FLAT ROOFS REPAIR
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Repairs to a water damaged flat roof in Failsworth, Manchester.
A small leak in a felt roof left unrepaired had damaged the existing chipboard deck. Both the felt and chipboard had to be removed. New OSB* decking was installed and a Firestone Rubber EPDM* surface membrane bonded to the deck. UPVC upstand side trims and lower edge gutter trims also installed to direct rainwater into the gutters.
Materials
OSB is short for Oriented Strand Board. As the name suggests this material is made of thin strands of wood bonded together with resins. The inner core bonding agent is isocyanate-based or melamine-urea-formaldehyde, both of which are waterproof. The surface layer bonding agent is usually phenolic resin which is both waterproof and acts as a wood preservative.
EPDM is short for Ethylene Propylene Diene Monomer. It is synthetic rubber formulated to be especially waterproof and resistant to degredation by strong sunlight, water and airborne pollutants.
Science
Warm air holds more mositure than cold air. When the warm air percolates through the ceiling it takes with it moisture. When this moisture hits a boundary such as the waterproof decking above the thermal insulation the cool surface causes the air to release the water vapour. Just like condensation on the inner surface of a glass window. This moisture builds up over time soaking the thermal insulation so it becomes useless and will rot the roof timbers.
There are two ways to prevent this problem: either provide a small amount of ventilation above the thermal insulation, or place a vapour barrier on the ceiling. In practice two coats of good quality emulsion paint will do the trick. Another way is to use foil backed plasterboard for the ceiling.
Always consult the experts — Roof Expert Manchester
