Ilmington Farm House – Stone Mullion Steel Window Replacement

Replacing windows in stone mullions can be very awkward for modern window systems. Almost all stone surrounds such as these were originally designed to hold incredibly thin steel casements: beautiful thin frames, but unbelievably poor thermal efficiency as a result. Most direct replacements don’t meet today’s building regulations and almost all thermally-efficient solutions are just too large – they would be overhanging the internal cill!

This is where we introduce Alitherm Heritage. The depth of our standard timber windows is around 115mm. Heritage Aluminium is only 47mm, yet it can still achieve a U-value of 1.5.

For this project, the final look is a very steel-like finish: black is traditionally used for metal casements, and it works exceptionally well here. The dark frames in-board of the stonework looks so much more natural than the bright white frames that we removed, and the black handles to match just make a lot of sense over the other chrome and white options. The lack of glazing bars gives the house a far cleaner design, and really helps to lift the property away from the previous plastic-like design language.

All glass units are argon-filled with a low-emissivity layer as standard – this means that the glass is always working to keep heat where it should be. The Low-E layer prevents a large percentage of infrared (and ultra-violet) from passing through the glass. So, if it’s warm inside, the glass helps to retain the heat. If it’s warm outside, the glass helps to keep the interior cool.

Although this heritage aluminium window is mainly designed for stone mullions, you can see from the photos that it also works in other areas. For example, we were able to produce the dormer windows thanks to manufacturing flexibility: the frame depth was increased to suit the space left by the old window, and the frame width was slightly increased to allow room for the internal plaster to sit in the correct place.

Products used:

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