Lightbox 23 is a 2-unit net zero infill project in inner NE Portland. The project features super insulated wall, roof and sub-slab assemblies plus high performance mechanical and ventilation systems. Topping it off (literally) is a 10kW solar array on each unit. The project has been certified net zero by Earth Advantage.
The design is a split level floor plan with the floating stairs acting as the central spine. Each floor opens to the half level above and below through the open slot the stairs create. The exterior tube forms step up the facade to the corner view deck where Mt. St. Helens and Mt. Adams are visible to the north. Being a corner lot each unit faces a different street and the plans / facades are mirror images of each other.
Lightbox 23 is a speculative project by Lightbox Portland, who is dedicated to high performance, high density modern development. 3 more Lightbox Portland / Steelhead Architecture projects are currently in process.
How is the project unique?
Lightbox 23 is unique as a speculative development net zero project. Many custom home projects have achieved the net zero status but very few developers have committed to this level of high performance construction.
What are the sustainability features?
Net zero construction simply means generating as much, or more, energy as is used by the building. On the supply side this means a 10kW solar array for each unit. That's the easy part. Reducing the energy load is the more interesting part of the equation. Super insulation is a huge part, and relatively inexpensive. We used 2x8 walls filled with blown in cellulose then added 2" of EPS (rigid insulation) to the outside of the plywood / WRB for a thermal break. There are 3" of EPS below the concrete slabs (no crawl spaces ever used). The roof assembly is similar to the walls with the combination of blown in and rigid insulation for a ventless assembly.
Our air barrier is another huge piece. We used Henry Blueskin as the WRB and air barrier over plywood (no OSB). With repetitive joint sealing and searching out leaks we achieved a blower door test of 2.36 ACH50 (air changes per hour at 50 pascals of pressure) which is 4-5 times better than an average house. All of these tight and super insulated envelope measures equals very little heat / cooling loss and therefore much less energy use.
For the mechanical system we used ducted heat pumps - all electric which have far greater efficiency the gas systems. There is in fact no gas used on site at all, again to increase efficiency and reduce penetrations. The system also includes an independently ducted HRV (heat recovery ventilator) to provide controlled air exchanges without loosing energy.
