Metal roof underlayment

Derrell Labatte
10/7/2015
Hello experts! Looking for some advice or direction on an underlayment for my new metal roof. Not sure what kind I should go with as I plan to leave the shingles on and do the metal roof over them. I did have a little bit of ice damming last year. I believe the pitch of my roof is a 4-10? Its not a very steep pitch. Just curious if there is a special kind of underlayment that adheres better to shingles than not? I was looking at GAF Weatherwatch 2.0 or something of similar nature I'm sure would be best. Thanks in advance for the help!
Todd Miller
Isaiah Industries, Inc.
10/7/2015
Thanks so much. First of all, I would refer you to your metal roof manufacturer for their input. WeatherWatch is a self adhering ice and watershield product bot approved by GAF for installation over existing shingles. It also I believe has a granulated top surface that most folks do not advise for use under metal.
Eric Novotny
An informed customer is the Best Customer!
10/7/2015
+1 Depending on what metal you use, they will have specific recommendations on underlayment/slip layer.
Derrell Labatte
10/7/2015
Thanks for the quick response! Well the roof manufacturer isn't very specific. In fact they are Mennonites. Make good roofing, but didn't say anything about underlayment. Do I need to be concerned about a self adhesive style when putting ontop of the existing shingles? will it stick or become a issue in the future?
Eric Novotny
An informed customer is the Best Customer!
10/9/2015
You will not be sticking the underlayment to the shingles. It needs to function as a "slip layer" in effect to protect the backside of the metal and allow it to move along the surface without scratching itself against the shingle granules.
Guest User
10/12/2015
Need info regarding installation of a metal roof. I have a friend th at had some Amish people install their roof. They put sheet insulation on top of the old roof. My friend said it is to reduce condensation to prevent the metal roofing from rotting. We have had several estimates, and nobody has said anything about th is. Is this standard installation practice, or what? We need some help since we are in the deciding stages of who will do the roof. Thank you for your help and support. Cindy Ryan
Todd Miller
Isaiah Industries, Inc.
10/12/2015
Cindy, with normal construction consisting of from, the inside out the following: Ceilings, vapor barrier, insulation, vented attic space, roof deck, underlayment, metal roof No sort of rooftop insulation would normally be used. Is there anything unusual about your home construction?
Eric Novotny
An informed customer is the Best Customer!
10/12/2015
+1 to Todd's feedback. What, where, and if there is a vapor barrier depends on where the home is located as well as your roof/attic construction type.
Guest User
10/13/2015
No, the only thing I could say is there is about 2 layers of asphalt shingles, and 1 of cedar shakes. It is an old farm house, so I wouldn't think there was anything unusual about the construction. (We are in Michigan, and I'm not sure what the other gentleman is talking about as far as roof/attic construction type. for Erics' reply) Todd thank you for responding. Do you know of any condensation concerns regarding metal roofing, and wouldn't the roof venting keep this from occurring??
Eric Novotny
An informed customer is the Best Customer!
10/13/2015
I would be very cognizant of code in this case. I don't think you can do a roof over when you have that many layers.
Guest User
10/22/2015
I am planning on installing a new metal roof over existing shingles after installing a new layer of 30# felt. I have read elsewhere that I should also install a rosin paper layer layer to act as a slip layer between the felt and new metal roofing. Is this correct and where do I find this paper? Thanks in advance.
Todd Miller
Isaiah Industries, Inc.
10/22/2015
Red rosin paper is sort of like Kraft paper ... it is not heavily used any more. The industry has gone more toward Synthetic Roofing Underlayments which serve both as underlayment and slip sheet.
re roll
10/27/2015
I have new construction for a 1200 sq ft garage apartment.; The rise on the roof is just 4' . The dimensions are 35'x45'. I have heavy felt/tar paper over 4x8' osb with foil paper on the inside of the attic. I want to put a metal roof 26 gauge, 36' wide sheets over the tar paper. Others tell me that if I do not have a air barrier/space between the metals and the roof surface, that the osb sheeting may delaminate or the glue melt from the heat. My builder wants to put the metal flat on the tar paper. Please give me some advice. [email protected] Randy
re roll
10/27/2015
I have new construction for a 1200 sq ft garage apartment.; The rise on the roof is just 4' . The dimensions are 35'x45'. I have heavy felt/tar paper over 4x8' osb with foil paper on the inside of the attic. I want to put a metal roof 26 gauge, 36' wide sheets over the tar paper. Others tell me that if I do not have a air barrier/space between the metals and the roof surface, that the osb sheeting may delaminate or the glue melt from the heat. My builder wants to put the metal flat on the tar paper. Please give me some advice. [email protected] Randy
Todd Miller
Isaiah Industries, Inc.
10/27/2015
First of all, make sure that the metal panel you're installing does not have a pitch requirement steeper than your roof. Next you should have a "slip sheet" on top of the asphaltic paper you have installed. This could be something called red rosin paper. Another option is to install a layer of synthetic underlayment over the felt paper. Synthetic underlayment acts as underlayment and a slip sheet.
Guest User
11/2/2015
I am planning to put metal roof on a porch overhang. The underside will be exposed and I don't want fasteners (screws) to penetrate through the sheeting. How long are the fasteners? Can I get installation instructions?
Todd Miller
Isaiah Industries, Inc.
11/3/2015
Mike, it is not uncommon to use 1" screws but shorter lengths may be possible. Installation instructions will vary based upon what product you install and should come from the manufacturer.

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