Old open fire chimney

[TheKeymeister]

Mother in laws house is suffering with damp and I suspect part of it may be caused by the old open fire in one room that hasn't been used in probably 20 years, as it's been used as a bedroom.
Chimney pots are completely open at the top, letting in rain water, birds, draughts and other undesirable stuff.
There will be scaffolding up soon as some work is being done on the roof, so would like to do something with it while we've got the opportunity if possible/required.

Would it be best fit a cowl to let a bit of air still go up and down, or fit a cap and shut it off. The fireplace itself will be staying, it'll either have the grate left in place for show purposes, or an electric fire fitted one day. Is it best to leave the fireplace end completely open, partially open or block it up completely - I suppose it depends on whats at the top?

House was built some time in the 1800s, I've attached pictures of the chimney pots, and also some of adjoining properties and how they've done it. If anyone can give me a good guess of the size that'd be great as I'll struggle to get a measure until the scaffold is up, then it'll be a mad rush to get the bits before it comes back down again...

Also, while I'm at it, the aerial strapped round the chimney stack is not in use and partially fell off years back. Can I just undo the wire strap that looks like its holding it in place and get rid of the whole lot, or does it serve another purpose? My chimney at home has a similar wire strap, but no aerial as it's in the loft...

 

[blup]

It's impossible to tell from photos, only an inspection can identify problems and likely solutions.

Don't cap the chimney off, a cowl which allows circulation of air through the chimney will keep rain out whilst maintaining ventilation, but the problem could also be within the chimney where salts have been drawn in from the brickwork as a result of heat from the fire when it was in use. Those salts attract moisture which can create damp.

Sweeping the chimney will help remove nests etc. Rain can also cause damp through poor, or missing, pointing; or inadequate flashing.

The first photo suggest some major work has been carried out in the past

I would personally leave the aerial in place unless it's part of something structurally unsound.

Your roofer will doubtless be able to give you an expert view as he will have the advantage of a proper inspection.

These are just my observations as a DIYER

Blup