2012 was the first year the International Energy Conservation Code required residential construction to pass an air leakage rate test, better known as a blower door test. My area of the country requires the test to be at or below 3 air changes per hour at the test pressure of 50 pascals (ACH50). (Other areas, typically warmer climates require 5 ACH50.) Most new construction in my market has no problem passing the test, but I have had a handful of houses fail, usually the failed tests are by a builder having their first blower door test or the project is a very small home.
My current fee for the typical code required blower door test is $250 (price increases for large and complex homes). If the home does not pass, I begin looking for the causes at a per hour rate of $100. Once the issues are found, someone, usually the general contractor or insulating contractor will have to perform air sealing to correct the deficiencies and the home will be required to have a second test. My rate for a second test is $150 (the fee is reduced because I’ve already calculated the volume of the home which greatly reduces the time on site). This process repeats until the home passes. Without a passing test, most jurisdictions will not issue an occupancy certificate. It’s beneficial to pass a test the first time.
Passing a test
There are a few ways to almost guarantee a passing test. The best way is to understand where houses leak air and design an air sealing strategy with that in mind. There are a lot of great ideas and method to perform air sealing during construction, nothing is overly difficult, a lot of information can be found on GBA and other publication on air sealing.
A way to catch an issue early is to have a mid-build blower door test. This test is typically performed after Mechanical, electrical and plumbing (MEP) systems are installed, windows and doors are in place, but before insulating. The biggest difficulty with this test is how to address a vented attic or roof which is often open to the outside. A method I’ve used is to install polyethylene sheeting on the ceiling, sealed to the wall framing. (I live in a very cold climate; polyethylene is common in my market.) Other areas might use drywall or a smart vapor control product. I’ve also tested with closed cell spray foam installed in unvented roofs and conditioned attics. Problems can be identified with a test and corrections made before insulation and finishing materials are installed.
Another option is to use a third-party air sealing technology, such as Aerobarrier. This process is typically performed at the same point in the building process as the mid-build blower door test, after MEP systems are in place but before insulation and finishing. The Aerobarrier process includes pressurizing the home and then releasing an aerosol sealant fog that is suspended in the air. The sealant floats until it is caught in an air current. This current will lead to a penetration to the exterior where it will build up around the opening until it is sealed. A couple advantages to this method of air sealing is time savings, the process usually only takes a few hours, and the level of air tightness is chosen, you get to pick, the tighter the home, the more time the sealing process takes and the higher the cost.
The Failed Test
As I said earlier, I have blower door tested a few houses that have failed. There can be many reasons for a failed test, sometimes the choice of a product is the reason. I had several failures in a group of duplexes that were built over the course of three years, they failed in part because of the water heater that was selected. The water heater was a natural venting gas unit installed in a small mechanical room. The water heater used interior air for combustion and required a
combustion air vent to the outside. Per the ANSI/RESNET/ICC 380 testing standard, these vents, and the flue for the water heater must remain open during a code compliant blower door test. Simply moving to an electric or some type of sealed combustion water heater would eliminate the required combustion air vent and the homes would have passed.
Another product I still see on occasion is the standard recessed light fixture. You would think by now builders would know not to use this product in an area where it penetrates the air barrier and displaces insulation. A new home I recently tested failed partially because this type of lighting was chosen. This same home also had an unsealed attic hatch. These two conditions combined with the home being small, 8,000 cubic feet, contributed to the new home failing the test, even though the home was only leaking a little more than 500 CFM at 50 Pascals. The attic hatch was an easy fix, simply caulk the drywall access panel shut, air sealing the recessed cans, especially in a cathedral ceiling is much more difficult. This contractor caulked the recessed fixture housing to the drywall, which helped some. A better choice is to eliminate the traditional recessed cans and move to the recessed light “look” that uses a thin LED light fixture and a standard flanged air sealing electrical box that can be sealed to the drywall.
As a side note, the 2021 International Energy Code has an option for blower door testing small structures using the cubic feet per minute of air flow per square foot of surface area (CFM50/Ft² of surface area). The structure needs to be 1,500 square feet or smaller and must achieve a leakage rate of no more than 0.30 CFM50/Ft² of surface area. The home above that failed the standard ACH blower door test achieved 0.15 CFM50/Ft² of surface area. If tested to the 2021 code allowing the CFM50/Ft² of surface area, this home would have passed.
Another common area of air leakage is between the foundation and framing. The new home in the upper photo had a very low blower door test, 1.04 ACH50, but this air leak at the floor was easy to see with thermal imaging. This home will experience very cold wintertime temperatures, there’s a good chance this small area in the master bedroom will have damp drywall in this corner. The lower photo is a home that just passed at 2.74 ACH50. There were several areas around the home where leakage under the bottom plate was evident. Traditionally we are using a sill seal or some other type of gasket to seal the bottom plate to the floor or foundation. I also suggest sealing the exterior sheathing to the foundation using a tape, sealant, or fluid applied membrane to further reduce air movement in these areas.
These two images are of the same new home. Two of the wall mounted mini-split heads are leaking air during the blower door test, I see this all the time. The air is moving around the line set, condensate drain and electrical wire penetration (though some of the air may also be moving through a condensate line that is open outside). Feeding solid copper piping through a wall and making the connection to the head, often after the home is finished makes air sealing tough. In new projects I’m involved with, I try to move the heads to an interior wall, right next to an exterior wall and run the line set before finishing whenever possible. A small amount of slack can be provided in the tubing to allow for some movement and adjustment to the line set without breaking the air seal.
The biggest area of deficiency in air sealing I see in both old and new construction is properly addressing the ceiling or roof. Even a simple roof, which I rarely see in new construction, can be a challenge to air seal. A good air sealing connection between the wall and roof is often missing. There are interior wall intersects that prevent continuous air control. We then poke a bunch of holes in the air barrier with plumbing pipes and electrical wiring and boxes. Add a forced air heating system with ducts in the attic space, now there’s a whole bunch more holes. Change the simple roof to one with multiple roof lines, dormers and cathedral ceilings, air sealing just became a nightmare for even the best at building very tight structures. With that said, the ceiling is the most critical area to get right.
The second most important area to address is low, connecting the foundation to the framing. Tying dissimilar materials together to form an effective air seal can be tough. Concrete foundations and slabs rarely end up perfectly flat. The dips and humps can create a pathway for air to move into the structure. This is where I prefer to see a belt and suspenders approach, gaskets with the addition of tapes or sealants.
I see less issues with air sealing walls, but there are still some. There are several good options on how to air seal a window or door. We punch several holes that connect the inside to the outside with electrical wires, vents and outside water spigots. These need to be made both water and airtight.
Blower door testing is not going away, I wouldn’t be surprised if in future energy codes, the requirements for building tightness become more stringent. With a basic understanding of where a home leaks air, a strategy can be designed, and a code compliant blower door test can be passed the first time.