Moisture in flat roof systems with an insulation layer has been a long-standing issue for the roof industry. It is now realised, that it is unrealistic and too costly to try to completely keep moisture from entering a roof assembly during its service life. The approach, therefore, should be to keep moisture levels low within a roof assembly by providing a path for moisture to periodically escape. A design strategy that assumes roof assemblies may get wet and permits them to dry, presents a more forgiving and perhaps less costly alternative. Moisture may enter a roof assembly in a number of different ways. From the interior by diffusion and convection. During construction from moist materials or rain. Later on, rain water may enter through leaks in the roofing. From laboratory experiment, computer calculations and practical experience it is concluded, that the Self-Drying Roof concept works for both cold- and warm deck roof systems in climate zones where a vapor retarder is needed, if the traditional water proof vapor retarder is substituted by a water permeable vapor retarder.

Note Reprint from the proceedings of the Ninth Cogress of the International Waterproofing Association, Amsterdam, April 26-28, 1995.

• drying potential of building envelope
• experiment: laboratory
• roof

1. eds. Annex 41 Final Report, Volume 1: Modelling Principles and Common Exercises
2. Empirical validation of a transient computer model for combined heat and moisture transfer
3. Experimental investigation of the hygrothermal performance of insulation materials
4. Full-scale testing of indoor humidity and moisture buffering in building materials
5. Global building physics
6. International building physics toolbox, general report
7. Investigation of Microclimate by CFD Modeling of Moisture Interactions between Air and Constructions
8. Latent heat flow in lightweight roofs and its influence on the thermal performance of buildings
9. Model and experiments for hygrothermal conditions of the envelope and indoor air of buildings
10. Moisture buffer value of building materials
11. Moisture Buffer Value of Materials in Buildings
12. Moisture buffering of building materials
13. Moisture conditions of non-ventilated, wood-based, membrane-roof components
14. Moisture: its effects on the thermal performance of a low-slope roof system
15. Non-isothermal water vapour transmission through porous insulation. Part 1: The climate chamber
16. Organic insulation materials: effect on indoor humidity and necessity of a vapor barrier
17. Test cell measurements of moisture buffer effects
18. The importance of moisture buffering for indoor climate and energy conditions of buildings
19. The International Building Physics Toolbox in Simulink
20. Tools for performance simulation of heat, air and moisture conditions of whole buildings
21. Whole-building Hygrothermal Simulation Model  

1. A "follow-up" study of moisture conditions and performance of moisture sensors in flat roofs provided with exterior insulation in the late seventies