bearnst bearnst
12/24/2003
We are building a house and plan on installing a metal roof on the structure. Our builder says that we should install the metal roof by simply putting 1 x 4 lat boards on the rafters and installing the metal roof to the lats. My wife and I say that we should sheath, lay roofing felt, then put the 1x4 lats and then install the metal roof. Who is right? Will we experience much condensation using the second method? If so, what can we do to minimize it.
Todd Miller
Classic Products, Inc.
12/24/2003
The answer to this is determined pretty much solely by what type of metal roof you choose. Many styles of residential metal roofing require solid decking beneath them. However, some can be installed over open lathe and some over battens installed over solid decking. Moisture and condensation are controlled through proper ventilation and in many cases a vapor barrier between the living space and the attic. Use this website to find some products you like and then inquire with their manufacturers as to the proper installation procedures.
Guest User
12/25/2003
I have had a metal roof for 14 years now. I only put 2 X 4 perlins on 2 foot centers for my metal roofing. However I am looking into weather I should lay sheating down with felt paper due to when it warms up very quickly in the winter, the roof sweats and forms droplets. I have a vapor barrier and R39 in the ceiling but the mositure issue is due to a cold roof and the outside temps rising very quickly. I live in upsate NY. Is sheating the best bet or have the under roof sprayed with a foam insulation/ any help will be appreciated.
Guest User
12/28/2003
Many manufacturers, for residnetial applications in particular, are requiring solid decking and underlayment before the roofing is installed. Just the same, I am wondering whether your attic has soffit vents for intake and a roof ridge vent for exhaust. If not, installing good ventilation could eliminate the problems you have had.
Guest User
12/30/2003
I have full soffit vents meaning a complete row along the 42 foot length of the house on both sides and the along the full ridge. The funny part is I have this metal on an outside shed with full exposure to the weather and that will have droplets forming in the morning when it warms up. I do not beleive I have the severity of mositure some of the other folks are having but it is annoying. I have tried to contact the manufacturer of my metal roofing but haven't heard back yet. Are you saying there should not be any condensation if things are vented properly? Is the sheating just a path for moisture to take it out of the house? As a second precaution I am adding insulation that has a poly film over it so the moisture will not deteriate it so fast. thanks in advance for your help.
Todd Miller
Classic Products, Inc.
12/30/2003
Condensation occurs when the dewpoint is reached. Dewpoint is based upon the amount of moisture in the air. Reducing the amount of moisture in the air makes it less likely to hit dewpoint. Good ventilation will help to carry out moisture and it will also help to keep the attic cooler. Both of these things help to avoid condensation. Adding decking beneath the roofing also acts as an insulator. The bottom of the decking will not get as cold as the bottom of the metal roofing will. However, just the same, I have seen condensation on the bottom side of decking too. It sounds like you have full soffit vents and a ridge vent. As long as the airflow is not restricted and as long as you do not have other vents in place elsewhere which would dissrupt the airflow, you should be doing a good job of getting airflow through the attic. Are there sources of excessive moisture in the home? This would be things like exhaust fans lacking or not vented to the outside, a lot of houseplants, a ventless gas stove, water in the crawlspace or basement, etc. If anything like this exists, correcting it could help dramatically.
Guest User
12/31/2003
thanks.......I was planning to put gable vents in each end of the house but maybe that may not be a good idea since that may disturb the flow. I have seen condensation on the inside of my porch which has wood roof inside and metal on the outside, so I do understand what you are saying. We just had a 40 degree swing in a few hours a week or so ago and everything showed condensation including the wood. I have been here 14 years and never seen it so bad. Just scared me a bit. But when I went in the attic this week there were a few wet spots but notthing soaking so maybe again my problem is not as bad as some folks and mother nature is the culprit right now. No plants or other issues you mentioned but I may still l llo into removing the metal and putting down sheating. Also what type of contractor would do the foam spraying on the undersode of the metal? do you think it would be cost effective to go that root or will that casue other issues later? thanks again for your help.
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