The least noticeable part of your dormer is the most vulnerable

What stands out on a dormer is the front: the frame, the glass, the cladding on the cheeks. The little flat roof on top is not even visible from the street. Structurally it is the component with the shortest life and the biggest consequence when it fails — it lies horizontal, it holds water, and it sits directly above a living space.

Anyone having that roof renewed immediately faces a second question: insulate at the same time or not. Dutch consumer authority Milieu Centraal names the best moment to insulate a flat roof as the moment the covering has to be renewed anyway. The logic is that opening it up, the edge finishing and the junctions are paid for once instead of twice.

There is also a route to avoid. Milieu Centraal calls insulating a flat roof from the inside a bad idea because of the risk of moisture and wood rot, stating that the risk of moisture in the roof construction or mould on the ceiling is high. On a dormer that is extra tempting — it is easy to reach from inside — which is exactly why it is worth saying.

In practice: assess the little roof at every painting round, since someone is up there anyway. Blisters, bare patches, puddles still standing after a day and loose edge finishing are the signals. A dormer renovation costs € 1,500-6,000 and is almost always the cheaper route than waiting until replacement with a plastic (€ 6,500-11,000) or timber (€ 10,000-20,000) unit is the only option. Every guide rate is in the price index.