Approved Document C refers to BS 5250 as the means of compliance
Accredited Details have been prepared which provide guidance on how to avoid thermal bridging and achieve the airtightness requirements.
The Accredited Details for all warm and cold roofs include airtightness and ventilation requirements
BS 5250 Code of practice for the Control of condensation in buildings was created in 1975 as a direct consequence of the problems identified in the 1960s and early 70s
To reduce the risk of harmful condensation it recommended eaves to eaves ventilation in the loft space
It was amended in 1983 and 1989 when high level ventilation was also recommended for pitches of 35° and over or spans in excess of 10m
In 2002 the standard was reviewed and the recommendations for high and low level ventilation were retained.
An amendment was published in December 2005 which introduced reduced ventilation requirements for vapour permeable underlays and when a well-sealed ceiling is installed.
Code of practice for the airtightness of insulated ceilings and the control of air movement into pitched roofs at ceiling height.
This code provides detailed guidance on how to achieve the airtightness of ceilings in both cold and warm roofs.
The airtightness of ceilings - energy loss and condensation risk
This paper gives the technical background to the changes introduced by the amendment to BS 5250
Some 8 to 10 % of the annual energy demand of a house is lost through the ceiling by air leakage.
Unlikely that significant improvements in energy efficiency and condensation risk can be achieved by limiting loft ventilation.
An Alternative Approach to meet the requirements of the Building Regulations is to follow the recommendations of Certificates issued by the British Board of Agrément or BRE Certification Ltd (formally WIMLAS)
The Secretary of State has agreed that these Certificates will give assurance that the product or system to which the Certificate relates, if properly used in accordance with the terms of the Certificate, will meet the relevant requirements
The BBA has issued Certificates for the use of vapour permeable underlays without ventilation in cold and warm pitched roofs.
These certificates only refer to dwellings. Outside the scope are shops, offices, industrial buildings, schools and hospitals.
The product must be installed with a convection tight ceiling. Note: this is a higher standard than a well-sealed ceiling.