To pass the blower door test in the Prescriptive Path in the new Michigan Energy Code requires a home to be equal to or less than 4 ACH50 (air changes per hour with the blower door depressurizing the home to -50 Pa). How do you get your home to pass? If you are building a home with a full, daylight or walkout basement, your home should have no problem passing. Frankly, if you are over this number, there is something wrong. We are seeing the average number for a home with a basement/walkout/daylight to fall between 2.25 and 2.75 ACH 50. Many builders who are working with us on air sealing techniques are finding there home consistently under 2.00 ACH 50. The lowest one we have tested was .92 ACH50. We are definitely seeing a pattern to the structures that either fail or are near failing. Here is a list of structures that are more likely to fail:
- Multifamily units – Condos or apartments that have one or more common walls with an adjoining unit typically have higher blower door numbers (in this case higher is not better). The common wall is generally not air sealed and insulated the same way as a traditional exterior wall. This allows for significant leakage through the common wall or walls.
- Structures built slab on-grade. The ground is a good air-sealer. In this type of structure, all the exterior walls are above grade, which means there is opportunity for much more leakage then a home with a good percentage of the walls below grade.
- Structures built with a crawlspace verses a basement. Again, same concept as the slab 0n-grade home.
If you are building a structure that meets the criteria of one of the above scenarios, then you need to make sure you are paying extra attention to the air sealing and insulation of the home.
Ways to help pass a blower door test:
- Make sure your insulator has an air sealing package along side the insulation. Many times insulation and air sealing get jumbled together. Even though these two concepts are very related, they need to both get planned out. A home without an air sealing plan, has a good chance of failing.
- Consider using a spray foam product, especially on the rim/band joist area. Many builders are starting to switch to an open cell spray foam on the above grade walls and rim joist area. Open cell foam is not as good (from an air sealing standpoint) as closed cell foam, but you do get some of the benefits and its much more cost effective. In my opinion all builders should be using a spray foam product on the rim/band joist.
- If you have a project that is going to be slab 0n-grade, crawlspace or multi-family, make sure you come up with a very detailed insulation and air sealing plan to give yourself the best chance at passing. Don’t just wait to the end of the project and hope it turns out.
- Move to the Simulated Performance Path in the Michigan Energy Code. As I mentioned at the beginning of this post, the 4.00 ACH50 number is a Prescriptive number, meaning there is no wiggle room. The Simulated Performance Path has flexibility and allows trade offs and one the the potential trade offs is the blower door test number. This means there is a good chance you can go over 4 ACH50 on a project if you are making up for it in other areas of the home. This path allows the builder flexibility, but requires you to work with a building science consulting firm.
The best thing you can do as a contractor is make sure you are working with a building science consulting firm that has experience blower door testing. We test enough homes per year, we can generally tell the likelihood of passing by just looking at the prints and specs. On projects that have a higher probability of failing, we work closely with our clients to generate a plan to get the structure to pass.
Whether or not you agree with the new regulations requiring blower door testing, its a very important part of the building process and needs to be taken seriously. Start working with a professional today! Call us at 616-419-8558.