TR-08 – Window Cill Detail

This detailed drawing shows a typical window-cill junction within a rendered masonry cavity wall with partial-fill rigid insulation and an insulated cavity closer.

The drawing illustrates the window frame, proprietary cill, insulated cavity closer, clear residual cavity, rigid cavity insulation, inner and outer masonry leaves and internal plasterboard finish. It demonstrates how the frame, cill, insulation, damp-proofing and airtightness layers should be coordinated to reduce moisture penetration, air leakage, thermal bridging and surface-condensation risk.

Supporting notes cover:

• Proprietary window-cill installation and support.
• Minimum projection beyond the finished render.
• Throating and drip formation.
• Flexible DPC or cavity tray beneath the cill.
• Turned-up ends and stop ends.
• Insulated cavity-closer installation.
• Minimum window-frame overlap with the insulated zone.
• Cavity and insulation continuity.
• Internal airtightness seals.
• Render beads, reinforcement and weatherproof sealing.
• Junction SAP reference E3 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 for an A3 sheet.

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