Your roofing contractor should know enough about attic ventilation to properly vent your attic. The requirement by the Building Code (2009) is 1 square foot of ventilation for every 300 square feet of attic floor space. So if you have a home that is 1500 sq. ft. you will need approximately 5 sq. ft (720 sq. in.) of ventilation, split between intake and exhaust vents. Intake vents are usually in your soffits, while exhaust vents are at the top of the roof.
In the example above, you should have 15 roof louvers (can vents) with a NFA (net free area) of 50 sq. in. each. Alternatively you could go with a ridgevent like ShingleVent II (what we use), in which case you’d only need 40′ (or 10 pieces) of ridgeventing.
At New Heights Roofing we recommend increasing ventilation to 1:150 ratio from 1:300 since it will greatly increase the air flow in your attic, keeping your home cooler in the summer and helping to prevent ice dams in the winter. To do this without covering your roof with roof louvers, we recommend a concealed, continuous ridgevent like ShingleVent II.
If your home is not properly ventilated and your shingles fail early, they won’t be covered by the manufacturer’s lifetime warranty. Without proper ventilation your warranty will be reduced to 10 years, with no SureStart protection.
Installing Over Non-Approved Roof Decking
Your roofing contractor should be able to tell you what type of decking your home has and if it is an approved deck to install shingles on. Examples of fully approved decking are plywood (minimum 3/8″), OSB (minimum 7/16″) and wood board sheathing (minimum 1″). If the wood board sheathing is large (1×6, 1×8, 1×10, or 1×12) it may cause buckling in the shingles so extra precautions should be taken. It may be necessary to install new 4’x8′ sheets of plywood to provide a solid, smooth surface to attach shingles to.
Loadmaster and Homasote roof decking are “permission-required” decks and must be installed according to manufacturer instructions and may require special fasteners to meet the warranty requirements. Other roof decks like Cementitious wood fiber board, gypsum, and insulation boards are not approved and require an approved decking be installed over them. These decks are not common among residential homes.
If there is existing water damage, dry rot, or any other damage done to your sheathing the shingles installed on top of it will not be covered by the manufacturer warranty. An example of this is an undiscovered leak where the wood is not repaired before reroof. If that piece of plywood fails in the future, the shingles installed over it will not be covered by the warranty.
Another way a roofing contractor may void your warranty is by not prepping the roof decking properly after tearing off an existing roof. If there are existing nails sticking up that poke through the shingles, the damage will not be covered by the manufacturer warranty.
To prevent any of these scenarios, we recommend tearing off all existing roofing material (including the old felt paper) so we can get a good look at the roof deck and inspect it thoroughly for damage. We also take our time and scour the roof deck for existing nails that were left behind and either pound them into the decking or remove them completely. New Heights Roofing takes every extra precaution to be sure our customers will never have a problem with their roof in the years ahead.