Building Control guidance - renovations

Building Regulations L1b & L2b have now been extended to cover repairs, alterations, replacement and renovation of what are called the building's 'thermal elements'. This applies equally to both domestic and commercial buildings.

'Thermal element' is defined as wall, floor or roof (not including windows, doors , roof windows or roof lights), which separates a thermally conditioned part of the building ("the conditioned space i.e. heated or cooled space") from:

  1. the outside air or ground; or
  2. in the case of floors and walls, another part of the building which is
    1. unconditioned ( unheated or cooled ); e.g. floor over an unheated garage
    2. a conservatory / carport / porch extension; or
    3. conditioned to a different temperature , e.g. wall between a low level heated stock area and the main shop floor.

It will include all parts of the thermal elements between the surfaces bounding the conditioned space and the external environment or other part of the building as the case may be.

Also, for the avoidance of doubt, 'renovation' in relation to a thermal element is defined as the provision of a new layer in the thermal element or the replacement of an existing layer, but excludes decorative finishes, and 'renovate' shall be construed accordingly.

The intention is to improve energy performance standards when the thermal elements as a whole or layers within them are replaced or provided. As part of this the approved document L1B and L2B signal that where the renovation work affects less than 25% of the face area of the thermal element reasonable provisions would be to do nothing to improve energy efficiency.

Requirements relating to thermal elements

Where you intend to renovate or replace a thermal element you are required to carry out cost effective improvements.

The new building regulations provide guidance on what are considered cost effective insulation upgrades and the requirements for new replacements:

  • i.e. re-plastering a wall, simple stud work with insulation between and plasterboard would be required or insulation backed plasterboard. Please check on the thickness required for the insulation with building control before you start, (different insulations have different thermal properties which will influence the thickness)
  • i.e. re-roof covering, if possible 280mm of glass fibre insulation over the ceilings, with adequate roof void ventilation

Other examples of controllable work, requiring a Building Regulation submission

  • Re-tiling the roof or providing a new covering or sarking felt
  • Renewal or replacement of ceilings under a roof space or flat roof (with or without the renewal of the supporting structure)
  • Renewal of cladding to external walls and/or dormer cheeks
  • Renewal of internal wall finishes to an external wall (excluding decoration) or where you are applying a finishes for the first time e.g. re- plastering or dry lining of walls
  • Replacement of solid or timber floor at ground level or over an unheated space

Replacement windows are controlled fittings in their own right and are controlled under the Building Regulations L1b and L2b.