A commercial storage unit in Workington had a large concrete-decked flat roof that was leaking through degraded asphalt. Our felt roofing specialists applied a three-layer torch-on overlay system directly onto the prepared concrete, providing a cost-effective waterproofing solution without the disruption and expense of removing the existing deck.
This industrial storage unit on an estate in Workington had a 90-square-metre concrete-decked flat roof originally waterproofed with mastic asphalt. The asphalt had developed numerous cracks — particularly across the expansion joints in the concrete slab — and several areas had debonded from the concrete, creating hollow sections where water pooled above and slowly percolated through the cracks to the unit below. The tenant was storing temperature-sensitive equipment and needed a rapid, reliable solution. Full roof replacement was impractical due to the cost of removing the heavy concrete deck and the structural implications of changing the roof system. The building owner needed a waterproofing solution that could be applied directly over the existing concrete and completed within a week to minimise the tenant's disruption.
After power-washing and cleaning the concrete deck to remove all loose asphalt, moss, and debris, we applied a bituminous primer to the entire surface to promote adhesion. A three-layer torch-on felt system was then installed: first, a self-adhesive vapour control layer to prevent moisture transmission from the concrete; second, a polyester-reinforced underlay sheet torched in place; and third, a heavy-duty SBS-modified cap sheet with a mineral aggregate finish torched onto the underlay. The three-layer specification was chosen for this commercial application because the additional underlay provides an extra waterproofing layer and improves the system's ability to bridge cracks in the concrete substrate — critical given the known expansion joint movement in this deck. All upstands at the parapet walls were formed using the same three-layer system, dressed 150mm up the wall and terminated with a lead-covered trim. New outlets were installed at two locations where the internal downpipes pass through the deck, with pre-formed GRP sumps bonded into the felt layup. The entire 90-square-metre roof was completed in 4 working days.
The overlay system has performed flawlessly since installation, with the tenant reporting zero water ingress through two full winters of West Cumbrian weather. The three-layer system's crack-bridging capability has accommodated the seasonal thermal movement of the concrete deck without any stress cracking in the felt. The mineral aggregate cap sheet provides excellent foot traffic resistance for maintenance access, and the light grey colour reflects more solar heat than the old black asphalt, noticeably reducing summer temperatures inside the unit. The building owner was particularly pleased with the cost saving — the overlay approach cost approximately 40% less than a full deck replacement would have. We provided a 20-year guarantee on the felt roofing system.
This commercial-grade felt roofing system comprises three distinct layers, each serving a specific function. The self-adhesive vapour control layer at the base prevents moisture transmission from the concrete deck. The polyester-reinforced underlay provides tensile strength and crack-bridging capability across the substrate's expansion joints. The SBS-modified mineral-finished cap sheet delivers the primary waterproofing with UV protection and foot traffic resistance. Together, these three layers create a robust system rated for a minimum 25-year service life on commercial applications.
The cap sheet uses a high-quality SBS (Styrene-Butadiene-Styrene) modified bitumen compound with a slate grey mineral aggregate surface. The SBS modifier maintains flexibility at temperatures as low as -25°C, preventing the cold-weather cracking that is the primary failure mode of standard bitumen felt. The mineral aggregate provides excellent resistance to foot traffic, UV degradation, and hail impact, making it ideal for this commercial Workington application.
The solvent-based bituminous primer penetrates the porous concrete surface, displacing any residual moisture and creating a tack coat that ensures permanent adhesion between the concrete deck and the felt system above. Proper priming is essential for overlay systems to prevent wind uplift or delamination.
The parapet terminations use proprietary lead-covered trims that are chased into the brickwork and dressed down over the felt upstand. This traditional detailing method provides a durable, maintenance-free termination that withstands decades of thermal movement and weather exposure.
Our felt roofing specialists handle commercial and residential flat roof projects throughout Workington and West Cumbria. From overlay systems to full strip and replacement, we deliver reliable waterproofing solutions with written guarantees. Contact us today for a free commercial roof survey.
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