Arinsal Fire Reveals Fatal Flaws in Energy-Efficient Roof Retrofits

Architect Pau Iglesias of Ariet Studio has identified key weaknesses in the roof designs of buildings hit by the recent Arinsal fire, based on his on-site observations. The flames spread mainly through the roofs, not the facades or interiors, turning energy-efficient upgrades into pathways for rapid combustion.

The structures involved had a standard retrofit: fresh insulation layered over original wooden shingle roofs, separated by a ventilated air chamber. This prevents moisture buildup and preserves the underlying wood in normal conditions. However, during a fire, the gap acts as an open conduit. Circulating air inside accelerates burning, enabling flames to travel swiftly and undetected under the outer layer. As a result, the blaze could leap seamlessly between buildings.

Iglesias pointed out stark differences in insulation performance. Extruded polystyrene (XPS) ignites easily and promotes spread; polyisocyanurate (PIR) resists better yet remains combustible as an organic material; rock wool, being non-flammable, serves as a solid firebreak. These distinctions, often overlooked in planning, turn decisive in crises.

Strong winds that day supplied relentless oxygen, heightened flame intensity, and dispersed embers, which sped transmission across roofs and hampered suppression efforts. Firefighters faced steep hurdles accessing concealed fires, frequently resorting to tearing off coverings for direct attack.

Such designs must align with Andorra's fire safety rules by curbing spread and aiding responder access, Iglesias noted. The event highlights priorities in contemporary building: selecting robust materials, dividing roofs into sections, factoring in evacuation timelines—"the core design rule is ensuring safe exit before structures turn hazardous"—and embedding protection from the outset. Many efficiency-focused approaches, he cautioned, expose flaws under duress.