Detailed Construction Drawings

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Outline ACDs Acceptable Construction Details

Design and Flexibility and Enhancement


Detailing significance

Traditional design and construction practice has concentrated on insulating exposed walls, floors and roofs of buildings, to reduce thermal transmittances (U-values). Until recently there has been limited focus on the heat losses that occur at the junctions between construction elements and around openings, or on the heat losses that occur because of uncontrolled air leakage. As standards of insulation have improved, the proportion of the total heat loss that may be attributed to these causes has increased.

Enhanced Thermal Performance

Relatively straightforward changes in construction detailing can deliver reductions in ψ values at key detail areas. For example, certain ground floor to wall junctions can be improved by about 80% and ceiling to gable wall junctions by about 85%. Issues to be addressed with regards to airtightness and thermal performance at key junctions are provided in the following sub headings 1 to 10 of this document. These include:

Substitution of normal medium-density concrete blocks by insulating blockwork:

  • at the ground floor zone in external walls

  • behind back cills at external wall opes

  • at the attic insulation level in party walls; and

  • at parapet roofs

Installation of a wind barrier in ventilated roof spaces, to reduce the wind chill effect on open-cell attic insulation

Use of a purpose-made air-tight membrane around the envelope, with joints taped and sealed, particularly at junctions in the external wall, around service penetrations, and at internal and external corners