Loft Condensation,Vapour Barriers,Paints etc

nad1611

malc_b wrote: »

Is the stove and the loft condensation related? Just because they happened at the same time doesn't make it cause and effect. If the loft condensation is caused by the stove then it would happen when you run the stove and there must be some fumes getting into the loft, so you need to get that sorted otherwise you are dicing with carbon monoxide poisoning. BTW I assume this stove has a chimney and isn't one of these no chimney room heaters. If it is then you will get a lot more moisture in the air with those which would add to the moisture load in the loft as hot air rises and I doubt the ceiling is air tight.

I see you say you had loft insulation done. Are you sure that the condensation isn't caused by this extra insulation (which makes the loft colder of course). Typically you need to improve the loft ventilation when you increase the loft insulation. Modern houses have vents at the eaves and at the ridge. Older houses just had them at the eaves and hot (wet) air rises. The usual fix is to wedge open the roofing felt at the overlaps to increase the ventilation. You can buy products to do this, Google felt lap vent to find page like this, or you can be like me a cheapskate and cut triangular wedges from waste polystyrene.

Thanks for this. A lot of info, so great. To answer a couple of questions. The insulation was done about 5 years ago, we've never had a problem with condensation at all before last winter, even though as you say the loft has been colder since the insulation. As the only thing that had changed since the condensation began,was getting a multi fuel burner installed, we presumed it had to be that. With regard to the chimney, yes it has a chimney and was fitted by a Hepas installer. We have a carbon monoxide detector on the lower level and as the HEPAS installer gave us one for free, he put that one on the upper level, just by the loft hatch. Obviously I don't know how sensitive the detectors are but if CO was getting into the loft, I am guessing that would be detected? Particularly as we had the loft hatch open when we were checking the condensation.

I don't imagine heat would leak from the chimney within the loft, one because the chimney remains cold even with the stove running and is cool to touch and the fact that there is a flue from the stove attached to a chimney liner which runs up the length of the chimney.

nad1611

malc_b wrote: »

I would since it is plain wrong! The warmer air is the more water it can hold. The colder the less it can hold. As air cools it eventually reaches 100% humidity, the dew point, and you get condensation. Now the outside air at most could be 100% at the outside temperature. Bring that air into the loft and it will be warmed, just a bit, by the heat leaking from the house. Hence it's humidity will go DOWN.

The opposite effect occurs with air leaking from the house into the loft. That is warm and potentially has a high humidity. When that gets into the loft it cools and its humidity goes up. What you need to do is get that to the outside and replace it with outside air, which is why you vent.

This makes perfect sense to me, you've explained it so well. :T
So it seems, we need to double check on the ventilation and add additional ventilation if necessary. I'll check out the wedges for the felt. Thanks everyone.
Just got to get up there and do it now...groan!

Kiran

If your flue goes through your loft albeit inside a chimney you will also be warming the air in what would ha e previously been a cold area. The flue temp is say 200-250 C ish on an efficient burn, over time the brickwork will warm up a bit like a storage heater and give off heat into the loft which will then condense on the cold surface of the roof. As above, providing sufficient ventilation to the loft space should cure the issue.