Cold roof

from Wikipedia, the free encyclopedia

A cold roof , also a double-shell or ventilated roof, is a double-shell, ventilated roof structure. The term was coined to distinguish it from the warm roof and the inverted roof for flat roof shapes in which there is an air layer between the heat-insulating layer and the roof seal, which is in contact with the outside air via sufficiently dimensioned ventilation openings on at least two sides of the roof. Due to the similarity of the construction with its ventilated air layer on the outside of the insulation, correspondingly designed pitched roofs are often referred to as cold roofs .

Working principle

Scheme drawing of the roof. The wind can ventilate freely under the rafters . Only below is the thermal insulation.
  1. Wooden grate
  2. Leaf sieve
  3. Inlet funnel
  4. gravel
  5. sand
  6. Wood cement
  7. Rafters
  8. Inlet sheet
  9. Ventilation hole
  10. Masonry
  11. Drainage channel
  12. Thermal insulation
  13. Concrete ceiling
  14. Ceiling cladding

In the case of cold roofs, the moisture that diffuses from the building through the ceiling is carried away by the ventilation located under the roof skin . Room side has the insulation therefore not necessarily by a vapor barrier to protect, often enough a vapor barrier . The layer of air above the insulation level and the ventilation openings must be designed to be so large that an adequate exchange of air can actually take place for moisture removal. Ventilation openings are arranged in every rafter field, on pitched roofs on the eaves and ridge, on flat roofs on two opposite sides and usually also in the middle - then in the form of ventilation hoods. Because less heat is supplied to the air cavity of a cold roof as the insulating effect of the insulating layers increases, the risk of damage also increases if moisture is introduced. In addition, with increasing thermal insulation on flat or steeply sloping roofs, the convection in the air cavity also decreases. Therefore, for cold roofs with no and very little inclination, higher diffusion resistances of the vapor barriers are required in more recent literature than in older literature. In addition, through a reference is made to the need for airtight layer to prevent the convective flow of air from heated rooms in insulation and roof cavity consistently.

construction

With flat roofs that are designed as cold roofs, the insulation is below the rafters or in the lowest area between them, with concrete roofs between the supporting timbers of the roof waterproofing. The ventilated roof cavity is located between the upper areas of the rafters or the supporting timbers. Continuous formwork is laid over the roof beams , onto which the roof waterproofing and any additional protective layers are applied. Often, ventilators are installed in the formwork and roof waterproofing for additional ventilation of the cavity. On the room side of the insulation layer, an airtight layer and a vapor barrier are arranged, mostly in the form of an airtight bonded vapor barrier film and airtightly connected to adjacent components. Often there is another cavity on the inside of the vapor barrier, which can be used as an installation level, between the battens of the interior cladding on the room side (e.g. plasterboard ). Because of the difficulty in the practical production of permanently airtight connections of the vapor barrier film, especially in corner areas, and because the necessary ventilation requires additional installation height and sometimes complex ventilation elements, flat roofs with increasing thermal insulation requirements are rarely designed as classic cold roofs.

In the case of a pitched roof designed as a cold roof, the thermal insulation material (e.g. clamping felt, rock wool ) is clamped between the rafters of the roof structure in such a way that a sufficiently high layer of air remains on the top of the insulation between the rafters. Then a shortfall is applied to the rafters , e.g. B. in the form of a sarking membrane , formwork with roofing membrane or sub- roof panels . Then counter battens are applied to which the roofers can attach the storage battens that support the roofing. Even with the sloping cold roof, there is an airtight vapor barrier on the room side of the rafters and the insulation, sometimes an installation level and then an interior cladding.

See also

Individual evidence

  1. ↑ Karl Gösele , Walter Schüle: Sound • Heat • Humidity: Basics, experience and practical advice for building construction , Bauverlag GmbH, Wiesbaden and Berlin, 5th edition 1979, ISBN 3-7625-1192-6 , pp. 289-291
  2. ↑ So already with Peter Neufert : Bauentwurfslehre , Vieweg-Verlag Braunschweig Wiesbaden, 33rd edition 1992, ISBN 3-528-58651-6 , p. 79, where an s D value of the vapor barrier of at least 10 m is required compared to 2 m from Karl Gösele , Walter Schüle: sound • heat • humidity. Basics, experience and practical advice for building construction , Bauverlag GmbH, Wiesbaden and Berlin, 5th edition 1979, pp. 289–291
  3. ↑ Jürgen Blaich: structural damage. Analysis and Avoidance . Published by the Federal Materials Testing and Research Institute. Fraunhofer IRB Verlag, Stuttgart 1999, ISBN 3-8167-4709-4 , p. 154