Roof Insulation vs. Condensation

[Welshman]

This isn't a tractor project, but since there are a number of other construction threads here, I'll ask my questions.

My sportsmen's clubhouse is 30'x48' and of pole barn construction. Currently there is no insulation and our plan is to finish the inside as funds permit. We shoot year round and need to keep the place warmer in the winter.

We have an opportunity to buy some 4'x8' sheets of 2 1/2" thick polyiso foam board that is faced with a fiberglass layer on both sides, at a very good price. Our plan is to install this on the roof purlins, which are 2x4's on end, that run parallel to the ridge.

One of our members, a former roofer, has concerns that condensation may form in the cavities (24" x 3 1/2") formed by the covering of the purlins. The building is heated as best we can, about 5 hours a week, in the winter.

Should we be concerned about this, and if so, is there a cheap way to mitigate it?

Thanks in advance.

 

[RNeumann]

Your roofer is right.

One way to mitigate this would be to add eave and ridge vents along with 1x or better yet 2x material vertically. Then attach your ridged insulation to that. Another option would be to add a flat ceiling inside- that would save heating costs and a true vented attic would help.

 

[aczlan]

Your roofer is right.

One way to mitigate this would be to add eave and ridge vents along with 1x or better yet 2x material vertically. Then attach your ridged insulation to that. Another option would be to add a flat ceiling inside- that would save heating costs and a true vented attic would help.

Unless you need the vaulted ceiling space, I would go with putting the panels along the bottom of the trusses, making a flat ceiling (assuming a standard triangle shaped roof truss).
That way, you have less volume to heat so you should be able to heat it with less fuel.
I have a friend who did that in his shop and was very happy with the results. As I recall, he ripped sheets of plywood into 6 in wide strips and attach them to be bottom of the trusses with the strips centered on the trusses.
Then he put the insulation up above the plywood strips so that it is held up on the edges by the plywood strips and sits between the bottom chord of the trusses.

Aaron Z

 

[Welshman]

Your roofer is right.

One way to mitigate this would be to add eave and ridge vents along with 1x or better yet 2x material vertically. Then attach your ridged insulation to that. Another option would be to add a flat ceiling inside- that would save heating costs and a true vented attic would help.

I'm not clear on what you mean by "1x or 2x material vertically".

 

[Welshman]

Unless you need the vaulted ceiling space, I would go with putting the panels along the bottom of the trusses, making a flat ceiling (assuming a standard triangle shaped roof truss).
That way, you have less volume to heat so you should be able to heat it with less fuel.
I have a friend who did that in his shop and was very happy with the results. As I recall, he ripped sheets of plywood into 6 in wide strips and attach them to be bottom of the trusses with the strips centered on the trusses.
Then he put the insulation up above the plywood strips so that it is held up on the edges by the plywood strips and sits between the bottom chord of the trusses.

Aaron Z

The trusses are on 8' centers and are not rated for attaching any material of any weight. We had originally planned on bat insulation at the roof and a suspended ceiling, but then the "deal" on the foam board came along.

 

[RNeumann]

I'm not clear on what you mean by "1x or 2x material vertically.

Sorry- a 1x4 or 2x4 that runs perpendicular (from eve to ridge) to the existing 2x4s. This would create a vertical air channel that should prevent mold and rot. I’d space them every 2’. You could also do 2x2 or 1x2. The idea is to allow air to move up toward the ridge.

 

[SirMaxwell]

The trusses are on 8' centers and are not rated for attaching any material of any weight. We had originally planned on bat insulation at the roof and a suspended ceiling, but then the "deal" on the foam board came along.

Couldn't you just drop those 4x8 foam sheets between the trusses. Surely they don't weigh that much. And while it will not look 'downtown', it will look 'Hunting Camp', provide a flat roof and be much much quieter and warmer. Ohh, it has fiberglass mats, so there that covers the deco. Some wood smoke, a couple of Deer Heads, some misc antlers, a stuffed Badger if you can swing it, one or more singing Bass, and pip, Bob's your Uncle.

 

[RNeumann]

Couldn't you just drop those 4x8 foam sheets between the trusses. Surely they don't weigh that much. And while it will not look 'downtown', it will look 'Hunting Camp', provide a flat roof and be much much quieter and warmer. Ohh, it has fiberglass mats, so there that covers the deco. Some wood smoke, a couple of Deer Heads, some misc antlers, a stuffed Badger if you can swing it, one or more singing Bass, and pip, Bob's your Uncle.

I think I should be offended but I’m laughing to hard. I’ll give you 7 days to apologize.....haha

 

[Welshman]

Sorry- a 1x4 or 2x4 that runs perpendicular (from eve to ridge) to the existing 2x4s. This would create a vertical air channel that should prevent mold and rot. I’d space them every 2’. You could also do 2x2 or 1x2. The idea is to allow air to move up toward the ridge.

Thanks. While there is no ridge vent, we do have two powered vents near the ridge that may suffice with some modifications to the duct work.

 

[Welshman]

Couldn't you just drop those 4x8 foam sheets between the trusses. Surely they don't weigh that much. And while it will not look 'downtown', it will look 'Hunting Camp', provide a flat roof and be much much quieter and warmer. Ohh, it has fiberglass mats, so there that covers the deco. Some wood smoke, a couple of Deer Heads, some misc antlers, a stuffed Badger if you can swing it, one or more singing Bass, and pip, Bob's your Uncle.

I think the foam board would sag too much over time only being supported on the ends, and then we've got a fair amount of electrical that would have to be moved. On the other hand, we already have the wood smoke, one deer head and some antlers. We would have to substitute a bear skin for the badger. Actually, we're trying to get away from the "hunting camp" look.