Published 12 June 202612 min readIWI · HygrothermalLCI 114A · RCI 56A · SIA 180Updated June 2026
Insulating from the inside without creating defects
A protected façade, a co-ownership that cannot decide, architectural expression to preserve: when external insulation is not possible, internal wall insulation (IWI) remains the way forward. It is the most demanding insulation technique to design — not because it is complicated to install, but because it changes the physics of the wall. This guide explains when IWI is justified, what happens inside the wall, which systems to choose, and where defects arise.
When IWI is required — and when it should not be used
Let's say it clearly from the outset: external wall insulation (EWI) remains the reference solution whenever it is possible. It keeps the wall warm, addresses thermal bridges continuously, and does not consume living space. Geneva law points in the same direction: the LCI art. 114A specifies that the thickness of external insulation added to an existing building is not counted in the floor area ratio, in the building envelopeLCI (L 5 05) art. 114A: peripheral insulation of an existing building counts neither towards floor area ratios, nor the building envelope, nor boundary distances — unless an HPE floor-area bonus was already granted.République et canton de Genève (via Lexfind) — Loi sur les constructions et les installations diverses (LCI), L 5 05, art. 114A1988-04-14 · accessed 2026-08-20, or in the distances to property boundaries. In other words, in Geneva, building envelope limits are no longer an argument against EWI.
IWI is therefore not a matter of convenience — it is the option left when the façade cannot change. Four typical situations:
Heritage
Protected or high-value façade
Protected zones, 19th- and early-20th-century ensembles, buildings with mouldings, dressed stone or exposed molasse sandstone: covering the façade is excluded or rejected at the preliminary review stage. IWI becomes the only way to insulate the walls.
Co-ownership
Collective decision not achievable
The façade is a common part: EWI requires a decision by the condominium association and collective financing. An owner renovating their unit can, however, insulate from the inside — provided it does not create a defect for the building.
Partial intervention
An apartment, a room, a unit
Renovating a single dwelling, converting an attic or fitting out ground-floor commercial space: scaffolding and a façade site are not justified. IWI makes it possible to act at the scale of the unit, at the pace of the interior works.
Complement
Specific walls within a wider project
Even in a renovation using EWI, some walls are only accessible from the inside: party walls that have become external, walls onto a narrow courtyard, gable walls at the boundary. IWI then completes the envelope strategy.
Insulating from the inside means moving the cold into the wall. The question is not whether water vapour will get in — but how it will get back out.
What about French-speaking Switzerland and neighbouring France?
The logic is the same everywhere: EWI by default, IWI when the façade is constrained. In the French-speaking cantons, municipal regulations and heritage inventories (architectural surveys) play the role of Geneva's protected zones. In neighbouring France, the Architectes des Bâtiments de France (ABF) often require IWI within protected perimeters; MaPrimeRénov' supports wall insulation mainly through the "rénovation d'ampleur" pathwayFrance Rénov': in the 'rénovation d'ampleur' pathway, support by a Mon Accompagnateur Rénov' is compulsory and at least two insulation measures (walls among them) are required.France Rénov' — Anah / Ministère de la Transition écologique — MaPrimeRénov' pour une rénovation d'ampleur2026 · accessed 2026-08-20, which is compulsorily supervised by a Mon Accompagnateur Rénov'.
02 — Understanding before insulating
Wall physics: what IWI changes
An uninsulated old wall is crossed by a constant flow of heat. This waste has a useful side effect: the wall stays warm and dry. IWI interrupts this flow — that is the point — but it simultaneously places the entire masonry on the cold side. In winter, a wall that used to sit at 12–15 °C behind the plaster can drop close to the outdoor temperature behind the insulation.
The dew point migrates into the wall
Indoor air contains water vapour (cooking, showers, occupants). This vapour diffuses through the materials, from the warm inside to the cold outside. As long as the temperature inside the wall stays above the dew point, the vapour remains gaseous. But behind an IWI system, the temperature drops sharply at the interface between the insulation and the wall: if enough vapour reaches it, it condenses there. This is interstitial condensation — invisible, because it occurs behind the lining.
The consequences develop silently: dampening of the masonry, mould on the hidden face of the lining, corrosion of the fixings, frost damage to porous materials — and, in old buildings with timber floors, rot in the joist ends embedded in the now cold, damp wall.
