There has been much talk and reaction to the changes to H1 Energy Efficiency, and then there has been push back from Industry. Some say the industry isn’t ready for these changes and that there simply isn’t ways to comply that are common or easy.

So, I did a little design exercise. Armed with the proposed changes that may come into effect in November this year or perhaps 6 months later, how would our current architectural design and common construction practices need to change to meet the new minimum requirements? The results might surprise you.

I will start from the bottom.

There are two values for floors, one for slab on ground and the other for suspended timber floors in 5th edition of H1 Energy Efficiency.

For the slab on ground there has been an increase from a construction R value of R1.3 to R1.5, R1.6 and R1.7 depending on climate zones.  A Firth Rib Raft floor system can achieve this with the right floor area to perimeter ratio.  Not something that necessarily will require additional cost, but perhaps some more design consideration into the form of the building. This system has been in common use for years now and is one of the solutions for Architectural designers and Engineers on sites requiring Engineered floor slabs which is often the case. (Refer to extract from Firth) Depending on the zones and requirements simply adding additional under slab insulation and a thermal edge with care to the form of the slab can achieve compliance. 

For suspended timber floors a minimum Construction R value is up from R1.3 to R2.5, R2.8 and R3.0 respective of climate zone. The reason for the higher requirement for the suspended floors, is there is no insulating effect of the ground, as for slab on ground floors. Pink batts have a snug floor product with an R value of R2.6 and Mammoth have a product that has a rating of R2.8. I would recommend sealing off the insulation layer from the air to increase its effectiveness too. Yes a little more cost here and some may argue deeper floor joists and structure is required to accommodate the insulation. Conversly your pile centres can be changed and potentially the number of supports for the joists reduced. Again, not too hard to achieve with our current construction methodology and current product availability. It just requires some thinking at the Architectural concept design stage and can potentially be designed to be cost neutral should the structure be maximised. (Refer to Design navigator draft calculation below)

For Walls, this has increased from R1.9 in places to R2.0. Mammoth tested their product in various constructions and their friction fitting product which has been available for years easily achieved values over this for standard construction practise in 90mm timber framed walls with brick veneer and weatherboard claddings on a drained cavity. Pink batts has an R2.8 wall insulation product that is 90mm wide. This achieves a minimum construction value of R2.25 for horizontal weatherboards, standard Gib lining and a flexible building wrap. Again, very common practise so no major and costly implications in construction and products that are currently available.  (Refer to Extract from Mammoth Air lay Insulation Brochure below)

Then there are ceilings. Flat ceilings are easier than skillion ceilings, but the bulk of NZ homes have flat ceilings. Here doubling up the insulation layers whilst reducing it to a minimum of R3.3 within 500mm from the eaves (for clearances to roofing underlay) is feasible with any number of insulation products. ­­ (Refer to Design navigator draft calculation below)

So in summary. Many homes use Engineered floor slabs already and are probably achieving the proposed Construction values already or with some additional insulation and thermal breaks easily achieve the minimum. Timber suspended floors are more problematic, but they are also predominantly in our older housing stock, and we know those are poor performing. Walls, well this is easy, not rocket science. Ceilings, it’s as simple as another layer of insulation.

Will it cost more than a current minimum code house, yes if it’s not able to be designed out. But will it break the bank, I don’t believe so. These changes can be easily accommodated with some of the suggestions I have made above. It's possible, it’s feasible, and it's necessary if we are to start to change our current building industry to be a healthy home provider. It's time to consider the people who live in what we create.


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Offsite NZ Member    Licenced Building Practitioner    New Zealand Green Building Council
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