Convertible
lofts.

Ridge height. This is the first filter. Below 1.80 metres at the highest point, the space is not comfortably habitable as it stands — the genuinely usable floor area becomes too small. Above that, conversion can be considered; from 2.20 or 2.50 metres, it becomes comfortable.

Roof pitch. The steeper the roof, the larger the usable floor area for the same height. Below about 30 degrees, the usable volume shrinks quickly: you gain square metres of floor that you cannot stand up in.

Roof structure type. A traditional roof structure leaves a clear volume: conversion is straightforward. A trussed rafter roof fills the loft with triangulated timbers — not a deal-breaker, but it changes the nature and cost of the project.

It is the most persistent misconception, and it wrongly leads owners to give up. A trussed rafter roof can be altered: the triangulation cluttering the volume is replaced by a load-bearing structure — beams, posts or underpinning — that carries the loads differently.

The operation is well understood, but it is not joinery: it is structural engineering. It requires a preliminary study, rigorous phasing (nothing is cut before the new supports are in place) and careful execution. It is typically the kind of job where money saved on the study is paid back tenfold.

Our in-house design office validates feasibility and sizes the new structure before any costing. If the operation is not economically justified given the space gained, we will tell you: in some cases, adding a storey costs less for a better result.

The job is never just a matter of fitting insulation and plasterboard. First you need a floor that can take the load: the joists of an unconverted loft were designed to carry their own weight and light storage, not partitions, furniture and occupants. Reinforcement or a new floor is frequently required.

Next you need access. The stairwell opening takes up space on the floor below — this is often the real headache of the project, and it is resolved at design stage, together with the loft layout. Then come the openings: roof windows or dormers, which bring in light and determine whether the space counts as habitable floor area.

Finally insulation, ventilation, electrics, heating and finishes. With insulation, there is a trade-off to consider: insulating from the inside eats into the very height you were after; insulating from the outside with sarking keeps it all — but that means redoing the roof covering.

Converting a loft creates floor area, and that triggers obligations. A prior declaration (déclaration préalable) is enough below a certain threshold of area created; above it, a building permit is required. If the exterior appearance changes — adding dormers or roof windows — authorisation is needed even for a modest area.

The key point not to miss: for a private individual, using an architect registered with the Ordre des architectes becomes mandatory as soon as the total floor area exceeds 150 m² after the works. It is the total, not the area added — and a loft conversion often tips a house over the threshold.

Our manager holds a French state architecture degree (DEA), and we work as project manager and general contractor. When the threshold requires an architect registered with the Ordre, we work with registered architects: the project is not blocked, it is simply organised differently.