Energy retrofit: what actually works in old buildings

Old walls need to dry inward

A stone or solid brick wall absorbs rain and releases it inward. Sealing the inside with a vapour-tight membrane stops that release, and the moisture stays in the wall until it finds a cold point — usually a beam end or a window reveal.

That is why the materials matter as much as the thickness: breathable insulation, a vapour-permeable finish, and a detail that lets the wall dry. In a timber chalet, the logic is reversed: the frame must be kept dry and ventilated, and the vapour barrier goes on the warm side.

The order, again

Airtightness first, because it is cheap and it makes every other measure work. Ventilation second, because an airtight building without ventilation is a damp building. Insulation third: roof, then floor, then walls. Heating last, sized for what the building has become.

Skipping the first two steps and going straight to a heat pump is the most common error in Alpine renovations. The machine works, the bills do not fall, and the client concludes that insulation is useless.

What the certificates do not say

A calculation gives a theoretical consumption. What decides comfort is the detail: the junction between the wall and the floor, the seal around the windows, the ventilation in the bathroom, the temperature of the surfaces you touch.

That is why a retrofit is designed junction by junction, not by choosing a product range. The best insulation installed with a gap performs worse than a modest one installed continuously.