SIP build a good PH option But be fair when comparing cost to build

16 November 2021 by Jason Quinn

“How much space do you need? Do you need a TV room, a rumpus room, a dining room, and a living room? New Zealand is an amazing country: get out of your house, get in amongst it.”

That’s James Clarke talking (English builder and owner of NZSIP), and as a fellow immigrant, I have to agree. First rule of “eco-homes”: make them small. James has just completed a three-bedroom home for his family that is just 70m2; naturally it is built from structural insulated panels (SIP).

The Homed story on the Stuff network is keen to talk about cost for a low-energy build, comparing  Clarke’s cost of $4285/m2 to the national average home cost of $2325/m2. But this is unfair, for several reasons. It’s not reasonable to compare a custom home like Clarke’s to one produced by a group home developer, whose mantra is almost always, “build ‘em big and build ‘em cheap”. You have to compare apples to apples. Based on what we see, anything custom starts at $3500/m2, often closer to $4000.

Big and cheap works for group home builders because they can bloat the house with dumb space that is cheap to build (think oversized bedrooms, lounges, hallways). Kitchens and bathrooms are where the money is and a small, well-designed house still needs those rooms but can’t spread the cost over a lot of cheap floor area.

James has also clarified in a Facebook post that the 70m2 kitset NZSIP has developed (of which his family home is an example) costs $300K completed to turn-key: everything’s included except the land. The article is confusing on this point so the clarification is helpful.

We consider SIP to be a great option for a Passive House build. SIP can be used for roofs and floors as well as walls. They keep out drafts and you get the performance you pay for as the insulation is continuous and factory-installed.

One point missing from Homed’s article is that SIP builds, like all new homes and not just those built to the Passive House standard, need continuous ventilation. You can make a case for using MVHR in the South Island and continuous extract ventilation up north, although MVHR does deliver better air quality.

We’ve carried out the Passive House design on several projects that have used NZSIP panels. SIP are very suitable for high-performance construction and make achieving the very high-quality envelope easier for builders who are working on their first Passive House project.

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