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I am about to start installing a metal roof onto my ranch house in central Louisiana.
First, I want to know if I need to use underpayment on top of the shingles and under the battens.
Second I would like to know if I can use ring shank nails to attach the battens instead of screws.
Not everyone interprets the International Building / Residential Code this way but I feel it does call for underlayment in all cases. Regardless of code, though, I think it's a good idea.
Not all metal roofs require battens ... so that is something to discuss with your contractor and even perhaps the metal roof manufacturer.
I would suggest screwing down the battens if you use them. Particularly if you install an exposed fastener metal roof, there is a lot of pressure on the battens and having them screwed in place is wise.
Ok, now I am doing this work myself as I used to be a carpenter and have the capabilities necessary. But I was wondering if you think the cross battening is a good idea. The metal company I am using says I can lay it directly over the shingles but they “don’t recommend it”. I understand where they come from as it could present liability on their part to say go ahead and lay it on the shingles, but from what I can tell using a quality underlayment would negate the concerns most have about direct application to the existing roof.
Using a good thick underlayment would prevent any rubbing of the metal with the coarse shingles during the expansion and contraction of the metal roof during heat cycling. So the only other question is the benefits of battens as it pertains to “above sheathing ventilation”.
What are your thoughts on this?
Thanks ... there is a lot involved in making this decision. Is it a through-fastened panel you're installing? How "flat" is the current roof deck / plane? Battens make things more complicated ... drip edges have to be longer, gutters may need to be raised ... there could be issues with dormer windows, etc. Battens also make the roof harder to talk and can negatively impact wind resistance a bit. That said, a thermal break does help a great deal with energy efficiency, especially if it is vented. One option would be to use an entangled mesh product such as RoodAquaGuard Dry-Tech on top of your underlayment -- gains you a thermal break but not really any actual ventilation, but is pretty thin and doesn't really raise the roof level nor impact walkability.
The roof is pretty shallow. I’d guess a 3/12 or so.
And it’s very simple, it is a straight gable ranch house with a perpendicular gable attached. So a one story L shaped house essentially.
There is one chimney.
My uncle is a contractor and he never uses battens in central florida. Being that I’m in central Louisiana I figure the humidity is similar and the hurricane threat is similar as well. So really I want to just use a quality underlayment honestly I just need some reassurance that it’s a good move. I’m worried about any foreseen issues.
Is your attic well vented, with both intake and exhaust vents?
I have a couple whirlybird spinning vents. But as for I take I’m not sure.
I would encourage you to address ventilation. A great source of information on ventilation is www.airvent.com Good ventilation will help withenaergy efficiency and also help guard against condensation issues in the attic. The new roof, without any sort of thermal break, could drop the roof deck temperature enough to cause condensation in the attic that has not occurred before. Ventilation will carry that warm moist air out and prevent it from condensing.
Oh I forgot to mention I have ventilation at the gable ends of my house.
Yeah, if there is a way to add intake in the eave soffits and then close off the gable vents, that would be best,. Then you could also replace the turbines with a ridge vent ... or keep the turbines. Right now, air is going right from the gable vents to the turbines, meaning that you are getting very little air flow through the bulk of the attic.
Ok. I think I understand. The air flow is co fined to the high area of he attic and not in the Mo section. We need to add vented soffit so as to get intake at the soffit and exhaust at the turbines or ridge vent.
Ok I see so we are only getting air flow at the high part of the attic. We need to add vented soffits so as to get air intake from the bottoms of the attic to exhaust at the ridge.
So to sum up, I would be fine to just put down an underlayment then scre the metal right to the shingles roof providing I make sure that I have good ventilation from soffit to turbine
Given what you have told me, I am comfortable with that application.
Excellent. Thank you sir
My question from Tennessee:
My roof is scheduled to go on soon. My house a ranch style and is about 40 years old --- not sure on age of roof. I have had a couple of leaks in the last couple of years. My contractor says that he it is ok to put 29 gauge metal over existing shingles. He said no need for underlayment. Should I get him to put a synthetic underlayment on top of shingles? Should I get him to use wood strips? Or should I just get him to take the old roof off and start new?? Help please would be appreciated.
If you have just one layer of shingles, then you should be fine to go over them. Please keep in mind that any bad dips or swales in the roof will still be there. I would advise a layer of underlayment over the old shingles and synthetic is fine. I interpret the International Building Code as requiring it. Not everyone interprets the code that way but it is still good to separate the back of the metal from the granulated shingles. Assuming you have good attic ventilation (meaning balanced and adequate intake and exhaust), you should be okay without the wood strips.
Thank you so much for the reassurance. I've had so many people say different things. I just wanted to make sure I'm making a good decision to go with metal instead of a roof tear off and shingles. Appreciate it.
Hello,my question is ,i'm installing a metal residential rib panel roof over my existing shingles on a 07 model mobile home with a 3/12 pitch roof. After removing the attic vents i noticed that there is hardly any insulation,maybe 1''or 2''. Will it hurt to fill the attic full of blown insulation while i have access through vent holes before installing metal or will it cause a problem being completely filled. I''m laying a synthetic felt over shingles and stripping with 3/4 furring strips. Also what vents on a mobile home can be covered and what vents half to be vented through metal. My mobile home is all electric. Thanks!
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