In internal wall insulation, dynamic hygrothermal simulation (such as WUFI, per EN 15026) is the rule and not the exceptionEN 15026 sets the minimum criteria for software modelling coupled transient heat and moisture transport; Fraunhofer IBP states WUFI meets all of its requirements (deviation < 2.5 %).Fraunhofer IBP — WUFI — Benchmark test of EN 150262016 · accessed 2026-08-20: WTA leaflet 6-4 prescribes moisture-protection verification by coupled heat and moisture transport calculation (WTA 6-1, 6-2 and 6-5). It models temperature, humidity, rain and drying hour by hour over several years. It is a few days' study — set against the cost of a lining that has to be removed because of mould.
The two risk criteria to demand from the study
A hygrothermal study is not judged on a reassuring conclusion but on two quantified criteria. Mould: the surface relative humidity, indoors and at every interface within the wall, must stay below 80 % as a monthly meanISO 13788:2012 § 5.1: 'There is a risk of mould growth when monthly mean surface relative humidities are above a critical relative humidity, φsi,cr, which should be taken as 0,8'.ISO — ISO 13788:2012 — Internal surface temperature to avoid critical surface humidity and interstitial condensation (extrait officiel, § 5.1)2012 · accessed 2026-08-20 — this is the φsi,cr = 0,8 criterion of EN ISO 13788, refined by the Sedlbauer isopleths, which combine humidity, temperature and exposure time. Timber decay: the moisture content of embedded joist ends must remain durably below 20 % by massAQC pathology sheet 'Attaques des bois par les agents biologiques': wood-destroying fungi develop above a durably sustained moisture content of about 20 % in the timber.AQC — Agence Qualité Construction — Fiche pathologie bâtiment — Les attaques des bois par les agents biologiques2013 · accessed 2026-08-20, the threshold above which wood-destroying fungi develop. Both figures must appear in black and white in the report, backed by multi-year curves.
NRG positive rule of caution
No IWI on a wall whose moisture condition is unknown. Rising damp, a cracked façade, exterior render not watertight against driving rain: these defects must be diagnosed and treated before the insulation is installed. IWI installed on a damp wall systematically makes the situation worse — the insulation removes drying to the inside and cools the wall.
03 — Choosing a system
IWI systems: four families, two philosophies
All IWI systems answer the same question — how to manage water vapour — but according to two opposing philosophies: blocking the vapour before it reaches the cold wall (vapour barrier), or letting it in and redistributing it so it gets back out without damage (capillary-active materials). The choice depends on the wall, its exposure, and the execution reliability that can be guaranteed.
Framing + plasterboard lining · philosophy: block the vapour
The most economical and widespread system. Its reliability rests entirely on the absolute continuity of the vapour barrier: every joint, every penetration, every electrical outlet must be sealed. High-performing on paper, it is not very forgiving of execution defects — a punctured vapour barrier concentrates vapour on a few points of the cold wall. Best reserved for low-risk walls and contractors experienced with the technique.
Insulation-plasterboard composite boards (PUR, EPS or mineral wool laminated to plasterboard) fixed with adhesive dabs. Quick to install, they minimise the loss of floor area thanks to high-performance insulation. Points requiring attention: the joints between panels and the air gaps behind the adhesive dabs, which can short-circuit the vapour retarder. Careful panel layout and treated joints are essential.
Full-surface bonding + mineral render · philosophy: manage moisture
Porous mineral panels bonded over their full surface, without a vapour barrier: any condensation is absorbed by capillarity, redistributed and released back into the indoor air during dry periods. Less insulating per centimetre, more expensive, but tolerant of defects and the unexpected — this is the reference system for old walls and heritage buildings. Full-surface bonding (no air gap) is essential for it to work.Calsitherm: boards must be bonded 'hohlraumfrei und vollflächig' (void-free, full-surface); dab or partial bonding is not system-compliant and causes uncontrolled condensation behind the insulation.Calsitherm Silikatbaustoffe GmbH (fabricant — prescription de mise en œuvre) — CALSITHERM Klimaplatte — Technische Hinweise 20182018 · accessed 2026-08-20
Humidity-variable vapour retarder · good hygric behaviour
Wood fibre panels with a humidity-variable vapour retarder (which opens to diffusion in summer to let the wall dry out), or hemp concrete sprayed directly onto the masonry. Good hygroscopic capacity, compatible with old masonry, and consistent with Geneva's priority for low-embodied-carbon materials (LCI art. 117)LCI art. 117: 'Any construction or significant renovation must be designed and built with materials that minimise its carbon footprint'; art. 118 sets the calculation method.Office cantonal de l'architecture / EPIQR+ — Articles 117-118 LCI — présentation de Francesco Della Casa, architecte cantonal, République et canton de Genève2024-03-14 · accessed 2026-08-20. Like all systems, they require careful hygrothermal design.
