Insulation in an attic space should not be recommended unless ample and enduring ventilation is present or maybe a part of the work scope. Sufficient cross-ventilation should be maintained above all attic insulation by giving either low and high vents or gable-end vents where possible. One square foot of net-free vent area (NFA) should be given for every 300 ft2 of attic area having vapor barrier present holding 50% to 60% of the vent area present near to roof ridge and 40% to 50% present near to eaves. One level of venting might be used given that sufficient cross ventilation can be preserved. Exceptions: Ventilation that may not properly have a balance to fulfill 50/50 high low requirements as per roadblocks can use at least 75/25 ratio to meet the program guidelines.
When cross/ lower venting is not possible because of roadblocks;
The energy specialist should follow One square foot of net-free vent area (NFA) provided for every 150 ft2 of attic area. All suggested ventilation must be attained by installing high ventilation options.
Acceptable Roadblocks to installing lower ventilation
- 3rd story soffits
- Steep/ uneven grade for ladders
- Soffits with open rafter tails
- Soffits that are too narrow for vents
- Aluminum soffits
- Non-perforated vinyl soffits
- Cellulose is already blown into soffits
- Call LV for other reasons
Options for high ventilation include:
- Ridge Vent
- High Gable Vent
- Window Gable Vent
- Roof Vent
- Turbine
Options for high ventilation include:
- Soffit Vents
- Low Gable Vent
Ridge Vent:
These vents are installed at the roof ridge and stick up above the roof a few inches. Mass Save Contractor installation restrictions like the incapability to install ridge vents in slate or tin roofs might apply.
Gable Vents:
Gable vents are usually rectangular and made from wood, aluminum, or vinyl. Gable vents cannot be installed via asbestos siding. Mass Save Contractor installation restrictions like the incapability to install gable vents in aluminum siding might apply.
Soffit Vents:
Soffit vents are usually made from aluminum. Mass Save Contractor installation restrictions might apply like the incapability to install the soffit vents in aluminum soffits.
Propavents:
Suggest at least one propavent with each present soffit vent and for proposed soffit vent to enable proper air transfer. For uninterrupted soffit vents or ventilated drip edges, propavents shall be suggested for every rafter bay. Additional propavents might be essential to deliver satisfactory airflow at each soffit vent like with roof truss or other 24 OC spaced construction.
Prop-Vent Half:
Recommend only when needed to maintain 1” insulation clearance from the top of the vent chute.
Window Vents:
When attics cannot be ventilated by other means and windows exist, recommend gable vents to be installed in the existing window sash. Plywood will be constructed around the gable vent which is then fitted into the place of one of the window sashes.
Roof Vents:
Roof vents are typically made of metal. Contractor installation restrictions may apply such as the inability to install roof vents in slate, tin, or flat roofs. Follow manufacturers’ recommendations related to minimal roof pitch requirements for each specific roof vent. Turbine Vents: Turbine ventilators also known as whirlybirds have an NFA of 4.0 sq. ft. This type of vent should only be recommended when upper ventilation of 4 sq. ft or more is required.