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Acceptable Construction Details

Design flexibility and enhancement


Design flexibility and enhancement

Detailing significance

Traditional design and construction practice has concentrated on insulating heal loss 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 psi values at key detail areas. Issues to be addressed with regards to airtightness and thermal performance at key junctions are provided in the section entitled Achieving Thermal Continuity and Airtightness 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 effects on permeable insulation

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