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Why have there been no increases in wall R-values?

We’re speculating that MBIE has chosen to leave residential wall R-values at R2.0 to avoid further issues with interstitial condensation. BRANZ Research has shown many common NZ walls are not robust with respect to managing moisture and increases in insulation compound this. Typical 90mm timber stud walls with batt insulation are already close to failure when it comes to preventing interstitial condensation.

This update has placed a greater emphasis on the framing ratios when calculating construction insulation values. When you consider that current average framing ratios have been found to be around 34% (BRANZ ER53) with some reaching as high as 55%, the current typical assumptions of 18% of construction R-value will likely need discussion with this latest update.

We expect changes to ventilation and heating to come with the next code update, at which point further wall R value increases would be expected.

It is worth noting the substantial increase to commercial buildings. Previously, this was R0.3 which could be accomplished by an uninsulated wall. Now, commercial buildings have a sliding scale that increases with colder climates and exceeds the residential requirements in every climate zone. As a reference, we suspect the residential code will follow the same model and targets in the next code cycle along with improvements to heating and ventilation (projected 3-5 years).

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