The existing roof structure can remain under a new photovoltaic roof if its condition and parameters match the design. This cannot be confirmed by comparing the weight of the coverings alone. The timber, the connections, the geometry and the required support for the new system must be assessed. An integrated steel roof offers an opportunity for an aesthetic modernisation of the house, but the decision to retain the structure should be based on an inspection and on calculations. It is not only a question of the absence of visible cracks. Moisture, signs of biological damage, deflections and the condition of the connections are also significant. Particular attention is required at chimneys, valleys and wall plates. There, an earlier leak may have been active for a long time, even if no large stain appeared on the finished attic.