Damp in blocked up chimney - old house

[GrendelsMum]

One for the old house owners here.

We have a large central chimney stack, probably dating to about 1620, which is no longer used for fires, but is used to ventilate the boiler. It seems to be acting as a source of damp - in that the walls on two sides are damp at the base.

There are no vents at the bottom of the chimney as far as I can see.
Our builder suggested that one issue with the damp was that that there should have been a ventilation grill inserted when the fireplace was blocked up, in order to allow it to breathe. He also suggested that we should put a cap on the chimney the next time we've got scaffolding up round the house.

I'm going to run it past our architect at a meeting we're having next week, but thought I'd also ask here.

Has anyone else come across a similar issue, and if so, have similar causes and solutions been mentioned?

Dunno, but bumping for you because our former landlord is facing the same thing.

You definitely need to ventiilate it or fully open it and use it and the damp will stop Thats what we have done and the fire is lovely x

If it's still being used to ventilate the boiler, surely you shouldn't be capping it off at the top?

I'd suggest that the builder takes a couple of bricks out, perhaps one on each floor assuming it goes right up through the house, and insert ventilation grilles in them.

And Noddy's right, if you can reopen it as a fireplace, do so! I love our open fires.

Mumblechum I wondered that about caps, but apparently you can get special caps that don't fully cap it off but which keep much of the rain out, or something along these lines, for this situation.

Noddy I knew that you would suggest opening it up, but we already have one vast fireplace at the other end of the room (which has the stove in that heats the room), and I think that two in one room is more than I can cope with!

Right, it sounds like the verdict probably is to pop a ventilation grill in downstairs now, and perhaps to put ventilation upstairs when we work on those rooms. I shall put this to the architect next week.

Thanks very much! Mumsnet wins again.

I agree that you need ventilation, I'd get a couple of chimney sweeps round to have a look or a chimney specialist (look in the Yellow Pages).

IME architects are good at ideas but less good on the building/practical aspects of houses.

defo defo need ventilation. My dad is a property nut and in all houses we have been viewing it either had to have fireplace or vent in (and if the chimney breasts had been taken out but chimney stack was still there then walk away as that is a ton of bricks supported on nothing!)

It turns out that English Heritage have kindly answered my question already: www.climatechangeandyourhome.org.uk/live/chimneys_and_flues_faq.aspx#faq2

Thanks very much people for all your help! I'm amazed at the wealth of info that MumsNet can offer.

The architect is actually a conservation architect and specialist in 17th century buildings, hence wanting to run it past her - I can see it sounded a bit bizarre to ask her about chimneys otherwise.

It looks like the only question now is where to put the ventilation - whether we have to have it somewhere where it will be obvious, or whether we can get it at right angles to the fireplace, in the hallway.