Radical Preservation on the Sunshine Coast

Radical Preservation on the Sunshine Coast

“It looks like it rose out of the ground or that it’s been there for 100 years,” says Lincoln Construction Project Manager Blair Keeling.

This impression is by design and partly due to Keeling’s efforts, as he was the project manager for the Treehouse, as the home is affectionately known. Completed just within the last year, the home was erected in the middle of a forest and Keeling’s team were tasked with doing so while minimizing any disturbance to the mature trees on the property. By prioritizing a combination of performance, durability, and conservation, the team behind the Treehouse managed to create a stunning high-performance home that also highlights how respecting and preserving the natural landscape can shape a project and produce something uniquely beautiful.

Many of the trees in the surrounding old-growth forest tower over the home. Photography by: KRJ Photos

Seeing the Forest…

Located on British Columbia’s Sunshine Coast, the Treehouse sits between the mountains and the ocean on a property that is close to one-sixth of an acre (0.17)—about the size of a modest property in a town. However, unlike a typical town, the property is on a steep and heavily forested slope.

The property was purchased in 2022 by Amanda and Curtis. Keeling notes that they were intimately involved with the design and planning of the home from the beginning, and that Curtis, a plumber by trade, was especially hands-on. “We’re extremely appreciative of the fact that they had that vision early on,” Keeling says. “By far, they were some of the best clients we’ve worked with.”

The owners approached Lincoln directly to see if their vision was feasible. That vision: Build a home in an old-growth forest that does not disrupt, damage, or displace the existing ecosystem. In addition to placing preservation at the top of their priorities, Amanda and Curtis also wanted the house to perform exceptionally well and were even familiar with Passive House standards.

The folks at Lincoln agreed to take on the project and contacted GNAR Inc, a sustainable architectural firm based nearby. Keeling explains that the two have had a good working relationship that’s developed over the years, and that they have a similar philosophy when it comes to building.

Establishing the footprint of the Treehouse before construction begins.

Mark Kavanagh of GNAR says the firm is sustainability- and performance-driven. This is not a surprise due to B.C.’s energy codes, which are more rigorous than other provinces in Canada, but GNAR goes above and beyond. As Kavanagh explains, all designers are expected to take Passive House training courses when they join the firm. “I think it just makes sense and that’s how building should be done,” says Kavanagh. Even if not all their projects are certified, they are guided by the principles of Passive House from the start of the project. “It might cost a little more upfront, but you are future proofing your house. It’s a long-term investment.”

Kavanagh says that most clients are eager to build sustainably at first, but that some begin to waver when they realize that there are upfront costs that have to be considered. The owners of the Treehouse, however, were aware of these costs and this helped keep the project moving. “If your client is super motivated to make it work, then that is obviously a huge help,” Kavanagh says. “Because we’re always motived to do stuff like this.”

More than just having a desired aesthetic and meeting higher than code levels of performance, they also wanted to avoid hurting the old-growth trees. “We've done other designs where we had the building step around existing trees and done it in a really cool way,” Kavanagh says. However, this was different. “The trees were number one—everything else came second.”

Fencing off one of the Tree Protection Zones.

For the Trees

For a more casual preservationist, surveying a forested property means documenting the location and diameter of each tree above a given size. It rarely requires a high level of precision. In this case, however, Curtis measured each tree by hand, and an arborist was brought out to consult. The arborist made recommendations to ensure the root systems of the trees were not harmed due to excessive soil compaction and added mulch to parts of the property that were going to see heavy foot traffic. By working with a surveyor and the arborist, the team was also able to map out a series of “no-go” zones that were then cordoned off with protective netting.

Similar to baseball legend Willie Keeler’s advice to batters (“hit ‘em where they ain’t”), the footprint of the house had to fall within the negative space of the landscape to avoid removing or damaging mature trees. “We had detailed drawings of the trees and the root systems, and then we had to work backwards with the structural engineer,” Kavanagh says. “It was all about nesting it into context,” he adds.

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“The whole shape of the building steps around the trees, but it’s also close enough that you can reach out the windows and actually touch the trees,” he continues. Feeling as though one is part of the forest is an enormous perk, but Kavanagh adds that GNAR worked with the arborist to better understand where they needed to create more distance to give trees room to grow and approximately how much each individual tree would be expected to sway. This informed the shape of the house, the overhangs, and even the decks. It also ensures that the trees and house can coexist without damaging one another.

“One of the trees goes up through all the decks,” Kavanagh says. “We had to be careful about how much distance we left around the tree to allow for that sway.”

Topography Matters

Another challenge for the team was the topography of the site, as it sits on a steep slope. Given the project’s other priorities, this made the use of a slab on grade foundation impossible. Foundation work tends to require extensive excavation before pouring concrete footings and walls, which would have significantly disturbed the forest floor and the root systems of the trees.

Instead, GNAR and Lincoln worked with structural engineer Tim Stockton of Allester Group and decided to use screw piles for the foundation system with the addition of a small concrete foundation wall that anchors the home into the hillside and creates a suspended floor. Screw piles are steel rods that are driven several feet into the ground, where they also serve as anchors. In some cases, the holes for the screw piles brushed with just a few centimeters of nearby root systems, but they managed to drill the holes for the Treehouse’s foundation without harming any trees. Once the screw piles were put in place, concrete was then poured into forms to create footings and lock the piles into place. Keeling notes that, in this instance, these concrete footings sit above the roots.

In addition to cutting way back on the amount of excavation and leveling necessary, the use of screw piles reduced the amount of concrete that needed to be poured. Keeling estimates that the screw pile system required 75% less than a conventional pour for a slab foundation. Moreover, the screw pile foundation offers flexibility and resilience in the event of earthquakes, which are unfortunately quite common along the Sunshine Coast.

