Pay Attention to What's Underneath
Warranty Considerations of Under-Deck Sprayed-in-Place Foam InsulationG.K. Sharman
Incorrectly installed under-deck spray foam insulation can void the Atlas shingle warranty because spray foam insulation products applied directly to the bottom of the roof deck do not allow for crucial eave-to-ridge airflow.
Atlas does not warranty its shingles when spray foam is applied directly to the underside of the deck.
Asphalt shingle installers or design professionals are responsible for providing adequate ventilation that meets warranty requirements and local codes.
Ventilation Is the Key
As Paul Casseri, Atlas product manager, shingles and underlayment division, explains:
- Spray foam insulation may create an unvented attic. An improperly designed and constructed unvented attic may be subject to vapor condensation and moisture accumulation in the attic space, which may penetrate into the habitable areas of the building and may cause mold and mildew. It may also lead to premature deterioration of insulation, wood and other roofing and construction materials.
- Spray-foam insulation applied to the underside of the roof deck will prevent free flow of air on the bottom side of the deck and the associated dissipation of heat that occurs with traditional vented attic construction.
- Lack of adequate ventilation immediately below the roof deck may lead to unacceptable deck movement and premature roofing system failure. Ensuring proper design and construction of unventilated spaces and appropriate management of moisture are the responsibility of the building owner, design professional and contractor.
Atlas Roofing requires that attic ventilation meet or exceed the FHA minimum requirements of at least 1 square foot of net-free unrestricted air flow for each 150 square feet of attic floor space, or 1:300 with a balanced system. While some model codes include an allowance for reduced vent area when the system is properly balanced, an unbalanced system may result in performance and durability issues.
Correct Installation of Spray Foam to Maintain the Warranty
Atlas Roofing does approve and warranty the use of Atlas shingles with spray foam in certain situations:
- The system must maintain a free flow of air on the underside of the roof deck from soffit to ridge.
- Baffles should be installed between the rafters before spray foam insulation.
Atlas Roofing will accept the installation of asphalt roofing shingles and/or self-adhered roof underlayment over highly insulated roof decks insulated with any type of foam insulation when an effective means of providing air flow directly below the nailing surface — such as baffles — is permanently installed.
The best option for a solution for providing under roof decking ventilation would be to install a vented nail base over or a minimum 1-inch baffle system under the original roof decking.
The vent baffles or chutes create a space between the roof deck and the insulation. Installers can also use or construct a ventilated deck sub-assembly, which is applied over or in place of the existing deck.
This solution provides the eave-to-ridge airflow needed to achieve adequate ventilation for shingle performance and warranty requirements.
The provided air flow must be continuous from the eaves through to the highest point of the roof area, available directly below the decking to which the underlayment and shingles are attached.
The best approach is to employ the right amount of vent area, installed as part of a balanced system. Always provide at least 50%, but no more than 60%, of the total required ventilation at the eaves or lowest portion of the roof possible.
Always follow Atlas Roofing’s recommendations for minimum ventilation and ensure that each cavity is insulated.
For more information, visit AtlasRoofing.com.