Converting a Flat Roof Into a Roof Terrace

Converting a flat roof into a roof terrace can add significant value and usable space to a property. It's a project that requires careful planning across multiple disciplines — structural, waterproofing, planning, and finishing.

Planning Permission

Creating a roof terrace almost always requires planning permission, as it creates a new elevated outdoor space from which neighbours may be overlooked. Make this your first step before investing in any design work.

Structural Considerations

A roof designed purely as a weatherproof cover may not be strong enough for regular human access and furniture loads. A structural engineer must assess the decking, joists, and supporting walls, and specify any necessary upgrades.

The Waterproofing System

Roof terraces require an inverted warm roof system with a heavy-duty, traffic-resistant waterproofing membrane. The membrane is protected by insulation boards, then paving slabs, composite decking, or similar. The quality of the waterproofing is critical — once covered, it's expensive to access.

Drainage

Roof terrace drainage must be carefully designed. Outlets must be sized for the expected rainfall and must be accessible for maintenance. A secondary overflow is required to prevent flooding if the primary drain blocks.

Balustrades and Safety

Any roof terrace requires building regulation-compliant balustrades. These must be at least 1.1m high and strong enough to resist the forces specified in the building regulations. This is non-negotiable on safety grounds.