience make that decision.
Click to expand...

There you go.

Say you are dealing with HOME DESPARADO. Go to their online catalog, find the product you need and order it. It will be delivered to the near-by store for pickup.
 
You will be more than likely trying to keep the heat out than keeping it in as most of us up north insulate for. The craft paper is really a pretty poor vapor barrier by all accounts and is really better at stopping air movement than it is at stopping moisture. Where you live moisture could really be coming from both directions depending on the time of year. you have the OSB, foam and siding and I would assume they taped the joints so I think you are well covered in protection from moisture coming in. I would put it up with the craft paper to the inside as it will be easy to staple up and then drywall without plastic. If the bonus room is just in framing now I would even think about building it out to get a thicker insulation layer in the walls. If you have rafter area that needs insulated you will need to maintain airflow under the roof from the soffits to the ridge vent. Another area is in the garage ceiling. Is the garage ceiling finished and was it insulated?
 
I'd go with paper-faced fiberglass. It provides enough vapor barrier but it's imperfect sealing also helps prevent moisture build-up in the walls which can happen in humid climates like much of the SE US has every summer. That styro outside of the wall sheathing goes a long way to reduce the Sun's radiant heating effects which can be problematic here too.

Phil
 
Thanks to all for your suggestions. All walls (interior and exterior) are 2x4 construction. Looks like I will be using kraft faced fiberglass insulation.
I still will need to install soffit vents, and ridge (gable end) vents, and an attic exhaust whirleybird. Not using an integrated ridge vent on this one.
The 1/2" foam board on the exterior was not only taped, but each joint was caulked as the foam board was installed. (This entire project was an "inherited" thing, so I had no input on it).
The garage framing was done w/ 2x6 P.T., 16"o.c., w/ approx. 12" cross-braced engineered I-Beam , 16" O.C. for the overhead. Same siding, foam as the upper story.
The garage ceiling has not been insulated or finished in any way. It is just a work/storage area for now. I'll post some pictures in another thread pertaining to the insulation of that area, and subsequent finishing.
Thanks again.
David.
 
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