If you haven’t already, please read Part One of this blog series first, as it provides some background information on the R-value and thermal efficiency, which we build on below.
Understanding R-value and thermal efficiency
The thermal efficiency of the whole building is the result of the thermal performance of the individual elements eg walls, roof, windows and siting. Just looking at the R-value of the insulation in a wall and ceiling is not going to give you the true thermal performance of the home.
Calculating thermal performance
When our designers calculate the thermal performance of a home they use a formula to determine the overall efficiency and this is affected by a number of factors, including the materials used and the location of each element.
To calculate thermal efficiency, each window and its orientation and size is entered into a calculation tool and the same process is repeated for each wall and the roof. The materials used in the wall also have an effect on the total R-value of the wall. BRANZ has a great tool called ALF which you can use to calculate the thermal efficiency of a home, and to give you the R-value of different wall construction methods. For example, a masonry veneer wall has less R-value than a wall with insulated plaster cladding like the STO product we use, both with R2.6 wall batts.
The importance of insulation
When it comes to insulation, we use R2.6 wall batts and R3.6 ceiling batts as standard in our homes. However, you also have the opportunity to upgrade the insulation by increasing the thickness of the batts in the walls and ceiling. Or you can choose to go one step further and apply passive design building principles to your home by using thicker wall framing to enable you to install thicker wall batts.
Ventilation and orientation of windows
The ventilation in the home also affects the thermal efficiency which is why we use good quality extractor fans above the showers and rangehoods as standard.
Window orientation is another important factor. For this reason, our homes have large north-facing windows for solar gain and we try to keep the south-facing windows smaller to reduce heat loss.