Published 12 June 202643 min read · the essentials in 2 minHPE · Minergie® · SIA 380/1 · RCI art. 56AUw · ψg · Position in wall · External insulationUpdated September 2026
Window replacement: the position in the wall matters more than the glazing
Windows are often the first works decided — and most often decided too early. Choosing triple glazing at Ug = 0.50 W/(m²K) and then setting it into a bare reveal, with no insulation and no settled façade strategy, can double its effective thermal bridge. This dossier sets out the values that really count — Uw, Ug, ψg — why the position in the wall is the decisive factor, and in what order the decisions have to be settled before ordering.
Ug — thermal transmittance of the glazing alone [W/(m²K)] · triple glazing: typically 0.50–0.70
Uf — transmittance of the frame [W/(m²K)] · standard PVC: ~1.2–1.4 · passive-grade timber-aluminium: 0.7–0.9
ψg — linear transmittance of the glass edge [W/(m·K)] · steel spacer: 0.10–0.12 · warm edge spacer, a low-conductivity non-metallic spacer bar: 0.03–0.06
Ag, Af — areas of glazing and frame [m²] · lg — perimeter length of the glass edge [m]
ψg is often the least visible figure on a quotation, and yet it is decisive. On a window of 1.2 × 1.4 m, the perimeter of the glass edge is about 4.6 m. A steel spacer (ψg = 0.10 W/(m·K)) adds 0.46 W/K of extra heat loss — the equivalent of degrading Uw by about +0.27 W/(m²K)EN ISO 10077-1: ψg applies to lg, the visible glazing perimeter — sill included — not to the window's outer perimeter (5.2 m here). Glazing ≈ 1.06 × 1.26 m: lg ≈ 4.6 m; 0.46 W/K over 1.68 m² = +0.27 W/(m²K).NBN / Buildwise — NBN EN ISO 10077-1 — Performance thermique des fenêtres, portes et fermetures — Calcul du coefficient de transmission thermique — Partie 1 : Généralités (ISO 10077-1:2017)2017 · accessed 2026-09-04 across the whole window (1.68 m²). Moving to a warm-edge spacer (ψg = 0.04) cuts that contribution to 0.18 W/K — a gain of 0.28 W/K without touching either the glazing or the frame.
The frame usually accounts for 20 to 30% of the total area of a standard window. Replacing ordinary double glazing (Ug ≈ 1.1 W/(m²K)) with triple glazing (Ug ≈ 0.60) gives a clear gain on the glazed area. But if the frame moves at the same time from standard PVC (Uf ≈ 1.3 W/(m²K)) to a passive-grade timber-aluminium frame (Uf ≈ 0.8 W/(m²K)), the frame alone accounts for 15 to 20% of the total improvement in Uw. Ignoring Uf when comparing quotations means reading only part of the datasheet.
Component
Common value in refurbishment
High-performance value
Effect on final Uw
Ug — glazing
1.0–1.1 (standard double glazing)
0.50–0.60 (passive-grade triple glazing)
≈ −0.5 to −0.6 W/(m²K) on Uw
Uf — frame
1.2–1.4 (standard PVC)
0.7–0.9 (passive-grade timber-aluminium)
≈ −0.1 to −0.2 W/(m²K) on Uw
ψg — glass edge
0.10–0.12 (steel spacer)
0.03–0.05 (warm edge)
≈ −0.2 to −0.3 W/(m²K) on Uw
ψinstallation — reveal
0.10–0.15 (inboard installation, bare reveal)
0.03–0.05 (within the insulation plane)
≈ −0.5 to −1.0 W/(m²K) on effective Uw
ψinstallation is not part of the product Uw — it is added after installation. It is the figure that can wipe out on site every gain won in the ordering office. Sources: EN ISO 10077-1:2017, EN ISO 14683:2017, PHI certification criteria for transparent components.
The solar factor g — the forgotten half of Uw
Ug measures the losses; the solar factor g measures the gains. Glazing at g = 0.50 lets 50% of the incident solar radiation through as heat — free passive solar gains in winter. PHI sets no g threshold on its own: its glazing criterion couples the two, Ug − g × 1.6 ≤ 0 W/(m²K). Glazing at Ug = 0.70 must therefore reach g ≥ 0.44; at Ug = 0.50, g ≥ 0.31 is enough. Note: some thermally excellent triple glazings (Ug = 0.50) come with g = 0.45–0.48 — the trade-off between insulation and solar gains has to be judged orientation by orientation. On a north or shaded façade, very low Ug triple glazing is justified. On a strongly exposed south façade, a slightly higher g can cut the heating demand more than a further reduction of Ug.
02 — Choosing the glazing
Triple glazing — when it pays and when it does not
Triple glazing has become the benchmark of high-performance refurbishment, rightly so in most French-speaking Swiss and Geneva contexts. But the decision deserves to be put project by project: triple glazing costs 20 to 40% more than high-performance double glazingA market order of magnitude, depending on manufacturer, format and year. No open primary source supports it. See point 4 of the arbitration report.Source to be established — unverified figure, is heavier (hardware, reinforced frames) and can, in certain configurations, slightly reduce passive solar gains. The right question is not "triple or double?" but "what total Uw after installation, for what budget, in what wall build-up?"
