The terms “blower door,” “envelope leakage” and “air sealing” all describe the most useful building durability performance tests an owner or builder can utilize.

A HERS blower door field verification measures the total volume of air that is replaced in a space every hour. Simply explained, the blower door building performance test mimics the effects of a 20-mile-per-hour gust of wind passing over a structure or space at a constant rate and pressure. The blower door HERS verification is pre-determined on the energy compliance path chosen for a project based on the California Energy Code design phase (CF1-R) energy documents completed and produced by a certified energy analyst or CEA.

When we consider the science behind this testing, blower door verification is simply the ability to effectively seal or compartmentalize a space while maintaining a controlled natural flow of ventilation through built assemblies. Exhaust or supply ventilation with a blower door test is more cost effective than opting for balanced ventilation systems, especially in more moderate climate zones.

This test is more involved than most may think. When breaking down the preparation phase for the blower door test, you’re looking for smarter constructability during both design and the implementation phases. Proper compartmentalization of residential spaces has shown to yield financial savings for ownership as well as a substantial increase on project ROI. Design teams can streamline ventilation systems while not compromising tenant comfort. For example, since the blower door is a relatively easy to pass measure, it can be utilized with exhaust ventilation in leu of expensive balanced ventilation systems that may not be needed in more moderate climate zones.

Industry professionals and big builders commonly misinterpret blower door verifications as a troublesome or unachievable energy compliance method, but it may be one of the easiest HERS verifications to comply with. A few simple milestones can be implemented to ensure a project and building are aligned with blower door testing. Implementing a detailed rough phase checklist and accurately identifying key air leakage points within a structure through design phase reviews can substantially increase a structure’s chances of a successful blower door leakage results.



When you apply this compartmentalization process, you must start from the ground-up. Applying advance framing techniques with an increased number of installed rigid air barriers to create a more draft resistant framing approach can drastically improve results at final inspections; although, advanced framing techniques are not required to pass blower door tests.

Addressing the rough state of the space before finished walls are installed gives a general contractor and builder more flexibility to address additional concerns early while also providing a healthier environment for tenants. Being involved during construction gives a structure or space more of a chance to eliminate sources of unconditioned air transfer into dwelling spaces through rough framing assemblies, exterior penetrations through the envelope and even utility inlets.

When we move into the final phases of building construction, we also consider the “finished sealing” measures implemented within a dwelling unit. For example, locations behind electrical outlet face plates, where the outlet box meets the surrounding drywall, can create an increase in the amount of air that is calculated during the blower door verification test. Here, like many finished drywall penetrations within the units, caulking will be required to eliminate direct pathways for unconditioned air to move through freely. Blower door testing truly starts at the framing stages and carries over to the final state of a space.

In conclusion, consulting with an experienced 3rd-party green sustainability consultant, like VCA Green, on realistic “green” construction phase techniques and solutions that are achievable in construction is necessary for cost-effective project development. The next time you consider implementing energy compliance paths, don’t hesitate to include this useful building science verification to lengthen the life span of your building and decreased future maintenance costs down the road.

Contributing Writer: Kevin Perez, Construction Phase Manager

Moe Fakih, Principal