This steel-framed industrial unit on the Derwent Howe estate in Workington has a flat roof bounded by blockwork parapet walls on three sides. The junction between the flat roof membrane and the parapet walls had been a persistent source of leaks since the building was constructed in the early 2000s. The original flashing detail used a self-adhesive bituminous flashing strip applied directly to the rendered blockwork — a budget solution that had never been fit for purpose on a building of this size and exposure. Over the years, the adhesive had failed and the strip had peeled away from the wall in multiple locations, allowing water to run behind the roof membrane and into the warehouse below. The building owner had engaged two previous contractors who had applied further layers of bituminous sealant and flashing tape over the top, creating a mess of overlapping patches that still leaked. Water ingress was damaging stock, disrupting operations, and creating slip hazards on the warehouse floor. The total run of parapet wall requiring attention was approximately 42 linear metres across three sides of the building.
After accessing the roof via a mobile elevating work platform, we stripped all existing flashing materials back to bare blockwork and cleaned the render surface thoroughly. We then installed a continuous treated softwood batten at the correct height to form a consistent line for the new flashings. New Code 5 lead cover flashings were installed in 1.5-metre sections — the maximum recommended length to manage thermal expansion — with each section let into a chase cut into the render and secured with lead wedges. Critically, we incorporated proper expansion joints between each section using a folded lead detail that allows each piece to expand and contract independently without pulling on its neighbours. The lower edge of each flashing was dressed over the existing roof membrane upstand with a minimum 75mm overlap, sealed with a compatible adhesive to the membrane surface. At the two internal corners where parapets meet, we formed bespoke corner pieces using traditional bossing techniques to ensure completely watertight junctions. The chases were pointed with a flexible polysulphide sealant rated for the industrial environment.
The building has been completely leak-free since the work was completed over 18 months ago, through two full winters of Workington weather including several periods of sustained heavy rain. The Code 5 lead flashings provide a robust, industrial-grade solution that will not require maintenance for decades. The proper expansion joint detailing has eliminated the stress failures that caused the original flashings to fail — each section moves independently with temperature changes, preventing the cumulative forces that tear rigid flashings from the wall. The building owner estimated that the elimination of stock damage and operational disruption paid for the lead flashing project within its first year. This is a good example of how investing in proper leadwork upfront saves significant money compared to repeated temporary repairs that never fully resolve the problem.
Code 5 lead (2.24mm thick) was specified throughout this project due to the long, exposed parapet runs and the industrial environment. The additional thickness compared to Code 4 provides critical resistance to thermal fatigue — on a south-facing parapet in Workington, surface temperatures can swing 40°C or more between a winter night and a summer afternoon, causing significant expansion and contraction. Code 5 can withstand many more thermal cycles before fatigue cracking develops, making it the correct specification for commercial flat roof parapets.
A continuous pressure-treated softwood batten was fixed to the parapet wall to provide a consistent fixing line and support for the lead flashings. This batten creates a slight stand-off from the wall surface, forming a capillary break that prevents water from being drawn behind the flashing by surface tension. The treatment protects the timber against rot for 30+ years, ensuring long-term structural support for the lead work.
The chase joints were sealed with a two-part polysulphide sealant specifically rated for commercial and industrial applications. Polysulphide provides excellent adhesion to both lead and cementitious substrates, remains permanently flexible to accommodate thermal and structural movement, and resists UV degradation and chemical exposure better than standard silicone sealants. This is essential in a trading estate environment where the roof may be exposed to fumes and pollutants.
The overlap joint between the lead flashings and the existing flat roof membrane was sealed with an adhesive specifically formulated for compatibility with both materials. Using an incompatible adhesive can cause plasticiser migration from the membrane, leading to premature failure of the bond. Our specification ensures a permanent, flexible joint that maintains its integrity through the full range of thermal cycling experienced on this Workington building.
From parapet flashings on industrial units to heritage leadwork on residential properties, Mr Roofer UK provides expert lead work services across Workington and West Cumbria. We deliver permanent solutions that eliminate persistent leaks — no more temporary patches. Contact us today for a free survey and quotation on any commercial or residential roofing project.
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