TR-09 – Window Jamb Detail

This rendered window jamb detail shows a typical junction within a masonry cavity wall incorporating partial-fill rigid insulation and a proprietary insulated cavity closer.

The drawing illustrates the window frame, inner and outer masonry leaves, clear residual cavity, rigid cavity insulation, insulated cavity closer and internal plasterboard reveal. It demonstrates how the window frame, insulation, vertical damp-proof course, airtightness layer and external weather seal should be coordinated to reduce moisture penetration, air leakage, thermal bridging and surface-condensation risk.

A brick-faced version of this window jamb detail is also available. For broader energy-efficiency requirements around openings, consult Approved Document L.

Supporting notes cover:

• Minimum window-frame overlap with the insulated zone.
• Insulated cavity-closer installation.
• Vertical DPC continuity at the jamb.
• Window-frame fixings and packers.
• External weatherproof sealing.
• Internal airtightness around the opening.
• Plasterboard reveal construction.
• Render stop beads and reinforcement around opening corners.
• Junction SAP reference E4 and the calculated PSI value shown on the drawing.

The customer receives one downloadable PDF construction drawing, prepared at a scale of 1:10 and formatted to fit an A3 sheet.

The detail must be coordinated with the selected window, cavity closer, insulation and render systems. Dimensions, fixings, seals and installation requirements should be checked against the relevant manufacturers’ instructions and the project-specific wall construction.