Chapter 1: Why are there damp patches in the loft of our Zebon Copse era house?
What we find
Houses from the late 1980s were commonly roofed with concrete interlocking tiles over a bitumen felt underlay, the sheet laid across the rafters beneath the battens to catch any water that gets past the tiles. Thirty-odd years of sun and frost leave that felt dry and cracked, and it tends to fail first where it drapes over the ridge board and where it laps at the valleys. A damp patch in the loft with no matching hole in the tiles is the classic sign.
Condensation is the other suspect. Lofts of that era were often topped up with insulation that has since been pushed hard against the eaves, blocking the airflow, so warm air from the house condenses on the cold underside of the felt. A good survey separates the two, because one needs new felt and the other needs ventilation put back.
What we fix
From inside the loft we look for daylight, wet timber and drip marks, then lift a few tiles on the outside to inspect the felt and the battens beneath. If the problem is a local tear, we reslate the area with new felt and relay the same tiles. Where condensation is the cause, we fit eaves ventilators and tile vents and pull the insulation back from the eaves so air can pass. Our guide on whether you need tile vents explains how that works.
When the felt has perished across whole slopes, patching stops being honest and a strip and re-cover is the right answer. A concrete-tile re-roof on a typical three-bedroom semi is reported across the UK at £6,500 to £10,500, with the fixed quote following the survey. Our pitched roofing page sets out how those jobs run, including the breathable underlay we would use in place of the old felt.