Guest User
8/3/2003
Is it okay to install over sagging rafters if shimmys are used to level? In addition, is 3/8 decking enough to support after wet/bad portions are replaced? What is the recommended barrier 30lb felt or other? Thanks,
Todd Miller
Classic Products, Inc.
8/4/2003
Most metal roof products have been tested over 3/8" decking. However, I strongly suggest that you request installation specifications for the product you'll be installing and review them in advance for this information. Your use of shims, I assume, would be as needed on top of the decking (?). This would require the use of a metal roofing product which can be installed over lathe or purlin rather than just over solid decking. Again, you'd need to check this out with the manufacturer of the product you're using. 30-pound felt is a traditional underlayment for metal roofing. Depending upon building code requirements and your climate, it might be wise to use a slip sheet between the roofing and the underlayment. A slip sheet would be something like red resin paper and its purpose is to prevent the metal roofing and the 30-pound felt from adhering to one another. There are also new underlayments available which are polymer based which would not require a slip sheet.
Guest User
8/4/2003
From discussing with others, shims are used to level rafters. In this case possibly re-deck my home with at least 1/2 inch or do they install metal roofs without any decking? Does the decking provide additional sound barrier? Either case, I understand additional insulation in the attic is necessary to insure energy savings. Thanks so much for your reply.
Todd Miller
Classic Products, Inc.
8/4/2003
Okay, I have a clearer understanding now. Putting shims on top of the rafters sould be okay, provided the rafters are structurally sound. If there appears to be something real strange going on, calling in a structural engineer might be appropriate. Some metal roofs are approved by their manufacturers for installation over lathe / purlin which would need to be run horizontally across the rafters. However, many residential metal roofs are intended for installation over solid decking only. This will need to be confirmed with the manufacturer of the roofing you choose. Decking certainly helps with sound insulation, no matter what type of roofing is being installed. For winter efficiency, insulating on top of your ceilings is critical. Additionally, for both winter and summer efficiency, you need to have positive ventilation in the attic. One of the best ways to achieve this is with a combination of ridge and soffit vents.
Guest User
9/19/2003
I have a 100 year old house ,the existing roof is purlins w/ ceder shake w/ a asplault single installed 20yrs. ago. can a metal roof be installed without stripping esisting roof's?
Guest User
9/19/2003
I have a 100 year old house ,the existing roof is purlins w/ ceder shake w/ a asplault single installed 20yrs. ago. can a metal roof be installed without stripping existing roof's?
Todd Miller
Classic Products, Inc.
9/19/2003
There have certainly been many metal roof installations over this type of existing situation. Several things to keep in mind: 1) A shingle, shake, or tile profile will be more "forgiving" of any unevenness in the existing roof than would be many vertical seam metal roof panels. 2) Building codes in your area may require a special exemption / waiver in order to allow installation over two layers of old roofing. 3) Need to make sure there is not an existing weight problem. A big benefit of metal roofing is low weight. Steel roofs weigh 80 - 135 pounds per square and aluminum weighs 40 - 70. 4) Large dips or swales in the roof may still be visible after the new roof is installed. 5) Need to make sure that the new roof you choose is approved by its manufacturer for this type of installation and that steps are being taken to ensure secure fastening. 6) Check to add ventilation to the roof if necessary when the re-roof is done. 7) Any areas of existing leaks or rot need to be addressed before proceeding. Good luck.
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