Passive House Windows

This particular window is an aluminium-clad timber frame. The timber in our sample from Logikhaus is FSC (Forest Stewardship Council) spruce. Their most common (& economical) option FSC Pine. The timber part of the frame is what you see on the inside of your building, and the aluminium is what you see outside. This means there’s no re-painting externally or maintenance required due the durability of the aluminium-clad exterior.

Not inside! Condensation can occur on the OUTSIDE which is where you want it to occur! Unfortunately, standard double-glazing in Australia is normally made with aluminium-frames which are not thermally-broken (beware of those that say they are “thermally-improved” which is essentially greenwash!). Aluminium is a metal which is an excellent thermal conductor (which is why we use metal pots and pans to cook with). However when it comes to your building-envelope, we don’t want the outside temperature conducted (transferred) inside – this is what’s known as a thermal-bridge. In winter if you touch the inside-face of an aluminium window frame you’ll feel that’s almost as cold as the outside temperature…and this is why condensation regularly occurs inside.

This sample is a timber frame that aluminium-cladding externally for durability & low-maintenance. We have a number of clients who opt for uPVC for same high thermal performance, but are lower cost. Some of our clients prefer natural materials wherever possible so aren’t so keen on ‘plastic’ from an ecological perspective even though they’re excellent in reducing operational-energy (& therefore lowering life-cycle carbon emissions substantially).  A #fabricfirst approach is if we get the thermal envelope right it greatly reduces heating/cooling & lifetime operational energy (which is a larger % than the embodied energy). So we prioritise Operational-Carbon first, then Embodied-Carbon second. In an ideal world (& if no budget constraints), we do both and aim for Living Building Challenge too! Another point worth noting is that usually you are inside looking out through the glass to the view beyond, and NOT looking at the window frame – this is worth considering in terms of aesthetics.

Even with locally-made windows, many of the parts that make them up are also coming from elsewhere in the world. Studies have been done looking at life-cycle analysis of the transport by ship, and it’s very minimal. If they were air-freighted it would have a much larger carbon-footprint.

Ask your Architect/Building-Designer or Certified Passivhaus Designer/Consultant first as they’ll have experience in this area.

There are many suppliers of windows all over the world, and more being added to the Certified Passivhaus Component database all the time. More are coming to the Australian market all the time, as demand is increasing. China has had a huge uptake of Passivhaus projects, and has dozens of new high-quality Certified window manufacturers so there could be more cost-effective options available soon.

It’s worth noting that you don’t need “certified” Passivhaus windows for a Passivhaus project, but their specifications and data must be available to input for the thermal modelling.

Between each pane of glass in an IGU, is a “spacer” that seals the gap (which is often filled with Argon gas). Some window manufacturers have these spacers are made of metal, which is a thermal-conductor as noted above – so avoid these!

This the measure of thermal-conductivity (the inverse of the R-value which is a measure of thermal-resistance). We know that higher R-values are better – adding more insulation with more R-value in our roofs in our climate is a good thing). However, with U-values the lower the number is better. In building-science and Passivhaus modelling, we also measure roof/walls/floor of the ‘construction assembly’ in U-values also.

Some companies provide these, but they’re very expensive so you’d be better to go with a triple-glazed door instead! Do be aware that most timber/aluminium front doors sold in Australia have very little thermal-insulation properties at all!