One quiet challenge in Australian energy assessment is that we don’t always have the right words for the job.
In the US, a “knee wall” clearly describes a wall that separates conditioned living space from an unconditioned attic. It’s a precise term, and that precision matters, because once you can name a part of the building envelope, you can design, assess, and insulate it properly.
In Australia, we tend to blur this distinction. We don’t really use the term attic; instead, we talk about roof space, and the walls that border it often fall into a grey area. They’re not external walls in the traditional sense, but they’re not internal either. As a result, they’re frequently overlooked in both design and modelling.
This is a problem, because uninsulated knee walls are performance killers.
In winter, they become a major heat loss pathway, allowing warm air to bleed into cold roof space. In summer, they act as a radiant heat source, dumping roof heat straight into living areas. The impact can be dramatic, especially in homes with sloping ceilings, dormers, or habitable rooms tucked under roofs.
This is why knee wall insulation is critical to building performance, and why I have updated my Gold Star heat load software to make knee wall insulation easier and clearer to input. The software now explicitly recognises these walls as part of the building envelope, rather than letting them disappear into undefined zones, (the capacity to model knee walls was always in the software but it was a bit of an annoying work-around).
Better terminology, such as “knee wall” and “attic” leads to better decisions. Better decisions lead to better buildings.
Sometimes, improving performance starts with simply calling things by their proper name.