Besides the shingles and external environmental factors, internal factors can also affect the performance of roofing shingles. These internal factors, such as your roof’s ventilation, can cause deck movement or deck deterioration, which in turn can inhibit the ability of asphalt shingles to protect your roof and home. An important step that should be taken by your contractor is to assess the condition of the existing roof structure, deck, and ventilation. Any shortcomings should be dealt with before the new layer of asphalt shingles is applied, since shingle failures attributed to deck and ventilation problems are not covered by some warranties.
Speak to your roofing contractor about the following concerns, and ask what additional concerns are common to your region.
Poor Ventilation:
Although not usually recognized as a major design consideration, proper ventilation of the attic area is an essential factor in gaining the maximum service life out of the building materials used in the roof assembly, as well as improving the home’s heating and cooling costs.
Insufficient ventilation under the roof deck may cause various problems on the roof, including ice dams, movement of the roof deck, ridging in the shingles, apparent roof leaks, and premature aging of the shingles. Older homes are seldom ventilated to current building code requirements and are particularly subject to these sorts of problems.
Ventilation requirements can range from 1 sq. ft. of ventilation for every 300 sq. ft. up to 1 sq. ft. of ventilation for every 150 sq. ft., according to the Asphalt Roofing Manufacturers’ Association. Ventilation requirements will vary depending on factors including the slope of the roof, and the type of roof.
The building code will also vary from region to region. Consult ARMA, your local building code, or your roofing contractor for more details.
Deck Movement or Failure:
A solid roof deck is an extremely important component in any good roof structure. If the roof deck is not solid, deck movement or deck deterioration can occur. This can impair the performance of the asphalt shingles, putting your roof and home at risk. It is important to note that the condition of the roof deck is beyond the control of the shingle manufacturer, and shingle failure due to deck movement, deterioration, or collapse is the homeowner’s responsibility. This is one reason why it is important to have your roofing contractor assess the existing roof structure, and remedy any shortcomings before the new asphalt shingles are installed.
Ice Dam Backups:
Roof structures will sometimes “leak” due to the formation of ice dams. Ice dams are formed by the continuous melting and freezing of snow due to heat escaping from the house or by the backing up of frozen slush from the gutters. The melted water flows under the snow and freezes as it reaches the unheated soffit, thus creating the ice dam. When this occurs, water can be forced under the shingles and into the attic, causing damage to the home’s ceilings, walls, insulation, gutters, eave and roof. To reduce the chances of damage caused by ice dams, consider doing the following:
- Keep the attic space cold by insulating it from the warm house interior, thus reducing or eliminating the heat needed for snowmelt.
- Use high heel trusses, insulate to the outside of the plates and install baffles to ensure ventilation at the eaves.
- Ensure that the outer edges of the gutters or eaves trough are lower than the slope line to allow snow and ice to slide clear.
- Ensure gutters are free of debris.
