Facade Insulation (ETICS or Ventilated Rainscreen)

Applying an insulation layer to the external wall — either a conventional external thermal insulation composite system or a ventilated rainscreen facade.

How does external wall insulation work?

In most existing buildings, the external wall is the largest component of the building envelope by area and thus a major heat loss path. External wall insulation applies a continuous insulation layer on the outside and thereby lowers the wall's U-value, i.e. the thermal transmittance in W/(m²·K). Two systems are common: with an external thermal insulation composite system (ETICS), insulation boards are glued and dowelled directly onto the masonry and finished with reinforcement and render. With a ventilated rainscreen facade, the insulation sits on a substructure, with an air gap and cladding in front of it. With 14 to 20 cm of insulation (λ = 0.035 W/(m·K)), the U-value of a typical old wall drops from 1.2 to 1.6 to 0.15 to 0.20 W/(m²·K). Planning the thermal bridges is decisive – those points such as balcony slabs, window lintels, plinths and parapets where the insulation layer is interrupted and a disproportionate amount of heat escapes.

Which buildings benefit from external wall insulation?

The measure is suitable for detached houses, apartment buildings, office buildings and schools with load-bearing, uninsulated external walls. It is particularly economical when render or facade refurbishment is due anyway, because scaffolding and surface work are then not attributed to the insulation alone. In multi-storey buildings, fire protection requirements for insulation material and fire barriers must be observed. For listed or highly articulated facades, external insulation is often ruled out; internal insulation then remains as an alternative. For cavity walls, blown-in cavity insulation may be the cheaper solution. A ventilated facade with wood fibre or cellulose is a good choice when ecological criteria and circularity are priorities.

What does external wall insulation actually deliver?

Heating energy savings are typically 25 to 40 %. Mathematically, the saving is derived from facade area, U-value difference, heating degree days of the location and heating system efficiency; a correction factor of 0.85 accounts for thermal bridges and real occupant behaviour. For an apartment building with 600 m² of opaque facade, this gives around 61,500 kWh of natural gas per year, equivalent to about 12.4 t of CO2. The investment is 150 to 220 €/m² for ETICS and 250 to 380 €/m² for a ventilated facade with wood fibre. Over a 40-year service life, the measure pays back in 15 to 30 years, considerably faster if facade refurbishment is due anyway or in combination with window replacement and heating optimisation.

Energy carrier

Erdgas, Heizöl, Pellet, Fernwärme, Strom → Erdgas, Heizöl, Pellet, Fernwärme, Strom

Savings potential

25-40 % Heizenergie

Worked example

A post-war apartment building has 600 m² of opaque facade area of 38 cm brick masonry without insulation. The U-value of the existing wall is 1.4 W/(m²·K), heating is by a gas boiler with 85 % efficiency, and the location has 3,500 heating degree days. After applying an external thermal insulation composite system, the wall achieves a U-value of 0.18 W/(m²·K). The saving is calculated from area times U-value difference times heating degree days times 24 hours, divided by 1,000 and the boiler efficiency, multiplied by the thermal bridge factor of 0.85: 600 × (1.4 − 0.18) × 3,500 × 0.024 / 0.85 × 0.85 = 61,488 kWh/a. The building thus saves around 61,500 kWh of natural gas per year, which at an emission factor of 0.201 kg/kWh corresponds to about 12.4 t of CO2 annually.

Investment & payback

WDVS: 150-220 €/m²; VHF Holzfaser: 250-380 €/m² · Service life: 40 a · Payback: 15-30 a

Applicability

Requirements

Exclusion criteria

Typical buildings

Frequently asked questions

How much does external wall insulation cost per square metre?

An external thermal insulation composite system (ETICS) costs 150 to 220 €/m² of facade area, a ventilated rainscreen facade with wood fibre insulation 250 to 380 €/m². This includes scaffolding, insulation material, fixing and finish. If render refurbishment is due anyway, a large part of the additional cost is eliminated, because scaffolding and surface work are incurred in both cases. Thermal bridge details at balconies and window reveals can increase the price noticeably.

How thick does external wall insulation need to be?

For a U-value of 0.15 to 0.20 W/(m²·K), 14 to 20 cm of insulation with a thermal conductivity of 0.035 W/(m·K) is required. OIB Guideline 6 (the Austrian building code) requires a U-value of no more than 0.25 W/(m²·K) for refurbishments in Austria; Passive House standard is 0.12 W/(m²·K). With greater insulation thicknesses, the saving increases only marginally, which is why 16 to 18 cm is a good compromise in practice.

What is the difference between ETICS and a ventilated rainscreen facade?

With ETICS, the insulation boards are glued and dowelled directly onto the wall and then rendered. With a ventilated rainscreen facade, the insulation sits on a substructure, in front of which there is a ventilated cavity and a cladding of wood, metal or panels. The ventilated facade is more expensive but more robust against moisture and algae growth, easier to dismantle, and can be combined with natural insulation materials such as wood fibre or cellulose.

Is external wall insulation worthwhile on a listed old building?

Where heritage protection imposes conditions on preserving the facade, external insulation is generally not permitted. In this case, internal insulation is the technical alternative, with which U-values of around 0.35 W/(m²·K) are achievable. For cavity walls, blown-in cavity insulation without changing the facade appearance may also be an option. Consultation with the Austrian Federal Monuments Office (Bundesdenkmalamt) is mandatory before planning.

How quickly does external wall insulation pay back?

The payback period for external wall insulation is 15 to 30 years, over a service life of around 40 years. The poorer the existing condition and the higher the energy price, the faster the measure pays off. If the insulation is combined with a facade refurbishment that is needed anyway, the payback is shortened considerably, because only the additional cost of the insulation layer needs to be offset.

Related measures

Standards & sources

Metering points in the EDM Toolbox

Erfolgsmonitoring via Wärmemengenzähler im Heizkreis + witterungsbereinigtem Vergleich (HGT-Korrektur über LineMetrics-Wetterdatenanbindung). Optional Oberflächentemperatur-Sensoren an kritischen Wärmebrückendetails.

All measures