Current building science research has discovered that the air tightness of the building envelope is very important to a building’s energy performance, thermal and moisture control, and indoor comfort. But most conventionally built buildings are sorely lacking in terms of air tightness, and this is particularly true for old brick buildings. Brick construction is not an inherently air-tight assembly, and in traditional masonry construction the wall assembly consisted of several whythes of bricks joined together with mortar. On this house the front wall was built with a better quality fine brick with tight thin mortar joints, while the side and rear walls were built from common brick with larger looser mortar joints. This was common practice for the side and rear walls of the rowhouse construction where the mortar often has gaps between the bricks.
We hired Mid Atlantic AeroBarrier to perform the air sealing of the building. The process they use involved pressurizing the house and the emitting a vaporized sealant into the space. The sealant product the use is GreenGuard certified for low chemical emissions. The high pressure in the house causes the sealant to collect at the small cracks and seams as the air is escaping. As the sealant collects at the cracks they are gradually sealed and the building becomes tighter. The guys at Mid Atlantic AeroBarrier ran the process for about 2 ½ hours. When they started the pressurized house registered an air leakage rate of 11.41 air changes per hour (ACH). After 2 ½ hours their process had reduced the air leakage rate to 1.68 air changes per hour (ACH) – resulting in an 85.3% reduction in the air leakage of the building envelope! We could see visible areas where joints and cracks had filled with the escaping sealant. This is a simple yet ingenious process that seals the entire envelope including tiny joints that would not otherwise be able to be accessed.
After the air sealing was complete, we were able to turn our attention to insulation. Since we have no attic we needed to achieve the maximum insulation values in the roof framing cavities as possible. We decided to go with closed cell spray foam as the first layer. 3” of foam was installed on the underside of the roof sheathing and 1” of foam was installed along the inside of the exterior walls. The remainder of the roof and wall framing cavities were filled with batt insulation. This gave us an R-51 at the roof and an R-20 in the exterior walls. This strategy of installing spray foam on the interior of the sheathing and then filling the remainder of the framing cavity with batt insulation is commonly referred to as “flash & batt” and draws on the inherent air sealing capacity of the spray foam as it expands and fills voids and cracks. The batt insulation is flexible and installs quickly to fill the balance of the framing cavities. With these air sealing and the insulation measures complete we are looking forward to improved energy efficiency, enhanced indoor noise control and thermal comfort. We think that it will all be well worth it when those bitter cold winter nights arrive.
This image shows the wall cavities with the layer of closed-cell spray foam applied.
new of the upper level showing the layer of closed-cell spray foam applied to the underside of the roof sheathing and to the interior of the wall sheathing.
This view shows the batt insulation installed in the wall cavities. Notice the white caulk joints and spray foam around the door frame that was installed as part of the air-sealing.
View at the upper level showing the batt insulation completed at the roof and wall cavities. (Also pictured: the drywall has been delivered and is ready to install).