Over the past year or so, the majority of the insulation queries I have received concern the changes to NZBC H1 and how to use the Calculation Method.
So I thought my first Detailed post should be a worked example of the Calculation Method in action. When should you use the Calculation Method?
The Calculation Method is particularly useful if:
- Glazing is above 30% of the total wall area — but less than 40%
- You have mixed wall claddings
- Design requires reduction of construction R-values in one area, and to meet compliance you need to increase the R-value in another area.
The example is of a house in Climate zone 1, with a large north facing window. The designer in this example has been asked to reduce the cost of this window and one of the options is for the window to be single glazed and the level of insulation increased.
In the example I have used the BRANZ Calculation Spreadsheet and the BRANZ House Insulation Guide to work out the construction R-value of the various building elements.
February 12, 2012 at 8:40 pm
Hi David. NZS 4218:2009 is not a referenced document in H1 and therefor it’s use is an alternative solution to the building code. (The DBH missed this when they amended the compliance document in 2011.)
Your methodology is correct for the calculation method,(NZBC H1/VM1 1.1.3.) And as single glazing at 0.13 is half the double glazed score of 0.26 ait is acceptable.(NZS 4218:2009. 4.2.8)
Point this out to the Inspector and he should reverse his decision. Be nice and respectful as everyone makes errors.
Hope this helps.
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