In this guide
4. Further information: insulation and thermal elements
Making significant changes to thermal elements (wall, floor or roof) would normally require Building Regulations approval and require the thermal insulation of the element to be upgraded to a reasonable standard. Wall, floor or roof are defined by Regulation 2(3) of the Building Regulations 2010 as being thermal elements.
The extent to which the work on the element is controlled and the amount of upgrading needed depends on the particular circumstances of the thermal element. Generally, when it is renovated then it should be upgraded, where it is cost effective to do so, to the standard set out in the Approved Document. See section 5 and Appendix A of approved document L1B.
The definition in Regulation 2(3) is extracted here for convenience from the Building Regulations 2010
(3) In these Regulations "thermal element" means a wall, floor or roof (but does not include windows, doors, roof windows or roof-lights) which separates a thermally conditioned part of the building ("the conditioned space") from:
(a) the external environment (including the ground); or
(b) in the case of floors and walls, another part of the building which is:
(ii) an extension falling within class7 of Schedule 2; or
(iii) where this paragraph applies, conditioned to a different temperature,
and includes all parts of the element between the surface bounding the conditioned space and the external environment or other part of the building as the case may be.
(4) Paragraph (3)(b)(iii) only applies to a building which is not a dwelling, where the other part of the building is used for a purpose which is not similar or identical to the purpose for which the conditioned space is used.
Further guidance on this is available in approved document L1B covering:
- Guidance on thermal elements (Section 5 pages 17-18)
- Explanation of when renovation works trigger requirement for upgrading insulation and what additional work may be required.(see Appendix A and Table A1 pages 21-23)
You should fully consult the Regulations and the Approved Document and, if you are in any doubt, seek advice before commencing work. The definition of a thermal element does not include windows, doors, roof windows or rooflights.
Insulation can be placed between the ceiling joists. Again, the thickness will vary depending on the material you choose to use.
If the roof has no ceiling then the insulation can be placed between the rafters and ventilation maintained as described above - in which case the ridge should also have vent tiles installed to allow for through ventilation.
Further guidance on insulating roofs can be found in approved document L1B, Table A1.