The two figures that decide: µ and sd
The vapour permeability of a material is read from its water vapour diffusion resistance factor µ (dimensionless, µ = 1 for air) and from its sd value = µ × thickness, expressed in metres of equivalent air layer. Conventional vapour barrier: sd above 15 m. Humidity-variable vapour retarderPassipedia (PHI), interior insulation: 'a minimum value of more than 15 m should be complied with for the effective water vapour diffusion-equivalent thickness' of the vapour barrier.Passipedia — Passive House Institute — Thermal protection using interior insulation2019 · accessed 2026-08-20: variable sd, around 0,25 m in summerpro clima INTELLO product data: humidity-variable sd from 0.25 m (summer, wall drying out) to over 25 m (winter, wall protected). Typical range for humidity-variable vapour retarders.Eurabo (distributeur — donnée produit pro clima) — pro clima INTELLO — frein-vapeur hygrovariable, valeur Sd 0,25 à >25 m2024 · accessed 2026-08-20 — when the wall must dry inwards — rising above 10 m, and up to 25 m, in winter, when it must be protected. Capillary-active materials: µ ≈ 2–3 for calcium silicate and mineral boardsMultipor technical data sheet: µ = 2 (λD 0.042) to µ = 3 (λD 0.045/0.047). Calsitherm Klimaplatte: µ = 3 per European approval, 3.6 measured. Materials effectively open to diffusion.Xella / Multipor (fabricant — donnée produit) — Multipor Mineraldämmplatte — Technisches Datenblatt2023 · accessed 2026-08-20, hence effectively open to diffusion, which is precisely the point. Wood fibre for IWI: µ = 5.STEICO internal technical data sheet (wood fibre for IWI): µ = 5, λD = 0.038 W/(m·K), density 160 kg/m³, bonded over ≥ 80 % of the surface.STEICO SE (fabricant — donnée produit) — Fiche technique STEICO internal — isolant support d'enduit intérieur2021 · accessed 2026-08-20 A system is only coherent if the sd of the vapour control plane matches the drying capacity of the wall — the hygrothermal study establishes that, not the product data sheet.
How thick? Less than you think
In IWI, more insulation is not better: each additional centimetre cools the wall further and increases the risk of condensation and frost damage. Practice converges on moderate thermal resistances — typically 6 to 10 cm depending on the material — giving a renovated wall around U ≈ 0,25–0,40 W/(m²K). The SIA 380/1:2016 element-by-element limit value is 0,25 W/(m²K) for a wall undergoing conversion (0,17 W/(m²K) for a new element)Implementation guide EN-102 (SIA 380/1:2016): opaque element against outdoor air, limit value U = 0.17 W/(m²K) for new build and 0.25 W/(m²K) for conversion.Service de l'énergie et de l'environnement, République et canton de Neuchâtel — Aide à l'exécution EN-102 — Isolation thermique des bâtiments (SIA 380/1, édition 2016)2025-11 · accessed 2026-08-20: a well-designed IWI approaches that value from above without always reaching it — and the Geneva framework provides for this: RCI art. 56 (the implementing regulation of the LCI, rsGE L 5 05.01)RCI (rsGE L 5 05.01) art. 56: 'The thermal quality of the building envelope must, unless a particular case applies, comply with the SIA 380/1 standard in force.'République et canton de Genève — SILGeneve — Règlement d'application de la loi sur les constructions et les installations diverses (RCI), L 5 05.01, art. 561978-12-27 · accessed 2026-08-20 requires SIA 380/1 compliance "unless a particular case applies", and the justification can be based on the building's overall performance rather than element by element. The hygrothermal study sets the maximum admissible thickness — not the insulation catalogue.
IWI within a label strategy
A wall with IWI does not rule out an HPE renovation target (heating demand ≤ SIA 380/1 limit values increased by 50 %, REn art. 12BREn (L 2 30.01) art. 12B, HPE renovation, variant a): MoPEC 2014 weighted energy demand limits increased by 70 % and SIA 380/1 heating demand increased by 50 %.République et canton de Genève — SILGeneve — Règlement d'application de la loi sur l'énergie (REn), L 2 30.01, art. 12B2010-09-01 · accessed 2026-08-20), a Minergie® Rénovation certification, or an EnerPHit component-based approach — which explicitly provides for internal insulation with adapted requirementsUnconfirmed claim: the PHI document 'Criteria for the Passive House, EnerPHit and PHI Low Energy Building Standard' could not be opened. To be sourced or removed before publication.Source to be established — unverified figure. Performance lost on the walls is offset on the roof, windows, ventilation and airtightness.
