Part L1B - Highly Glazed Extension

Part L1B - Highly Glazed Extension

We provide SAP calculations for highly glazed properties in-line with Building Regulations Part L1B. Our assessors are fully qualified and accredited to issue an L1B highly glazed reports, which determines whether the excessive glazing will increase the amount of carbon emission of the property or not. 

Compliance is determined by comparing the amount of glazing in the proposed extension to a defined glazing amount set by Building Regulations Part L1B, which should be not greater than 25% of the floor area of the extension plus the total area of the openings no longer exposed. If such extension exceeds that number, then it is classified as ‘highly glazed extension’ and therefore a calculation must be done to justify the excessive amount of glazing. 

The calculation is done by using the ‘whole dwelling calculation method’, and it uses SAP 2012 methodology to show calculated carbon dioxide (CO2) emission rates from the actual dwelling and proposed extension and compare it to emission rates of the notional dwelling with extension built to the building regulations standards. This method incorporates great design flexibility, which allows for quick alternations to the project if any are necessary. 

A good provision would be to design the extension using the standards for new thermal elements, which are:

• wall U-value of 0.28 W/m2K,
• floor U-value of 0.22 W/m2K,
• pitched roof insulated at ceiling with U value of 0.16 W/m2K,
• pitched roof insulated at sloping ceiling and flat roof with U value of 0.18 W/m2K,
• windows and rooflights with U value of 1.60 W/m2K,
• glazed doors with U value of 1.80 W/m2K.

A good provision would be to extend the existing heating system into the extension. 

Choosing Ashby Energy Assessors means you will get specialist advice throughout the project, along with practical solutions. Our professional reports contain all the information required by building control to ensure you can continue with your project without hesitation.