TEAR-OFF OR OVERLAY
The question often comes up about whether an existing composition shingle roof should be torn off or if an overlay (or recover) is possible. Overlays save on time, labor, and disposal costs. If the existing roof has only one layer, lays flat, is less than 10 years old, and there aren’t any problems with the roof deck, removal is not necessary.
Regardless of whether you overlay or tear-off; you should properly ventilate your attic. In almost all cases, continuous soffit and ridge vents will provide maximum cross ventilation.
If any of the following are true, a complete tear-off of the existing roof system is highly recommended and should be considered.
- Too many layers- If a roof has more than one layer of roofing, the roof should be torn off. In most cases this is a code requirement. Codes rarely permit more than two layers of roofing. To determine this, all you need to do is contact your local building inspections department.
- Bad Decking- if spongy areas are noticed when walking on a roof, or if you see sags between the rafters or trusses, there’s a chance that some of the roof deck may be deteriorating, delaminated or damaged. Deterioration can be attributed to dry rot or delamination to the plies of the plywood due to glue failure. Dry rot is wood rot and caused by certain types of fungi and if it isn’t taken cared of , it can spread. If there is suspicion of bad decking, then a full tear off should seriously be considered.
- Ice Dams- ice dams can be a big problem. In areas where the average January temperature can be below 30 degrees F and no ice and water protection membrane is present on the roof then a full tear off should be considered. Fifteen year old and older buildings with no ice and water protection and no prior problems, can suddenly experience thousands of dollars in damage when a freak cold front hits.
- Existing roof is in poor condition- If existing roof is in really poor shape, such as tabs being severely curled, rows are crooked, cracks running vertically, then complete tear off and replacement should be considered. If these problems exist a layover is not going to solve future problems.
- Shorter life span- There is no known documented research, but most roofing manufacturers agree that with an overlay, the average life span of the shingles will be shortened by about 10% to 30%.
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