Garage Ceiling Insulation Question

[kngelv]

I have this posted on the Heating/AC forum but with 75 views and no responses I figured I'd try here. I recently had a 22' x 24' garage built. It is a typical garage with 8' walls and a center peak around 12'. It has continuous soffit vents and a ridge vent. The walls are insulated and covered. I want the ceiling insulated but want the attic area open for storage, so any insulation must be attached to the underside of the roof. Based on that I have – I believe – two options. I can have spray foam installed making the roof completely sealed or I can run baffles from vent to vent and install kraft faced batts. I am wondering if there are any issues with the kraft faced batts being uncovered? Thanks.


James

 

[Falcon67]

My old shop had kraft faced batts on the ceiling between the joists. I never got around to putting anything else up there. 12 years in there, no issues except that I could make it nice and comfy. Just be careful with fire, etc. If your rafters are 2x6, then R13 would be the most you could do and leave an air space. You could later get energetic and cover that with foam board and then maybe a light paneling. OSB may add too much weight.

 

[moserjj]

If you plan to vent your garage with soffits and a ridge vent like you have, you can't foam the roof underside deck. If you really want the insulation on the deck, you'll have to put the foam vents all the way and you could batts over that. I would put insulation in the attic floor, fir it up if you have too. That's what I did. I didn't want my attic space to be insulated/heated, just a waste for me

 

[kngelv]

The vent baffles are only for the rolled batts. If I insulate with spray-foam then it will be directly on the underside. The quotes I received for 490 sq ft of ceiling space was $1380.00 for 3" of foam and $415.00 for baffles and R-19 batts.

James

 

[slickgt1]

I don't see the point of insulating the roof deck in a vented space. You should plywood the attic floor, insulate with roxul or something under it, and then sheetrock.

 

[Falcon67]

The vent baffles are only for the rolled batts. If I insulate with spray-foam then it will be directly on the underside. The quotes I received for 490 sq ft of ceiling space was $1380.00 for 3" of foam and $415.00 for baffles and R-19 batts.

James

If you spray foam the roof deck, then - as I understand anyway - it becomes part of the conditioned space and you do away with your venting, both soffitt and ridge. You no longer need it. Houses built with the roof and exterior walls insulated like this form a sealed envelope and venting is not done, other than air exchange controlled via the air conditioning system.

 

[kngelv]

I have to insulate the roof directly because I need an open attic for storage. I have stuff that would never fit through an attic hatch. Yes, if I go with spray-foam then vents are unnecessary. If using batts then I have to have baffles running from the soffit to the ridge, otherwise you'll get shingle de-lamination. Air can slowly move through fiberglass batts. My main question is whether there is an issue with exposed kraft-facing in a garage ceiling. Covering it would be a pain.

James

 

[slacker garage shop]

Just my opinion. Its going to be hard to keep down at floor level with a open ceiling but many guys have done it. A couple ceiling fans will help big time. As far as insulation I really like the foil faced 4x8 sheets. I used 1 1\2 thick sheets and the reflective finish really helps brighten things up. Personally I would close it in and put in a drop down staircase to access the attic.

 

[K'ledgeBldr]

My main question is whether there is an issue with exposed kraft-facing in a garage ceiling. Covering it would be a pain.

That issue would be- fire!
Just like in basements years ago- builders could insulate the framed exterior walls with kraft-faced batt insulation. Not anymore. It was deemed a fire hazard because basements had heating appliances. So, then they started using unfaced batts. That was short-lived because of the change in the code mandating the 'envelope' of the conditioned space. Basically; it meant insulating the ceiling of the basement/floor of living space.

Granted, money is always an issue. But, in your case I think the spray foam is the better way to go (Not only will you get a much higher R-value but, there will be no other labor involved. If you have trusses, your depth is only 3-1/2" that not enough for a baffle and a batt. And if you have 2X6 rafters you only have enough space for a baffle and a R-13 batt. If you want at least an R-19 you'd have to add a 2X2 to the edge of the rafter to increase the depth of the cavity).
Not that it's any less susceptible to fire but, it will stay in place and garages by nature usually have great air circulation by the mere fact that they have large doors.

 

[Falcon67]

No issue with the kraft facing unless you take a torch to it. As I posted, it lived with it exposed on ceiling and walls for 12 years, no problem.

>I have stuff that would never fit through an attic hatch.
Me too. I built 4' x 4' uninsulated attic access panels in the old shop, had about 1000 lbs of stuff up there. I had four big movable panels total - on each end center and on each side center. I insulated the rest of the ceiling. IMHO, if you plan well you can insulate the joists and still have access. If your joists are 2' OC, you could easy make a 2' x 8' access panel(s) with rigid foam on the back. Even with uninsulated panels that large, you can still heat and cool the space. My 12K BTU AC unit could easy keep my 20x24 at 75F when it was 100+ outside.

 

[kngelv]

Another reason for insulating directly below the roof is it makes the garage seem larger. My neighbor built the exact same size garage a month after I did mine. He put in an attic hatch and covered it with drywall. It seems smaller because of this. I get a bit claustrophobic in there. I'm think that maybe I'll do the batts and then cover it all with foam board or some kind of sheathing. This will still be less than half the cost of spray-foam.

James

 

[Vvmvbb]

If you have soffits and ridge vents, can't you just cover the rafters with silver board?

 

[Motofixxer]

Research diy spray foam kits. They are available many places. Could be a cheaper option.

 

[GN4WHLN]

Just my opinion. Its going to be hard to keep down at floor level with a open ceiling but many guys have done it. A couple ceiling fans will help big time. As far as insulation I really like the foil faced 4x8 sheets. I used 1 1\2 thick sheets and the reflective finish really helps brighten things up. Personally I would close it in and put in a drop down staircase to access the attic.

I was thinking of doing the same thing. My garage is similar to the OP except mine is not vented. Can the foil faced foam sheets be left exposed? I weld in the garage, so fire is always a concern. Also, for me the cold is controllable in there in the winter between the wall insulation and heater. In the summer, however, I can feel the heat radiating from the roof down to the floor and thought the foil faced foam would reflect and insulate enough to cut that back substantially.