10 December 2020
Window thermal performance and the terminology that comes with it can be confusing. Manufacturers may quote u-values for certain elements of the window, but it’s the whole window u-value we’re interested in, and even better, the installed window u-value. Generally, the glazing has a higher performance than the frame, so the less frame the better. We therefore need to know the area and length of frame / glazed edge (psi values) to understand the whole window u-value.
The British and European standard for calculation is for the whole window u-value, so this is what we should expect from manufacturers. However, the Passivhaus methodology also takes into account how the window is installed into the wall. This gives a more complete picture of a building’s fabric performance, and highlights the importance of robust window installation detailing, i.e. where in the wall a window should be installed and how thermal bridging can be minimised.
We have a good grasp of building fabric performance, which is key to designing for low energy and thermal comfort. Talk to us about your low energy retrofit, extension, or new build project.