LOCATION
B&M Penrith
WATERPROOF SYSTEM
Project Type: Retail Shop Re-roof (Overlay)
System: Two-layer torch-on modified bitumen felt
Location: High-street retail unit (occupied during works)
Roof Type: Flat timber deck with existing aged felt.
BACKGROUND TO THE PROJECT/CHALLENGE
A local retail shop required a cost-effective roofing upgrade due to persistent leaks and aging waterproofing. The existing felt roof was approximately 18 years old, showing signs of blistering, splitting at laps, and water ingress around roof penetrations.
Because the deck remained structurally sound and the shop needed to remain operational, a 2-layer overlay felt system was selected instead of a full strip and replacement.
Moisture testing confirmed the insulation below was dry and suitable for overlay. Core samples verified deck integrity.
PROJECT SOLUTION
A two-layer torch-on modified bitumen system was specified:
The system provided:
Scope of Work
The project began with thorough preparation of the existing roof surface. All debris and loose mineral were completely removed to ensure a clean working area. Any blisters present in the roofing membrane were carefully cut out and flattened to create a smooth, stable surface. Existing splits were reinforced to prevent further deterioration. Once these repairs were completed, a primer was applied across the prepared surface to improve adhesion for the new roofing materials.
Following preparation, the underlay was installed. The underlay membrane was torch-applied and bonded directly to the properly prepared surface to ensure a secure and durable base layer. All side laps were sealed at 100mm to provide a watertight seal and maintain the integrity of the system.
The final stage involved installation of the cap sheet. This layer was fully torch-bonded to the underlay to create a strong, weather-resistant finish. Side laps were formed at 100mm, with end laps set at 150mm to ensure full coverage and protection. The cap sheet featured a mineral finish, providing enhanced UV resistance and long-term durability of the roofing system.
THE OUTCOME
The 2-layer overlay felt system proved to be a practical, durable, and cost-efficient solution for this retail property. By retaining the existing substrate and applying a fully bonded modified bitumen system, the client achieved long-term protection without major operational disruption.
By installing a 2-layer overlay system rather than carrying out a full strip and replacement, we significantly reduced the environmental impact of the project. Retaining the existing waterproofing eliminated the need to dispose of large volumes of roofing membrane, reducing landfill waste and transport emissions.
This case demonstrates that, when correctly assessed and installed, overlay felt roofing can extend a flat roof’s service life significantly while maintaining business continuity.
We worked closely with RMLFS for this job.
For more about our market leading waterproof membranes check out System Endura 4.5 BBA and the rest of the Lancastria range or call our team on 0161 777 9009 to place your order.
Get in touch
Lancastria Group
(main office and hoist hire)
Unit J, Woodrow Way, Irlam,
Manchester, M44 6ZQ
Lancastria
(deliveries and collections)
Unit 8, Woodrow Way
Irlam, Manchester
M44 6ZQ
For deliveries and collections please go to Unit 8. On Woodrow Way, take the first right immediately around the corner from Howdens and Andrews Tiles. Our warehouse is the second unit. If you get to our main Lancastria office, you have come too far.
