HOW MUCH WILL IT COST?
A STUDY IN THERMAL ENVELOPE PERFORMANCE
When you’re building your dream home, wouldn’t it be super to know that the wall and roof options you chose were the most energy efficient and cost effective for your home?
We’re working on a project where the client asked us to model different wall and window combinations to see which was the most thermally efficient and price competitive for their particular situation. They are based in the lower North Island, in what is Climate Zone 3, under the 2021 H1 amendments.
Four different thermal envelope combinations were modelled against three different window systems and while that was happening, a local builder & quantity surveyor priced ballpark square metre construction rates for each thermal envelope option.
The options chosen were:
Light timber framing – The Superhome Movement’s Superwall (or what MBIE calls a warm wall), consisting of 140mm framing and a 45mm service cavity.
Outsilation – Rigid insulation on the outside like they do in Europe and a warm roof.
SIP Panels – A New Zealand manufactured panel with an expanded polystyrene (EPS) core.
Hybrid – SIP Panels walls combined with a warm roof. (Full construction breakdowns are provided below)
Each thermal envelope was paired with three different New Zealand made window systems.
• A New Zealand wide supplier of aluminium joinery using a “code minimum” thermally broken system.
• A North Island supplier of aluminium joinery that has slightly better performance characteristics.
• A South Island supplier of aluminium joinery, that is being used in passive house construction.
The results were benchmarked against the 2007 H1 Requirements, the 2021 H1 Requirements and the Superhome Movement’s BASE, BETTER, BEST voluntary guidance from their Healthy Home Design Guide.
www.healthyhomedesignguide.co.nz
The outcome is shown in the table below for the heating demand of this particular property.
We found the results very interesting, as on a kWh/(m2a) basis, the thermal envelope systems all look very similar. But remember this needs to be multiplied out for the size of the home. The other factor is that some systems are easier to make airtight than others and go up quicker.
As can be seen from the table above and was noted by the person who provided the prices, it’s the windows specification that provides the biggest bang for buck. Something some of us have been banging on about for quite a while https://www.abodemagazine.co.nz/home/2021/9/3/windows-for-warmth?rq=window, you can now look through for yourselves!
By using the best performing window system your budget can afford, you can clearly see that it is possible to drop your heating demand to nearly a half of that when sitting inside a standard shiny silver shocker!
Further, look at how much better financially you fare, when your power bill comes in, compared with the worst house than can legally be built. (Code Minimum 2021)
So there you have it, facts and figures, not sugar coated, but perhaps wrapped up in some fluffy, or not so fluffy stuff, as the (ply rigid air barrier /bracing layer) case may be.
I have my clear favourite peering through the pinus radiata monoculture, do you?
What is the carbon footprint of each option? That might be the subject of a future article.
In cooperation with
The Webster family
Plan B Architecture
Alan Craig Design
HEALTHY HOME COOPERATION
Healthy Homes for all Kiwis. Housing is about people. People working together in cooperation to provide Healthy Homes for people to live in.
Damien McGill: Engineering Happy Healthy Homes for People & Planet
