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Methods for assessing the risks of refurbishment

Methods for assessing the risks of refurbishment. Chris Sanders School of Engineering and Built Environment 25th September 2012. What happens to traditional stone walls when internal insulation is added? The Standard methods for assessing moisture problems in walls BS5250 & ISO13788 WUFI

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Methods for assessing the risks of refurbishment

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  1. Methods for assessing the risks of refurbishment • Chris Sanders • School of Engineering and Built Environment • 25th September 2012

  2. What happens to traditional stone walls when internal insulation is added? • The Standard methods for assessing moisture problems in walls • BS5250 & ISO13788 • WUFI • Modelling measured data from sandstone walls in Glasgow with WUFI

  3. ISO 13788:2012 • ‘Glaser’ method • Moisture movement by vapour diffusion alone • Twelve calculations with constant monthly mean climates • Predicts accumulation and evaporation of condensate at interfaces

  4. ISO 13788 Prediction

  5. ISO 13788 misses out: • Materials are hygroscopic, liquid water stored in pores • Materials can start wet from built in water or rain ingress during construction • Water moves by a combination of vapour and liquid flow • Material properties are effected by moisture content • 2D and 3D flows can be important • Driving forces change on diurnal scales • Air movement through structure

  6. ISO 15026 accounts for • heat storage in dry building materials and absorbed water; • heat transport by moisture-dependent thermal conduction; • latent heat transfer by vapour diffusion; • moisture storage by vapour sorption and capillary forces; • moisture transport by vapour diffusion; • moisture transport by liquid transport (surface diffusion and capillary flow). • solar and longwave radiation; • precipitation (normal and driving rain); • wind speed and direction. • AIR MOVEMENT NOT INCLUDED

  7. Software compliant with ISO 15026

  8. WUFI needs complex material properties

  9. Climate data needed by WUFI • Hourly values of • internal and external temperature • internal and external humidity • solar and longwave radiation • precipitation (normal and driving rain) • wind speed and direction.

  10. Elder Street GovanInternal andexternal monitoring

  11. How do we model a traditional stone wall?

  12. WUFI Materials Database

  13. WUFI – Sandstone moisture contentGlasgow climate repeated for 10 years

  14. WUFI – Mineral wool moisture contentGlasgow Climate repeated for 10 years

  15. Relative humidity at the interface between the mineral wool and sandstone

  16. Effect of VCL on RH at Mineral Wool/Sandstone interface

  17. Moisture movement within the mineral wool

  18. WUFI calculated sandstone moisture content and driving rain using the climate data from Govan

  19. Comparison of measured conditions at the mineral wool/sandstone interface with WUFI calculations

  20. Conclusions • BS5250 & ISO13788 do not provide realistic assessments of insulated stone walls • WUFI, which complies with ISO 15026, provides a fuller picture • WUFI needs detailed material property and climate data which are not generally available • WUFI can be used to assess the importance of different processes within a wall, but unless very detailed information on the structure and materials is available, is unlikely to produce precise predictions

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