Highly Glazed Extensions

As part of Building Control sign-off, all new extensions must comply with Approved Document F1:Conservaton of Fuel & Power (NI). This Approved Document forms part of the government’s plan to limit carbon emissions and tackle fuel poverty. In most cases the design specification for the extension will surpass the minimum allowable standards and compliance with Approved Document F1 will be straight forward. However, one common area where extensions do not automatically comply concerns the amount of allowable windows, doors and roof lights: referred to as the 25% glazing allowance.

The 25% glazing allowance is equal to 25% of the floor area of the extension plus the area of any openings that are no longer exposed as a result of the extension works. For designs where the proposed area of glazing is in breach of this allowance a SAP calculation can be used to demonstrate compliance and achieve Building Control sign-off. SAP is the government’s approved methodology for assessing energy performance in dwellings. By conducting 2 SAP calculations (Notional vs Proposed, before vs After) it is possible to show that features of the design that do not meet the minimum standards of Approved Document F1 (such as the level of glazing) have been compensated for elsewhere in the design.

We can provide you with a SAP assessment to make sure your extension is compliant with Approved Document L1 of the Building Regulations. Using SAP to determine cost effective and practical solutions we can ensure compliance is achieved irrespective of how much glazing is included in the design.

It is common for projects that we assess to achieve a pass first time. If the extension does not achieve a pass, we will provide solutions to bring it back into compliance. These could include changes to the thermal insulation within the extension, cost effective and practical energy performance improvements to the the existing house, or specifying higher performance glazing within the extension.

Once changes have been agreed we shall provide SAP reports for submission to Building Control.

To undertake an “Equivalent Carbon Approach” SAP calculation we will need a copy of the Building Regulation drawings for the proposed extension & existing property (floor plans, elevation drawings and section drawings) and a copy of the supporting construction notes/insulation/heating specifications. (Full list linked below)

Stroma Certified Energy Assessor
Elmhurst Energy Accreditated Member
IATS Approved

For More Information Please Speak to our Team

Contact Thermcal today to discuss your project requirements