External thermal insulation (ETI)

External thermal insulation (ETI) involves wrapping the building in a continuous insulating layer applied to the facade, then protected by a render or cladding. The goal is to drastically reduce heat loss, eliminate thermal bridges (floor edges, window and door reveals, lintels), and improve winter and summer comfort… all without sacrificing interior space. ETI is well-suited to renovations in occupied buildings and improves energy/carbon indicators such as the Bbio coefficient and the summer comfort DH (depending on the materials and colors).

ITE: definition and common systems

Two large families:

Exterior insulation composite systems (ETICS) : EPS, rock wool, or wood fiber panels glued/anchored to the facade, covered with a reinforced base coat and then a finishing coat (texture, color). This is the most common solution in residential buildings.

Insulated cladding : insulation is placed behind a frame (wood/metal) and a ventilated facing (wood, laminate, metal, terracotta, etc.). Very mechanically robust, weather-resistant, and aesthetically customizable.

Insulation materials:

EPS (expanded polystyrene) : very good R/€, lightweight, easy to coat; acoustic limit and reaction to fire depending on the range.

Rock wool : non-combustible, better acoustics, good plaster support; higher density and cost.

Wood fiber : interesting summer phase shift, bio-sourced appearance; sensitive to water → careful details.

Key technical points: 

Fixings (gluing/plugs), resistant base (XPS/ROC + suitable coating), flashings and copings, profiles (corners, water drips), treatment of frames and thresholds, joinery connections, rain barrier/air gap for cladding, light colors (albedo) on very sunny facades.

Advantages, limitations and points of attention of ITE

Interests

• Cuts structural thermal bridges (slab edges), increases wall temperature → comfort and less condensation.
• No loss of living space, work possible on occupied premises.
• Improved summer comfort (internal inertia preserved, phase shift possible with dense fibers).
• Renovated facade: aesthetics, weather protection, increased heritage value.

Boundaries

• Significant cost (scaffolding, accessories, cladding).
• Urban constraints/PLU: overhang at the property line, appearance of the facades, need to convince the co-ownership.
• Sensitive details: continuous balconies, returns of paintings, hard points (blinds, railings).
• Fire and height: specific requirements (choice of insulation/facing, firestop strips, AT/DTU).

Points to consider

• Design of singular points: facade bases, shock/moisture-resistant base, drip edges under supports, insulation returns in reveals.
• Vapor/moisture migration: consistent Sd rules, rain barrier behind cladding, water drainage.
• Colour & expansion: light colours in full sunlight, expansion joints, straight starting rails.
• Fixings and loads: anchors for shutters, blinds, railings, offset brackets.
• Coordination: joinery (exterior surface mounting), ventilation (extensions), networks (rainwater, boxes).
• Quality of execution: flatness, reinforcement swaddling, compliant doweling, Technical Approvals/DTA respected; anticipated maintenance (algae/shocks).

Anecdote — “Winters calmed in Saint-Étienne”

In Saint-Étienne, a 1960s apartment building suffered from significant thermal bridges and cold walls in winter. The residents' association voted for external thermal insulation composite systems (ETICS) using 140 mm rock wool, light-colored on the south side and with a reinforced base on the parking lot side. Window and door frames were insulated with extended sills and new flashing; the railings were fitted with offset brackets. The following winter: complaints of cold walls disappeared, mold was eradicated, and heating costs were significantly reduced. The president of the residents' association smiled: "We didn't add any insulation inside... we just put a coat on outside—and it fits perfectly."