04 — Where it is won or lost
Critical points: cross walls, window reveals, pipework, air
With EWI, the insulation wraps the building continuously. With IWI, the insulation plane is interrupted by the building's own structure: every cross wall, every slab, every window reveal crosses through the insulation. This is where heat flows — and defects — concentrate.
Critical
Cross walls and slabs: structural thermal bridges
Cross walls and slabs in contact with the façade wall remain connected to the cold wall. At these junctions, the surface temperature drops — leading to mould on ceilings and in corners. Treatment: insulation returns (Flankendämmung) of the order of 40 to 50 cm on the cross walls and slabsPassipedia (PHI): 'flanking insulation along the interior wall (ca. 40 cm)', with ≥ 20 mm at the window reveal and an insulation wedge on the underside of the slab.Passipedia — Passive House Institute — Thermal protection using interior insulation2019 · accessed 2026-08-20, their length confirmed by the thermal bridge calculation per EN ISO 10211, which checks surface temperatures.
Critical
Window reveals — RCI art. 56A
Jambs, lintels and roller shutter boxes are the coldest points of the insulated wall. RCI art. 56A subjects window reveals to specific energy requirements: in existing buildings, the U-value of the whole reveal — glazing, frame and roller shutter box — must be brought to 3,0 W/(m²K) or belowRCI art. 56A: reveals in existing buildings U ≤ 3.0 W/(m²K); in protected zones or listed buildings, the derogating variants (glazing only, heritage window, second internal window) require U ≤ 1.0.République et canton de Genève — SILGeneve — Règlement d'application de la loi sur les constructions et les installations diverses (RCI), L 5 05.01, art. 56A1978-12-27 · accessed 2026-08-20. In protected zones, and for listed or inventoried buildings, derogating variants are admitted on justification — replacing the glazing only, a new heritage window, a second internal window — each with a U-value ≤ 1,0 W/(m²K). In practice: insulate the jambs even with a thin layer (2–3 cm of a high-performance panel such as aerogel or thin calcium silicate) and treat the joinery-to-insulation junction as a continuous plane.
Caution
Pipework in the now-cold wall
A water pipe embedded in an external wall insulated from the inside ends up on the cold side — a freezing risk in winter. Water pipes must be moved to the warm side (within the lining or interior partitions). Electrical boxes, meanwhile, penetrate the vapour barrier: plan for sealed boxes or a service cavity in front of the airtightness plane.
Caution
Airtightness: no convection behind the insulation
If indoor air can circulate behind the insulation (an unsealed air gap, a lining not sealed at floor and ceiling), it carries its vapour directly onto the cold wall — convection transports far more moisture than diffusionpro clima (DIN 4108-type test): 0.5 g of water/m² per winter day by diffusion through an sd = 30 m vapour retarder, versus 800 g per metre of a 1 mm gap by convection — a factor of 1600.pro clima Suisse — Éviter les dégâts au bâtiment2020 · accessed 2026-08-20. The airtightness plane must be continuous and connected to the floor, ceiling and joinery. This is also a condition for real-world performance.
Joist ends: the detail that decides the system
In buildings with timber floors, the joists are embedded in the façade walls. After IWI, these embedments sit in the cold, potentially damp zone of the wall — rot in the joist ends is the most severe defect documented in internal insulationAQC pathology sheet 'Attaques des bois par les agents biologiques': wood-destroying fungi develop above a durably sustained moisture content of about 20 % in the timber.AQC — Agence Qualité Construction — Fiche pathologie bâtiment — Les attaques des bois par les agents biologiques2013 · accessed 2026-08-20. A dynamic hygrothermal check is mandatory — demonstrating that the moisture content of the embedded ends stays durably below 20 % by mass —, a capillary-active system is strongly recommended, and in some cases moisture monitoring of the embedments is warranted.
05 — Geneva context
IWI and Geneva heritage: the case of late-19th-century buildings
The Geneva building stock affected by IWI largely belongs to the urban ring dating from the late 19th and early 20th centuries: buildings in massive masonry — rubble stone, brick, dressed stone and molasse sandstone — with moulded façades, timber floors and generous ceiling heights. These buildings often fall within protected zones or protected ensembles under the LCI; work on them is subject to review by the CMNS (Commission des monuments, de la nature et des sites — Commission for Monuments, Nature and Sites), and covering the façades is generally excluded there.
