Insulation, Radiant and Vapor Barriers - Insulating Shed/Barb with no soffit
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jollybgood
04-10-08, 07:49 PM
I bought a house last year that has a two story barn/shed in the back yard.
It's approx 18 x 14 feet. New construction with vynyl siding. Typical barn-like roof with steep roof.
I insulated/heated the first floor last year. Stayed very warm and toasty all winter. Second floor was sealed off and was left unfinished.
Now I'm turning my attention to tackling that second floor.
I insulated/drywall the front/back walls. Added a few windows and a door (that will eventually go out onto a deck/stairs).
I've been leaving the roof/ceiling and side walls/knee walls for last before insulating putting up dry wall.
The trusses are 2x4s.
There's no ventilation at all. (no soffit and no roof vents).
Obviously I want to do the job right and I'm concerned about ventilation/condensation. But I also don't want to do more work than necessary.
The shed is less than two years old. I'd rather not add a ridge vent/drip vent if I can avoid it.
I was thinking of doing the following;
• Adding two Roof vents along the top of the roof.
• Adding four (two on each side) roof vents lower down on the roof right before the point the slop drops off steeply.
• using 2x2's to bring the 2x4's out to 2x6 and then using rolled R19 insulation between the trusses (24 inch on center). That should give me 2" or so of air flow between the rafter and roof sheeting.
I'm thinking that should create air flow high on the roof where it's not so steep and the sun hits it directly.
But there would still be no air flow on the lower part of the roof where it's steeper.
The solution I'm thinking of is to add small vents on the front back wall that open into the knee walls. I don't have much room for vents there -- maybe 16 inches by 16 inches.
Do you think this would be adequate for a small building with a steep roof?
Other than a drip edge vent (which I've only just read about) I can't think of any other way to add air intake.
BTW Building is heated with electric heat btw. No plumbing or water sources inside. So I expect humidity to be relatively low if that makes a difference. Not heated 24/7 -- only 4 to 8 hours during the day when I'm working out there.
I'll only have about 12" of clearance between the sheeting and ceiling at the apex -- Not sure if there's enough room for an electric exhaust vent.
Anyway I'm open to suggestions.
Update to my question.
I just measured the roof pitch on what is effectively the 'side walls' (where the barn roof drops off steeply).
It's 29/12. Incredibly steep. Would this be a factor to my advantage? Meaning -- can I treat those areas of the roof as though they were walls (keeping two inches of airflow between the sheathing/insulation) and just deal with the upper (flatter) portion of the roof as far as ventelation issues?
It's approx 18 x 14 feet. New construction with vynyl siding. Typical barn-like roof with steep roof.
I insulated/heated the first floor last year. Stayed very warm and toasty all winter. Second floor was sealed off and was left unfinished.
Now I'm turning my attention to tackling that second floor.
I insulated/drywall the front/back walls. Added a few windows and a door (that will eventually go out onto a deck/stairs).
I've been leaving the roof/ceiling and side walls/knee walls for last before insulating putting up dry wall.
The trusses are 2x4s.
There's no ventilation at all. (no soffit and no roof vents).
Obviously I want to do the job right and I'm concerned about ventilation/condensation. But I also don't want to do more work than necessary.
The shed is less than two years old. I'd rather not add a ridge vent/drip vent if I can avoid it.
I was thinking of doing the following;
• Adding two Roof vents along the top of the roof.
• Adding four (two on each side) roof vents lower down on the roof right before the point the slop drops off steeply.
• using 2x2's to bring the 2x4's out to 2x6 and then using rolled R19 insulation between the trusses (24 inch on center). That should give me 2" or so of air flow between the rafter and roof sheeting.
I'm thinking that should create air flow high on the roof where it's not so steep and the sun hits it directly.
But there would still be no air flow on the lower part of the roof where it's steeper.
The solution I'm thinking of is to add small vents on the front back wall that open into the knee walls. I don't have much room for vents there -- maybe 16 inches by 16 inches.
Do you think this would be adequate for a small building with a steep roof?
Other than a drip edge vent (which I've only just read about) I can't think of any other way to add air intake.
BTW Building is heated with electric heat btw. No plumbing or water sources inside. So I expect humidity to be relatively low if that makes a difference. Not heated 24/7 -- only 4 to 8 hours during the day when I'm working out there.
I'll only have about 12" of clearance between the sheeting and ceiling at the apex -- Not sure if there's enough room for an electric exhaust vent.
Anyway I'm open to suggestions.
Update to my question.
I just measured the roof pitch on what is effectively the 'side walls' (where the barn roof drops off steeply).
It's 29/12. Incredibly steep. Would this be a factor to my advantage? Meaning -- can I treat those areas of the roof as though they were walls (keeping two inches of airflow between the sheathing/insulation) and just deal with the upper (flatter) portion of the roof as far as ventelation issues?