Answer: Adding new layers of asphalt shingles over old ones can reduce the useful life of the shingles or even the roof itself in many ways:
1) Added layers of shingles means added weight on the roof. That makes the structural roof components work harder and can lead to failure of the roof structure itself.
2) Additional shingle layers may mask a leak instead of fixing the problem. For instance, a homeowner may have discovered a leak and added another layer of roofing material without ever knowing when the leak started or the extent of the damage. Adding a layer without inspecting the sheathing below may simply bandage a larger problem.
3) Nails used to attach the new layer may not be long enough to penetrate through the sheathing. This weakens the attachment and makes shingles more susceptible to wind damage.
4) Depending on the extent of the roof replacement, the flashings – protective coverings that direct water away from openings and seams in the roof – may not have been updated. This makes them a weak link in the new roof and a place for possible water intrusion.
Inspectors use several clues to determine the number of layers of shingles. Many times layers can be counted at the lower edges of the roof. A close look at the flashings or the nail pattern evident from below the sheathing in the attic may provide further clues. Your inspector will perform visual inspections of the roof and attic as part of a general inspection provided access is available. What’s best is to remove the old shingles and other materials entirely and start fresh.
Question: What is a flashing and why is it important?
Answer: Flashings, made of aluminum, galvanized steel, copper and plastics, are meant to cover and protect areas around penetrations in the walls or roof of a home, to prevent water problems. Many roof leaks are actually not a failure of the roofing materials, but a failure of flashings.
Flashings may be visible, concealed or partially concealed. When operating as intended, flashings divert water away from chimneys, windows, doors, valleys, the intersection of various rooflines, skylights and pipes and stacks. When they fail, whether from wear or tear or improper installation, water can find its way into the weak spot, damaging walls and floors.
Chimney flashings are particularly complicated because chimneys may have their own foundation independent from the rest of the house. In this case, the roof can actually move independent from the chimney. The flashings must be installed to account for this movement. Particularly wide chimneys require special flashing called crickets. This is a kind of splash-guard on the side toward the roof to prevent water or snow from inching higher than standard flashing would protect.
As part of a general home inspection, a professional inspector will inspect visible, accessible flashings to ensure they are functioning and properly installed. The inspector will observe both the inside and outside of wall and roof openings where flashings are common to determine if any evidence of failure or leakage exists. Findings should then be adequately explained and recorded in a written report.
If you like this post, please read “What the inspector told me about your wet basement”