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Built-Up Felt Flat Roof System - Retail

Repaired 105m sq. Flat roof

Two flat roofs, a main flat roof above a shop unit and a smaller adjacent roof on a shop front roof in central Manchester, UK

The existing roofs leaked, letting in water when it rained and we quoted for repairs to the defective flat roofs. Our initial roof survey identified rotten decking below defective felt membranes and so a complete reroof was required.

Medium Sized Flat Roof

• The total area: 105 metres square
• The existing defective roof covering - felts and chippings - and timber decking was stripped back to the sound roof joists and removed for disposal

• Poor drainage had caused the initial problems, so to prevent recurrence of water ponding we mechanically fixed 'firring pieces' (triangular wedges 3" to 0") to the joists. This added a pitch or fall to the new timber deck
• The roof areas were then redecked with 18mm Exterior grade WBP (Weather and Boil Proof) plywood decking. This ensures a high level of water resistance due to the water resistant adhesives used in construction
• To avoid ponding at brick wall abutments we installed 50mm x 50mm tilt fillets. The tilt fillets are 3 edged raised upstands that channel the water to the front gutter
• Renew felt covering with built up felt system to the specification discussed and agreed with each client - based on the merits of each proposal and based on the roof usage requirements and the costs agreed to suit the budget

• Felt roof consists of three layers of sheet felt material applied using the 'Torch on' system. 'Torching on' is ideal for many small to medium sized roofs because the felts are bonded together by the melting and setting of bituminous compounds.
• Torch-on felts contain the bituminous compounds that when heated with a gas torch melt and fuse the materials to forms a dense, void less, waterproof and impermeable barrier with total lap security
• Precautions against fire were required because direct heat was applied.
• Aluminium metal edged trims were supplied and installed, mechanically fixed along the edges of the roof
• 150mm Sheet lead flashing was supplied and installed at the abutment, mechanically plugged at 300mm centres
• Flashings were finished and sealed using a flexible lead sealant
• We applied a reflective paint to the top felt layer to form a surface that would protect against and prevent damage by UV radiation (solar) damage.