I want this post to 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.