As designers, we face countless challenges in trying to improve the condition of existing structures. Often, adding internal or external insulation to walls is not feasible due to the impact of this approach on internal floor areas and the risk of interstitial condensation. Meanwhile, the replacement of single-glazed windows which are no longer fit for purpose is one of the most effective and common means of reducing heating demand. Can reusing these replaced windows, for a different purpose, be part of the solution?

Millions of windows will need to be replaced across the UK in the residential sector alone to meet our net zero targets. With this potential influx adding to the already high number of windows being removed from our existing buildings, there is an opportunity to reclaim them to improve thermal performance while utilising the thermal mass of traditional facades to provide passive means of heating and cooling.

How? By repurposing the glazing to create Trombe walls.

What is a Trombe wall?

A Trombe wall is a type of passive heating and cooling system that uses sunlight to naturally regulate the internal climate of a building.

A double-skin façade is created by placing a layer of glazing in front of a wall with thermal mass, such as masonry or concrete. During the day, sunlight passes through the glazing and hits the wall, which absorbs the heat. The wall holds this heat and slowly releases it into the building over time, reducing the immediate impact of solar gains on internal temperatures. While the sunlight has a shorter wavelength and is easily conducted through glass, the longer wavelength heat re-emitted from the wall cannot pass through glass as easily. As temperatures decrease at night, the stored warmth is released into the indoor space, keeping it comfortable without using extra heating energy.

They can also help with cooling. During summer months, Trombe walls can be used to prevent heat from entering the building by venting the stored warmth within the buffer zone to the outside before ever reaching the internal spaces. By venting overnight, the thermal mass of the wall is ‘recharged’ so that it can absorb heat again the next day.

Trombe walls are an excellent solution for improving the passivity of our existing buildings. The additional layer can also improve the overall thermal performance of existing masonry and concrete walls.