To meet the thermal insulation requirements, the thermal resistance (R) of the cavity closer should be minimum 0.45m²K/W. The following minimum depths of cut Thermalite® (excluding mortar), of width matching that of the inner leaf block, will comply with this figure:
- Turbo: 50mm
- Shield: 68mm
- Party Wall: 72mm
- Hi-Strength 7: 86mm
- Detail 17. Window frame
See also BRE IP 17/01 ‘Assessing the effects of thermal bridging at junctions and around openings’.
The window frame should overlap the closer block by minimum 30mm.