Extensions, Alterations & Conversions in the new L1 2021
Since the 15th June 2022 the new building regulations for England have been in force. The new part L covers the conservation of fuel and power (previously split into L1A and L1B).
This article will be focusing on extensions, alterations and conversions in the new part L1, summarising the important and most commonly used standards that are required for the works on an existing dwelling or change of use to a building.
To what buildings do these new regulations apply:
These regulations will apply to existing buildings that are proposing or undergoing building works. In summary works that will affect the build-up of the building or changing the use of a dwelling. These works could include; alterations, extensions, loft conversions, glazing replacement, change of use. Depending on the type of building and the works being done, will determine the extent of which set of requirements will need to be met.
The two biggest changes for extensions, alterations, and conversions are the new minimum standards for fabric efficiency, and the requirements for new heating systems.
Standards for fabric efficiency:
The fabric efficiency of a building is split into the thermal efficiency of each material used in the build-up of a building. This is measured in U-Values, if you would like a deeper explanation of U-Values, check out this article https://www.erscltd.co.uk/the-significance-of-u-values-in-buildings-and-construction/
New elements:
New elements in existing dwellings and extensions include the following work;
- A new thermal element
- Replacing a thermal element
- Replacing windows, doors, or rooflights
- Extending an existing dwelling
- Addition of a conservatory or porch
| Element | Previous U-Value W/m²K | New U-Value
W/m²K |
% Improvement |
| Roof – Flat/Insulated at Rafters | 0.18 | 0.15 | 18% |
| Roof – Insulated at Joists | 0.16 | 0.5 | 6% |
| Wall | 0.28 | 0.18 | 36% |
| Floor | 0.22 | 0.18 | 18% |
| Window | 1.60 | 1.40 | 13% |
| Doors | 1.80 | 1.40 | 13% |
Improvements to existing thermal elements:
- A new layer to the external surface such as cladding or rendering
- A new layer to the internal surface such as dry-lining
- Replacing an existing layer, stripping an element to its basic structure and building it back up
- Replacing the waterproof membrane of a flat roof
- Addition of cavity wall insulation
- More than 50% of the surface of the thermal element is being renovated
When a thermal element is being renovated, additional factors must be considered. For example, if a building is listed or under specific planning conditions there could be restraints on how much an element can be built up. Further this section explains how certain areas of a thermal element can be improved without improving the whole fabric. The factors to be considered include:
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The work can be classed as a major renovation (when more than 25% of the surface area of the building element is being renovated)
Heating Requirements:
New boilers will have to reach an efficiency of 92% rather than the previous 88%, and the heating systems should have a maximum flow of 55 degrees. This lower temperature eliminates burn risk, however may lead to larger radiators being required. Despite this, it will make it easier to later upgrade dwellings with Air Source Heat Pumps or Ground Source Heat Pumps, which mirrors the government’s move to sustainable resources for a low-carbon heating future.
Summary:
The work needed to achieve compliance for any existing building going under any extensions, alterations and conversions is considerably more than on the previous regulations.
Within the new approved document, the minimum U-values for new thermal elements or replacement elements in an existing dwelling can be seen in Table 4.2(Limiting U-Values for new fabric elements in existing dwellings). Existing fabric elements of a building such as conservatories that will become thermal elements will need to reach the minimum U-Values stated in table 4.3(Limiting U-Values for existing elements in existing dwellings). This table should also be followed when renovating existing thermal elements of an existing dwelling, and when the project is a material change of use.