Windows gain more heat in summer and lose more heat in winter than any other surface in the home so you'll want to consider how the sun moves over your home through the year so you can optimise the position of your windows and doors. In the winter you'll likely want to capture the sun and in the summer you'll likely want to reduce the solar gain to keep the house cooler.

Positioning windows and doors in such a way to encourage air movement means that a breeze will pass through the whole of the room to move unwanted warm and damp air. Ideally, windows would be at different heights and not directly in line with each other across a room to achieve cross-ventilation. Good ventilation removes the airborne moisture that is harder to heat and contributes to condensation.

Window systems are responsible for 35-50% of heat lost from your home so any improvement you make will have a big impact on the overall thermal performance. Double glazing with an inert gas fill such as argon or krypton between the glass sheets helps to slow the flow of heat in and out of the house as the gas is a poor thermal conductor. This can be further improved by choosing a thermally efficient frame.

A thermally efficient frame,  such as ThermalHEART^® or uPVC Klima Series helps to reduce the transfer of hot and cold temperatures through the frame. In May 2023, the minimum R-Value requirement for four zones increased meaning buildings in these regions will need Low-E glass in a thermally improved frame. This expands to all zones from November 2023.

The way the windows and doors are installed into the building can also make a difference to their performance. Centrafix™ installation is a BRANZ appraised alternative solution to NZBC E2/ES1 and aligns all insulation elements – wall, window frame, glazing – to prevent cold air from circulating around the window and door frames, improving the whole window system’s thermal performance by over 20%[2].

Glass plays an important role in the thermal performance of the whole window system. Low-emissivity (Low-E) glass has a transparent coating that reduces the amount of heat that passes through the glass while still letting light through. Low-E coatings can be tailored to maximise or minimise the sun's energy coming in making them a popular choice for improving the thermal performance of your home - no matter your home's climate or orientation. Look for products that are designed for New Zealand's conditions such as Solux-E by AGP which also provides excellent light transfer and clarity for light, bright rooms.

To further improve the thermal performance of your glazing use an inert gas fill such as argon or krypton and a warm edge spacer to add insulation between the panes of glass. 

You will come across R-values and U-values as you research thermally efficient products. Architects and engineers use these values to calculate the thermal efficiency of the whole building envelope. R-values refer to a material's resistance to conductive heat flow. A U-value is the measure of how much heat is transferred through the material. A lower U-value indicates better insulation properties so for better thermal efficiency you'll want to choose products that have a low U-value to bring down the overall U-value of your home. Consult your architect or manufacturer to learn more about these values in relation to specific products or your building. You can also use this zone map to understand the Regional R-Value requirements.

The Window Energy Efficiency Rating System (WEERS) is a 6-star system assessing the thermal performance of the whole constructed unit. WEERS combines the thermal performance of the frame and glazing, together with the size of the window to calculate a rating between one and six stars, six being the system that offers the highest efficiency. Currently, the highest performing system is our Klima Series uPVC system when used with low-E double glazing. Our manufacturers can assist with these calculations.