​Design guidelines for improved thermal performance

There are many approaches you can take to improve the thermal design of a house.

Increasing insulation almost always reduces the heating energy required. Commonly-available bulk insulation products up to around R2.8 can be specified for 90 mm framing, while with 140 mm framing, insulation up to R4.0 can be used.

In a modern home, windows can be a significant area of heat loss. Double-glazing in simple aluminium frames with 4 mm glass and an 8 mm space between panes has an R-value of just R0.25. These units are commonly specified but give relatively low performance. By contrast, a thermally-broken aluminium frame with a 12 mm space and low-e coating on one interior glass surface has an R-value of R0.39 – significantly better. Window R-values up to R0.53 are possible with timber, uPVC or fibreglass frames, a low-e coating and argon gas in the space between the glass panes.

Increasing the size of north-facing windows may lead to net benefits (while large south-facing window size often leads to increased net heat losses). The net result depends on window type, shading, and other design factors.

Ideally, the living areas in a home should face true north or within ±20 degrees of north for maximum solar gain.

Increased thermal mass leads to larger warm-up loads but also increases the usefulness of gains. The net result depends on other design factors such as amount of solar gains, insulation levels, climate, heating schedule and others.

Heating energy consumption is very sensitive to the selected heating schedule and heating level. A good approach is to calculate the heating energy for different heating patterns to get a sense of how realistic any calculated savings are, considering the uncertainties in how the occupants will heat the building.