The Kiln Apartments: New Extremes in Thermal Standards

The design of a small apartment project in Portland, Oregon, began with the concept that the building would wrap its clients in comfort and be the “kiln” that shapes the living environment. “The owner's goal was to build a small apartment project that pushed the limits on the building envelope's efficiency,” says David Posada, sustainability manager at GBD Architects. “So we enthusiastically accepted the challenge and started working right away.”

According to Posada, “Achieving the next incremental step of higher performance for buildings can be harder to do.” Their firm has begun to use the Passive House standard, one of the most stringent energy standards in the world, for their residential projects. “The Passive House standard requires a building to use very little energy as measured per square foot of floor area. The energy use intensity, or EUI, of a residential or commercial building that meets the Passive House standard is often 60-80% lower than a conventional building. The Passive House Planning Package (PHPP) is an energy model that uses an Excel spreadsheet to analyze heat gains and losses from the envelope, glazing, ventilation, infiltration, equipment, and occupants to calculate annual energy consumption,” he says. In the design of the Kiln Apartments, the design team consulted with manufacturers to solve some of the difficult problems when designing a tight envelope.

Photo courtesy of GBD Architects

Installing a building insulation blanket behind the sunshades at the Kiln Apartments helped the architects meet Oregon building codes and Passive House standards.

Their firm approached the challenge by starting with analyzing the loads and finding the most efficient systems. The architects designed custom window sunshade “eyebrows” to manage solar gain, but were stymied by the heat loss caused by these components through thermal bridging. Thermal bridging is caused when heat transfers through a conductive material from the outside to the inside of a building and vice versa and can affect both the heating and cooling systems. As Posada explains: “In the past, heat loss from thermal bridging might have only been a percent or two of the total heating load in winter, but after adding more insulation and upgrading the windows, thermal bridging from window frames or penetrations in the skin can make up a bigger fraction of your total heating load.”

Posada recounts the challenge for this project: “For the Kiln Apartments project, we needed sunshades to reduce heat gains from high-angle summer sun and allow the lower wintertime sun to penetrate and provide some of the heating load. Structurally, the simplest solution was to attach these metal sunshades directly to the exterior wall sheathing right at the head of the window. But this created a cold bridge or thermal break that bypassed the 4 inches of exterior rigid insulation right at the window rough opening, the weakest link in the envelope. Most Passive House projects have only managed to meet their energy targets by providing continuous exterior insulation that wraps into the rough opening and overlaps the window frame. To reduce the thermal bridging of these shades, we needed a thin 'gasket' to keep the metal from touching the wall sheathing and conducting heat directly from the framing.

“We can't just insulate our way to higher-performing buildings; we have to be more conscious of how moisture moves through the wall or heat energy finds the weakest link in the envelope. Metal framing can create thermal bridges right through thick layers of insulation, so energy codes have started requiring continuous insulation outboard of the framing. It is common to support cladding, awnings, or sunshades with shelf angles or metal connections that can short-circuit that continuous exterior insulation. There will always be tricky conditions at window openings, material transitions, or penetrations where you need support for heavy items attached to your structure. You can't always fit the insulation you really need.”

Working with the manufacturer, GBD Architects specified a thin-profile, flexible building insulation blanket with R-9.8 per inch insulation performance that could be cut to fit the sunshade attachment area. Using this material on the Kiln Apartments helped the architects not only meet Oregon building codes, which are more rigid than the national average, but also satisfy the even more stringent Passive House standards.

Photo courtesy of GBD Architects

Advanced building insulation blankets (hidden behind this narrow window sunshade eyebrow) are used to control thermal bridging at the Kiln Apartments in Portland, Oregon.