A valid technique of putting new roofing shingles over old ones is called ‘re-roofing’.
The following six points will help you decide whether or not this method is the right one for you.
Check your local building codes to ensure that re-roofing is an approved roofing method. These building codes provide specific guidance for projects. The International Building Code, 2012 Edition (IBC 2012), specifically Chapter 15, addresses regulations for re-roofing, and it covers topics such as drainage, load support, and other safety stipulations.
CONVENIENT AND COST-EFFECTIVE
If the old roof shingles are still in relatively good condition, and they are NOT curled, cupped or misshapen, then re-roofing might be a more convenient and more cost effective option for you. The new shingles are placed directly over the old ones, so the messy and laborious step called ‘tearoff’ is skipped. However, the ‘tearoff’ step is necessary only when a roof is completely replaced. The roofers tear off the old roof all the way down to the deck or plywood.
The International Building Code limits re-roofing to only two layers of shingles. This is because a reroof project doubles the weight of the roof. Each 100 square foot section of shingles adds approximately 350 lbs. to the existing roof support. This can cause the deck to sag between the trusses or rafters. Then, with any additional weight such as roofing equipment during installation or snow, the roof could buckle and collapse.
Good roofers will perform a ‘walking inspection’ of the old roof They would look for spongy spots or other problem areas which could contain mold or roof rot. These areas must be repaired before the re-roofing project begins.
DOUBLE LAYER ROOF
A home inspector will be able to identify a double layer roof. This will alert the homeowner or home buyer that the maximum roof capacity has been reached. Consequently, the next new roof would require a full roof replacement.
Many shingle manufacturers will not offer a warranty on their products if the shingles are installed on a reroof project. So, be sure to verify that your roofer uses shingles which provide a re-roofing warranty.
A solid water-tight roof is essential for every home. Re-roofing is still widely used by roofers. However, if any of the above points leave you feeling concerned, then a complete roof replacement might be your best option.
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