Serving MA and Southern NH
Roof Clean Plus LLC
(978) 340-2390
Warnings to consumers about power washing and offers to “seal coat” roofs from our competitors.
POWER and PRESSURE WASHING: asphalt roofs, slate and cedar shingle roofs are susceptible to extensive damage from this method. Some roof cleaning companies offer this service. However, it is not recommended on asphalt roofs as it may dislodge granules, which can lead to premature shingle failure. It can also break brittle shingles and lead to further damage of your home with unseen leaks.
SEAL COATING: Drainage and permeance: Field coating asphalt shingles is at odds with one of the fundamental working principles of shingled roofing. Shingled roof coverings shed water. In other words, shingles rely on gravity to do most of the work of keeping out water. Sometimes, water travels underneath shingles via capillary action, wind force or when large volumes drain down valleys. When this occurs, shingles allow water to run down and to the outside surface of a roof.
When a coating is applied over roof coverings installed shingle-fashion, especially when it is intended to seal shingles at edges or form a continuous membrane, drainage paths for water trapped under the roof’s outer surface may be cut off. Although wind-driven rain or water entry because of capillary action may be controlled or eliminated, the most common water entry locations where dissimilar materials meet at flashing elements can remain problematic. The potential for damage to underlayment and deck sheathing, as well as leaks from water infiltrating at flashing locations, is increased.
Additionally, depending on the coating type, field application over asphalt shingles may lower an asphalt shingle roof system’s vapor permeability.
Asphalt shingle roof systems are vapor permeable because joints between individual shingles allow vapor to pass through. Some coating formulations are effective vapor retarders. Applying a vapor-retardant coating to an asphalt shingle roof system’s surface likely will compromise a roof assembly’s self-drying characteristics.
Some roof assemblies may accommodate this with existing or additional ventilation. For other roof assemblies, the change in moisture transport resulting from coatings may be too much to maintain a noncondensing environment in attic or ventilation spaces. Reference: American Society of Home Inspectors