Zwischensparrendämmung

Zwischensparrendämmung, often translated as “cavity insulation between rafters,” refers to the thermal insulation installed in the space between the roof framing members of a building. The technique is commonly applied in residential and low‑rise commercial construction to improve the energy performance of pitched roofs without altering the external roof silhouette. Materials used include mineral wool, glass wool, wood fibre boards, cellulose or flexible foils, chosen according to fire‑safety, vapour‑diffusion and acoustic requirements.

The installation process typically involves filling the cavity between the rafters up to the underside of the roof covering, while maintaining a continuous insulation layer. In many cases a thin ventilated gap is left beneath the roof membrane to prevent condensation, especially when moisture‑permeable materials are used. In Germany and other European countries, the method is regulated by the Energieeinsparverordnung (EnEV) and the Building Energy Act, which prescribe minimum U‑values for roof constructions; Zwischensparrendämmung helps achieve values of 0.11 W/(m²·K) or lower when combined with appropriate plaster or boarding.

Compared with Außen­sparrendämmung (external roof insulation), the cavity approach preserves the external appearance of the building and can be retrofitted without major façade changes. However, it often yields lower overall thermal resistance because the insulation thickness is limited by the existing rafter spacing, and careful detailing is required to avoid thermal bridges at the ridge, eaves and wall junctions. Proper vapor‑control layers and adequate roof ventilation are essential to prevent mold growth.

Zwischensparrendämmung remains a widely accepted solution for improving the energy efficiency of existing structures and for new builds where architectural constraints dictate a seamless roof profile. It is part of broader strategies that combine roof, wall and floor insulation to meet contemporary climate‑protection goals.