Blenheim Low Energy Home Blenheim

Photo credit to: Matthew Croad

“A poster child for no drama,” is how building scientist Sara Wareing describes this appealing Blenheim home. It could have all gone very differently. The architect had not designed a PHI-certified project before and the plans were already well developed by the time the client decided to seek certification. The home’s form factor was quite high and eaves or overhangs didn’t feature, despite a great deal of glazing on the north side.

But the client made early decisions that made their life easier and the project run smoothly. Firstly, they had hired a committed builder with experience in building to PHI standards, who convincingly outlined the benefits of certification. The project was modelled early and well. At the builder’s suggestion, Sustainable Engineering Ltd was engaged to deliver an initial performance model and then undertake the Passive House design. SIP construction made it easier to achieve an excellent airtightness result.

Lastly, and perhaps most importantly, the client was happy to aim for the PHI Low Energy Building certification. It was a target that gave the team breathing room and was readily achievable without having to substantially revise the design. It was a smart choice according to Sara, who carried out the initial performance model. That process assured the design and build team that they were on track.

The early analysis identified overheating as the biggest risk and Sustainable Engineering provided various options for how to moderate this. Substantial change to the architectural design was not required. Instead, different glass options were evaluated, along with various shading options. Reliable building performance predictions gave the homeowner a sound basis on which to make their decision. A seasonal canvas shade sail was chosen to shield the north face from summer sun.

The Passive House design was also undertaken by Sustainable Engineering and went smoothly. The builder described the designer as practical and easy to deal with, and someone who focused on solutions. One of those solutions was casting ventilation ducts for the MVHR into the foundation slab, as there was no space in the ceiling. 

Because certifiers must be totally independent, Sustainable Engineering engages PHI to certify projects its team has designed.  “Because we are also certifiers, we know very well how to prepare submissions for certification,” observes Sara. “The process of certification at PHI goes very smoothly and that benefits the client in several ways. It’s efficient, there isn’t drama and PHI rewards the efficient way we submit documentation with a better price, which is passed onto the homeowner.”

Sara describes Low Energy Building certification as a fantastic achievement. “There’s an unhelpful characterisation of LEB by some as being a consolation prize. That’s inaccurate and diminishes what a worthwhile achievement LEB certification is.” (The same point was argued at length in this blog post that called Low Energy Buildings “a crucial stepping stone that indicates how we get from … the historically tragically low Building Code minimum to zero carbon building”.)

The clients are very happy in their new home, particularly enjoying the consistent temperature right throughout the house. Asked by friends whether they would build again, their answer is ‘No, we don’t want to leave this house!’.

Project Team

Architecture Altar Projects - altarprojects.co.nz
Passive House Design Sustainable Engineering Ltdsustainableengineering.co.nz
Builder Fairfield Construction - fairfieldconstruction.co.nz
Structural Engineer The Healthy Home Cooperation Ltd - healthyhome.kiwi
Certifier PHI

Passive House Metrics

  • Heating Demand21.0 kWh/m2/year
  • Heating Load13.4 W/m
  • TFA169.5m2
  • Form Factor4.5
  • Air leakage @ 50Pa0.4 ACH/hour
  • PER demand39.5kWh/m2/year

Passive House Database - TBA

Construction Details Average Values

  • U-value External Walls 0.20 W/(m2K)(R4.99)
  • 165mm Formance Neopor SIPS with 45mm service cavity insulated with Knauf batts.
  • U-value Floor0.22W/(m2K)(R4.5)
  • Max Raft S-grade EPS solid pod slab.
  • U-value Roof 0.18W/(m2K)(R5.52)
  • 215mm Formance Neopor SIPS
  • U-value Glass1.16 W/(m2K)(R0.87)
  • Lightbridge double glazing
  • U-Windows1.5 W/(m2K)(R0.7)
  • Optimal Windows
  • Ventilation Efficiency 82%
  • Stiebel Eltron 280

 

 

Photo: Matthew Croad

Photo: Matthew Croad

Photo: Matthew Croad