Three particularities to factor in from the study stage
Molasse sandstone does not tolerate damp. Present in many Geneva plinths and door/window surrounds, molasse is a soft, porous stone, sensitive to frost and wetting cycles. Cooling a molasse wall through a poorly designed IWI accelerates its deterioration — on the street side, precisely where it is visible and protected. The hygrothermal study must model the actual stone, not a generic wall.
Timber floors call for caution. Joist ends embedded at every level, on every façade: the critical detail from point 04 recurs dozens of times in a late-19th-century building. This is the main argument in favour of capillary-active systems in this building stock.
The legal framework offers some latitude. RCI art. 56A provides for exemptions for protected buildings, on justification. Envelope compliance is assessed under SIA 380/1 "unless a particular case applies" (RCI art. 56) — and weighing heritage protection against energy performance is an established practice of the Geneva authorities. A moderate, well-designed IWI, combined with high-performance windows, a well-insulated roof and controlled ventilation, makes for a defensible case before both the OCEN and the CMNS.
IDC: the lever that makes IWI relevant today
Many of these buildings exceed the IDC threshold of 125 kWh/m²·an (450 MJ/m²·an) that triggers a mandatory auditREn art. 14: exceeding an IDC of 125 kWh/m²·an (450 MJ/m²·an) requires an audit and improvement measures within 12 months.République et canton de Genève — SILGeneve — Règlement d'application de la loi sur l'énergie (REn), L 2 30.01, art. 142010-09-01 · accessed 2026-08-20 — some exceed the significant-exceedance threshold that triggers mandatory works — 222 kWh/m²·an (800 MJ/m²·an) until 31 December 2026, 180 kWh/m²·an (650 MJ/m²·an) from 2027 to 2030REn art. 14: significant IDC exceedance at 222 kWh/m²·an (800 MJ) until 31.12.2026, 180 kWh/m²·an (650 MJ) from 2027 to 2030, then 153 kWh/m²·an (550 MJ) from 2031.République et canton de Genève — SILGeneve — Règlement d'application de la loi sur l'énergie (REn), L 2 30.01, art. 142010-09-01 · accessed 2026-08-20, then 153 kWh/m²·an (550 MJ/m²·an) from 2031 (REn art. 14). When the façade cannot change, IWI is one of the levers to consider for bringing the index down, alongside the roof, windows and systems. See the guide Renovating in Geneva: IDC, standards and strategy →
In French-speaking Switzerland, cantonal architectural surveys (Vaud, Neuchâtel, Fribourg) produce the same constraints on historic centres — with the same technical responses. In neighbouring France, ABF perimeters around historic monuments lead to the same trade-off: the façade is untouchable, and internal insulation is studied case by case.
06 — Lessons learned
Common errors and documented defects
IWI failures tend to look alike: they rarely stem from the material, almost always from a design error or an execution defect at a critical point. The typical cases below recur throughout the technical literature and failure investigations.
Error
Defect observed
Prevention
IWI on a damp wall (rising damp, untreated driving rain)
Increasing moisture in the masonry, efflorescence, render delamination, widespread mould behind the lining
Prior moisture diagnosis; treat the cause of the dampness before insulating
Vapour barrier punctured or not connected (outlets, conduits, joints, partition bases)
Condensation concentrated at the leaks, localised mould stains, odours — often discovered years later
A drawn-up airtightness plan, a service cavity, inspection before closing up
Excess insulation thickness ("while we're at it, let's put 18 cm")
Wall too cold: interstitial condensation, frost damage to the masonry, deterioration of soft stone
Thickness set by the hygrothermal study, not by U-value ambition
Untreated reveals and cross walls
Mould on window jambs and at ceiling/façade corners — the cold point has moved, not been eliminated
Systematic insulation returns, thin insulation of the jambs (RCI art. 56A)
Water pipes left in the cold wall
Frozen pipes in the first hard winter, water damage in the new lining
Move the pipework to the warm side during the works
Ventilation overlooked after the dwelling is sealed up
Rising indoor humidity, condensation on residual cold points, degraded air quality
A ventilation concept at minimum, or balanced mechanical ventilation with heat recovery, in every IWI project
Verification limited to a summary Glaser check on an exposed old wall
Wall validated on paper, damaged in reality — driving rain and capillarity were not in the calculation
Dynamic simulation (WUFI, EN 15026) for old walls, embedded timber, exposed façades
The common thread among these defects: they are invisible at handover and appear in the second or third winter. Hence the importance of design — the contractor cannot fix a wall that was poorly conceived.
