Condensation prevention: loft ventilation - a discussion paper.

This is the third item in a series on methods for predicting condensation risks within structures. It answers criticisms made of the method described in NO 1729, on the basis that the method does not give the same answers, nor does it take account of the effect of the occurrence of condensation on the vapour pressure gradient within the structure, as does the graphical method described in NO 1728. The present item explains how the original equations may be altered to produce the same answers as the graphical method, and goes on to discuss the practicalities of the ventilation of roof spaces, with particular reference to the current and anticipated future requirements for the insulation of roofs, and draws conclusions relating to the inclusion of vapour-resistive layers and the position of the insulant.