Section 11: Work to fabric elements in existing buildings
General
11.1 This section provides guidance for work to fabric elements in existing buildings, including all of the following types of work.
a. Renovating an existing thermal element in an existing building – follow paragraphs 11.2 to 11.4.
b. Making a material change of use to a building – follow paragraphs 11.5 to 11.8.
c. Making a change to a building that constitutes a change to energy status – follow paragraphs 11.6 to 11.8.
NOTE: For new and replacement elements in existing buildings, 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 the 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 in Table 4.2 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.
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 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 buildings other than dwellings, is when a building satisfies any of the following:
a. is used as a hotel or a boarding house, where previously it was not
b. is used as an institution, where previously it was not
c. is used as a public building, where previously it was not
d. is not described in classes 1 to 6 in Schedule 2, where previously it was
e. contains a room for residential purposes, where previously it did not
f. contains at least one room for residential purposes, having previously had a greater or lesser number of rooms for residential purposes
g. is used as a shop where previously it was not.
11.6 A change to energy status is when a building 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 building.
NOTE: A material change of use may result in a change to energy status.
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 standards as outlined in paragraphs 4.7 to 4.8.
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 4.1.
NOTE: This does not apply to display windows or high-usage entrance doors.
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 4.4.
In addition, all of the following should be met.
a. New or replaced thermal elements should meet the standards in Table 4.1.
b. New or replaced windows, roof windows, rooflights and doors (controlled fittings) should meet the standards in Table 4.1.
c. The area of openings in the newly created building should not be more than 25% of the total floor area. A larger area of openings may be achieved by following 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.
NOTE: Consequential improvements may be required when there is a material change of use or change to energy status and Section 12 should be followed.
11.8 As an alternative to paragraph 11.7, an approved calculation tool may be used to demonstrate that the building primary energy rate and building emission rate from the building after the material change of use would be no greater than if the building had been improved following the guidance in paragraph 11.7.
