Vapor barrier or not

[MyLilMule]

I'm a contractor, I wouldn't bother putting any additional vapor barrier, the metal will be enough. What is the roofing material, is there a ridge vent?

Roofing is architectural asphalt shingles. Ridge vent down the entire length. Soffits are vented the entire length on both sides and I used those vent chutes in every rafter space to make sure there was air flow from the soffit to the ridge. The ceiling is framed as, I guess you would call a tray ceiling. Walls are 8 feet, but I had a collar tie placed at the 9 foot level. Rafters are 12" on center. Low pitch roof, somewhere around a 4:12, maybe a bit steeper.

 

[Eddyde]

That's the beast way to go with venting. What's the R value of the insulation? you mentioned 6" that would only get you R19-21 max, if so you might consider a layer of rigid foam boards before you put up the metal.

 

[MyLilMule]

That's the beast way to go with venting. What's the R value of the insulation? you mentioned 6" that would only get you R19-21 max, if so you might consider a layer of rigid foam boards before you put up the metal.

R19 in the sloped portion of the roof (about 3' each side) and R30 in the center section (about 12'). They are 2x6 rafters, so not a lot of room.

The rigid foam is not something I had thought of. Thanks for the suggestion. I'd probably limit it to 1", though, I can't afford to lose a lot of ceiling height. Too many machines. It would at least add R5 to the ceiling, but I'd have to compensate with longer screws for the tin. Do they make those screws in that length?

 

[Eddyde]

It would help, a good foam board will add around R6.5 per inch, it is also easier to seal creating an air-tight installation. longer screws are available.

 

[Alcap]

Not an answer to your question but one I have . In my mind Im thinking your climate is like mine here in NE Pa . Cold winters , hot humid summers . If your shop isn’t climate controlled wont the metal ceiling build condensation during times of temp. swings that we have during the seasons ?

 

[woodchucker]

Roofing is architectural asphalt shingles. Ridge vent down the entire length. Soffits are vented the entire length on both sides and I used those vent chutes in every rafter space to make sure there was air flow from the soffit to the ridge. The ceiling is framed as, I guess you would call a tray ceiling. Walls are 8 feet, but I had a collar tie placed at the 9 foot level. Rafters are 12" on center. Low pitch roof, somewhere around a 4:12, maybe a bit steeper.

I'm going to go out on a limb here..

If you are insulating the roof, then you need those air chutes in every rafter space/bay.
They are protecting the sheathing. They allow air to flow to the sheet of ply to keep it dry. I put a bid on a house where the owner had blocked the path, and didn't use the trays. My home inspector found an inch of mold and rotted ply when he did the home inspection. He said the roof (complete) needed to come off and it be re-sheathed and roofed. He also said many of the rafters were wet and soft and probably needed replacement. We fortunately bailed, it was the second house where we had a huge problem awaiting us. The first was well water that was so heavily contaminated with TCE, that it would require 2 carbon filters..

Anyway, I'll continue... After a major storm in Phillipsburg NJ my roofer for my current home, told me about how many of the new homes that were built near the Home Depot were rotted away .. They were less than 5 years old, but they could not be repaired. He said it was like paper machet. All closed up make it air tight building requirements.. made it a water balloon from the inside... Much of the new requirements is theory, and after a few years, they see the results and change it... hopefully.. sometimes not.

 

[MyLilMule]

Soffits are vented the entire length on both sides and I used those vent chutes in every rafter space to make sure there was air flow from the soffit to the ridge.

I'm going to go out on a limb here..

If you are insulating the roof, then you need those air chutes in every rafter space/bay.

Maybe I'm not the only one that doesn't read the entire post.

 

[woodchucker]

Maybe I'm not the only one that doesn't read the entire post.

I read it... I think my brain read it as every other rafter... sorry.

 

[vtcnc]

As long as you have unrestricted airflow from soffit to ridge vent you should be good with out an interior vapor barrier.

I’m in NW Vermont, I did put ice shield on the roof sheathing as an added layer of protection. But inner barrier for insulation. I used foam board and left the gap behind it.


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[extropic]

As long as you have unrestricted airflow from soffit to ridge vent you should be good with out an interior vapor barrier.

I’m in NW Vermont, I did put ice shield on the roof sheathing as an added layer of protection. But inner barrier for insulation. I used foam board and left the gap behind it.


Sent from my iPhone using Tapatalk

I'm trying to get a mental picture of what you wrote. By "gap" behind the foam board, do you mean the rafter bays or some other volume?