Triple glazing justified
Refurbishment towards HPE or Minergie®
HPE — haute performance énergétique — and, above it, THPE — très haute performance énergétique — are two statutory Geneva standards, not labels: Minergie is only one of the admitted routes to demonstrating them. Uw ≤ 1.0 W/(m²K) against the outside is the SIA 380/1:2016 limit value, in new build as in refurbishmentge.ch, "Assainissement énergétique des fenêtres": replaced windows must meet the element requirements of SIA 380/1, "soit maximum 1 W/m².K".République et canton de Genève — Assainissement énergétique des fenêtresaccessed 2026-09-02. To reach an installed Uw ≤ 0.85 — the PHI criterion for the window component in the cool-temperate zone — triple glazing is indispensable, short of combining a passive-grade frame, warm edge and a perfectly insulated reveal. In French-speaking Switzerland, as soon as the target is CECB C or better in refurbishment — the CECB being the cantonal building energy certificate, a grade calculated from the building rather than a metered consumption — triple glazing becomes the obvious choice on north, east and west façades.
Triple glazing justified
North and east façades, or wind-exposed ones
On these orientations passive solar gains are limited, and the ψg of triple glazing is offset by the reduction in winter heat losses. The heating load on the north façade of a building refurbished with triple glazing can fall by 30 to 50% against standard double glazing — a direct contribution to reducing the Geneva IDC — indice de dépense de chaleur, the actual heating and hot water consumption read off the building's meters, not a calculation.
To be assessed
Strongly exposed south façade
On a south façade without external solar shading, triple glazing at g = 0.45 can cut winter passive solar gains by 10 to 15% compared with high-performance double glazing at g = 0.62. If the building lacks thermal mass, summer overheating may also be harder to control. Assess the Ug / g trade-off orientation by orientation on a PHPP balance.
To be assessed
Listed or inventoried heritage
In Geneva, joinery on buildings that are listed, entered in the inventory of buildings worthy of protectionRCI art. 56A para. 4 let. b: buildings that are listed, entered in the inventory of buildings worthy of protection and/or covered by a site plan, within the meaning of the LPMNS.rsGE L 5 05.01, silgeneve.ch — RCI — Règlement d'application de la loi sur les constructions et les installations diverses, art. 56 et 56Aaccessed 2026-09-02, or covered by a site plan under the LPMNS, requires a permit. RCI art. 56A para. 5 allows four exceptions to the energy requirements for themRCI art. 56A para. 5 let. a: "le remplacement du seul vitrage par un vitrage dont le coefficient d'isolation thermique est égal ou inférieur à 1,0 W/(m2 K), lorsque la menuiserie ou la serrurerie sont conservées".rsGE L 5 05.01, silgeneve.ch — RCI — Règlement d'application de la loi sur les constructions et les installations diverses, art. 56 et 56Aaccessed 2026-09-02, including replacing the glazing alone with glazing at U ≤ 1.0 W/(m²K) while keeping the existing joinery. Double glazing at Ug ≤ 1.0 W/(m²K), warm edge and a profiled timber frame matching the original appearance may therefore be the only technically and legally possible option.
The cavity gas — argon or krypton
The Ug of triple glazing depends largely on the gas filling the two cavities. Argon (Ar) is the standard: typical Ug of 0.60–0.70 W/(m²K) depending on cavity width and low-e coatings. Krypton (Kr) reaches Ug = 0.50–0.55 W/(m²K) with narrower cavities — useful where weight is a constraint — but at a markedly higher cost. In most residential refurbishment projects, argon with two low-e coatings and a warm-edge spacer reaches Ug ≤ 0.60 W/(m²K) — comfortably enough to satisfy the PHI criterion Ug − g × 1.6 ≤ 0 — without paying for krypton.
Triple glazing and weight — a practical point often forgotten
Standard 4/16/4/16/4 mm triple glazing weighs about 30–35 kg/m² — against 18–22 kg/m² for double glazing. On a large 2 m² light (60–70 kg), hardware, tracks and sometimes the frames have to be sized accordingly. In refurbishment, where existing outer frames are kept, check their load-bearing capacity before specifying large-format triple glazing. An 80-year-old solid timber outer frame may be structurally sound and still need reinforced hardware.
Triple glazing at Ug = 0.55 set into a bare reveal performs worse than double glazing at Ug = 0.9 set within the insulation plane with an insulated reveal. The catalogue value is not the installed performance.
French-speaking Switzerland — Minergie 2026.1
The Minergie label regulations set no Uw or Ug value per component: the window is judged by the overall balance and by the airtightness of the envelopeMinergie label regulations 2026.1: no numerical Uw or Ug requirement per component, not even for Minergie-P in refurbishment. The page claimed "installed Uw ≤ 0.80 for Minergie-P": that value is not there.Minergie Suisse — Règlement des labels MINERGIE®/MINERGIE-P®/MINERGIE-A®, version 2026.12026-01-01 · accessed 2026-09-02, measured to SIA 180:2014 and ISO 9972:2015, with qE50 ≤ 0.8 m³/(h·m²) in new build and ≤ 1.6 in refurbishmentMinergie regulations 2026.1, § 6.2 "Airtightness of the envelope". The regulations cite SN EN ISO 9972:2022; the edition retained on this site remains ISO 9972:2015 with SIA 180:2014.Minergie Suisse — Règlement des labels MINERGIE®/MINERGIE-P®/MINERGIE-A®, version 2026.12026-01-01 · accessed 2026-09-02 for Minergie-P and Minergie-A. The "Minergie-P Uw of 0.80" that circulates on quotations appears nowhere in the regulations. In practice, meeting those balances almost always calls for triple glazing (Ug ≤ 0.60), a high-performance thermally broken frame (Uf ≤ 0.90) and a warm-edge spacer (ψg ≤ 0.05).
