TB/19 – Warm Flat Roof Detail

This warm flat roof detail illustrates the junction between an insulated masonry cavity wall and a timber roof with rigid insulation above the deck.

It is intended for architectural designers, building professionals, contractors, developers and self-builders coordinating waterproofing, insulation, drainage and airtightness. For a plain-English explanation of warm-roof construction, see our related guide; Approved Document C provides the official moisture-resistance guidance.

The detail shows:

• Single-ply membrane or GRP waterproofing
• Proprietary separating or isolation layer
• 210 mm Kingspan Thermaroof TR27 rigid PIR insulation
• Continuous vapour-control layer above the roof deck
• 22 mm external-quality plywood or OSB3 roof deck
• Timber joists and structural falls
• Foil-backed plasterboard ceiling
• Vapour-control layer turned up and sealed at the roof perimeter
• Continuous roof-edge insulation
• Aluminium perimeter trim
• Fascia board and mastic seal
• Wall plate and masonry cavity-wall junction
• Cavity ventilation
• Calculated psi value of 0.038 W/m·K
• Temperature factor of 0.92

The accompanying notes cover waterproofing, insulation, vapour control, roof decking, design falls, finished falls, outlets, emergency overflows, upstands, edge trims, airtightness, condensation control and fire performance.

What This Warm Flat Roof Detail Includes

• One downloadable PDF construction drawing
• A3 landscape sheet
• Drawn at 1:10 when printed at 100% on A3 paper
• Drawing reference: TB/19
• Detail title: Flat Roof Detail

Important Information

This is a standard construction detail intended to provide general guidance. Roof joists, trimming members, falls, restraint and connections must be designed for the particular project by a suitably qualified structural engineer.

Waterproofing must form part of a compatible proprietary system installed by an approved specialist contractor. Insulation thickness, condensation control, drainage capacity and fire performance must be confirmed through the project-specific design and manufacturers’ requirements.

The stated psi value and temperature factor apply only where the illustrated construction, geometry and materials are followed.

The drawing does not include structural calculations, roof-drainage calculations, a condensation-risk assessment, SAP assessment or Building Regulations approval.

The PDF is supplied for use by the purchaser on their own projects. It may not be resold, redistributed or reproduced for commercial resale without written permission.