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I'm preparing to drywall my attached garage and have run into conflicting opinions on if I should staple the insulation flanges to the sides of the stud or the face. I live in the San Francisco bay area, so it rarely freezes and winters are mild. I am planning on installing faced insulation bats in the exterior walls. I don't believe I need to install a vapor barrier, but will be double checking with the city building inspector if they are necessary.

I am inclined to staple the paper flange to the face of the stud in order to more completely fill the stud cavity. However, I've read that some people say this can cause drywall screws to pop more easily. It also makes it harder to glue drywall to the face of the studs (which I was not planning on doing). I am planning on doing only one layer of tape/mud and not planning on painting so I am not too worried about some popped screws.

Assuming the inspector doesn't care which method is used, which way should I go?

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2 Answers 2

up vote 4 down vote accepted

Attach to the stud face. The vapor barrier is not as effective if stapled to the stud sides. And as you say, the fill won't be ideal. (are your external walls 2x4 or 2x6?) The paper on the fiberglass is the vapor barrier. And a barrier is definitely needed where you live. Optionally, you can use unfaced insulation and a plastic sheet vapor barrier. I've done lots of sheetrock over insulation and the insulation is not the problem with popped screws. It can cover and hide forgotten screws/nails/bumps which will cause problems. One bonus is when there is a couple layers of paper between the sheetrock and studs, it can cut down on noise/vibration conduction through the walls.

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Which side of the insulation should the vapor barrier go on? In San Fransisco, it's often (if not always) more humid outdoors than indoors. –  TDHofstetter Aug 19 at 18:00
    
@TDHofstetter Vapor barrier always goes on the warm side of the wall. Air allowed to move to a colder portion of the wall will drop it's moisture as condensation inside the wall. –  Paul Aug 19 at 18:03
    
So which side is the warm side in San Fransisco? –  TDHofstetter Aug 19 at 18:05
    
@TDHofstetter Relative humidity might be higher outside than inside, but absolute humidity (total water content per mass of air) is surely higher inside than outside. Unless you are running a dehumidifier in the house... –  Paul Aug 19 at 18:08
    
It's a hard call in the Bay Area, especially with the windows open (as they often are)... indoor air VERY OFTEN (exactly) equals outdoor air, even overnight. –  TDHofstetter Aug 19 at 18:13

It doesn't matter at all. I actually used to make my crew attach to the face and they actually came back to me with this report.

If you read through the report you will see that there is a 1% difference in performance if you staple face or side. It is negligible.

On the flip side I will say I haven't ran across screws popping because of stapling to face and now I do it either way. For instance I tell them to do it on face if doing a basement and home owner requests this type of insulation - which I suggest against for basements but anyway. Reason for this is to keep the insulation away from the wet walls and allow extra room for moisture to evaporate and move. Really the stapling decision is made on a need basis now.

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