Waterproofing Railway Arches, London – Case Study

The Client

The project took place in Streatham, South London, where nine disused railway arches were transformed into high-end creative workspaces available for rent. Each arch included shared kitchen, shower, and toilet facilities, creating a modern and collaborative working environment.

The Brief

The client required a robust waterproofing solution to deliver a completely dry, habitable internal environment in line with BS 8102:2022 ‘Grade 3’ standard. With water ingress evident through the arched ceilings and at the wall–floor junctions, the waterproofing needed to be reliable, maintainable, and sympathetic to the structure’s historic form.

The Challenge

The existing arches suffered from persistent water ingress caused by rainfall and surface water penetrating through the railway deck above. As the structure could not be waterproofed externally, a Type C internal cavity drain membrane system was needed to manage and control moisture within the substrate. The challenge was to design a system that could handle active water seepage while maintaining the visual character and functionality of the converted arches.

The Solution

A complete PermaSEAL Cavity Drain System was installed throughout the arches. PermaSEAL 8 Clear cavity drain membrane was applied to both the arched ceilings and floors to provide a continuous, watertight barrier. Any ingressing moisture was channelled via perimeter drainage to a safe passive discharge point.

A timber batten and insulated plasterboard lining was fixed in front of the membrane, providing a service void for electrical and plumbing runs while maintaining a neat finish. On the floors, T&G chipboard was laid over the membrane, ready for the oak flooring that completed the high-specification interior.

Products Used

• PermaSEAL 8 Clear (40m) Cavity Drain Membrane - our high-performance Type C membrane delivering reliable water management and vapour control across walls and soffits.
• PermaSEAL Drainage Channel System - our robust perimeter drainage channel designed for efficient collection and direction of ingress to the designated discharge point, with straightforward installation.

Results

The finished workspaces achieved a fully dry, Grade 3 habitable environment, ready for immediate occupation. The PermaSEAL system allowed the project team to deliver high-end, stylish, and durable offices with confidence in long-term performance. The system’s maintainability ensures that any future servicing or monitoring can be carried out easily, providing lasting peace of mind for the client and occupiers.

Why This Matters

This project highlights how PermaSEAL cavity drain systems provide dependable internal waterproofing for challenging structures such as railway arches. By using a maintainable Type C system, the conversion achieved modern performance standards without compromising on aesthetic quality or usability.

Permagard – Providing Solutions. Inspiring Confidence.

At Permagard, we supply trade-trusted waterproofing and damp proofing systems supported by free technical advice and full system design support. With over 35 years of experience, reliable 1–3 day delivery, and proven solutions for basements, tunnels, and heritage structures, our team is here to help. Call 0117 982 3282 or email [email protected] to discuss your project.