07 — Key questions
What clients ask
How much living space will I lose?
Allow 8 to 14 cm of total thickness (insulation + lining) on each façade wall, depending on the system. For a 4 × 5 m room with two external walls, that amounts to roughly 0,8 to 1,2 m². It is real, but should be weighed against the comfort gained: the inner wall surface goes from roughly 13–16 °C to 18–19 °C depending on how hard the winter isISO 6946 calculation (Rsi = 0.13 m²K/W): Tsi = Ti − U·Rsi·(Ti−Te). Wall U = 1.8 at 20/0 °C → 15.3 °C; at 20/−5 °C → 13.5 °C; after IWI U = 0.30 → 19.2 °C.ISO — ISO 6946:2017 — Building components and building elements — Thermal resistance and thermal transmittance — Calculation methods2017-06 · accessed 2026-08-20, which removes the cold-wall sensation and often allows the thermostat setpoint to be lowered by a degree.
Can I insulate my apartment alone, without a decision from the co-ownership?
In principle, yes: IWI is carried out within your unit, without touching the common parts — this is one of its advantages. Two caveats: check the condominium regulations (some work that indirectly affects the structure or the façades requires notice or approval), and above all have the wall checked by a hygrothermal study, since a moisture defect in the wall would affect the whole building, not just your unit. In a building subject to authorisation (protected zone, listed building), check with the cantonal office before starting work.
How much does IWI cost?
NRG positive estimate as of June 2026 — no public Swiss cost database covers IWI specifically — supply and installation, finishes included: CHF 150 to 250/m²Internal NRG positive estimate (June 2026): no public Swiss cost database (CRB, KBOB, SIA Bulletin) covers internal insulation specifically. Order of magnitude, not contractual.Source to be established — unverified figure of wall for a mineral wool lining with vapour barrier, CHF 200 to 300/m² for composite panels, CHF 250 to 450/m² for a capillary-active system such as calcium silicate with mineral render. On top of this come the insulation returns, treatment of the reveals and any relocation of pipework — often 20 to 30 % of the budget, and the part that makes the difference between a healthy wall and a failure. The hygrothermal study represents a modest fraction of the total.
Is a hygrothermal study really necessary for a few centimetres of insulation?
Yes — and all the more so when the wall is old. It is precisely the thin layer that needs to be justified: the right IWI is one whose thickness, material and details have been checked for your wall specifically, with its orientation, its exposure to rain and its floors. SIA 180:2014 requires hygrothermal verification of modified walls; for old walls and embedded timber, a Glaser calculation is not enough and a dynamic simulation is required. A few days of study against years of hidden defects: the trade-off is easily made.
Is IWI alone enough to bring my IDC below Geneva's thresholds?
Rarely on its own. Walls account for a significant share of heat loss, but the roof, windows, ventilation and heat generation together weigh more. IWI makes sense within an overall strategy: it is the audit (mandatory above an IDC of 125 kWh/m²·an / 450 MJ/m²·an) that prioritises the measures and their timeline. A renovation planned holistically — even if carried out in stages — is better than a stand-alone IWI decided when repainting.
Sources and references (31)
Every figure and every claim in this dossier links back to its source. Hover or tap a footnote marker to see it.
Fraunhofer IBP — WUFI — Benchmark test of EN 15026(2016 · accessed 2026-08-20) EN 15026 sets the minimum criteria for software modelling coupled transient heat and moisture transport; Fraunhofer IBP states WUFI meets all of its requirements (deviation < 2.5 %).
Source to be established — unverified figure Unconfirmed claim: the PHI document 'Criteria for the Passive House, EnerPHit and PHI Low Energy Building Standard' could not be opened. To be sourced or removed before publication.
pro clima Suisse — Éviter les dégâts au bâtiment(2020 · accessed 2026-08-20) pro clima (DIN 4108-type test): 0.5 g of water/m² per winter day by diffusion through an sd = 30 m vapour retarder, versus 800 g per metre of a 1 mm gap by convection — a factor of 1600.
Source to be established — unverified figure Internal NRG positive estimate (June 2026): no public Swiss cost database (CRB, KBOB, SIA Bulletin) covers internal insulation specifically. Order of magnitude, not contractual.
A wall to insulate from the inside?
Moisture diagnosis, hygrothermal simulation of the wall, choice of system and execution details — the pre-works study costs a few days and avoids years of defects. Let's talk about your wall.