insulation advice -- am I doing it right?

[bnovak3478]

My garage is unheated and the ceiling drywall has been removed -- it also has HVAC vents running thru it and has no insulation in it -- however, the 2 walls that share the house are insulated. I am getting ready to insulate both the vents (with insulation wrap) for condensation and energy efficiency and the floor (ie my ceiling). My plan is to use R30 faced insulation with the paper facing up to act a moisture barrier. The ceiling will be re-drywalled with 5/8" drywall that will be glued and screwed to the joists, then mud and taped. Does this sound reasonable?
thanks/Bob

 

[CNGsaves]

Welcome to GJ. Great idea to insulate your garage.

Post up a few pictures so you'll get best responses.

 

[Rob_b]

Is there any drywall up there now? If not, use some 6mil poly across the joists, then drywall and finish as you said. The paperback insulation is good but poly would be better. If you can poly above the joists then do that. Tuck tape any joints and lay the poly down in between the joists then insulate. This will work better. Is your garage door insulated? How do you plan to heat it?

 

[MrMark]

where do you live? You may need to use unfaced batts. If in a warm hot place the last thing you want is a vapor barrier or strong retarder on the inside. The vapor barrier is only for really cold places that are predominantly in need of heating. Vapor barrier on the inside in an AC'd space for example would be disaster. Think of the warm moist outside air going into the attic and then hitting the cold dry air on the other side of your vapor barrier. What do you think is going to collect on the top of that barrier?

 

[philjafo]

If you live in a cold climate, sprayfoam. I'm just guessing that the ceiling in the garage was removed the figure out why the room above it was always so cold. Yes the sprayfoam is more expensive, but do you want to redo the ceiling a second time?

 

[rburke65]

Oh sure.....you want him to tell you where he lives for answers to an insulation question? That would be so much easier! What?......you guys can't handle a challenge?

 

[bnovak3478]

thanks for the quick replies! -- I live in northern Virginia (Fairfax county -- we run the full range of hot and cold temps) -- I wont be heating the garage, but definitely want to get the bedrooms above it warmer -- that is what I am insulating. Everything I read says to insulate with faced insulation -- face up to the bedrooms above it. I have several areas where the HVAC ducts are fit very tight against the joists (16" on center) and up against the the bottom of the sub floor of the rooms above the garage, I am spray foaming around these ducts -- with the other ducts, I am wrapping in insulation and then using the R38 with the faced vapor barrier to finish the job. After that, 5/8" drywall will be applied. Thanks for any more insight.

 

[bnovak3478]

thanks for the quick replies! -- I live in northern Virginia (Fairfax county -- we run the full range of hot and cold temps) -- I wont be heating the garage, but definitely want to get the bedrooms above it warmer -- that is what I am insulating. Everything I read says to insulate with faced insulation -- face up to the bedrooms above it. I have several areas where the HVAC ducts are fit very tight against the joists (16" on center) and up against the the bottom of the sub floor of the rooms above the garage, I am spray foaming around these ducts -- with the other ducts, I am wrapping in insulation and then using the R38 with the faced vapor barrier to finish the job. After that, 5/8" drywall will be applied. Thanks for any more insight.

 

[MrMark]

The faced insulation may be ok for you but I wouldn't be putting up any vapor barrier. You should study the building science website, as it gives the low down on vapor barrier/retarder by climate zone. Please report back your on your research.

http://www.buildingscience.com/docu...rs?topic=resources/vapor_barrier_code_changes

 

[MrMark]

looks like you are zone 4. According to the recommendations you should NOT use any form of vapor barrier or retarder on the floor assembly. That means unfaced batts. The article explains that vapor barriers are an artifact of arctic and extremely cold regions that are predominantly conditioned by heating. You are going to cool that room over the garage I'm sure and the warm moist air in the garage is going to move toward that cool dry air in the bedroom above. The warm moist air will condense on the underside of that vapor barrier in the summer.

I think the most recent studies show that if you can avoid using vapor barriers and retarders, you should.

I have a similar situation where the house is basically mixed heating and cooling. A traditional vapor barrier makes sense in the winter but is disaster in the summer, thus the best practice is to avoid altogether and let the wall and floor breathe.

 

[mechanicworkman]

Pictures are worth a thousand words