The traditional
roof structure.

A traditional roof structure is made up of large-section timbers — purlins, rafters, principal rafters, tie beams — jointed together and resting on the load-bearing walls. It leaves an open volume under the roof. It is the roof structure of all old buildings, from Savoyard farmhouses to village houses.

A trussed rafter roof — known as an industrial roof structure — is made of small triangulated sections, assembled in the factory with metal connectors and installed in series. It is cheap and quick, but it fills the loft with a web of timber that makes it impossible to move around.

This distinction determines everything else: what you can convert in your loft, what an alteration costs, and whether you can leave the structure exposed. Before any roof or loft project, it is the first thing we identify.

The warning signs are fairly easy to read when you know what to look for: a sagging ridge line or one that undulates, tiles shifting for no apparent reason, traces of damp on the timbers, fine sawdust on the floor — a sign of wood-boring insects —, timber that crumbles under the tip of a screwdriver, or joints that have moved.

The three main causes are damp (roof leaks, condensation, lack of ventilation), biological attack (house longhorn beetles, woodworm, dry rot) and overloading — often a roof covering replaced with a heavier material without checking the timber sections.

Not all of them lead to a complete rebuild. A locally damaged purlin can be replaced, a joint reinforced, a truss doubled. Our in-house design office assesses the actual condition before pricing: it is the only way to avoid both costly over-treatment and a patch-up that will not last.

In Savoie and Haute-Savoie, a roof structure is not calculated as it is in the lowlands. Snow loads increase with altitude and become the decisive sizing factor: timber sections, rafter spacing, bracing, bearings. A roof structure correctly sized at 400 metres can be seriously inadequate at 1,200.

The same applies to alterations. Adding a dormer, opening a stairwell, removing a tie beam to free up volume: each of these interventions takes material away from a calculated structure. On a mountain building, they cannot be improvised.

Finally, if you are redoing the roof covering, it is the right time to check the structure — and possibly to insulate from the outside. Sarking adds a load that must be validated, but it lets you keep the roof timbers exposed, which makes all the difference on a chalet or a converted barn.

A fine traditional roof structure is an architectural feature in its own right. Massive purlins, visible joints, weathered timber: on a chalet, a barn or a character house, it is often what gives the space its value. Hiding it under a flat ceiling means erasing the very reason you bought the property.

Keeping it exposed requires precise technical choices: insulating from the outside rather than the inside, treating the timbers rather than covering them, integrating electrics and ventilation without drilling into the structure. These decisions are made at the design stage, not on site.

We work as project manager or as turnkey general contractor, with our own teams. Our office is in Aix-les-Bains and we cover Savoie and Haute-Savoie.