Asbestos Roof Encapsulation — Global House, Surbiton
From failing roof to finished system
The Challenge
The whole roof showed age-related wear: surface discolouration, patch staining and suspected microfractures around fixings and valley intersections. No health hazard had been reported, but the direction of travel was clear — continued exposure to rainwater, UV and temperature cycling would keep degrading the sheets until fibre release became a real prospect.
Removal was never the sensible answer here. Occupied homes and active business units sit within a 30-metre radius of the building. Stripping 1,575 m² of asbestos cement in that setting means fibre disturbance, a controlled waste stream and months of disruption to third parties with no stake in the works. The sheets were still sound; it was the surface that had failed.
Project file
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The Solution — step by step
The system
- GacoWash biocidal clean — 1:9 dilution. Applied by low-pressure sprayer with soft agitation. No power washing — uncontrolled jetting of asbestos cement abrades the surface being contained and mobilises fibres into the run-off. Cleaning liquids and residues were recovered by manual wet-vac under the site safety plan.
- Closed-cell roofing foam — 25 mm. Two-component polyurethane foam, spray-applied in successive lifts. It self-bonds to aged asbestos cement across the full corrugation profile with no mechanical fixings.
- GacoFlex S42 silicone. A 96.5% solids, solvent-free high-solids silicone, airless-sprayed and checked with wet-film comb gauges every 20 m² as the work proceeded. Flexible, UV-stable and fully seamless over the foam beneath.
The system was applied continuously across all four pitched roofs including the rooflights, through the integral valley gutter — re-profiled with foam to restore fall to the outlets — along both external eaves gutter runs, and across the office roof. A membrane with a break in it is not a membrane.
Safety and quality
Full perimeter scaffolding, harness systems over the fragile roof zones, debris netting and sheeting adjacent to offices and footpaths, and a gazebo spray booth to contain overspray. Work stopped above 7 mph wind for foam and 10 mph for silicone. Ambient and substrate conditions were logged daily, foam depth was spot-checked with calibrated probes, and product batch numbers were recorded against the site log. A GacoFlex pro-rata limited material warranty was registered with the manufacturer against the completed roof.
Land Remediation Relief
Asbestos containment works of this kind can qualify for Land Remediation Relief — an HMRC corporation tax relief giving an enhanced deduction on qualifying remediation expenditure. On completion a formal Asbestos Land Remediation Works Report was prepared, setting out the condition of the roof, the justification for encapsulation over removal, the system specification and the protocols followed — the evidence base the building owner’s accountants need to assess a claim. Duratite is not a tax adviser; whether relief is available is a matter for the owner’s accountants.
The Outcome
1,575 m² of asbestos cement now sits beneath a single bonded system — closed-cell foam over the sheets, a seamless silicone membrane over the foam, and the same treatment carried through both gutter systems. Not one sheet was removed, no controlled waste was generated, and the occupied homes and businesses within 30 m were never exposed to a removal operation, because there was not one.
On the roof — the full picture
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