Area Weighted U-Value Method
Paragraph 4.5 of Part L1B, allows for the use of the area weighted U-Value method where glazing is in excess of the 25% limit. Under this method the overall area-weighted U-value of the extensions constructions and glazing should be better than that of a Notional Extension, of the same size and shape, that complies with the standards set out within the Reference Method defined in Part L1B.
This method does not need to involve an assessment of the whole property. It is best done at design stage, where levels of insulation and glazing types can still be tweaked to achieve a compliant result.
Where the existing dwelling is opened up to the extension, it is often the case that the area weighted calculation does not provide a compliant result – but all is not lost. The Whole Dwelling Calculation method can build on the work done to construct a more complex argument for compliance.
The Whole Dwelling Calculations Method
The final and most complex way of demonstrating an extensions compliance to Building Control is by carrying out a Whole Dwelling Calculation.
Under the Whole Dwelling Calculation method, SAP 2012 software is used to carry out a comparative SAP Calculation. The carbon emissions of the dwelling with the proposed extension will be compared to the carbon emissions of the dwelling with a Notional extension that complies with the standards under the Reference Method. Provided the emissions are lower with the proposed extension, it would comply with Building Regulations.
This method needs a survey of the existing property so that an energy model for the whole building can be produced. It takes more time but is often needed where the area weighted method does not provide a compliant result.
Compensating Measures
If the whole dwelling calculation method still doesn’t provide a compliant result, all is not lost! It is possible to specify some compensating measures to offset the effect of the extension. Examples range from very simple and low cost (Extra Loft Insulation) to more complex and higher cost (new more efficient boiler or new windows). We will always work with you to help you to achieve compliance for the lowest possible cost.
Need help with SAP Calculations pass?
At CAMSONS we can help you to achieve compliance by offering a variety of solutions to suit your design. We understand that in many cases, keeping your costs down is important so we offer affordable and efficient solutions to your insulation and energy needs by using tried and tested methods of meeting the requirements of approved document L while maintaining its modern look. Please Call 0333 577 5020 or email at info@camsons.co.uk.