Part L1B of the Building Regulations

Part L1B of the England and Wales Building Regulations covers extensions, building change of use, renovations and refurbishments. Part L1B is more complex than Part L1A and open to a degree of interpretation, dependent on the works being undertaken. Below is a brief outline of the key areas it affects.

When building an extension with more than the permitted openings area (25% of new floor area + existing openings covered by extension) or a non separated conservatory, a report, from an authorised SAP assessor, demonstrating compliance with Part L1B through elemental trade-off and/or whole dwelling trade-off will be required by Building Control.

When a property under goes a material change of use, such as when converting a large house into separate flats, it is necessary to provide a SAP report and PEA demonstrating elemental compliance as part of the initial building regulation submission. On completion an ‘as built’ SAP report is issued along with an EPC. Where more design flexibility is required an authorised assessor may use whole dwelling or building trade-off to demonstrate compliance.

For renovation and refurbishment projects it is necessary to be aware that if more than 25% of any existing thermal element is affected by works then the whole element should be improved to the required target U-value for that element. Controlled fittings (windows etc.) are also governed by minimum U-values when replaced, as are controlled services (heating and hot water systems etc.) with the efficiency of a new system not more than 2% worse than the original and no less than 86%. To demonstrate compliance or trade-off your obligation an authorised SAP assessor can provide all appropriate documentation building regulations.

Blewburton Limited can provide all of the above services and jobs are quoted on a case-by-case basis. For a formal quote, drawings of proposed changes/new constructions are required (as well as drawings of existing situation if available for material change of use), along with contact details of the Building Control Officer handling the case, so as to understand the output required.

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