Part L1B – Extensions.
Summary of Methods to Demonstrate Compliance for Extensions
Reference method
- Demonstrate new thermal elements meet minimum compliance standards (see App B).
- Demonstrate new controlled fittings meet minimum compliance standards (see App A).
- Demonstrate any retained elements that will become thermal elements of extension meet minimum compliance standards (App C).
- Where any retrained thermal elements are not upgraded to minimum compliance standards, demonstrate meeting the standards would result in a simple payback period greater than 15 years. This can be calculated by modelling the potential savings, in SAP software, of meeting the requirements, and comparing this with the cost incurred at installation.
- Demonstrate the total opening area does not exceed 25 percent of the extension floor area in addition to the area of former openings replaced by the extension.
- Demonstrate that any provided or extended fixed services are at least as efficient as before and comply with Domestic Building Services Compliance Guide.
- Demonstrate any removed renewables are being replaced with equivalent systems.
Area weighted average U-value method
- If the proposed extension does not meet all of the u-value and opening area requirements of the reference method; Demonstrate the extension would have an equal or better total u-value than an extension of the same size that met all of the u-value and opening area requirements.
- Demonstrate that any provided or extended fixed services are at least as efficient as before and comply with Domestic Building Services Compliance Guide.
Whole dwelling calculation method
- Demonstrate the CO2 emission rate of the whole dwelling with the proposed extension is lower than if the dwelling had a notional extension of the same size that meets the minimum compliance standards for thermal elements and controlled fittings.
