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
• Modelling measured data from sandstone
walls in Glasgow with WUFI
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
ISO 13788 Prediction
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
ISO 15026 accounts for
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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
Software compliant with ISO 15026
WUFI needs complex material properties
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.
Elder Street Govan
Internal and
external
monitoring
How do we model a traditional stone wall?
WUFI Materials Database
WUFI – Sandstone moisture content
Glasgow climate repeated for 10 years
WUFI – Mineral wool moisture content
Glasgow Climate repeated for 10 years
Relative humidity at the interface between the
mineral wool and sandstone
Effect of VCL on RH at Mineral Wool/Sandstone
interface
Moisture movement within the mineral wool
WUFI calculated sandstone moisture content and
driving rain using the climate data from Govan
Comparison of measured conditions at
the mineral wool/sandstone interface with
WUFI calculations
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