Passivhaus glazing selection guide

Window performance is specified by U-value, which measures heat loss per square metre per degree of temperature difference. Lower is better.

Two U-values are commonly quoted: glass-only U-value (Ug) and total window U-value (Uw). The total Uw includes the frame and the edge-of-glass spacer, both of which typically perform worse than the glass itself.

For certified Passive House, the target is Uw below 1.0 W/m²K, and preferably below 0.85 W/m²K. This is significantly better than standard double-glazed units in Australia, which typically achieve Uw 2.0 to 2.5 W/m²K.

When comparing window quotes, insist on Uw, not Ug. A supplier who only quotes glass U-value is either uninformed or hiding poor frame performance.

Solar Heat Gain Coefficient (SHGC) measures the proportion of solar radiation transmitted through the window. Higher SHGC lets more solar heat in; lower SHGC lets less through.

For the Adelaide climate, the optimal SHGC depends on orientation. North-facing windows benefit from high SHGC (0.5 to 0.7) so that winter sun warms the interior. East and west-facing windows benefit from low SHGC (0.2 to 0.35) so that summer sun does not overheat the interior. South-facing windows can use moderate SHGC (0.3 to 0.5).

The complication is that SHGC often trades against U-value. Very low U-value glass tends to have lower SHGC. A skilled Passivhaus designer will select different glass specifications for different orientations, balancing insulation against solar gain.

For homes that cannot be perfectly oriented, external shading (eaves, awnings, external blinds) is a critical supplement. External shading on east and west windows is often more effective than choosing a low-SHGC glass alone.

Three frame materials dominate the Passivhaus market in Australia.

uPVC (unplasticised polyvinyl chloride) offers the best thermal performance and the lowest cost. Total window U-values around 0.8 W/m²K are common with uPVC. The trade-off is limited colour range (mostly white, black, or dark grey) and size limits on larger windows.

Thermally broken aluminium is the mainstream premium Passivhaus choice in Australia. The frame is aluminium (for structural strength and design flexibility) with a plastic thermal break dividing the interior and exterior parts of the frame. Total U-values around 1.0 to 1.4 W/m²K are typical. Colour options are wide.

Timber frames are the third option, offering excellent thermal performance and a premium aesthetic. Common in European Passivhaus, less common in Australia. Suppliers include imported German brands. Longer lead times and higher cost apply.

For a typical Adelaide Passivhaus, thermally broken aluminium is the mainstream choice. uPVC works well for owners prioritising cost and performance over aesthetic flexibility.

The Australian window market for Passivhaus-grade product has grown significantly in the last five years. Suppliers in the Adelaide market include Ecowindows, PAARHAMMER, MayerLenz, Rylock, Vulcan, and imported German brands via Australian distributors.

Lead times are typically 12 to 20 weeks from order to delivery. This is significantly longer than standard commercial windows. Place the order early in the build program, ideally shortly after building consent is granted.

Get quotes from at least three suppliers. Prices for equivalent specification can vary significantly, and the mid-range often offers the best value.

Confirm the supplier holds an Australian Window Association certification and provides a written performance certificate for each window, showing the tested Uw, SHGC and air infiltration rate. Do not accept marketing claims without written certification.

Check the warranty terms carefully. Passivhaus-grade windows are a significant investment; a 10-year comprehensive warranty is a reasonable expectation from a premium supplier.

A high-performance window installed poorly delivers modest performance. The installation detail is as important as the product specification.

The window frame must be sealed to the airtight layer using a high-performance airtight tape. The gap between frame and structure must be filled with insulation (typically expanding foam or a compressible insulating tape) to eliminate thermal bridging.

The window position within the wall depth matters. Positioning the window in the middle of the insulation layer (rather than flush with the internal or external face of the wall) minimises thermal bridging around the frame. This is called a "warm frame" installation.

The sill and head details must be shown on drawings and reviewed by the Passivhaus certifier. Poor sill detailing is a common cause of condensation and thermal bridge at window perimeters.

Coordinate installation timing carefully. Windows should arrive on site after airtight layer detailing is complete, so the installers can seal the frames to the finished airtight surface. This sequence prevents rework at the airtight interface.