External wall insulation is a system of insulation boards fixed to the outside of the walls, covered by a mesh-reinforced base coat and a finishing render. In Spain it is called SATE. It wraps the house without taking room space, but it only performs well on sound, dry walls and with careful detailing at windows, eaves and the base. Spain’s building code sets thermal and condensation requirements for envelope elements renewed in a renovation.
What do the different names mean?
The names describe the same family of systems from different traditions. SATE (Sistema de Aislamiento Térmico por el Exterior) is the Spanish term you will see in quotes and town hall forms. ETICS (External Thermal Insulation Composite System) is the European technical term. EWI (external wall insulation) is common in Britain, and EIFS in North America. Whatever the name, the principle is a continuous insulating layer on the outside of the wall, protected by render.
This differs from cavity insulation, which fills a gap inside a double wall, and from internal insulation, where boards or linings are added on the room side. Each has its place; our article external or internal insulation compares them.
What are the layers, from the wall outwards?
- The existing wall, cleaned and repaired so that it is sound and flat.
- Adhesive bonding the boards to the wall.
- Insulation boards, of expanded polystyrene, mineral wool or other materials, depending on the system and the building.
- Mechanical fixings through the boards into the wall, where the system and substrate require them.
- Base coat with reinforcing mesh, which gives the surface its strength and resistance to cracking.
- Primer and finishing render, which give colour and texture and shed rain.
Accessories complete the system: base profiles, corner beads, mesh reinforcements at opening corners, sills, sealing tapes and capping pieces. The components are tested together, so mixing parts from different systems is a common source of problems.
Why insulate on the outside rather than the inside?
An insulating layer on the outside keeps the wall itself warm in winter and shaded from heat in summer, so the wall’s mass works with the house rather than against it. It also covers the edges of floor slabs and pillars, which in many coastal houses are the coldest points and the places where condensation and mould appear first. Rooms keep their size, and the work happens outside, so the house can stay occupied.
The downsides are real too: the appearance of the house changes, every opening and roof edge has to be redetailed, scaffolding is needed, and in a community the owners must agree. Our article is external insulation worth it weighs these points without savings claims.
What does Spain’s building code require?
The Código Técnico de la Edificación (CTE) deals with energy in its basic document DB-HE, updated by Real Decreto 732/2019. Section HE1 applies to interventions in existing buildings as well as new ones. In a renovation, envelope elements that are replaced, added or substantially modified must not exceed the transmittance limits in the document’s tables, and stricter overall criteria apply where more than a quarter of the building’s total thermal envelope is renewed. HE1 also asks that interstitial condensation within the envelope does not degrade it or significantly reduce its thermal performance. Buildings with official protection are excluded where compliance would unacceptably alter their character or appearance.
For an owner, this means insulation thickness and specification are not just a matter of taste or budget. Where a technical justification is needed, it is prepared by a qualified professional (how the code applies to your specific house: to be verified with a technician).
Where do external insulation systems usually go wrong?
- Damp walls insulated without resolving the cause, so moisture is trapped.
- Window sills left at their old depth, without a drip, so water runs behind the system.
- Roof edges where the overhang no longer covers the top of the insulation.
- The base of the wall, insulated down into soil or splash zones without a suitable impact- and moisture-resistant band.
- Penetrations — pipes, lamps, awning brackets — fixed through the render without proper sealing.
- Mesh missing or poorly embedded, especially at opening corners, which leads to diagonal cracks.
None of these is visible on the day the scaffolding comes down. They show over the following seasons, which is why the detailing should be discussed before the quote is accepted.
How does it behave on a coastal house?
Near the sea, a façade faces strong sun, wind-driven rain and salt-laden air. A well-installed system protects the wall beneath it from much of this, but its own finish takes the exposure instead. Light colours reflect more sun and generally move less with heat; dark colours on sunny elevations need care. Fixings and accessories should be corrosion-resistant. The render should be inspected periodically like any façade: cracks, impact damage and failed sealant around fittings repaired early. Our guide on façade maintenance by the sea gives a simple routine.
What should I ask a contractor before agreeing a quote?
- Which system will be used, and are all components from that system?
- How will the wall be checked and prepared, and what happens if damp is found?
- How are sills, reveals, eaves and the base of the wall detailed? Ask for sketches.
- Are mechanical fixings included, and how many per board are planned?
- How are existing fittings — lamps, downpipes, railings — removed and refitted?
- Has the community or town hall side been checked?
- Does the quote list each of these items separately?
A contractor who answers these clearly is more likely to deliver a system that lasts. Our villa builder checklist covers the wider selection questions.
Does it need maintenance?
Less than a painted render on a bare wall, but not none. An annual walk round the house is enough to spot impact damage near the ground, cracks around openings, algae on shaded walls and failed sealant at fittings. Small repairs are straightforward if done promptly; neglected damage lets water behind the system. When a finish eventually needs refreshing, it should be done with a coating compatible with the system rather than any exterior paint.
Official sources
Bauman Raymond Attila · Reforma Villas Costa del Sol · Avenida Antonio Belón 3, Marbella. Last reviewed: 05/11/2026.
