On an external wall insulation job there is not one thermal resistance threshold but three, and they do not measure the same quantity. Where insulation is triggered by a major façade refurbishment, the French thermal regulation for existing buildings requires an R value for the wall plus insulation of at least 3.2 m².K/W in zones H1, H2 and in H3 above 800 m of altitude, values in force since 1 January 2023. Certificate sheet BAR-EN-102 requires 3.7 m².K/W on the installed insulation alone, existing insulation being disregarded, and since the order of 29 December 2023 the MaPrimeRénov' guided route raises the requirement to 4.4 m².K/W for external insulation of façade or gable walls. Pricing a thickness against the wrong threshold means a file rejected at inspection and a gap absorbed on the margin.
The R value depends on the scheme, not on the building
Three thresholds, three scopes, three quantities measured
The table below is read from the file backwards: start from the funding the client is claiming, and derive the thickness to order. The same wall can therefore call for two different thicknesses depending on whether the job is a standalone measure or a whole-house retrofit.
| Scheme | What is measured | Required R value | Reference text |
|---|---|---|---|
| Insulation triggered by a major façade refurbishment | wall plus insulation | 3.2 m².K/W in H1, H2 and H3 above 800 m; 2.2 m².K/W in H3 below 800 m | thermal regulation for existing buildings, values in force since 1 January 2023 |
| Energy saving certificate, sheet BAR-EN-102 | installed insulation alone, existing disregarded | 3.7 m².K/W | sheet BAR-EN-102 version A65-4 |
| MaPrimeRénov' guided route, external insulation | installed insulation | 4.4 m².K/W | order of 29 December 2023 |
| MaPrimeRénov' guided route, internal insulation or external under justified constraint | installed insulation | 3.7 m².K/W | order of 29 December 2023 |
Whole wall or insulation alone: the distinction that changes the thickness
The gap between 3.2 and 3.7 is not a gap in stringency, it is a gap in what is being measured. The 3.2 regulatory threshold covers the assembly of substrate, new insulation and retained existing insulation: a blockwork wall already lined can reach it with a modest thickness. The 3.7 certificate threshold covers only the insulation being fitted, the existing being expressly excluded by the sheet. On a partly insulated wall, the order is therefore always placed on the more demanding basis, the one measured on the insulation alone.
Turning an R value into a thickness without picking the wrong lambda
The thickness follows from the target R and the product's declared lambda, not from a generic table. Sheet BAR-EN-102 states that thermal resistance is assessed to EN 12664, EN 12667 or EN 12939 for non-reflective insulation, and to EN ISO 22097 for reflective insulation. A product sold without a declared value assessed to one of those standards cannot support the evidence of completion, whatever its real performance.
Insulation triggered by a façade refurbishment
What triggers the duty, and what does not
The trigger rests on three cumulative criteria, to be checked façade by façade from the survey onwards. The one most often missed is the nature of the substrate: the text covers only walls made mainly of industrial materials.
| Criterion | Triggers the duty | Does not trigger it |
|---|---|---|
| Nature of the façade | more than 50% by area of fired clay, concrete, cement or metal | stone, cob, wattle and daub, timber, traditional lime render |
| Extent of the works | more than 50% of the façade, openings excluded | localised repair below that level |
| Nature of the works | stripping and renewing the render, or adding or replacing a cladding element | cleaning, repair, repainting, thick plastic coatings and waterproofing coatings |
| Building | heated residential or commercial building over 50 m² of floor area | listed monument, place of worship, unheated building, temporary structure under 2 years |
The four grounds for exemption and the evidence each requires
The duty falls away in four cases, but each calls for a different document on file. A technical constraint, meaning a risk of serious damage to the fabric, is evidenced by a reasoned note from a competent professional. An architectural constraint, where external insulation would degrade the architectural quality of the building or its surroundings, is evidenced by an architect's note. A legal constraint, incompatibility with the local plan, the surroundings of listed monuments or protected sites, requires no evidence at all. An economic constraint, finally, is established by a payback period strictly longer than ten years, calculated façade by façade. Spot inspections target precisely those documents.
Where the payback calculation is not required
The payback is deemed longer than ten years, with no calculation, in several configurations: building constructed after 2001, façade insulated after 2008, façade already insulated to a thermal resistance of at least 2.3 m².K/W, an energy audit less than ten years old concluding that insulation was not appropriate, balconies less than one metre deep, the need to reinstate existing mouldings identically, or works requiring asbestos removal. In those cases the client draws up the evidence themselves.
System, substrate and weak points
Accept the substrate before pricing, not after ordering
Pricing is built on an accepted substrate: cohesion, flatness, moisture content, active cracks, salt deposits, condition of existing render. Sheet BAR-EN-102 in fact makes that technical survey compulsory before the quote is drawn up, and requires checking on that visit whether any existing insulation can be kept as it is or must be made good or stripped out. The detail of what to record is set out in our guide to external wall insulation for masonry contractors.
Order a complete system under a technical approval
An external insulation system is ordered complete: insulation, fixing method, base coat, mesh, finish and accessories, all covered by the same technical approval. Mixing components from two systems takes the work outside the covered field of use and shifts the risk onto the contractor if anything fails. On an inconsistent substrate or a highly exposed façade, the choice lies between render on insulation and ventilated cladding with a rainscreen, which tolerates flatness defects better.
Check points at each phase
- Before fixing, check cleanliness, moisture, substrate cohesion and the setting out of the starter track.
- After bonding, check adhesion and the continuity of the dabs or the perimeter bead.
- At fixing, count the anchors, the embedment depths and the absence of crushing of the insulation.
- At finishing, record the treatment of reveals, sills, drip caps and movement joints.
These weak points carry most of the failure risk and are handled according to the system's own instructions, as set out in our article on sills, reveals and parapets in external wall insulation.
Pricing, securing the file and recording
Break the quote down façade by façade
The take-off is done façade by façade, openings deducted, with the running length of reveals, sills and returns that drives the accessories item. Then separate scaffolding, protection, removal and refitting of attached items, insulation, fixings, profiles, base coat, mesh, finish and waste disposal, and keep a contingency item for substrate making good. That breakdown prepares itself when Argile takes the façade quantities from the survey and deducts the openings from the areas to insulate.
The procedural conditions that sink a certificate file
They have nothing to do with thermal performance and are nonetheless the leading cause of refusal. The technical survey must precede the drawing up of the quote, and its date appears on the evidence of completion. A minimum of seven clear days must separate acceptance of the quote from the start of insulation fixing. The contractor must hold a recognised quality label covering the relevant field of work. The obligations attached to that qualification are set out in our article on RGE obligations, inspections and renewal.
The file you archive
The evidence of completion states that insulation was installed, the area fitted, the thermal resistance of the installed insulation and the date of the prior technical survey. Failing a thermal resistance, it states the brand, reference and thickness, supported by a document from the manufacturer or an accredited body. Add to the as-built file the system's technical approval, the delivery notes with batch numbers, the setting-out plan and dated photographs of each phase: that is what stands up to an on-site inspection or an expert report.
