underlayment over existing shingles

Guest User
7/17/2004
what is the true purpose of underlayment when installing a metal roof over existingg shingles?
Guest User
7/17/2004
There are many purposes. 1) It protects the back side of the metal from abrasion against the shingle surface when the metal expands and contracts. 2) It can somewhat help to smooth out the roof surface, at least a tiny bit. 3) It protects the old shingles from condensation which might develop on the back of the metal from time to time. 4) It provides extra water infiltration protection in the event of an installation error.
Guest User
7/29/2011
I have a question that hopefully you can help me out with. I am going to be installing a new metal roof on my home, i am having the asphalt roof removed and the contractor told me he is only putting down new tar paper, and the 1x4s to fasten the new roof down. Is this correct or does there need to be other forms of insulation put under the metal roof?
Todd Miller
Classic Products, Inc.
7/29/2011
There can be unique aspects to jobs which require certain things but generally speaking this sounds okay as long as the roof being installed is one which can be installed over battens. Not all metal roofs are intended to be installed over battens. Also, now is the ideal time to evaluate your attic ventilation. Good attic ventilation makes your home more energy efficient, helps avoid unhealthy and damaging accumulations of moisture and condensation, and also in northern climates will help avoid ice dams.
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