The site’s topography also created logistical challenges for the Lincoln team, as they were prohibited from driving trucks wherever they wanted onto the property and because there is no flat area where one could stage a crane. Instead, the crew had to unload virtually all the building materials at the base of the roadside and carry them to the job site by hand. Even the steel for the structural columns was brought up in pieces and welded together on site. “Even if you’re just walking up the hill with nothing in your hands—and you’ve done that half a dozen times back and forth—it’s a calf burner,” Keeling says.

In fact, only two machines were brought to the site: one to drill the holes for the screw piles and drive them into place, and a second to help the team bring in steel frames. The rest of the work was done by hand.

“We knew Lincoln could pull it off, because we’ve worked with them before,” Kavanagh says. “And we knew Allester could pull it off, because we’ve worked with them before, too.”

Inside the Treehouse

At 1,800 ft² (167 m²), the Treehouse is comfortable for a small family and even has space for a renter’s suite. What is slightly out of the ordinary is how the floors are situated. Kavanagh describes it as an inversion of a typical home.

The couple plan to rent the bottom floor, which contains a bedroom, bathroom, and small living quarters. The heart of the home’s mechanical systems also sits within a utility closet on this floor, and it consists of an electric heat pump to heat the water manufactured by U.S.-based Bradford White, an HRV system by Ontario-based Lifebreath, and air-to-water heat pump and water tank for the in-floor heating system (which was installed by the owner). Even though it is the lowest floor, it is still above ground, looks out to the forest, and receives plenty of southern light. The suite also steps out to a covered deck. The second floor is where the owner’s bedrooms are located. This floor has a covered deck so they can enjoy the outdoors even during rainstorms, while the third floor houses the kitchen and living room.

The lower level of the Treehouse.

The main or second level.

The upper level.

More than just providing cover in the event of a storm, the prominent overhangs eliminate the need for an active cooling system and help protect the cladding system from the elements. The team decided on vertical metal cladding by Alberta-based Westform Metals for several reasons. First and foremost, it is fire resistant and orienting the system vertically allows them to avoid horizontal areas where debris from the forest can accumulate and potentially become fuel for a fire. Like the cladding, the soffits on the decks are all metal, though the decking material is cedar.

As a general operating principle, Kavanagh explains, the firm follows the FireSmart guide published by the province, and they were especially conscientious when making materials choices for the Treehouse.

While fire hardening was a priority, they also wanted components of exceptional durability because of the difficulty of working on the jobsite and the house. If something needs to be replaced after 20 or even 30 years, it’s not going to be cost-effective.

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Durability was also a consideration when the team was considering fenestration. They opted for Innotech Windows + Doors’ tilt and turn Defender series, which are triple-pane and Passive House Institute certified components. “Any project we’ve used them on, we’ve always gotten good feedback,” Kavanagh says of the B.C.-based manufacturer. In addition to being durable, Kavanagh says their pricing is competitive and they perform well during blower door tests.

The wall assembly is 2x6 construction combined with a HUBER Zip system. Swelling was one concern with the Zip system, as this can be a problem in more humid climates like the Sunshine Coast. However, if tapes and flashing are applied immediately, this didn’t become a major issue, according to Keeling.

Another facet of GNAR’s airtightness strategy, according to Kavanagh, is to keep services outside of exterior walls to avoid unnecessary penetrations in the air barrier. (In colder climates further away from the coast where interior air barriers are more common, this strategy also makes it less likely for water lines to freeze.) The final blower door test was 0.28 ACH50, which Kavanagh says was a team effort, though he did make certain to credit Lincoln’s meticulous craftmanship and Keeling’s leadership on the job site, as well as the work of energy consultant Allison Kirk of SITKA Home Energy Solutions.

As shown in Figure 1, the team used fiberglass (R-22) for cavity insulation, as well as a 3-inch exterior layer of expanded polystyrene (EPS) for the wall assembly, resulting in an average R-value of 36. The roof assembly features a thicker layer of fiberglass insulation (R-42), but only 1-inch layer of EPS (see Figure 1), and has an R-value of 46. The assembly of the suspended floor combines elements of the wall and roof assemblies, and it includes a thicker layer of fiberglass insulation, as well as a 3-inch layer of EPS. Its R-value is 54.

Keeling notes that efforts were made to not use foam products, but difficulties with sourcing during the pandemic made getting all their first choices for materials unfeasible if they wanted to stay on schedule. “You can’t delay your project for a year because of insulation,” Keeling says. He also notes that EPS foam has a similar embodied carbon score to available alternatives, but came with a significant cost savings over those alternative. These factors helped tip the scales towards using a foam product.

Alternatively, the decision to use a torch-on membrane in the roof assembly was made with longevity in mind. While its use does require increasing the embodied carbon of the project significantly, Keeling notes that it has a lifespan of 50 years. The improved durability ultimately made it a palatable trade-off.

Collaboration Is Key

For future owners of Passive House and high-performance buildings or properties where preservation is a high priority, Keeling recommends reaching out to a builder either before or at the same time as an architect. It helps set budgets and timelines. It also helps everyone get on the same page as early as possible, which can make design and sourcing go smoother. This collaborative approach ultimately reduces delays and costs. Most important of all, getting both the builder and designer in the same room early on lets them conduct feasibility studies and frontload planning so that they can ensure the house goes up quickly without disturbing the landscape.

Getting the energy consultant involved early on can also help with compliance issues, especially if there is an effort to hit certain performance metrics or obtain Passive House certification. Similarly, having a structural engineer as part of the team from the beginning can help with site planning (especially with topographically difficult properties), which can affect building massing, orientation, and even glazing.

“Gone are the days of everybody working in silos,” Keeling says. “What you need is collaboration early on.”

All photography by KRJ Photos.