Reviewed Feb 2017Case 1: Intermittently occupied holiday homes have occasionally featured in claim notifications. This case was in a location which gets very hot in the summer and very cold in the winter, with large temperature swings during the day. In the ski season, damp bodies clothes and equipment are inside – along with too many bodies and too much hotwater – after which the house was promptly closed up. Throughout the year, because it is far warmer inside than outside, moisture vapour is drawn in from the damp surroundings. It rises into the roofspace through the ply and batten ceilings under the metal roofing, to be held in the insulation before condensing to stain the ceiling.The owners disregarded the architect’s recommendation for a light coloured butyl roof, so the areas laid in a black membrane get wickedly hot, with every penetration or open joint allowing moisture (at least partly from the plumbing traps in the WC pans basins and sinks) to be drawn into the roof cavity. Of course the heat accelerates the rate at which the wall/ceiling joints open up, increasing the damage and the moisture movement.Case 2: At this house, a steel frame supports a steeply sloping timber framed skillion roof with metal roofing over. In this situation, the thermal properties of the steelwork suggest the potential for condensation and cold bridging. On opening up to investigate the ridge flashing, it was discovered that the steelwork was rusted despite the flashing being 100% ok. Heat on the roof had drawn in moisture vapour between the metal roofing profile and the building paper and/or through the boarded ceiling. It had migrated to the highest point where it condensed on the steelwork, and over a period of years stained the timber ceiling. The problem was solved by introducing ventilation from the low point in the ceiling to draw air up and through an opening at the high point in the ceiling. The circulation meant that moisture was no longer trapped in the cavityCase 3: A similar story – but a combination of Case 1 and Case 2. Recessed downlights in the bathroom provided a perfect opportunity for interior moisture to enter the roof cavity, with predictable results. In another case, the use of negative details instead of scotias had a similar outcome.Case 4: The black membrane roof at inadequate slope allowed water to pool at poorly welded membrane sheet joints which duly failed. Destructive investigation found rotten ply substrate, rusted connectors and structurally significant rot on the Posi-strut trussed rafters, and sodden insulation which contributed to the discolouration of the gib ceilings and the initiation of rot and mould.Case 5: A newly occupied almost finished concrete house. The owners shut up the house when they were out at work, and the heat build-up during the day was sucking significant volumes of moisture from the unpainted concrete walls and floor. Quite how much was not appreciated until the dripping started at the low point of the living room ceiling, by which point the whole of the roof structure was near saturation point and unable to dry out unless completely stripped and ventilated for a significant period. Ongoing dampness would of course have led to rot before too long.