Neighbouring France — RE2020 and BBC Effinergie Rénovation 2024
RE2020 sets whole-building performance requirements (Bbio, Cep,nr) without imposing a minimum Uw on windows. On the grants side, window replacement left the single-measure track of MaPrimeRénov' — the parcours par geste, which funds one isolated measure with no prior audit and no required gain in classes — on 1 September 2026: it is now fundable only within a deep renovationDecree no. 2026-822 of 25 August 2026 (JORF no. 0199 of 27 August 2026), art. 4: annex 1 is replaced; the “isolation” grants leave the single-measure route on 1 September 2026, glazed elements included.Légifrance — Journal officiel de la République française — Décret n° 2026-822 du 25 août 2026 modifiant le décret n° 2020-26 du 14 janvier 2020 relatif à la prime de transition énergétique2026-08-27 · accessed 2026-09-04. The rénovation d'ampleur is the other route: a coordinated, supervised package of works tied to a gain in DPE classes. Since the rates change several times a year, rely on france-renov.gouv.fr rather than on a copied table. For the BBC Effinergie Rénovation 2024 label, which in housing requires label A or B of the DPE — diagnostic de performance énergétique, the French energy certificate issued on sale and on letting — — label C at the “première étape” step — and a measured air permeability Q4Pa-surf ≤ 1.20 m³/(h·m²)Effinergie guide of 26.06.2024 (order of 3 October 2023): DPE class A or B, i.e. < 110 kWhEP/(m²·yr) and < 11 kgCO₂e/(m²·yr); the “première étape” step: class C, < 180 and < 30.Collectif Effinergie — Guide d'application du label BBC Effinergie rénovation (arrêté du 3 octobre 2023)2024-06-26 · accessed 2026-09-04, triple glazing is almost always required in the cross-border Geneva area.
03 — The decisive factor
The position in the wall — more decisive than the glazing chosen
This is the most important technical point in this dossier, and the least visible in manufacturers' catalogues. The quoted Uw is calculated under standardised laboratory conditions (EN ISO 10077-1) — the window set in a test frame, with no real wall around it. That figure says what the product does. It does not say what the window does once installed in your wall.
The difference is ψinstallation — the linear transmittance of the thermal bridge created by the junction between window and wall. That thermal bridge depends directly on two parameters: the position of the window within the thickness of the wall, and the insulation of the reveals. The reveal is the return of the wall that frames the opening all the way round, between the window frame and the outer face of the façade — not the frame, not the glazing, not the sill, but the masonry itself seen in section around the window.
Three positions, three levels of real performance
Position 1 — Within the insulation plane (optimal)
The window sits within the thermal insulation plane of the wall — typically outboard, fixed in front of the loadbearing wall rather than within the thickness of the masonry (set out in §04), where external insulation is applied at the same time, or in the plane of the internal insulation where the wall is insulated from inside. The reveals are covered by the insulation system. ψinstallation is minimal: the installed performance comes close to the product Uw. This is the reference configuration for any refurbishment aiming at Minergie-P, EnerPHit or HPE/THPE in Geneva.
Position 2 — Mid-wall, partially insulated reveal
ψinstallation ≈ 0.06–0.10 W/(m·K) — an acceptable compromise
The window sits at mid-thickness of the masonry wall, with 3 to 5 cm of reveal insulation (PUR board or rigid mineral wool). The reveal thermal bridge is reduced but not eliminated. On an ordinary window (installation perimeter ≈ 5 m), a ψinstallation of 0.08 adds 0.40 W/K to the losses — degrading the effective Uw by roughly +0.25 W/(m²K). Acceptable if the product Uw is ≤ 0.70.
Position 3 — Set back inboard, bare reveal (to be avoided)
ψinstallation ≈ 0.10–0.15 W/(m·K) — performance wiped out
The window replaces the old joinery in the same position (on the inner face of the wall) with no reveal insulation. It is the simplest installation to carry out in refurbishment — and the most common where no design engineer is involved. The masonry reveal (brick, concrete) forms a continuous thermal bridge all round the window. On the same window as above: an extra +0.60 to +0.75 W/K. Triple glazing at Ug = 0.55 installed this way can end up performing no better than ordinary double glazing correctly set within the insulation plane.
5 m
typical installation perimeter for a 1.2 × 1.4 m window — the length over which ψinstallation acts
+0.50 W/K
additional heat loss for ψinstallation = 0.10 over that perimeter — equivalent to degrading the effective Uw by about +0.30 W/(m²K)
≠
catalogue Uw ≠ installed Uw: the gap between an optimal installation and an inboard one with no insulated reveal can exceed 0.5 to 1.0 W/(m²K)
Ordering windows at Uw = 0.70 and setting them into bare reveals means paying for performance you will never get. The design engineer has to sign off the position before the order, not after.
