Thermal separation
Approved document L, Conservation of Fuel and Power, Volume 2: Buildings other than dwellings, 2021 edition incorporating 2023 amendments, suggests that thermal separation:
Occurs where a building and a conservatory or porch are divided by walls, floors, windows and doors to which one of the following applies.
- The U-values are similar to, or in the case of a newly constructed conservatory or porch not exceeding, the U-values of the corresponding exposed elements elsewhere in the building.
- In the case of a newly constructed conservatory or porch, windows and doors have similar draught-proofing provisions as the exposed windows and doors elsewhere in the building.
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