Norris strawbale Passive House is one of a kind. It is located on the Port hills of Christchurch with a Northwest outlook across Bowenvale valley. It was designed by Elizabeth Guthrey and Delia Bellaby from Design & Make Architects and built by Everett Norris from Everhomes. The design team took a more natural approach to achieving an airtight building, with the use of natural plasters on the walls as part of the airtight envelope. Terra Lana wool insulation, strawbales and triple glazed timber windows keep the house warm. It has a compact two-story form to make the most of the small section and to allow for an orchard and garden. Furthermore, it enjoys spectacular views from the first-floor rooms and ground floor dining room, and has a dual entry from the road below and the lane above. It has a flexible floor plan to accommodate people as their lives change and a home business. There is a separate garage workshop with feature traditional timber frame trusses.

The walls are 430mm thick due to the size of the strawbales and plaster either side, they are a major aesthetic feature of the house with smooth curves rolling into the window reveals. This achieved a wall U value of 0.148  (R value 6.75). It has a skillion roof with 290mm of Terra Lana wool insulation and further insulation in the ceiling services cavity. By building on a hill with poor soils, the house was to be founded on deep piles; this became a benefit for the thermal envelope as the floor was super insulated between 290mm floor joists.

Passive House homes generally achieve a low frequency of overheating if there is carefully placement of eaves for shading or movable shading. This house needed 800mm eaves in many locations for a second reason; since there were a number of exterior walls with direct plaster over the strawbales, eaves were required for extra protection. Where a midfloor eave wasn’t desired, a further cavity and proprietary plaster or other cladding was required, such as on the West and South face of the house. While it isn’t common for a Passive House to be made with straw and natural plasters, the building system works surprisingly well. Proclima have a series of tapes, such as Contega tape that allows an effective junction between the internal plaster and Intello airtight membrane on the ceiling or from the timber windows into the plaster at the reveals. Finish plaster hides the airtight tapes and so the house looks like other strawbale plastered houses.

The house achieved 0.6 air changes per hour, 14.26 kWh/m2/a heating demand, and only 1% frequency of overheating. It also achieved a Homestar 10 rating due to other sustainability features, and Lifemark certification. Listen to the episode on the Passive House podcast to hear more and watch it on Grand Designs NZ (Season 10, episode 3).