In Geneva: HPE and the installed Uw
The HPE standard of REn art. 12B is not the same thing as Minergie®REn art. 12B: the Minergie® label or any equivalent label; or the MoPEC 2014 and SIA 380/1:2016 limit values; or CECB® class B/B; or a variant at 80% of the heating demand. The page wrote "HPE = Minergie®".rsGE L 2 30.01, silgeneve.ch — REn — Règlement d'application de la loi sur l'énergie, art. 12B et 12Caccessed 2026-09-02: the label is only one of the admissible variants, alongside compliance with the MoPEC 2014 and SIA 380/1:2016 limit values, the CECB® B/B class, and a variant at 80% of the heating demand. All of them are assessed on the overall energy balance of the building, not component by component. But the SIA 380/1 calculation does include linear thermal bridges — a high ψinstallation across all the windows can tip an HPE balance below target. On a Geneva rental building with 30 windows and a total perimeter of 150 m, moving from ψinstallation = 0.12 to 0.04 means cutting losses by 12 W/K, of the order of 1,000 kWh of heating a year in the Geneva climateOrder of magnitude: 12 W/K multiplied by roughly 90,000 K·h of annual degree-hours. The page said "100 to 150 kWh/m²·year", two orders of magnitude higher. The degree-hours are not sourced here.Source to be established — unverified figure. That alone does not decide an HPE balance, but it is a free item: it costs nothing beyond having been specified before the order.
04 — Preparing for external insulation
Outboard installation — preparing tomorrow's façade without blocking today's works
Outboard installation means fixing the window in front of the load-bearing wall — projecting on the outside — rather than within the thickness of the masonry. The window then sits in the intended insulation plane, present or future, and the reveals are covered by the insulation system. It is the standard configuration for any refurbishment with simultaneous external insulation; it is also the position to adopt when external insulation is expected in the medium term (3 to 10 years) but not yet decided.
Why outboard installation is the right decision in a partial refurbishment
Replacing the windows in the old position (on the inner face of the wall) while planning future external insulation creates a junction problem that is hard to solve: once the insulation goes on, the reveals will be too short to cover the full depth of wall plus insulant. Either the reveals are extended with made-up pieces (thermal bridge retained, heavy finishing work), or they are left bare (thermal bridge and condensation risk). New windows installed in the old position become an obstacle to the full façade refurbishment.
With outboard installation from the moment the joinery is replaced, the window is already in the right position for the future external insulation, which then meets the outer face of the frame cleanly. No additional reveal work is needed. ψinstallation drops immediately to 0.03–0.05 W/(m·K) — even before the insulation goes on — because the wall-to-frame junction sits at the outer face of the wall, where the thermal resistance is greatest.
The technical conditions for outboard installation
Technical
Fixing bracket
An outboard window is fixed to the load-bearing wall by metal brackets (stainless steel or anodised aluminium, thermally broken where possible). The fixing has to carry the permanent loads (glazing weight) and the variable loads (wind, operation). Sizing to EN 1991-1-4 for wind-exposed sitesNF EN 1991-1-4, Eurocode 1 part 1-4: "donne les bases pour l'évaluation de l'action du vent sur les structures des bâtiments et des ouvrages de génie civil". To be read with the national annex.AFNOR Éditions — NF EN 1991-1-4 — Eurocode 1 : actions sur les structures — Partie 1-4 : actions générales, actions du vent2005-11 · accessed 2026-09-02. Thermally broken bracket systems exist and reduce the thermal bridge of the fixing itself.
Technical
Airtightness and watertightness
The frame-to-wall junction has to be airtight on the inside (sealing tape or acrylic sealant) and watertight with drainage on the outside (impregnated pre-compressed sealing tape or EPDM strip). The ABC rule: Airtight on the inside — Backfilled with insulation in the middle — resistant to the Climate on the outside, vapour-open and watertight. In refurbishment this detail is routinely sacrificed to speed of execution — it is the origin of most water ingress on replaced windows.
Caution
Appearance and acceptance
An outboard window on a still-uninsulated wall visibly projects — it can surprise the building owner or the tenants if it has not been anticipated and explained. Communicating the logic of preparing for later insulation, in advance, is essential. In practice a 3 to 6 cm projection is barely noticeable on a façade — but a 15 cm projection to anticipate thick external insulation has to be presented and approved in the project file.
Caution
LCI art. 114A — external insulation outside the building envelope limits
In Geneva, LCI art. 114A para. 3 provides that the thickness of external insulation counts neither towards the building envelope limits nor towards the distancesLCI art. 114A para. 3: "l'épaisseur de cette isolation n'est pas prise en compte, ni dans le calcul du gabarit, ni dans celui des distances aux limites de propriété ou entre constructions".rsGE L 5 05, texte consolidé sur lexfind.ch — LCI, art. 114A — Isolation périphérique de constructions existantesaccessed 2026-08-29 to property boundaries or between buildings. This makes outboard installation followed by external insulation easier: the projection of window and insulant burdens neither the envelope limits nor the boundary distances. Watch para. 2 however: the exclusion from the floor area ratio granted by para. 1 falls awayLCI art. 114A para. 2: para. 1 “n'est pas applicable si les constructions bénéficient de rapports de surface augmentés en raison de la reconnaissance de la haute performance énergétique selon l'article 59, al. 1 et 4”.rsGE L 5 05, texte consolidé sur lexfind.ch — LCI, art. 114A — Isolation périphérique de constructions existantesaccessed 2026-09-04 if the building already claims the HPE/THPE bonus of art. 59. Check with the building permit office (OAC)ge.ch: the OAC, part of the territorial department, processes and decides building permit applications. The OCBA is the cantonal buildings office — a client body, not a permitting authority.République et canton de Genève, département du territoire — Office des autorisations de construire (OAC)accessed 2026-09-02 whether the building is in a protected zone, or whether the projection alters the appearance of the façade.
