In carrying out a loft conversion some way has to be found of reinforcing the triangular timber roof trusses so that the internal bracing can be removed, to make the space. In the invention this is done by fixing C-sections to the outline of the triangular trusses, preferably sandwiching the timber frame. For the C-sections to overlap at the corners, part of one flange, e.g., the upper flange of the horizontal beam, is removed, and then the beams are bolted onto the frame. The process can be carried out with minimal disruption to the roof as no transverse (longitudinal) reinforcement is needed. A dormer process can also be included, making use of a versatile reinforcement plate.