Compliant/Non-Compliant Building Elements!

Developers Risk Reduction in Final Dwelling Build-Out Numbers on Site.

Scheme Proposals Achieve Planning Approval but Risk Non-Compliance under Part L1A Overall On Construction

With the tightening of building regulations (Part L1a) DER v TER; designing dwellings to just meet the limiting fabric parameters listed for Part L1 Criterion 2 is more than ever unlikely to not only lead to a non-compliance overall due to the way compliance is calculated. It may also lead to a reduction in the number of dwellings which could eventually be built on a site due to the increase in wall thickness needed to achieve compliance. This potential reduction may not be picked up during the planning process where standard Part L compliant wall thicknesses are used in the scheme designs. The limiting fabric parameter listed in L1A for external walls is 0.30 W/m2K, this could be achieved through approx. 300mm wall. However dwellings with a wall construction of such a performance may not achieve compliance overall and a much improved U-Value may actually be required. This enhanced U-Value is likely to come at a cost or penalty in terms of thickness. For example The NHBC Foundation in its Part L Masonry Guide has published the following typical construction build-ups designed to achieve the enhanced U-Values;  all require a significant increase in wall thickness. Masonry Wall Type 1: fully filled external wall (Plasterboard on dabs, 100 mm blockwork, Mineral wool insulation (λ = 0.032 W/mk) 100 mm brickwork).
  Aircrete blockwork (λ = 0.15 W/mk) Ultra lightweight blockwork (λ = 0.28 W/mk) Dense blockwork (λ = 1.33 W/mk)
U-value Wall thickness Insulation thickness Wall thickness Insulation thickness Wall thickness Insulation thickness
0.18 W/m2K 390 mm 160 mm 405 mm 175 mm 410 mm 180 mm
0.15 W/m2K 425 mm 195 mm  
 Masonry Wall Type 2: partially filled external wall (Plasterboard on dabs, 100 mm blockwork, Rigid PIR insulation (λ = 0.022 W/mk), 50 mm clear cavity 100 mm brickwork).
  Aircrete blockwork (λ = 0.15 W/mk) Ultra lightweight blockwork (λ = 0.28 W/mk) Dense blockwork (λ = 1.33 W/mk)
U-value Wall thickness Insulation thickness Wall thickness Insulation thickness Wall thickness Insulation thickness
0.18 W/m2K 375 mm 95 mm 385 mm 105 mm 390 mm 110 mm
0.15 W/m2K 400 mm 120 mm 405 mm 125 mm 415 mm 135 mm
 Energy-Evaluation Consultants can aid in the review of House Types and Schemes to assess risk of non-compliance.
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