05 — The Geneva regulations
Reveals and RCI art. 56A — the Geneva provision that is often misread
The RCI (implementing regulation of the law on constructions and various installations, rsGE L 5 05.01) contains, in its article 56A headedrsGE L 5 05.01: the implementing regulation of the LCI is abbreviated RCI. Its art. 56A, "Isolation des embrasures en façade", covers "vitrages, cadres de fenêtres, caissons de stores, etc.". "RALI" does not exist.rsGE L 5 05.01, silgeneve.ch — RCI — Règlement d'application de la loi sur les constructions et les installations diverses, art. 56 et 56Aaccessed 2026-09-02 "Isolation des embrasures en façade" — insulation of façade reveals — energy requirements specific to glazing, window frames and blind boxes. The article extends RCI art. 56, which requires the thermal quality of the envelope to comply with the SIA 380/1 standardRCI art. 56: "La qualité thermique de l'enveloppe du bâtiment doit, sauf cas particulier, être conforme à la norme SIA 380/1 en vigueur".rsGE L 5 05.01, silgeneve.ch — RCI — Règlement d'application de la loi sur les constructions et les installations diverses, art. 56 et 56Aaccessed 2026-09-02 in force — but it targets explicitly the façade assembly around the opening.
What RCI art. 56A says in practice
Paragraph 1 covers new buildings. Paragraph 2 is the one that concerns refurbishment: reveals of an existing building that give onto heated rooms must be brought into compliance as soon as their thermal transmittance U reaches or exceeds 3.0 W/(m²K)RCI art. 56A para. 2: reveals giving onto heated rooms are to be brought into compliance "lorsque leur coefficient de transmission thermique U est égal ou dépasse 3,0 W/(m2 K)", by 31 January 2016 at the latest.rsGE L 5 05.01, silgeneve.ch — RCI — Règlement d'application de la loi sur les constructions et les installations diverses, art. 56 et 56Aaccessed 2026-09-02, so as to comply with SIA 180 and SIA 380/1 and with the sound reduction requirements of SIA 181 — work that was to be carried out by 31 January 2016 at the latest. Paragraph 3 refers to SIA 180 for airtightness. That 3.0 W/(m²K) threshold is the value of single glazing: the article targets first of all the stock still fitted with original joinery. A window replacement that leaves the reveal bare therefore does not automatically breach article 56A — but it hollows out the SIA 380/1 requirement to which the article refers, and it opens the condensation risk described below.
Paragraphs 4 and 5 deal with heritage: for buildings in a protected zone, listed, entered in the inventory of buildings worthy of protection, or covered by a site plan under the LPMNS, compliance work is carried out in the original materials, with profile dimensions and glazing subdivisions respecting the architecture of the building. Four exceptions are allowed: replacing the glazing alone with glazing at U ≤ 1.0 W/(m²K) while keeping the joinery, making a new window "in the old manner" with the same glazing, adding a second single-glazed outer window, or adding a second inner window at U ≤ 1.0 W/(m²K). Paragraph 6 further allows waivers where the requirements are disproportionate: they are granted on written request by the office responsible for energy (OCEN), by administrative decision within 3 months and after consultation of the servicesRCI art. 56A para. 6: waivers "sont accordées sur demande écrite par l'office chargé de l'énergie, par voie de décision administrative, dans un délai de 3 mois, sur préavis des services concernés".rsGE L 5 05.01, silgeneve.ch — RCI — Règlement d'application de la loi sur les constructions et les installations diverses, art. 56 et 56Aaccessed 2026-09-02 concerned — a waiver has to be applied for, it is never assumed.
Insulating the reveals — the common technical solutions
Solution
Typical thickness
λ of the material
Applicability
Rigid PUR/PIR board
3–6 cm
0.022–0.026 W/(m·K)
Best performance per centimetre — ideal where the depth of the reveal is constrained. Plaster finish or PVC reveal profile.
Graphite EPS board (λ 031)
4–8 cm
0.031 W/(m·K)
The external-insulation standard for reveals. Good compatibility with existing render systems. Economical.
Rigid mineral wool
5–8 cm
0.035–0.040 W/(m·K)
Good moisture resistance, suited to damp reveals. Thicker than PUR for the same thermal resistance.
PVC or aluminium reveal profile without insulation
—
Thermal bridge retained
Not reveal insulation at all. The masonry thermal bridge stays active: ψinstallation unchanged, condensation risk retained.
