Home Electrification Part One - Windows and Attic

My family and I moved across town in the fall of 2024. We had big renovation plans for the 1963, two story, colonial. My wife was dreaming of an open floor plan and new kitchen and I was brainstorming about energy efficiency and electrification. Before installing heat pumps, I wanted to make sure the house's envelope was insulated and air tight. Improving the envelope reduces the size of replacement equipment required, reduces heating and cooling energy costs, and improves comfort.

Kevin McNeely at McNeely Building Group did a blower door test on the house shortly after we moved in. Placing a frame with plastic sheeting and a calibrated fan in an exterior door frame, he measured the amount air leakage through the envelope. The results confirmed my suspicion that the existing envelope was very leaky. During the initial setup, Kevin asked if I had left a window open. I confirmed all the windows and storm windows were closed.

The test result was 10 air changes per hour at 50 Pascals (ACH50). This is how many times the air volume of the house would change over in an hour with an negative internal pressure of 50 Pa (equal to 0.0073 PSI). The 2021 International Residential Code (IRC) requires an air leakage of not more than 3 ACH50 in new construction. Michigan is still using the 2015 IRC without these requirements. Passive House building standards allow a maximum air leakage of 0.6 ACH50. My house had a lot of room for improvement on air leakage.

Our first home project last winter was to replace most of the windows. The original windows were single pane, wood framed windows with external storm windows. Many were hard to open and they noticeably leaked air. We selected vinyl framed, double pane replacement windows with low-E coatings. Where possible, we selected casement or awning style, which close more tightly than double hung windows. We increased the size of the bedroom windows to meet egress requirements, converted the dining room window to a sliding glass door, and added a long statement-making window in the primary bedroom. Being able to escape in a fire, shortening the walk to the backyard, and improved curb appeal are all great examples of project co-benefits along with the improved energy efficiency. Co-benefits are often the best selling points for energy efficiency measures.

Front of house with old windows (left) and new egress windows (right).

The next source of air leakage that I tackled was the attic. Air sealing the attic is critical to preventing air leakage in the winter. Warm air is buoyant and will rise into the attic through holes cut for wires and pipes, ceiling light fixtures, attic hatches, and gaps between the drywall of the ceiling and the top plate of the wall framing. The leaving air is replaced by cold air drawn in, usually around the basement rim joists and first floor doors.

Our attic had fiberglass batt insulation with cellulose blown over top. There was enough insulation in our attic but I was sure there was also a lot of air leakage through that insulation. A contractor vacuumed out the cellulose and removed all the fiberglass to expose the top side of the second floor ceiling. I found all the cracks I expected to and a big bonus gap. When an additional bedroom was added on to the second floor it was built around the existing chimney. The builder left a gap between the wall framing and the chimney in the attic. There was a 1-inch wide gap around 3 sides and a 7-inch gap on the last side. Even though fiberglass insulation had been stuffed in the gap, a massive amount of hot air rose out of this unintentional chimney every winter.

Opening in attic around chimney.

After the mechanical contractor installed heat pumps in the second floor bedrooms (more in a later post), the insulation contractor returned. They sealed the cracks and gaps with expanding foam and caulk. They used a strip of drywall to close the largest gap around the chimney. After air sealing, they installed better fitting baffles with blockers that prevent cellulose from entering the soffits. I installed a prefabricated, supper insulated and sealing attic hatch. Then the contractor blew in 15 inches of cellulose insulation for a total insulating value of R-50. For more information and tips on attic sealing projects see Energy Star's website.

Wall top plate gaps and penetrations before and after attic air sealing.

I improved other air leaks by replacing the weather stripping on an exterior door and foam sealing around gaps in the drywall of the garage. For a future project I plan to air seal the rim joists in the basement.