Reina Reliance – Heat Loss Glazing services
Heat Loss Calculations to Justify Excessive Glazing in an Extension
This method of calculation can be used for extensions to existing dwellings where it is considered that the total area of glazing in the proposed extension is in excess of the amount permitted by Building Regulations. Which is equal to 25% of the floor area of the extension plus the total area of any windows or doors which, as a result of the extension works, no longer exist or are no longer exposed.
Whilst there is no accreditation scheme associated with the above calculation method our assessors adopt the same understanding and principles of the SAP methodology to demonstrate compliance with Building Regulations Approved Document L1B (2013).
If the proposed extension is considered to have an excessive amount of glazing the Building Control Body will request “Heat Loss Calculations” to justify the amount of glazing in the extension. There are two methods available to demonstrate compliance.
- Area Weighted U Value Method – One way of complying would be to show that the average area-weighted U Value of all the elements in the extension is no greater than that of an extension of the same size and shape that complies with the fabric standards and the opening area standards referred to in the Building Regulations Approved Document Part L1B (2013).
- Actual versus Notional Method – Where greater design flexibility is required, it is possible to achieve compliance by demonstrating that the Dwelling Carbon Emission Rate (DER) of the existing dwelling and actual proposed extension, which includes the proposed amount of glazing is no worse than the Dwelling Carbon Emission Rate (DER) of the existing dwelling with a notional extension where the extension complies with the fabric standards and the opening area standards referred to in Building Regulations Approved Document Part L1B (2013).
To accurately produce the heat loss calculation it is important to have full planning drawings of the existing dwelling as it stands without the extension showing, in particular, dimensions of the openings that will no longer exist or no longer be exposed along with planning drawings of the existing dwelling with the proposed extension, including dimensions and specifications of windows, doors and roof windows and construction specifications for the wall, floor and roof of the proposed extension.
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