Indicative minimum thicknesses to reach ψinstallation ≤ 0.05 W/(m·K) on an ordinary masonry reveal (hollow brick, concrete wall). To be verified by calculation to EN ISO 14683 on the actual junction detail. Source: EN ISO 14683:2017 and NRG positive field practice.
Condensation on the reveals — the warning signal
Traces of condensation on the reveals after a window replacement do not point to a faulty product: they point to an untreated reveal thermal bridge. Condensation forms wherever the internal surface falls below the dew point of the indoor air. On an uninsulated masonry reveal with a high-performance window (product Uw ≤ 0.8), the surface temperature of the reveal can fall to 8–12 °C in winter — well below the dew point at 20 °C and 60% RH (≈ 12 °C). Mould follows within 6 to 18 months. It is the opposite of what was expected from replacing the windows.
Caution: the building owner's responsibility
In Geneva, where condensation or mould damage appears in the reveals after a window replacement, tenants can hold the absence of reveal insulation against the building ownerA legal characterisation with no citable article or case law. The original wording invoked civil liability; it has been toned down pending a legal review. See point 3 of the arbitration report.Source to be established — unverified figure — regardless of whether manufacturer and installer complied with the product's installation rules. Energy compliance of the works within the meaning of RCI art. 56 and 56A rests with the building owner, not the manufacturer.
French-speaking Switzerland outside Geneva
Vaud, Valais, Fribourg and Neuchâtel apply MoPEC 2014 through their own cantonal regulations, all anchored on SIA 380/1:2016 — MoPEC 2025 was adopted by the Conference of Cantonal Energy Directors on 29 August 2025EnDK, statement of 29 August 2025: the plenary assembly adopts the 2025 model energy provisions. These are recommendations to the cantons, in force only once transposed into cantonal law.EnDK — Conférence des directeurs cantonaux de l'énergie — Les cantons adoptent le Modèle de prescriptions énergétiques 20252025-08-29 · accessed 2026-09-02 and still has to be transposed canton by canton. Reveal insulation is not always spelled out there in an article equivalent to Geneva's RCI art. 56A — but it is implicitly required as soon as the limit value U ≤ 1.0 W/(m²K) for windows against the outside has to be demonstrated. Calculating the junction thermal bridge (EN ISO 14683) is part of the Minergie file.
Neighbouring France — DTU and labels
In France, DTU 36.5 (external joinery) governs the installation of windowsNF DTU 36.5 P1-1, "Travaux de bâtiment — Mise en œuvre des fenêtres et portes extérieures — Cahier des clauses techniques types", April 2010: new build and refurbishment, fixed on at least two opposite sides.AFNOR / Norm'Info — NF DTU 36.5 P1-1 — Travaux de bâtiment — Mise en œuvre des fenêtres et portes extérieures — Cahier des clauses techniques types2010-04-01 · accessed 2026-09-02. Reveal insulation is not systematically imposed by the DTU alone, but it is needed to reach the performance of the BBC Effinergie Rénovation 2024 label. In that framework the design engineer has to calculate the junction thermal bridge — files without reveal insulation do not pass Effinergie's review.
06 — The order of decisions
The classic mistake: ordering the windows before deciding the façade
This is the most frequent mistake seen on the ground in Geneva and French-speaking Swiss residential refurbishment, and the hardest to put right afterwards. New windows set in the wrong position create constraints that can last 20 to 30 years — their technical service life. Understanding why the mistake happens is what makes it preventable.
Why the mistake happens
Main cause
Windows are the most visible defect
Condensation, draughts, glazing that fogs up in winter: degraded windows are noticed immediately by the occupants, who ask for them to be replaced. The decision is taken on the basis of what is felt, not of an overall assessment. The building owner orders the windows with no prior energy balance — and often without even knowing that external insulation would be relevant.
Main cause
A window quotation is easy to get
A window manufacturer can send a quotation in 48 hours. A CECB® Plus takes weeks. The decision follows the fastest quotation — not the most complete assessment. With no owner's adviser or design engineer appointed early on, the building owner proceeds on the information available, which is the sales information.
In a rental building, the owner or the managing agent decides on the windows on a maintenance signal. The strategic decision (external insulation, HPE, Minergie) belongs to another level — often a deliberative body (owners' meeting, foundation board) with a longer decision cycle. Operational decisions come before strategic ones, creating expensive faits accomplis.
Common cause
Unawareness of the position problem
Joiners set the window where the old one was — that is their trade, not their role to prescribe the façade strategy. Absent instructions to the contrary from the design engineer, the window goes back at the same depth. Outboard installation is technically more demanding and less profitable for the contractor — it will never be offered spontaneously if it is not specified.
The recommended order of decisions
Step 1 — Overall assessment before any decision
CECB assessment or PHPP balance — setting the trajectory
In Geneva, the CECB® and the CECB® Plus have to be submitted to obtain the grant decision on measure M-10GEnergie, conditions of measure M-10: "Le certificat CECB® et le CECB® Plus doivent être fournis pour obtenir la décision de subvention".GEnergie, OCEN, République et canton de Genève — Amélioration de la classe CECB® pour l'enveloppe et pour l'efficacité énergétique globale — mesure M-10accessed 2026-09-02, the one that rewards a class improvement. The CECB gives the current classes and the gap to close. A PHPP balance (where the target is Minergie-P or EnerPHit) makes it possible to simulate the effect of the various measures in their order and combination. The cost of a CECB® Plus bears no comparison with the cost of a position mistake, which is paid over the twenty to thirty years of the window's life, in excess consumption and remedial work.
