The 'IDEAL House' in Beachlands is proven positive energy, Passive House Certified, and built with a 'mainstream' budget. Designed for a family of five, the aim was for it to be comfortable and healthy, as well as being able to produce a surplus of energy which is fed back onto the grid. Key features of the home include a high level of insulation, airtightness, triple glazed windows, heat exchanged ventilation, water harvesting and conservation, as well as specific energy-efficient design. The house has achieved an 8 Homestar Design rating and is in the final stages of Passive House certification.
The concrete slab was designed using a polystyrene pod system based on the original Rib Raft which was designed by Firth. The insulation was placed above the slab using a system called Batten and Cradle, offering noise absorption qualities and a service cavity used for the central vacuum system and some cabling.
Earthwool glasswool insulation was used to provide R5.2 in the ceiling between 900mm spaced I-beams. Pro clima's roofing underlay, SOLITEX MENTO, was used directly over the insulation in the skillion roof. The common 25mm air gap is not required as a non-porous membrane does not allow wicking of moisture through into the insulation. This means that designers can maximise the R-value within a given skillion roof cavity space.
Passive House requires a measured level of airtightness, which was achieved through the use of pro clima's INTELLO membrane. R2.8 batts were installed in the 90mm wall frame (R3.2 in a 140mm wall on the south side) after which the INTELLO was used to line the walls and ceiling. A 50mm service cavity was created with horizontal battens which was then filled with R1.4 Earthwool. This service cavity allows for improved thermal efficiency and ease of installing services. A blower door test was performed and the home achieved 0.45 air changes per hour (ACH) at 50 pascals which is well within the Passive House requirement of 0.6 ACH. The INTELLO offers the additional benefit of avoiding any chance of moisture loading into the insulation layer from internal sources, thereby avoiding interstitial condensation.
Ventilation is a key factor to maintaining a healthy environment in any home and is generally expected through the use of windows and doors. The IDEAL house included a Zhender balanced pressure ventilation system which brings in fresh air from the outside and passes it through a heat exchanger to recover the energy and heat the fresh incoming air. Of course, the use of this does not prevent doors and windows being opened.
A triple glazed airtight PVC window suite with low-e, argon filled glass was specified to achieve high levels of insulation as well as maintaining airtightness.
Sensors have been installed to monitor temperature, humidity and CO2 levels, and are managed by the University of Auckland.
The IDEAL house is regularly open to view. For further information, view the Ideal House website.