Roof repair decisions
New roof vs. Overlay
If you roof was damaged by wind or a tree during the storm and your shingle roof is beyond repair you could be presented with the option to ‘overlay’ your new roof. Overlay is when your existing shingle roof is not removed and covered over with a new shingle roof, this is a money saving option presented to many homeowners when it is time for a new roof.
The Pros and Cons
Pros:
- Saves Money- Contractor will save time (savings to homeowner) by installing new shingles over an existing roof. Tear-off is time consuming and messy and includes the cost of debris hauling to the truck or dumpster and then the debris dumping fees.
- Far less clean up of nails and shingles debris from landscaping.
- Less total time ‘under construction’.
Cons:
- Trapping the mass of the original shingle roof between the new shingles and the roof deck lowers the new roof’s ability to cool. The result is a hotter attic and possible additional air conditioning cost but mostly the baking of the new roof shingles from underneath decreases the life of the new shingles by up to 25 %
- Shingles are made from a fiberglass mat that is covered with liquid tar and then covered with stone granules. The mat holds the tar, the tar makes the shingle waterproof but it can easily be damaged by UV radiation (sunlight), this tar-covered mat is protected from the sun with the familiar granular stone covering. The baking of the overlay shingles causes the petroleum-based tar to out gas and become brittle sooner than if the shingle was only one layer and this leads to a shorter shingle life.
- Without removing the existing shingles you are unable to check the existing roof decking and flashings. Many older homes could use the wood strip sheathing retailed. Inspection of the wood deck can reveal rotted/warped wood or large gaps between the deck boards. Any rotten or damaged boards should be replaced before applying the new shingles. If there is any suspicion of bad decking, spongy areas or sagging areas then a full tear-off should seriously be considered.
- Is the original roof shingles are removed then the flashing, drip edge and vents can be inspected and repaired or replaced as necessary.
- The overlay roof adds additional weight to the roof framing system.
- The overlay roof may not lie as flat as a single layer roof applied directly to a flat wood deck.
- Without a tear off you are unable to apply ice and water shield along the gutter line. In many locals the building code requires the installation of ice and water shield and this will make a roof overlay out of the question.
The decision is yours – it the cost savings worth the negatives of a roof repair by overlay?
