Meir Roofing

Environmentally friendly polyurethane boards (PUR) and (PIR) boards are foamed with an inert gas or blowing agent that is locked into the cells and gives the board’s better insulation characteristics than foams which have air filled cells. The blowing agent must conform to internationally agreed levels of ozone depletion potential (ODP) and some blowing agents can only be regarded as transitional until all materials are developed to contain no significant ODP. There is no agreed definition of PUR and PIR formulations, but the term PIR type is used to describe rigid urethane foam with increased resistance to high temperatures, sufficient to withstand the heat of mastic asphalt on application. The cell walls are slightly permeable to air and over a period of several years the air will diffuse into the cells until it reaches atmospheric pressure. The thermal efficiency of the foam decreases over this period and this should be allowed for in the figures published for thermal conductivity. A suitable test for thermal conductivity of aged material is the ACERMI test from France and manufacturers should be asked to confirm that their quoted thermal conductivity properly allows for long term ageing. A selection of facings for differing waterproofing systems, flat, composite or profiled boards and cut to falls to ensure that all requirements are satisfied. Unfaced rigid urethane foam is likely to suffer movement from changing temperature and conditions. A glass tissue facing is therefore used to control the foam and produce a stable board to receive built-up roofing and asphalt. Board for built-up roofing is normally faced with perforated layer of bitumen coated glass tissue for good part-bonding of membranes and the board for asphalt is faced with glass tissue only. Partial bonding is not suitable for sloping roofs and a cork or fibreboard overlay should be added to allow a fully bonded system