The façade strategy determines where the windows go
Three scenarios determine where the windows go. (A) Immediate external insulation — windows within the insulation plane, installed at the same time. (B) External insulation in 3 to 10 years — outboard installation prepared in advance, brackets and sill sized for the future insulation thickness, reveals left accessible for the later junction. (C) No external insulation planned — internal insulation or no wall insulation at all: windows at mid-wall with maximum reveal insulation. Scenario (B) is the most delicate, because it requires a decision on the likely future of the façade — a decision the building owner has to take deliberately, not by default.
Step 3 — Technical specification of the windows according to position
Target Uw, Ug, ψg, reveal, bracket — the complete specification
Once the position is settled, the specification becomes precise: target product Uw (worked back from the required installed Uw plus the expected ψinstallation), minimum Ug and ψg, reveal system, bracket type where outboard, sealing detail (the ABC rule). The joinery contractor's quotation answers that specification — not the other way round.
Step 4 — Ordering and coordinated installation
Joinery, reveals and façade: a single works sequence
Joinery replacement and reveal insulation are carried out by the same contractor, or within the same works package. Where outboard installation goes together with external insulation, the insulation contractor is on site for the junction. Handover includes a check of the junction details; where the target is Minergie, the airtightness measurement (Blower Door test) is to be entrusted to an accredited provider. No window installed without its insulated reveal — the two are a single item of work.
Step 5 — File and grants
GEnergie and the Buildings Programme: one counter, one documented file
In Geneva, grants go through a single counter, GEnergie, the cantonal portal for energy grants: the federal Buildings Programme co-finances the cantonal measures and its platform is the submission route. The measure that rewards an envelope refurbishment is M-10, CECB® class improvement: CHF 60 to 390 per m² of energy reference area depending on use and on the number of classes gained, with a minimum of two classesGEnergie, measure M-10: CHF 150 to 390/m² for single-family housing, 90 to 210 for collective housing, 60 to 150 for other uses, minimum "+2 classes". The page said "20 to 30 CHF/m² per year saved".GEnergie, OCEN, République et canton de Genève — Amélioration de la classe CECB® pour l'enveloppe et pour l'efficacité énergétique globale — mesure M-10accessed 2026-09-02, on the envelope and on overall energy efficiency. In neighbouring France, window replacement has not been fundable by MaPrimeRénov' under the single-measure track since 1 September 2026; it survives only within a deep renovation. The files require documentation of the installation (photographs, junction details) — documenting during the works is easier than afterwards.
The order of decisions is not an administrative detail. It is the difference between a refurbishment that performs and an expensive one that does not keep its promises.
The question to ask before ordering any window
"In five to ten years, are you going to insulate the façade from the outside?" If the answer is "probably yes" or "we don't know yet", the window belongs in a prepared outboard installation with the reveal thought through. If the answer is "no, definitively" (protected heritage, documented budget constraint, internal insulation planned), then the inboard position with maximum reveal insulation is the right one. The only wrong answer is not to ask the question.
07 — Questions from professionals and building owners
What professionals and building owners ask
What minimum Uw does Geneva law require when replacing windows?
The U limit value for windows against the outside, under SIA 380/1:2016 and MoPEC 2014 to which RCI art. 56 refers, is 1.0 W/(m²K) — the same in new build as in refurbishment. That is the legal minimum. RCI art. 56A adds, for existing buildings, an obligation to bring the reveal into compliance as soon as its U reaches 3.0 W/(m²K). The HPE standard of REn art. 12B, for its part, sets no value per window: it is reached through the overall balance of the building, and in practice it presupposes triple glazing set within the insulation plane with an insulated reveal.
Why doesn't the manufacturer state ψinstallation in the quotation?
Because ψinstallation depends on the wall the window is set into — and the manufacturer does not know your wall. EN ISO 14683:2017 publishes tabulated values by junction typeEN ISO 14683:2017: "simplified methods for determining heat flows through linear thermal bridges at junctions of building elements", with tabulated default values.NBN / Buildwise — NBN EN ISO 14683 — Ponts thermiques dans les bâtiments — Coefficient linéique de transmission thermique — Méthodes simplifiées et valeurs par défaut (ISO 14683:2017)2017 · accessed 2026-09-02 (concrete wall, brick, timber frame and so on) for different window positions. Those values allow ψinstallation to be determined without numerical simulation. It is the responsibility of the design engineer or the specifier to bring that parameter into the specification — and to check that the installing contractor follows the detail prescribed.
Can windows be claimed under the federal Buildings Programme without external insulation?
Yes, but rarely on their own. In Geneva the measure that rewards an envelope refurbishment is M-10: it requires a gain of at least two CECB® classes, on the envelope and on overall energy efficiency, and pays CHF 60 to 390 per m² of energy reference area depending on use. But the CECB class improvement is calculated across the whole envelope, not on the windows alone. Replacing only the windows without touching the opaque elements rarely yields a 2-class CECB improvement on a building from the 1960s to 1980s — the jump usually comes from wall insulation combined with the windows. Better to simulate the scenarios before settling the order of works.
