Posted 09 October 2011 - 06:11 PM
One thing worth looking at is any changes that have been made to the house, specifically loft insulation and whether or not adequate ventilation has been provided in the roof void.
My house, although much newer than your, developed severe condensation on the sarking and roof timbers. It was so bad that I started to get staining in places on the ceilings below, from water finding its way through the plasterboard. Having lived in the house for years, and having never had a problem until a few years ago, I couldn't quite understand why the problem had suddenly started.
The reason turned out to be the added insulation I'd added in the loft. I'd upped the insulation from a measly 100mm to 250mm, and this had cooled the loft space. The house was built with no soffit vents, just air bricks in each gable end wall. The sealing between the bathroom and the loft, and the sealing around the loft hatch was poor.
Adding soffit vents, and sealing the loft hatch and bathroom ceiling where pipes went up from the airing cupboard, has removed my problem. It may well be that your problem is similarly exacerbated by added insulation to the loft, without adding better ventilation at the same time.