My Dad lives in a 1940's bungalow with a fireplace in his bedroom thats sort of blocked with a badly fitting piece of board, consequently all the heat in his room literally disappears up the chimney. I was on the roof today and the chimney doesn't even have a cowl of any sort so the rain will be going in too. Question is can I just mortar a slab over the top and block the bottom properly so its just like a wall cavity. Any advice appreciated.
A cavity wall has air moving through it, I would advise that whatever you do with the chimney, it still has air drawn up it, it will help the house and its occupant/s to breathe and not suffer from excessive condensation.
Make and fit a better fitting register plate with a vent or grill in it and at the top of the chimney, fit a cowl, there are some available that are low profile and keep the flue open.
probably want to dry it out first but yes
One of these and a thick piece of polystyrene with a few vent holes in the lower part of the chimney, just out of sight
you can get a mushroom to drop into the pot which vents it or knock the pot of and cap it using mortar and some slate laid flat to forms vents. cover the slates with mortar higher in the middle to provide a little fall and make sure the mortar slopes up under the vents to prevent water getting into the flue.
inside block up the fireplace leaving a hole about 6/7" long and 4" high, plaster up and then stick a 9" x 6" plaster vent over the hole. could use a plastic vent but i think the plaster ones look better and can be painted wall colour.
Thanks for the advice, will have to get back up there next weekend and sort it.
We capped ours, mushroom type jobber, and put a slide vent in the room. Normally left open to stop damp but can close it when the wind is howling.