Capping an unused chimney/flue

[overlandrover]

Last year we had our soild fuel boiler replaced by an electric boiler. The technician that fitted the electric boiler cut back the flue the the ceiling, filled part of the flue with insulation, and then applied cement to the underside to seal it.

Over the winter, especially after driving rain, brown water has dripped through this cement, leaving stalagtites of a gooey matrial, and a bad stain on the ceiling of the boiler cupboard.

The recent dry weather means it hasn't been too much of a problem lately, and it would be a good time to remove the existing hood top, leave the flue to air out, and then cap the chimney permanently.

A builder has recently advised us to cap the chimney with a waterproof cement, sculpted into in a pyramid shape. I would prefer to simply use a pier cap which would have a 1½" overhang all around.

I plan to remove the flue as far as possible, but I think this is going to be difficult.

My concern is that moisture and condensation always finds a way into the flue, and regardless of the capping technique we may still get rusty water dripping through next winter.

Does anybody think the proposal is a good idea?
If so, should the flue be filled to the brim with some material (such as fibreglass, or perhaps polystyrene beads as per cavity wall insulation?)
Should the void between the flue and the chimney also be filled?

I look forward to your advice.

 

[masona]

It's really best to take the flue right out and put in air-vents at the bottom as well at the top to allow air circulation which will stop the condenation otherwise you will have an ongoing problem

Nice drawing

 

[Tiso]

You never block off a chimney even if is not used as there will be many years of damp stuck to the inner linner wall of the chimney. The correct soultion is for a plaster air vent at the bottom a chiney cowl at the top. The cowl will let the wind flow tghrough and will dry out the chimney lining and keep it dry. Below is a link for such a cowl
http://www.loftshop.co.uk/products_detail.asp?catID=5&typeID=20&pID=30

 

[overlandrover]

Thanks for your replies.

Since my last message, I had a go at removing the cap in order to assess the extent of the flue and leaking. As per usual, it turns out I was wrong.

There's only a concrete liner, and there's no evidence of water leaking down the inside - only nice uniform soot.

I can't make out what's at the bottom of the chimney, but it might be the insulation. That said, once the cap was removed, the bricks came away with frightening ease.

Three courses of bricks later, and I'm realising that the water must be seeping through the mortar between the brickwork and the lining. A woodlouse crawling out of the mortar told me how damp it was, even at that altitude!

I don't believe there is any airflow between the liner and the brickwork, and I'm now faced with two options:
- Get the chimney repointed and re-cap it with a better hood.
- Relocate the TV aerial, and dismantle the chimney altogether.

I chipped away the top section of the liner, and currenlty have the shorter chimney wrapped in tarpaulin!

Seeing as the chimney's current function is only to hold up the TV aerial and grow stalagtites on the ceiling, I favour the latter option.

Repairing the roof will be the fun part, but I think we have some leftover tiles behind the garage. I may still seek some of your advice about patching the roof!

Thanks again
Chris

 

[par1sons]

I reckon your best option based on the photos you have attached is to completely get rid of the chimney stack and then replace the hole left with roof tiles, dead easy job to do. The stack on your roof doesn't look very big so the job of removing it shouldn't be hard.

If you decide to keep the stack then you have to remove the crap in your flu and then cap it correctly so that condensation doesn't form in your flu.

I recently removed all the chimney breast from my house and capped the chimney to allow for ventilation. Removing the stack on my roof was not an option because its bloody massive and its shared with my next door Neighbour.

OH THE JOY OF BUILDING

 

[iangh]

with all chimneys the issue is what are they holding up, or what is holding them up.
In the latter you cab easily take down a stack from the top.
But taking it down from the bottom needs building control approval as they are structurally part of a building, also of course in a semi will affect the Party Wall Act 1972.
Yours look easy to dismantle from the top and tile over.
need felt, battens tiles.