The importance of airtightness just took a giant leap forward.
The Wilden Living Lab’s latest study compares two different investments in home insulation: sealing gaps where air leaks versus an upgraded wall assembly. The results were surprising and indisputable. It seems that making sure the building envelope is properly sealed not only costs substantially less than upgrading to a higher quality wall assembly, it also had a greater impact on reducing the home’s energy consumption.
A quick analogy to illustrate the importance of sealing gaps: It is a well-known fact in the outdoor garment industry that seams are a major point of weakness. You can dress yourself for extreme low temperatures with several high-performance layers, but your protection will still only be as good as the sealing of the seams of your layers. The same applies to home insulation. If the unconditioned outdoor air finds a crack in the seams between walls, it will enter your home and significantly diminish the effectiveness of your wall assembly.
On average, poor airtightness accounts for up to 40% of heat loss from buildings.
Poor airtightness also plays a similar role in heat gain during the summer months. These losses and gains need to be made up with air conditioning that costs energy and money. Keep in mind, that even if the walls, roof and windows have the highest possible R-values, they will not work to their full potential when the shell of the home has a high air leakage rate.
Airtightness is measured in air changes per hour (ACH) and is calculated by dividing the outdoor air flow into the home by the home’s volume. The energy step code that is currently in place in most of British Columbia’s municipalities (Step Code 3) requires 2.5 ACH. This means all the air in the house exchanges 2.5 times within one hour. By 2032 it will be mandatory to build every home to net zero standards (Step Code 5) with an air exchange rate of 1 ACH.
BC Step Code ACH requirements for single family homes (3 stories and less) constructed in all climate zones in BC.
Groundbreaking research generates valuable results.
The goal of the Wilden Living Lab is to quantify how investments in insulation, air sealing and clean energy will pay back in energy and carbon emission savings, and in doing so encourage the building of homes to future standards. The Kelowna-based research initiative brings together FortisBC, UBC Okanagan, AuthenTech Homes and Wilden, Kelowna’s largest master-planned development. It is supported by the national research organization Mitacs.
The Wilden Living Lab research compares two identical homes that have been built side by side to different standards. The Home of Tomorrow has an air leakage rate of 1 ACH. The Home of Today was built to lower code requirements but thanks to good workmanship sits at 1.3 ACH. Researchers from UBC’s School of Engineering collected data from both homes over the course of three years. Based on this data they modeled a home built to Step Code 3 with an ACH of 2.5. To determine the efficiency of a low air exchange rate they compared this model home with the Home of Tomorrow.
Why prioritize sealing gaps over a wall upgrade?
Modeling suggests you can double the energy saving for a quarter of the cost.
Results show that an upgrade from ACH 2.5 to ACH 1 with the same R values of walls and windows saved 4% of the home’s energy consumption per year. The payback time for the additional investment of $1,120 in workmanship to seal the home was 16.5 years.
Alternatively, the research team looked at a home where the air leakage was kept at the rate of 1 ACH and only the wall assembly was upgraded to Step Code 5 standards. At a cost of $4,480 – four times what it took to seal the home – only 1.85% of energy was saved per year, resulting in a payback time of over 132 years.
Of course, the most effective solution would be to do both – seal the gaps and upgrade the wall assembly – but that may be beyond your budget. If you have limited funds, Wilden Living Lab partners recommend you focus all efforts on airtightness. The second priority would be to invest in wall insulation. Next would be an efficient HVAC system that, ideally, uses clean heating and cooling sources such as geothermal, air source or Renewable Natural Gas.
If you would like to get a more detailed insight into the research results, here’s the full report from UBC/School of Engineering’s research team.
The Next Generation Home
Wilden Living Lab partners are currently building a third home that explores innovative technologies to make constructing a net zero residential home possible in today’s market. Sign up for the Wilden Living Lab newsletter to follow the results.