Insulating Attic truss, metal roof, bubble wrap.

[alternet]

I am hoping to insulate and close off my attic ceiling soon but having a hard time thinking about the concepts and varied posts about it. My main question: Since the bubble wrap stuff is a vapor Barrier is it ok to insulate under it with using typical baffle, insulation, drywall? Even if this would seemingly only leave me with about 4 inches of insulation because of the 2x6 top truss piece.

My situation is a metal roof, on top of bubble wrap, on top of 2x4 purlins (or whatever) on top of the attic room trusses ~ with ridge vent, eve and gable vents. Currently nothing else is insulated, I figure to start at the top after I get the electrical finished. It's a multipurpose storage man cave that I would like to insulate to help with climate changes here in Pennsylvania. I am not a wood worker, metal fabricator, or diehard mechanic.

Can anyone help answer my question?

 

[rayra]

if by 'bubblewrap' you mean the metallized / mylar stuff, it's meant as a barrier to radiant heat from the roof sheathing. It's also used as a barrier in wood-sheathed shingle roofs, but there it is typically attached to the inner face of the rafters (where drywall would attach). In those it also serves as a baffle layer, turning each rafter space into a sort of flue working in conjunction with soffet and ridge vents.

My understanding is that you can go ahead and insulate that space between rafters (and drywall), as if that bubblewrap was not there. Just don't jamb it tight to the roof steel with your insulation bats, or it negates its effectiveness as a thermal barrier. But then so does compressing fiberglass insulation, anyway. Pick the right size / thickness of your insulation batts for the depth of your rafters. Typically R-19 is a good fit for a 2x6.

A picture of what you've got now and some more description of just what you are trying to accomplish might net you better answers.

 

[alternet]

Here is an existing pic (not sure if the link will work from an iPad). You can see the trusses, purlins, and some of the foil shining. Keep in mind there is eve/soffit & ridge vents. I just want to close it up and insulate.

 

[alternet]

I guess. like you said, just forget they are there? Install baffles? Then insulation, then vapor barrier, then drywall etc? Keeping an air gap up to the ridge.

Here you can see better.

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Here is a picture between truss going down to eve/soffit vents.


Here is the underside of the ridge vent.



Here is a picture going out the gable side you can see soffit vents out there too.

 

[alternet]

My main question: Since the bubble wrap stuff is a vapor barrier is it ok to insulate under it with using typical baffles, insulation, then drywall?

 

[alternet]

Does anyone know what I should do here? Is my situation that strange? I posted pictures as asked.

 

[jack stand]

I would cut & fit ridgid foam sheets in between your trusses. F/G insulation would prolly get wet and moldy, useless. The pink or blue foam is usually about 4-5 "r"value per inch. Also f/g insulation dramaticaly looses it's "r" value with air moving through it, I'm sure that there is a lot of air movement under your metal roo & purlins along with your venting.
You could do the foam in "layers", I would use the "can" foam to seal the edges of each layer to the framing.

 

[InTheMitten]

Similar setup in my pole barn and we did NOT use kraft face and/or a vapor barrier, but I do have a nice airgap/air run. I was advised by an insulator to do it this way. I've got R30 fiberglass in mine with scissor trusses.

My roof structure is built as follows:
Scissor trusses placed 24" O.C.
7/16 OSB Sheeting
15 LB Felt
Roof Steel like yours with a ridge vent.

On the inside, I baffled at the soffits and am fully vented all the way around. I was able to "hang" my R30 in a way that provided a nice air gap from the soffit all the way up to the ridge in every bay.

Been working very well for me.

On yours, with the horizontal perlins the way they are, if you want to achieve the same, you need to space down probably 1" and I like Jack Stand's idea. Use some 3/4" Fomular and create an air channel from soffit to ridge. Then fiberglass is your cheapest.

 

[alternet]

Mine is a pole barn/building (post frame) construction ~ just a little hybrid.

I do like the rigid foam idea. Do you guys have any good ways to cut the rigid foam? I guess it would be a lot easier to cut 3/4 than the 2in I used in another project. I would have to cut many pieces manually to fit in the 24in OC.

I was thinking about using the pre-made baffles for 24in OC. It would save on cutting time and they would be spaced appropriately for the air gap. I also like that I could overlap them for moisture drain (if any moisture got in the soffit vent area). But it would be about $300 on just baffles. Something like these: http://www.homedepot.com/p/ADO-Products-Durovent-23-1-2-in-x-46-in-Attic-Ventilation-System-with-Built-In-Baffle-10-Ctn-UDVB234610/202389935

InTheMitten - What did you use or how did you baffle your soffits? You have R30 f/g? I am guessing that is in the bottom cord and not the top cord? No craft faced or vapor barrier for the ceiling? Is that for moisture exit?

 

[jack stand]

A small table saw is the best way, but you could always snap a line and just use a skill saw. You can get a cheapo table saw with legs for about $130 at Lowes/HD. They really are not a bad saw for the money, and you'll get a straighter edge and save time as well.

 

[Evilunclegrimace]

Don't use a power saw to cut foam, it makes a mess and is unhealthy. Buy yourself a cheap serrated bread knife to cut the foam. As far as the foam goes look around for commercial roof foam (isocanurate) as it comes in thicker boards up to 4" if I remember correctly and is around 6.5R per inch.

 

[InTheMitten]

Mine is a pole barn/building (post frame) construction ~ just a little hybrid.

I do like the rigid foam idea. Do you guys have any good ways to cut the rigid foam? I guess it would be a lot easier to cut 3/4 than the 2in I used in another project. I would have to cut many pieces manually to fit in the 24in OC.

I was thinking about using the pre-made baffles for 24in OC. It would save on cutting time and they would be spaced appropriately for the air gap. I also like that I could overlap them for moisture drain (if any moisture got in the soffit vent area). But it would be about $300 on just baffles. Something like these: http://www.homedepot.com/p/ADO-Products-Durovent-23-1-2-in-x-46-in-Attic-Ventilation-System-with-Built-In-Baffle-10-Ctn-UDVB234610/202389935

InTheMitten - What did you use or how did you baffle your soffits? You have R30 f/g? I am guessing that is in the bottom cord and not the top cord? No craft faced or vapor barrier for the ceiling? Is that for moisture exit?

Sorry for the slow response!

My soffits are baffled using the plastic version of what you posted for 24" O.C. The R30 F/G is the entire length of my roof. With the scissor trusses being design as they are, the R30 fit bottom to top just fine. Just as you get up more toward the top, it provided a much larger air-gap. No big deal.

Correct on the vapor barrier thinking. Plus, the steel on my ceiling pretty much acts as one.