metal roof

Started by tom41, December 09, 2010, 11:39:14 AM

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tom41

This summer I built a 683 sf cabin with metal roof. I used 1x4's 24" apart to fasten the metal down with screws/rubber washers. everything was fine until cold weather this past week. Now the roof is sweating inside the attic. A friend now tells me I should have put tar paper down before installing the metal roof. I need some help on suggestion of what to do now without taking off the roof. is tar paper the right material to use and is it ok to go up in the attic and staple it to the rafters? sure need some "late" advise now! thanks for any suggestions
Tom

astidham

You can have the underside spray foamed, not sure any other solution.
"Chop your own wood and it will warm you twice"
— Henry Ford


MountainDon

That is what I was going to suggest as well. It works very well and in some places the only way to get a metal roof approved when there is no roof sheathing (OSB or plywood).

While we at this allow me to ask a question. Is this a ribbed metal roof? Did you install it with the screws in the flat area or in the ribs?

Just because something has been done and has not failed, doesn't mean it is good design.

tom41

this is the heavy guge metal 36" wide with 4 ribs, and the company that sells the metal says to screw in the flat part, not on the rib. the screws have a hex head with a metal washer and a rubber gromet. the roof doesn't leak for its been on since late spring. it has just started sweating in the last 2 weeks since it has turn very cold here in middle tn. and the cabin is kept warm by propane. the addict has 19R insulation, but I am now thinking there is not enough ventilation. I wonder if anyone knows the average cost of having the metal sprayed with the insulating foam? thanks for the quick replys
Tom

MountainDon

Direct vent propane heater or a non vented? Non vented types will result in a lot more humidity in the air.

More insulation is not the solution. Insulation won't stop the migration of the water vapor. A means to prevent moisture laden air from contacting a cold surface is required. If the ceiling could be vapor sealed to perfection and if the attic was well ventilated that might do it. The best solution is to remove the cold metal plane. With the roof already on foam may be the best way. Call around and get an estimate. Pricing can vary from place to place. Once you know that cost you can balance that against other methods. 

Tar paper (roofing felt) under the roofing could help as any condensate would drop onto the felt and be absorbed. It would then evaporate and pass out of the attic if the attic is well ventilated.

Just because something has been done and has not failed, doesn't mean it is good design.


NIGHTOWL

Hi tom41
I put the felt paper under my roof as I roofed one sheet at a time running up and down under each sheet as I had seen on this forum.
It WORKS well seen no dripping.
mine is over 1x4 sheeting.
I see no reason why it wouldnt work for you to put it up now!
If you can get it stapeled up to hold it should work.
It would not cost much to try, its your cheapest way.

NIGHTOWL ;)

tom41

thanks eveyone for the suggestions and help. yesterday I installed 2 15x20" gable vents. this seems to have helped so far as I have notice no condensation on the metal in the attic. The metal ridge cap is not a vented one, so I want to do that also (when it gets a little warmer!) if they make one for metal roof. There are no soffit's on this cabin, and gutters have already been added so I guess soffit vents are out of the question, unless there are other alternatives for vents down lower on the roof. thanks

Don_P

Gable and ridge is typically frowned upon, the thinking is that the gable will then short circuit to the closest point on the ridge and leave the center unvented. The thinking I've heard is gable to gable or soffit to ridge.

Just from a code perspective, and I've broken this one on occasion too, tarpaper is supposed to be run across the roof and attached shingle fashion, not up and down the roof.