Key facts

  • Funding Body/Client: The Department for Communities and the Local Government (DCLG)
  • Project Partners:  Building Science Ltd.
  • Total Project Value: N/A
  • UCL/IEDE Project Value Share: N/A
  • Duration: 2003-2005
  • Status: Complete

The as-built performance of unventilated lofts in a diverse sample of dwellings in England were monitored over a 12 month period to record the temperature and humidity conditions in the roof system. The monitored results were compared with commercially available computer calculation methods intended to predict the condensation risk in building elements. One of these packages was based on the ‘Glaser method’ (as described in BS EN 13788:2002), the other is a more ‘advanced’ simulation tool.

PI: Tadj Oreszczyn

Co-Is: Michael Davies and Ian Ridley

R: Dejan Mumovic 

The computer programmes appear to model the trends of temperature and vapour pressure in the batten spaces correctly. However, due to uncertainties in the input parameters it was not possible to determine the reliability of the calculation methods for this purpose with a high degree of precision. BS 5250:2002 as amended clearly sets out the sources of error which arise due to the simplifications inherent in the ‘Glaser method’. It is important to note that to be most useful to designers, any calculation method should ideally predict the condensation risk in unventilated roof systems via incorporation into a whole building simulation package. Neither of the two commercially available calculation packages tested had this facility. The following report was produced:

  • Selves, N., Ridley, I., Mumovic D., Davies, M., Oreszczyn, T. (2005) Evaluation of Unventilated Pitched Roofs with Breather Membrane, Office of Deputy Prime Minister, Building Regulations Division Project Number: CI 71/6/1 BD2414, London. 

The Final Report delivered for ODPM Building Regulations Division under the Building Operational Performance Framework 

For further information please contact: Tadj Oreszczyn