By Metal Roofing Consultants.
Like any other kind of roofing system, a metal roof is only as good as it’s installation. As a homeowner, it is important to do your research on both metal roofing materials and the contractors who will install them on your home. Consider looking at past jobs and seeing what previous customers have to say so you can find a true expert to protect your investment. Check also for proper insurances and licenses, and make sure the crew that will be installing your roof is the same crew that was on the reference jobs you visited.
Due to their very low weight, many metal roofs can be installed over existing roofing materials. This is particularly the case when going over old composition shingles. Additionally, the formation of many of the heavily profiled shake and tile profiles of metal roofing can even permit installation over wood shingles or wood shakes.
Before deciding to install over an existing roof, you should consult the manufacturer or an experienced contractor because weight is not the only issue. In many cases, building codes prohibit more than two layers of roofing, although building inspectors have been known to waive that restriction for metal roof layover installations. If there is an existing weight problem with the structure or if there is question as to the integrity of the structure or roof decking, those issues must be addressed before installing over the existing shingles.
In some cases, particularly with wood shingles and shakes, the old roofing must be removed from the edge perimeter of the roof and even the lumber can be removed and replaced with fresh lumber before proceeding with the roof installation. Metal can also sometimes be installed over existing slate and asbestos slate roofs. However, again, the manufacturer or an experienced contractor should be consulted. Existing tile roofs and, in most cases, existing metal roofs, need to be removed prior to a new residential metal roof installation.
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Original article source: American Metal Roofs