Book Description

THIS PUBLICATION HAS BEEN ARCHIVED.

Whilst this publication can still be purchased some of the information in it has been superseded by more recent research and standards. The BRE Group does not accept any responsibility whatsoever for any loss or damage, including - without limitation - indirect or consequential loss or damage arising from use, or loss of use, of data or profits arising out of, or in connection with, the use of this document.


Typically about 20% of the air entering a house leaves via its loft, adding to the risk of condensation in the loft and reducing the energy efficiency of the roof. This airflow, together with the ventilation of the loft space, is not accounted for in standard diffusion-based methods of condensation risk analysis, which therefore do not apply to cold pitched roofs.

This paper describes the airflow routes between a house and its loft and the steps that can be taken to reduce the flow. The methods that can be used to measure the airtightness of ceilings are discussed and a method is proposed for assessing the condensation risk, taking into account the airflows.

The paper explains why reducing airflow through the eaves does not improve the energy efficiency of a house and gives recommendations for improving the airtightness of ceilings in new houses and in existing homes. Reducing airflow through the ceiling both saves energy and reduces the risk of condensation in the loft. 12 pages.

Contents:
Introduction
Cold pitched roofs
Damage caused by moisture
Airflows
- Loft ventilation
- Airflows through the ceiling
- Airflow routes from living areas of the house to the loft
Heat and moisture transport into the loft
- Effect of reducing the ventilation in the loft
- Effect of reducing airflow through the ceiling
Methods of reducing airflow through the ceiling
- New build
- Existing ceilings
BS 5250 definition of a well sealed ceiling
Measurement of ceiling airtightness
Assessing condensation in pitched roofs
Conclusions and recomendations
References