September 29, 2022

Re-Sequence the Blower Door

It’s the mid-construction stage10am in Vancouver on a Tuesday and the house is fully insulated. Drywall is delivered and ready for installation.

The Certified Energy Advisor (CEA) is on site setting up the blower door fan for a mid-construction test. There’s a nervous feeling; the results will mean proceeding to drywall installation or a FAIL meaning making repairs and scheduling another test.

The passing score for this test is 3.5ACH – the maximum volume of air allowed to leak from the house under a depressurized environment. It’s the same score required to pass the final blower door test once the house is fully complete.

The blower door test begins and the house is depressurized. The poly begins to tighten up showing its resistance and immediate signs of leakage can be felt flowing into the house from all directions. Visually, it’s impossible to determine the origins of this leakage – everything is covered, everything is taped, everything looks perfect.

Test results shows a 3.2ACH, the CEA issues a PASS. The municipal insulation inspection gets booked for Wednesday and drywall installation starts Thursday. There’s also something else in the air – confidence that once the drywall is installed, air leakage will further be eliminated and there will be no problems meeting the 3.5ACH final blower door score.

It’s been months of construction and lots of money spent since the mid-construction test and the home is now ready for the final test. The CEA is back, initiates the final blower door test. It reads 3.9ACH, despite layers of materials installed on the walls; failure means the building permit cannot be finalized.

(Builders often accept a marginally-passing blower door test result at mid-construction as a testament of success. But this test is always performed in the best possible scenario: the poly being fully intact with all penetrations, device boxes, pot lights, window openings tightly taped. Once drywall installation begins, all the poly’d surfaces get cut open, exposing unaddressed air leaks. Drywall installation doesn’t help to reduce air leakage, it likely worsens it.)

When builders are stuck at the final blower door test, there is no easy way to fix the problem

some turn to minor non-destructive repairs such as taping or spray foaming. But the majority of the time, builders are stuck with a blower door test score that cannot be reduced without stripping apart the house for further troubleshooting.

To avoid this common and costly episode

it’s crucial to approach the build with a better airtightness strategy long before getting to this stage.

It’s also time to re-sequence this building requirement. While mid-construction is an important stage to evaluate the installation of poly, doing the blower door test after the drywall installation would provide the builder with an accurate reading of the airtightness, allowing for any changes or repairs to be made long before the finishing stages.

Too often, the current two-blower door test requirement leaves builders stranded at final completion. Adjusting when the tests are done can maintain a standard of energy efficiency during the build process, rather than apply band-aid measures at the end.

Municipalities throughout BC are striving for higher energy efficiency standards for homes, demanding increasingly airtight homes to be built year over year. In Vancouver, the 3.5ACH standard has been further raised to 2.5ACH, applicable to building permits issued after January 1, 2022. Once those projects begin to break ground, builders will face an increasingly difficult task of meeting the new airtightness requirements. How to address those air leaks is unique to each project, but the key is developing a process and strategy of when to address them.