Warmdach

Warmdach, or warm roof, is a roof construction in which the insulation is placed on top of the roof deck, so the deck remains within the heated envelope of the building. This contrasts with a cold roof built with insulation between or below the rafters and a ventilated air space above it.

In a typical warm roof, from interior to exterior the layers may be: interior finish, vapor barrier or retarder, roof deck (wood or concrete), insulation laid on top of the deck, a waterproofing layer, and the outer roofing material (tiles, slates, shingles, or membranes). The insulation thickness and material are chosen to meet energy performance targets; common insulation types include mineral wool, PIR/PUR foam, or expanded polystyrene. The system aims to minimize thermal bridges and keep the roof deck warm, reducing condensation risk within the roof structure when correctly sealed.

Advantages include higher thermal efficiency and simplified management of attic spaces since no ventilated rafter bay is required; improved airtightness and potential for thinner roof assemblies when designed properly. Disadvantages include the need for careful moisture management, as any leakage must be dried from the warm side; design errors can encourage mold or rot in the deck or insulation; typically higher initial cost and more demanding installation quality.

Compared with a cold roof, a warm roof avoids continuous ventilation cavities and is common in modern energy-efficient buildings, particularly with flat or low-slope roofs, and in many European markets.