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It should be remembered that building regulations usually state the minimum performance requirements and obviously in an ideal world we would always achieve far better. However, special considerations are given within part L of the building regulations for good reason as other factors when undertaking building retrofit must also be considered.


Under section 3.8 C of building regulations Part L1B: “special considerations” may apply to “buildings of traditional construction with permeable fabric” (HM Government, 2010, P8), and further states that when upgrading the thermal performance of an existing dwelling it should be “reasonable” “feasible” and deliver a “simple payback” (HM Government, 2010, P18). Retained thermal wall elements with a U-value higher (worse) than 0.7W/m2k are required to achieve an improved U-value of 0.30 W/m2k (for external or internal insulation) “provided this is technically, functionally and economically feasible” (simple payback of 15 years or less) (HM Government, 2010, P18). Where the standard is not feasible, it should be upgraded as far as practicable and “generally” “not be worse than 0.7W/m2k” (HM Government, 2010, P18).

Airtightness in buildings is also key to minimising heat loss though infiltration, cracks and gaps in the building fabric can lead to significant heat loss, under Part L of the building regulations existing dwellings are required to make ‘reasonable provision’ (HM Government, 2010b) to reduce infiltration as improving the airtightness of older solid wall homes is difficult and can also lead to further problems of moisture build-up and mould growth (Hall et al., 2013).

A note on regulations