I visited my brothers new (1970s) house last weekend. Unfortunately (or fortunately, depending on which way you look on it) I have become a bit of a condensation geek and spotted a damp patch in the corner of his bedroom, then, dripping water in the corner of his son's cupboard where it met the outside wall and ceiling.

We went up into the loft, which is very well insulated, and there was loads of condensation in the roof sarking. Immediate thoughts were there wasn't enough ventilation in the loft, but we spotted the ducting from the bathroom extractor fan came up into the loft and then had been vented through the sarking. We couldn't see any tile vent from the outside.

He hasn't used the fan this last week (opened the window instead) and the condensation has disappeared (even though temps have been well below zero). Having spoken to a roofer friend, he was told that other people have been experiencing a similar problem. It looks very much like the guy who fitted the fan bunged it into the sarking and the steam is being vented into the gap between the roof tiles and sarking without fitting a tile vent, assume because he couldn't be 'bovvered'.

Another issue is that because the ducting goes vertically up through a very cold loft the steam must be condensing as it passes through this space and water collecting at its base as the condensate runs down. Insulating the ducting would have helped prevent that.

Just another case of crappy British building really, to warn others.

If you use uninsulated pipework you can fit a condensate trap, basically its a inline coupler with a drain point.

Have a look at fans with thermo electric shutters, to stop your heat escaping when the fan isnt on

Tonyt

Posted By: suegreenbuildingI am wondering how many other loft condensation problems are related to crappy installation of ducting for bathroom vents.

I'd long wondered why we seemed to get so much condensation in our seemingly well ventillated loft...
...until, while installing more insulation, I moved the simple brown plastic vent tube that ran horizontally for around 7m across the joists to the outlet in the gable end wall. Doing that dumped water both in the bathroom (via the extractor) and onto the existing insulaton (via holes knawed through the plastic tube by rodents).

For years, every time the shower was used a large proportion of the extracted moisture must have been going straight into the loft via the holes, with most of the rest condensing in the long horizontal pipe run!

Now replaced with a sloping 'shiny' pipe run, with condensation trap and anti draught valves. 'Someday', that lot is to be replaced by a "straight through the wall" extractor with automatic shutter...