Renovating an
old house.

Traditional buildings, from before the war: farmhouses, village houses, stone or rammed-earth walls, timber floors and roof frame. Their thick walls have no barrier against ground moisture; they work by letting water migrate and then evaporate. Anything that seals them in — cement render, waterproof paint, lining stuck on without precautions — ends up trapping this water in the masonry.

The post-war house, from the 1950s to the 1980s: concrete block, hollow brick or concrete, often a light roof, with little or no insulation originally. The structural work is generally sound; it is the services (electrics, plumbing, oil-fired heating or convectors) and the thermal envelope that need redoing.

For both, the applicable thermal regulation is the one known as "element by element": every insulation layer, window, heating or ventilation system you replace must reach a minimum performance. This is the regime for all houses under 1,000 m² and for all buildings built before 1948, whatever their size.

The structure. Stepped cracks, sagging floors, attacked purlins or rafters, moving walls: this is the first area of uncertainty. An old house that looks sound can hide a cracked lintel or a weakened beam behind a false ceiling. We probe before costing.

Damp. Saltpetre at the foot of a wall, a cellar smell, blistering wallpaper: the cause has to be found (outside ground too high, gutter, unsuitable render, no ventilation) before insulating anything. Insulating a damp wall means sealing in the problem.

Asbestos. For a house completed before 1^st January 1997, an asbestos survey before works is mandatory, whether the works are done by you or by a company; its results must be passed on to the company. Floor tiles, adhesives, flues, roof sheets or renders may contain it. Any removal is entrusted to a company certified in asbestos removal.

Lead. Homes built before 1^st January 1949 must have a lead exposure risk report (CREP) to be sold or let. For the site, the issue is concrete: sanding or stripping old lead paint spreads toxic dust. It is better to know where it is before starting.

Electrics and energy. If you have just bought, reread the diagnostics file: the condition of the electrical installation is required at sale once it is more than 15 years old, and the DPE places the house on the energy scale. These are good starting points, not site surveys: they do not tell you what is behind the partitions.

In an old building, the sequence matters as much as the quality of each trade. Here is the one we follow, and the reason for each step.

1. Make it weathertight and secure what carries the load. Roof, roof frame, wall repairs, lintels, floors: there is no point insulating under a leaking roof covering or tiling on a sagging floor. This is the work of our masons and our carpenters, before anything else.

2. Treat damp at its source. Drainage or lowering of the outside ground, gutters, removal of cement renders on old walls. A stone wall needs a few weeks to start drying: this is the moment to give them to it.

3. Strip out and clear. Removal of partitions, linings and condemned coverings, after the asbestos survey and any asbestos removal. This is often where the house reveals what the visit did not show.

4. Replace the external windows and doors. Before the linings, to take care over the junction between window and insulation: this is the joint through which air leaks and thermal bridges pass.

5. Run the services. Electrics, plumbing, ventilation ducts, supply for the future heating: everything that has to disappear into the walls and ceilings is installed while they are open.

6. Insulate and close up. Wall linings, insulation of lofts or rafter slopes, ground floor, then partitions and ceilings by our plasterers. In a house made more airtight, ventilation is not an option: without it, interior moisture condenses on the cold spots.

7. Finish. Screeds, tiling, parquet, interior joinery, painting, kitchen and bathroom: the trades that show come last, on a dry, signed-off base.

Reversing two of these steps is expensive: a chase cut in a new lining, a window changed after the insulation, parquet laid on a screed that is still damp. That is the advantage of a project run by a single company: turnkey renovation fixes this order from the planning stage.

In a house from the 1960s or 1970s, the original installation often has neither an earth in every room nor residual current protection on each circuit, and the panel has been added to over the years. Adding sockets to this network means stacking up risks. When the house is open anyway, redoing the whole installation costs less than repairing it twice.

Our electricians redo it to the NF C 15-100 standard, the standard for new installations. A fully renovated installation that has to be reconnected by the network operator is covered by a certificate of conformity, issued by the company that carried out the work and approved by an accredited body: it is a regulatory obligation, and a guarantee for resale.

On a post-war house in concrete block or concrete, the usual solutions work well: internal or external insulation, loft, ground floor. The choice depends mostly on the facade, planning rules and the living space you accept to lose.

On a stone or rammed-earth wall, the priority is to let water vapour out. This points towards vapour-permeable insulation and renders (lime, hemp, wood fibre) and rules out cement on the masonry. Our masons regularly repair stone walls with lime; our guide to stone walls and their renders details these techniques, and the one on insulating walls from the inside covers the installation precautions.

One last point often overlooked: ventilation. An old house used to "breathe" through its defects — leaking windows, open flues. Once insulated and fitted with airtight windows and doors, it has to be given controlled air renewal again.

The price. On our projects in Savoie and Haute-Savoie, a full renovation comes to between €800 and €1,500 incl. VAT/m² and a heavy renovation, with structural repairs, between €1,500 and €2,500 incl. VAT/m², before grants. The breakdown by type of work and the local factors (altitude, access, protected areas) are in our guide to the cost of a house renovation in Savoie.

VAT. In a house completed more than two years ago, most works fall under the 10% rate and energy renovation under 5.5%. But a very extensive renovation can tip the project to 20%: this is the case if it renews most of the structure or facades, or if it redoes at least two thirds of each of the six finishing-trade elements (non-load-bearing floors, external windows and doors, partitions, plumbing, electrics, heating). We examine this at the programme stage; the rule is detailed in our guide VAT on works: 5.5, 10 or 20%.

Grants. MaPrimeRénov' whole-house renovation (rénovation d'ampleur) is aimed at main residences built at least 15 years ago and rated E, F or G; the project must gain them at least two energy classes, with the support of Mon Accompagnateur Rénov', who carries out the energy audit. The zero-interest eco-loan (éco-PTZ) can reach €50,000 for a whole-house renovation, repayable over 20 years at most. Both grants require the works to be entrusted to an RGE company; ours is RGE CertiRénov certified (no. CR-2026-73-0095). Amounts and scales change often: see our overview of MaPrimeRénov' and the 2026 grants and check them on france-renov.gouv.fr.

Permissions. Interior works generally require none. As soon as the outside appearance changes — windows, facade render, roof, a new opening — a prior declaration (déclaration préalable) is needed, with tighter requirements near historic monuments.