A building envelope for Zero Energy and comfort

Camp Glenorchy Eco Retreat

Achieving Zero Energy and providing a comfortable and healthy environment for visitors year-round were the drivers behind the design of the building envelope for Camp Glenorchy Eco Retreat’s cabins and communal buildings. The envelope plays a key role in the performance of any building. The roof, walls and ground slab, as well as the windows and doors, work together to keep the people inside comfortable and healthy. In addition to providing shelter, this physical barrier helps regulate indoor temperature and controls both moisture and airflow.

The solution chosen for Camp Glenorchy, which strikes a balance between comfort and energy efficiency, resulted from a collaborative design process guided by an evolving thermal model. Effort during this process focused on two key areas: regulating indoor temperature and controlling unwanted airflow. In practical terms this meant identifying the right level of insulation for the different elements of the envelope – a process aided by the thermal model’s results – and including details that would reduce unwanted air flow. As a result of this exercise, the envelope of Camp Glenorchy’s buildings uses up to 60% more insulation than that required by the New Zealand Building Code.

How was it done?

Walls and roofs

Cabins and bunk huts at Camp Glenorchy combine two different wall-construction systems. While these are typically used separately, at Camp Glenorchy they work together to create super-insulated external walls and skillion roofs. The two systems are:

  • Structural insulated panels (SIPs): these 142mm-thick self-supporting panels, made of polyurethane foam sandwiched between two layers of strandboard, form the first layer of insulation below the exterior cladding. Even when used as a standalone system, the thermal performance of these panels exceeds Building Code standards. SIPs are prefabricated, cut and pre-joined off-site and arrived at Camp Glenorchy ready to be assembled.
  • Timber frame: a traditional 90mm timber frame fitted with blanket insulation sits underneath the SIPs. Electrical wiring and pipes run inside this layer, reducing the amount of perforations in the more rigid SIPs and therefore the possibility of creating cold spots in the buildings.
Installation process of blanket insulation in one of the cabins' internal timber frame. The SIP panels can be seen behind the rafters and purlins.

Cabins and bunk huts also incorporate elements aimed at reducing unwanted airflow and moisture. INTELLO® PLUS, a smart membrane that acts as an air-tightness barrier and vapour control layer is installed in the interior of buildings. This continuous film sits between the timber frame and the lining of walls and roofs, protecting the buildings from condensation and draughts. In addition to the INTELLO® PLUS membrane, cabins at Camp Glenorchy have a weathertightness underlay (or building wrap) adhered to the exterior of the SIPs and use weathertightness tape in the joints between panels and around windows. This is done to prevent air or water from leaking into the envelope.

Section of a typical hut at Camp Glenorchy showing the two two different wall-construction systems.

Windows

Windows are typically one of the weak spots of a building envelope, allowing the highest transfer of heat between the inside and the outside. To reduce the speed at which heat is lost in the winter, Camp Glenorchy’s windows are triple-glazed and use timber frames, which offer better thermal performance than aluminium frames. Between glass panes, the presence of argon gas acts as an additional barrier to heat loss and increases the performance of the windows by up to 15%. Also, a ‘Low Emissivity’ (Low-E) coating maximises solar heat gain in winter by reflecting heat back into the rooms.

Concrete for Camp Glenorchy's slabs being poured
Concrete ground slabs use polystyrene pods and edge insulation.

Ground slabs

Insulated concrete floors not only provide a platform for Camp Glenorchy’s buildings to rest on, but are the medium used to deliver warmth to rooms in the winter through a water-based underfloor heating system. To improve their performance, these concrete floors use polystyrene in a grid of pods laid underneath the slab, as well as around the slab’s edges. Having better insulated slabs keeps the temperature of the slab stable and prevents the heat loss that typically occurs around the edges. It also maximises the benefits of the heating system by preventing the hot water that flows through its pipes from cooling down too quickly, thus saving precious energy.

Lessons learned during construction

While the design phase of any project offers the best opportunities for improving the performance of buildings, the quality of workmanship during construction will also have a major impact. Unwanted air flowing through the building envelope can create condensation and lower the wall’s construction R-value (thermal insulation rating), affecting both indoor air quality and energy efficiency. The draftier the building, the harder the heating system will need to work to keep indoor temperatures stable. At Camp Glenorchy, an increase of 5% in the energy used for heating caused by unwanted drafts could make all the difference in achieving the Zero Energy goal.

To prevent this from happening, airtightness was checked at multiple stages during construction. In the Homestead building, for example, testing for airtightness was done in three stages:

  1. Visual checks, both outside and inside the building were the first step in ensuring there were no gaps in the framing or between the frame and windows or doors.
  2. Further into the process, the construction team looked for air leaks using a simple test. Turning on the exhaust fans with doors and windows closed to create negative pressure, a lit incense stick was held close to joints in the frame and around the edges of windows and doors. A change in the smoke rising from the incense stick signalled a leaky spot, which was later fixed by verifying the weatherstripping, applying extra sealant or using building tape.
  3. The blower door test was the last step in the process. Usually a blower door test is done by an external technician. With windows and doors locked, and ventilation ducts sealed, negative pressure is applied to the building using a door-mounted fan. As the fan pulls air out of the building, the air pressure inside lowers, allowing outside air with higher pressure to flow in through gaps in the building envelope. Gauges connected to the fan measure the infiltration rate of the building expressed in air changes per hour (ACH). The lower the infiltration rate, the more airtight the building is.

Performance during operation

Now that Camp Glenorchy is open to the public, efforts made around the quality of the building envelope during design and construction are being put to the test by guests and staff. So far, Camp Glenorchy’s buildings are performing as expected. High levels of insulation, good airtightness and good ventilation are working together to create buildings that are healthy and comfortable year round.

It’s warm even when it’s frosty outside. And it is an all-round heat – there aren’t any cold spots.

“Guests often comment on how cosy and warm it feels in the Homestead building,” says Ann Margaret from Camp Glenorchy’s host services. “It’s warm even when it’s frosty outside. And it is an all-round heat – there aren’t any cold spots.”

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