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I need to replace my old metal roof and want to have a new standing seam roof installed. I have the following questions:
1. My roof decking consists of 1" thick boards. Can the new roof be applied over that, or do I need to install plywood over the old wood.
2. ONe contractor I talked to recommended putting Tyvek under the metal instead of felt paper. Is that ok?
3. Only the upper third part of the roof is over an attic. The lower parts are over a sloped ceiling. There is no soffit vent. I have not had any problems with condensation. Do I need to vent the new roof better?
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Hi! Thanks for the questions.
1)Chances are the 1" boards will be fine as a substrate.
2) I do not kn ow of any metal roofing manufacture who recommends Tyvek as an underlayment. There are some new synthetic underlayments but they are not Tyvek. Only use an underlayment whoch the roofing manufacturere approves of.
3) The International building Code calls for a minimum 1" vented airspace. Yes, for many reasons, I would look for ways of accomplishing this.
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Todd,
Are you saying that a proper installation of metal roofing over an existing composition roof requires a vented air space between the comp and metal panels? For example, are you saying that strips should be installed over the comp roof and then the metal screwed down to them?
Also, is felt required as an underlayment and if so, how should it be installed. I also plan on making sure the metal panel manufacturer knows we are going over a comp roof.
Thanks.
Ron
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Hi Ron,
No, I am sorry. That wasn't what I was saying. One of the problems with a forum like this is that our answers may address a particular situation but not every situation.
The previous author ("guest") had written about an area of their home with no attic space or ventilation. In that case, yes, I was suggesting that they look for a way to create ventilation on top of the current roof deck before installing the new roofing.
However, in "normal" construction with a vented attic space, my preference is to have solid decking, underlayment, and then metal roofing. The ICC required vented space is ideally beneath the roof decking in most cases.
I always suggest new underlayment over the old roofing. In some cases, the metal roofing manufacturer will specify what that should be. Generally, expect a layer of 30 pound felt and, with metal roofs that have a lot of contact with the underlayment, a layer of red rosin paper may be required especially in hot climates to keep the metal and the underlayment from adhering to one another.
Underlayment should be installed horizontally. Generally, it should lap over all roof dedges as well as penetrations and protrusions by at least 1.5".
In all cases, following the metal roofing manufacturer's instructions is critical.
5/5/2005
Isaiah Industries, Inc.
5/6/2005
6/12/2005
Isaiah Industries, Inc.
6/12/2005