Wall insulation for stone and rubble houses on the Cote d'Azur

A traditional Riviera wall, whether it's dressed stone, rubble fill or thick rendered masonry, doesn't work the way a modern insulated wall works. It doesn't resist heat flow so much as absorb it and release it slowly. Building physics calls this thermal mass: a heavy, dense wall soaks up heat during the day and gives it back hours later, once the sun has gone down. That's a useful trait in a climate with hot summer days and cool summer nights, and a liability in a mild winter with cold mornings.

On a January morning, an old stone house often feels colder inside than the outside air temperature would suggest, because the wall itself has spent the night radiating stored coolness back into the room. On an August evening, the same wall does the opposite: it keeps releasing the heat it absorbed all afternoon, long after the outside air has cooled. Neither effect has much to do with insulation value in the conventional sense. It's the mass doing the work here, something no resistance figure on a datasheet captures.

This matters directly for the ITE-or-ITI decision. Insulating the outside of the wall (ITE) keeps that mass inside the building envelope, on the warm side of the insulation layer, so the wall keeps doing its summer job of storing and delaying heat. Insulating the inside (ITI) puts a layer of insulation between the room and the wall, which cuts the room off from the mass entirely. You gain a warmer room faster in winter, but you lose most of the slow summer cooling the wall used to give you for free. Neither choice is wrong; they just solve different problems, and it's worth knowing which one you're solving before you commit.

The figures below are realistic pre-subsidy ranges for installed work in the Alpes-Maritimes. ITE costs more because the price includes insulation boards, a full render system and scaffolding. ITI is cheaper because it's boards and a plasterboard finish fixed to an existing wall, with no facade work involved.

Totals climb fast once you move from a single wall to a full house: 100m² of external wall at the low end of the ITE range is already 12,000 EUR before any grant is applied. That's why pairing ITE with a planned ravalement is worth considering: see our facade renovation page for how sharing one round of scaffolding between the two jobs changes the total.

Yes to both. ITE always changes the facade, because it adds thickness and a new render finish, and any change to a building's external appearance requires a déclaration préalable at the mairie, everywhere, including outside a historic centre. ITI, by contrast, leaves the facade untouched and generally doesn't trigger this requirement at all.

Where it gets harder is inside a protected perimeter, and a considerable share of the old town fabric on this coast sits inside one. In those zones, the Architecte des Bâtiments de France gives a binding opinion on the application: the ABF can refuse ITE outright on a facade considered of architectural or historic interest, or approve it only with specific render colours, textures or detailing that add cost. If your property is inside such a perimeter, it's worth asking the mairie before you commission any quotes: ITE may simply not be available to you, and ITI becomes the only realistic route to insulating the walls at all.

If ITE is approved and you're also due a ravalement (facade renovation), it's worth doing both in one project. Scaffolding is a real share of the ITE bill on its own, and putting it up once for both jobs instead of twice is a straightforward saving. Our facade renovation page covers what a ravalement involves and when the law requires one, which is less often than most French sites suggest.