Another how to insulate, scissor truss edition

[12husky]

I am scratching my head over the 100 different option to insulate my pole barn ceiling.

Stats:
Eastern Shore of Maryland
36’x48’x12’
Wooden Poles on approximately 8’ centers
7/12 over 4/12 scissor trusses in 4’ centers with 2x6 top member
Bubble insulation under metal roofing
Vented soffit and ridge
Radiant heat in concrete slab
Used primarily for metal sculpture work

The tricky part is that I plan to put a mezzanine second floor in the back half of the shop and would like to keep the space between trusses open. This leaves the 2x6 top chord.

Do I need the venting?

One thought was fiberglass batts between the trusses and foam board on the underside of the top chord to seal everything off.

Ideas?

Thanks,
Matt





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[Bolson32]

Do I need the venting?

One thought was fiberglass batts between the trusses and foam board on the underside of the top chord to seal everything off.

Ideas?

1: You do need the venting, unless you spray foam the underside of the roof.

Ideas:

1:Spray foam the underside of the roof. Would be expensive, ~$1-$1.50 a board foot. You're going to have about 2000 sq ft. Depending on how thick you want to go, you'd probably need at least 3-4" so you're looking at $6-8000.

2: I'd probably just put some new ceiling joists up part way, put up a vapor barrier, dry wall it, and spray it full of cellulose. You're looking at substantially less money and you can DIY it with some buddies. Originally I was thinking OSB vs drywall as it's a bit sturdier, but you'd need to paint it and I still don't think you'd get a 4ft ceiling span without sagging. If you need to add new joists you might as well just use drywall. It's cheaper and you wouldn't have to paint it.

 

[12husky]

1: You do need the venting.



2: I'd probably just put some new ceiling joists up part way, put up a vapor barrier, dry wall it, and spray it full of cellulose. You're looking at substantially less money and you can DIY it with some buddies. Originally I was thinking OSB vs drywall as it's a bit sturdier, but you'd need to paint it and I still don't think you'd get a 4ft ceiling span without sagging. If you need to add new joists you might as well just use drywall. It's cheaper and you wouldn't have to paint it.

Which side would I put the vapor barrier?
From outside in: metal roof, bubble insulation, purlins, air gap, vapor barrier, blown in cellulose, drywall?




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[Bolson32]

Which side would I put the vapor barrier?

From outside in: metal roof, bubble insulation, purlins, air gap, blown in cellulose, vapor barrier, drywall.

Close, flip the plastic and the cellulose. Gotta have the vapor barrier to keep moisture OUT of your insulation. Moisture that's generated from within the building.

Staple the moisture barrier to the underside of the joists, drywall over it. You could use fiberglass batts, but I would imagine that to be super annoying with the pitch, and no real way to crawl in there. Leave a couple of attic hatches in your ceiling, stand there and blow the damn thing full. Easy peasy.

You'll also need to put attic baffles along the soffit line between the rafters. Keep the cellulose from plugging up your ventilation.

 

[12husky]

From outside in: metal roof, bubble insulation, purlins, air gap, blown in cellulose, vapor barrier, drywall.



Close, flip the plastic and the cellulose. Gotta have the vapor barrier to keep moisture OUT of your insulation. Moisture that's generated from within the building.



Staple the moisture barrier to the underside of the joists, drywall over it. You could use fiberglass batts, but I would imagine that to be super annoying with the pitch, and no real way to crawl in there. Leave a couple of attic hatches in your ceiling, stand there and blow the damn thing full. Easy peasy.



You'll also need to put attic baffles along the soffit line between the rafters. Keep the cellulose from plugging up your ventilation.

Thanks. The soffit baffles were the piece I was missing.


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[Bolson32]

Thanks. The soffit baffles were the piece I was missing.


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Yep, good luck. Going to be kind of a big project if you DIY. That's how I'd do it anyway, I'm sure there's more than one way to skin a cat though.

 

[12husky]

Yep, good luck. Going to be kind of a big project if you DIY. That's how I'd do it anyway, I'm sure there's more than one way to skin a cat though.

Yeah I will try to figure out a way to do it a piece at a time. Unfortunately all of my equipment is already in the shop so there will be lots of shuffling around.


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[Schumi]

I have a similar situation. Just built a 35'X40' garage with 11' ceilings. I used pre-engineered trusses for the hip roof. I have a 4" soffit, non-vented in anticipation of foaming the roof. The roof pitch is 14/12 on two sides and 8/12 on the other two. This made a really large roof area.

My question is this: if I spray foam the entire outside envelope (walls and roof), can I then put in blown-in cellulose on top of my drywall ceiling so I am not heating/cooling the huge attic?

Alternatively, if I don't spray foam the roof area and put in regular roof vents low on the backside of the roof will that be enough venting if I have a ridge vent?