Passive House Meets Affordable Multifamily Housing: Walsh Construction’s Lessons from the Field

By Jay Fox

The installer stood on the roof and told the quality team at Wash Construction he was certain he’d done a good job. The spray foam he’d installed at the wall-to-roof transition would pass whatever airtightness test they threw his way. The team then pressurized the wall cavity along the roof edge of the building, fed it fog from the kind of machine that once graced the stage of arena rock shows, and watched as the fog poured up through the parapet.

Walsh Construction Director of Learning and Development Martin Houston says the installer was crestfallen after seeing the fog escape from the building. Nobody doubted his efforts. After all, the incident occurred more than 13 years ago, and Walsh (as well as the entire industry) was still trying to find ways to refine and improve its roof and wall assemblies. Repeated failures, loads of testing, and a gradual evolution in technique ultimately allowed Walsh to discover a method for maintaining a continuous air barrier and thermal layer at even the most difficult of transitions. Learning from mistakes and systematically rectifying them, rather than slapping a Band-Aid on a specific issue to make it go away, is how they became one of the most well-respected contractors on the West Coast.

Houston and Walsh Quality Director Sharon Libby Eyerly recently shared their knowledge with Passive House California, and this post will take those lessons learned about high-performance building and share it with the Accelerator community.

From Code to Passive House

Walsh can date its founding back to 1961. Though its name has changed since that time, Walsh has remained consistent in its efforts to partner with mission-driven organizations and to improve communities in which it works within the Pacific Northwest.

Walsh has also been consistent in its dedication to quality, exemplified by how it established a quality program in 1999. The goal was to build better and more durable affordable housing, primarily by keeping water out. Walsh did not immediately jump from code to Passive House. Instead, the firm used tools like infrared imaging and whole-building airtightness testing to make incremental improvements over the years.

Taking It One Parapet at a Time

The simplest and most cost-effective way to frame a multifamily roof is with prefabricated trusses. The assembly includes a vertical leg that forms the parapet and a piece of blocking that aligns with the sheathing. Unfortunately, this can introduce problems with condensation because warm and moist air naturally moves toward the roof and this parapet, which has colder air on both sides during winters and even shoulder seasons. To reduce condensation, Walsh used to vent the parapets.

Of course, this introduced the problem of air leakage along the wall-to-roof interface. Even on buildings that tested quite well on their whole building airtightness tests, Walsh found significant leakage nearly along the entire parapet. Over several years, they found incremental solutions to mitigate the problem and incorporated them into standard practice. It didn’t occur all at once.

“We are evolutionary, not revolutionary,” Houston says.

“The problem is the framer has to wait until you've got a bunch of that peel and stick transition from the wall to the roof, which means you send a contractor away for about a week,” Houston says. Houston explains that having the contractors budget that time in from the beginning helps to ensure that they return to then build the parapet once the peel and stick layers from the wall and the roof have continuity. That ensures an airtight connection. They then put spray foam in the parapet that is equal in height to the insulation layer of the roof to ensure thermal continuity.

This is just one solution. The priority, Walsh has found, is to create workable details and to get framers and insulators working together to create a continuous air barrier and layer of insulation. If they can schedule the work in advance and have a clear understanding of how it needs to be sequenced, then the team can figure it out.

Leaks Are Not Only an Envelope Problem

Walsh has learned over the years that air leakage can occur far away from the exterior wall of the building. Some portions of the building that can be leaky and hurt airtightness scores are stair shafts, elevator shafts, and trash rooms and chutes. These parts of the building often connect to only partially conditioned or even exterior spaces.

To ensure that side is taped, Houston offers a simple solution: Tape the boot before lifting the fan into place. As rudimentary as this sounds, this is the kind of attention to minor details that can mean the difference between a building that hits its airtightness goals and one that just misses them.

Experience as a Teacher

Walsh got better at airtightness by making mistakes, testing, correcting those mistakes, and carrying the lesson to the next job. The fixes were rarely dramatic, and the improvement was a form of evolution, rather than revolution. In many cases, the fixes were simple. In others, they involved learning how to better coordinate with multiple trades to avoid problems with scheduling.

By learning from their experience in the field and refining their methodologies over decades, Walsh has learned to reliably deliver buildings that meet the most rigorous performance standards and to do so while partnering with mission-driven organizations across the Pacific Northwest and beyond.