General
11.1 This section provides guidance for work to existing elements in dwellings, including all of the following types of work.
a. Renovating an existing thermal element in an existing dwelling – follow paragraphs 11.2 to 11.4.
b. Making a material change of use to a dwelling – follow paragraphs 11.5 to 11.8.
c. Making a change to a dwelling that constitutes a change to energy status – follow paragraphs 11.6 to 11.8.
NOTE: For new and replacement elements in existing dwellings, the guidance in Section 10 should be followed.
Renovating thermal elements
11.2 Renovation of a thermal element means one of the following.
a. Providing a new layer through cladding or rendering the external surface of a thermal element.
b. Providing a new layer through dry-lining the internal surface of a thermal element.
c. Replacing an existing layer through stripping down the element to expose basic structural components (e.g. bricks, blocks, rafters, joists, frame) and then rebuilding.
d. Replacing the waterproof membrane on a flat roof.
e. Providing cavity wall insulation.
11.3 If a thermal element is renovated and one of the following applies, then the whole of the thermal element should be improved to achieve at least the U-value given in Table 4.3, column (b).
a. More than 50% of the surface of the individual thermal element is renovated (see paragraph 11.4).
b. The work constitutes a major renovation. A major renovation is when more than 25% of the surface area of the external building envelope is renovated.
NOTE: If paragraph 4.13 applies, Appendix C provides examples of renovation of an existing thermal element that are technically, functionally or economically feasible.
11.4 When assessing the percentage area that will be renovated of an individual thermal element, consider whether the element is being renovated from the outside or the inside, following Diagram 11.1 and Diagram 11.2, respectively.
Diagram 11.1 Renovation of a thermal element from the outside
Diagram 11.2 Renovation of a thermal element from the inside
Material change of use and change to energy status
11.5 A material change of use, in relation to dwellings, is when a building satisfies any of the following:
a. is used as a dwelling, where previously it was not
b. contains a flat, where previously it did not
c. contains a greater or lesser number of dwellings than it did, having previously contained at least one dwelling.
11.6 A change to energy status is when a dwelling was previously exempt from the energy efficiency requirements but now is not. The change to energy status applies to the building as a whole or to parts of the building that have been designed or altered to be used separately. For example, when a previously unheated space becomes part of the heated dwelling in a garage or loft conversion, a change to energy status applies to that space.
NOTE: A material change of use may result in a change to energy status, for example if a previously unheated loft is converted into a flat.
11.7 If there is a material change of use and/or a change to energy status, elements should satisfy all of the following.
a. Existing thermal elements should meet the limiting standards in Table 4.3, following the guidance in paragraphs 4.11 and 4.12.
b. If both of the following apply to existing windows, roof windows, rooflights and doors (controlled fittings), they should be replaced to meet the limiting standards in Table 4.2.
i. They separate a conditioned space from an unconditioned space or the external environment.
ii. They have a U-value higher than either of the following.
• For windows, roof windows and doors – 3.30W/(m2·K).
• For rooflights – 3.80W/(m2·K), calculated by following paragraph 4.5.
In addition, all of the following should be met.
a. New or replaced thermal elements should meet the standards in Table 4.2, following the guidance in paragraphs 4.7 and 4.8.
b. New or replaced windows, roof windows, rooflights and doors (controlled fittings) should meet the standards in Table 4.2.
c. The area of openings in the newly created dwelling should not be more than 25% of the total floor area. In buildings that contain more than one dwelling a larger percentage area of openings may be achieved by following the guidance in paragraph 11.8.
d. Any fixed building services including building automation and control systems and/or on-site electricity generation that are provided or extended should meet the standards in Sections 5 and 6.
11.8 As an alternative to paragraph 11.7, in buildings that contain more than one dwelling, the Standard Assessment Procedure may be used to show that the dwelling primary energy usage and total CO2 emissions from all dwellings in the building, after completion of the building work, would be no greater than if each dwelling had been improved following the guidance in paragraph 11.7.