What if the windows have already been replaced in the wrong position?
Two options depending on the situation. (1) If external insulation is planned: the insulation contractor can usually run the insulant out to the outer face of the frame and dress the reveals from outside — the thermal bridge is partly corrected, even though the window is not in the insulation plane. The result is not as clean as outboard installation, but the improvement is real. (2) If no external insulation is planned: insulate the reveals from inside, PUR board of at least 3 to 5 cm bonded to the masonry reveal, plaster finish. ψinstallation will not be optimal, but the condensation and the mould go away. In both cases the correction is decided by reading the building and its actual junction detail, not a catalogue.
Do triple-glazed timber windows last as well as PVC in the Geneva climate?
Contemporary timber frames (glue-laminated timber, pressure treatment or microporous paint) have a service life comparable to PVC in the Geneva climate, provided they are properly maintained (paint or stain according to the manufacturer, typically every 8–12 years on exposed faces). The technical advantage of timber is its naturally lower Uf compared with standard PVC: an 80 mm solid timber frame reaches Uf ≈ 0.90–1.0 W/(m²K) with no thermal break, where standard PVC sits at 1.2–1.4. Timber-aluminium frames combine timber inside (low Uf) with anodised aluminium outside (minimal maintenance) — the standard option on Minergie-P projects.
How does window replacement fit into an HPE or Minergie project in Geneva?
Replacing the windows alone is not enough to reach HPE — it belongs within an overall envelope strategy. And HPE does not mean Minergie®: REn art. 12B admits the Minergie® label or any equivalent label, but also compliance with the MoPEC 2014 and SIA 380/1:2016 limit values, the CECB® B/B class in new build or C/B in refurbishment, or a variant at 80% of the heating demand. In a coordinated project the windows are defined consistently with the walls and the roof, and the specification (installed Uw, ψinstallation, reveal) serves the variant chosen. The floor area ratio bonus of LCI art. 59 para. 1 — 25%, raised to 27.5% for high energy performance and to 30%LCI art. 59 para. 1: the area "peut être portée à 27,5% lorsque la construction est conforme à un standard de haute performance énergétique, respectivement à 30%". It is para. 1, not para. 4.rsGE L 5 05, silgeneve.ch — LCI — Loi sur les constructions et les installations diverses, art. 59 al. 1accessed 2026-09-02 for very high energy performance — depends on the standard the building reaches, not on the windows alone. Weighing up those variants before ordering the windows is precisely what advice is for.
When is the right moment to bring in NRG positive on a window replacement?
Before opening the first manufacturer's quotation. Early involvement — reading the building, setting the façade strategy, drafting the technical specification — is the shortest and the cheapest. A visit of 2 to 3 hours on site is enough to settle the optimal position of the windows, the target installed Uw, the treatment of the reveals and the coordination with any future external insulation. That step avoids irreversible decisions taken too early — and it determines whether the cantonal and federal grant applications will stand. Talk about your project →
Key points
What to take away, and in what order to act
Ask the façade question before any quotation. "Will you insulate externally in five to ten years?" A "we don't know yet" already calls for outboard installation.
Have the diagnosis done first. CECB or CECB Plus in Geneva, a PHPP balance where the target is Minergie-P or EnerPHit: the trajectory comes before the product.
Specify the position, then the product. The Uw to order is calculated backwards, from the installed Uw sought and the ψinstallation expected at the junction.
Never buy a window without its insulated reveal. The two are a single item of work; a bare reveal brings back condensation and mould within 6 to 18 months.
Document the installation as the work proceeds. Photographs and junction details: grant files require them, and after the fact they cannot be obtained.
GenevaRCI art. 56 and 56A: SIA 380/1 for the envelope, reveals brought into compliance above 3.0 W/(m²K), heritage derogations on written request to the OCEN. External insulation outside the building profile.
SwitzerlandMinergie sets no Uw or Ug per component: the window is judged by the overall balance and by the qE50 of the envelope. The "Minergie-P Uw of 0.80" appears in no set of rules.
Neighbouring FranceSince 1 September 2026, window replacement has left the parcours par geste of MaPrimeRénov': it is fundable only within a rénovation d'ampleur.
Sources and references (32)
Every figure and every claim in this dossier links back to its source. Hover or tap a footnote marker to see it.
Source to be established — unverified figure A market order of magnitude, depending on manufacturer, format and year. No open primary source supports it. See point 4 of the arbitration report.
Source to be established — unverified figure Order of magnitude: 12 W/K multiplied by roughly 90,000 K·h of annual degree-hours. The page said "100 to 150 kWh/m²·year", two orders of magnitude higher. The degree-hours are not sourced here.
Source to be established — unverified figure A legal characterisation with no citable article or case law. The original wording invoked civil liability; it has been toned down pending a legal review. See point 3 of the arbitration report.
Settle the order of works before you order your windows
The position in the wall, the insulation of the reveals and the coordination with the façade strategy are settled before the order — not after. Advice from NRG positive: reading the building, technical specification, coordination between external insulation and joinery, weighing up the standards — SIA 380/1, HPE, Minergie®, EnerPHit — for Geneva and French-speaking Switzerland.