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Insulation trumps building structure

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Dear Sir,

Last week I could design a new office or a sports club or a church extension in Wellington using walls built of 90 x 45 framing and insulated with R2.4 Batts.

This week for the same building I have to use 140 x 45 framing with R 3.6 Batts.

Similar for a skillion roof. Last week this would have been 140 x 45 rafters and R3.2 Batts, this week it is 290 x 45 rafters and R7.0 Batts. Now we have the introduction of new energy efficiency standards for the commercial building industry. From May next year, similar standards will apply to the residential construction industry. For the commercial buildings described above, the new standards represent a 34% increase in material costs for walls and a 150% increase for roof construction.

The new H1 insulation standard in the Building Code, introduced with the intention of reducing the energy use of buildings, is having an unintended consequence of increasing the building structure not for strength but to hold the insulation.

At a time when building materials and labour costs are continuously rising alongside the general costs of living, these changes will just add to that. The goal of producing affordable housing for first home buyers keeps moving further and further away.

It has been estimated that the payback period for this increase in insulation is between 20 and 100 years depending upon where in the country you are situated.

The focus on energy efficiency over structure or buildability means that we are now required to use materials less efficiently. That means more and more timber, more and more insulation, both materials currently in limited supply. Can our manufacturers keep up with the demand or will more delays be experienced again?

We need to move away from the narrow ‘carbon driven’ focus on energy efficiency to an overall efficiency in use of all materials.

Bruce Welsh
Registered Architect

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  1. Nice to see you support the fibreglass industry but the options might be; not to design skillion roofs, or use a phenolic foam board which will achieve the new R ratings within the same timber cavity. Going to phenolic foam won’t increase costs by 150% and it sure won’t slump in walls. .I’ve got 400mm of glass wool in my roof space and my home is toasty warm…


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