Vapor barrier on tong and groove exposed pine deck

Bob Dolton
3/1/2014
Current roof description: Florida location with prevalent humidity Tong and groove 2x6 pine vaulted ceiling deck on 4x10 cedar beams 4feet apart. Boards are visible from inside so there is no attic or crawlspace. The house was cheaply built in 1982. For insulation they have used a sort of paper compressed board sheets that are 0.5 inch thick. This insulation is horrible. Once the small leak is developed it absorbs the moisture within the insulation that acts as a sponge. Moisture spreads underneath the shingles and eventually rots the wood. So putting metal roof over the shingles is out of the question since the rotten boards will need to be replaced. I am planning to tear the old shingles and that useless insulation off and start over with the fresh deck replacing the rotted wood. I am planning to install the standing seam metal roof. I am confused with a couple of factors of what the correct insulation and vapor barrier I should use to be most condensation prone and cost effective. Another question that I have is whether the metal sheets need furring or batten strips underneath or should it be applied directly to the insulation. As far as I did the search there are people saying not to use furring/batten strips because that will cause the condensation underneath which is again plenty prevalent in Florida. Also since there is no attic it could be more noisy with a spaced out metal (drum effect) I was thinking of using R-MAX sheets available at Lowes or HD but not sure if they are approved for the roof application. Then I came across the product called Prodex http://www.insulation4less.com/Insulation4lessProduct-2-Prodex-Total-Fast-Action-48-Inch.aspx Do you think something like that could be used with metal sheets directly layered over this insulation. Do I still need to put a layer of tar paper or peel and stick barrier on the wood, then insulation on top, or insulation directly over the wood is enough? In any case I need your expert opinions about what would be the best way to put a metal roof over the inside exposed tong and groove pine. The mission is to -have a minimum or no condensation under the metal roof that could possibly make its way to the wood -reduce the outside noise transmission (rain, low flying planes, etc.) since there is no attic -minimize heat transmission from scorching Florida sun adding R value to it -be cost effective and long lasting application Any advice is appreciated Thank you in advance
Info @windowsonwashington.net
An informed customer is our best customer.
3/2/2014
If the roofing is decking and no insulation or attic above, this is how I would do it. - install ice/water over entire deck (non-granulated) - install rigid foam over roof deck to as much thickness as you can afford (ideally 3" min) - install foil faced foam on last layer and face toward the underside of the roof material - create vented space above roof deck via purlins and battens - create circulation at eaves and ridge You have a air sealed roof, insulated, and a vented design. Best of all the worlds.
Bob Dolton
3/2/2014
Thanks for your reply! it makes sense to layer the roof the way you suggest, the only problem is a cost issue since all layers add to it. My roof is 2040sq feet in size. I also see that you suggest using the battens. Can you please elaborate on the fact that condensation running down under might have a tendency to pool on the horizontally placed battens. Is there an option to install them on 45 degree angle? Would you recommend using treated wood battens? The worry I have that treated wood is corrosive to fasteners metal and eventually would still erode galvalume. I know that I would have to use not only galvanized but also dipped fasteners. Untreated wood would rot. Is there an alternative to wood battens? Can you please explain what adverse effect is to install the metal sheets directly on the faced foam board? Thanks in advance
Info @windowsonwashington.net
An informed customer is our best customer.
3/2/2014
Bob, I appreciate the concerns about cost. Foam isn't cheap but neither is getting a roof that will work properly. You could go thinner on the foam if you absolutely need to. I don't see that much condensation potential or it being problematic. As long as the space is vented, the condensing surface will normally be the top in the overnight hours (i.e. facing North surface). I wouldn't worry about PT battens. They are overkill. You can run the strips vertically and they horizontal overtop. This will create and unfettered drainable path. There are plastic battens but they aren't cheap. No real adverse affects other than direct transference of the temperature to the foam and into the structure.
Bob Dolton
3/3/2014
Thanks for your input again Eric, I was wondering why would it be wrong to put battens vertically? I am planning to use standing seam 16 inch wide galvalume panels. Install battens right under where the attachment points would be. This way the fasteners can go directly through battens into the deck. This will create uninterrupted drainage and venting. The decking is even and straight. I understand that when installed over shingles it makes sense to have battens horizontally to even out inconsistencies that might be there. Also there would be some strengthening factor since the 2x6 pine decking is horizontal. The only thing that I can see happening is dimpling or sagging in between the ribs. Do you know if this installation in some way would violate the code? I also need your thoughts about noise. I know in this case I have to out way between heat transmission if no battens are used or little bit noisier roof if panels are spaced out. I agree with you that thicker foam would dampen the noise more effectively. Thanks in advance Bob
Info @windowsonwashington.net
An informed customer is our best customer.
3/3/2014
Bob, You need to confirm that application and option with the panel maker. Noise issue is largely moot once you figure on the solid decking. Most of the noise associated with rain on a tin roof is from the lack of solid sheathing days.

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