Envelope leakage is a measure of the air tightness quality of the building envelope, an assessment of how much natural ventilation is supplied by air leakage and results may be used to assess energy losses resulting from uncontrolled air leakage. Envelope leakage allows air to enter the home from unknown sources that may contain air contaminants (e.g., moisture, pests, soil gases, dust and other particles). It is preferred to build a tight home and bring in fresh air from known sources via mechanical ventilation.
Envelope leakage testing results must be less than or equal to 5 ACH50 or 0.30 ELR
- CFM50: The volume of air in cubic feet per minute moved through the fan to maintain a 50 Pa pressure difference between the house and outside.
- ACH50 = ACH50 is the number of times the air volume in a building changes per hour at 50 pascals of pressure.
- ACH50 = (CFM50 * 60)/conditioned volume
- Envelope Leakage Ratio (ELR): The quotient of the CFM50 measurement divided by the square footage of the building envelope, or SFBE.
- Square footage of the building envelope (SFBE): Sum of the foundation/floor, exterior walls, ceiling areas
- ELR = CFM50/SFBE
Floor area and volume must be calculated using RESNET standards for conditioned floor area and conditioned volume.
The EarthCraft Technical Advisor will diagnostically test compliance of criteria at the final inspection.