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The Natural Philosopher[_2_] The Natural Philosopher[_2_] is offline
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Default Leaking chimney, but where is the water getting in? (see pics)

Calum wrote:
Hello all

I've just had a loft conversion completed on a victorian semi. The
rear of the house is one large dormer with a (nearly) flat roof, and
we've left the chimney stack in place as we might use the dining room
fireplace one day.

The problem we have is that rain is getting in somewhere and coming
through the chimney breast plasterin the new loft room, but the roofer
can't work out where this is coming from.

Here is a picture of the plaster with a roll of masking tape for
scale. There are pencil lines around the damp circles as I was
measuring to see if they got bigger.
http://yfrog.com/7bixtj

Here are pictures from the outside:
http://yfrog.com/4vso3j
http://yfrog.com/6ds5mj

The roofer has re-pointed and patched up the mortar slope to the (very
old and unused) central heating cowel. The cowel was covered in a
plastic bag, but that made no difference.

If it rains moderately for an hour, the patches appear/get worse and
then take a week or two to dry out. To me that looks like the water
is being funnelled down quite effectively.

Could it really be soaking in from the brick? What else could it be?


Bloody obvious.

You have a flat roof and **** all flashing on the stack.,


Go up and prise up the lead. Bet you its all wet underneath.


You need to take roofing felt an carry it up the sides of the stack, to
where the flashing starts, and probably mastic it in, then put in new
flashing and dress it several inches out along and over the roofing
felt. So that driving rain under the flashing has to go a long way and
then UP to the flashing top, before it meets the brick.

Yu might also, as others have suggested, at the same time repoint the
stack and remortar the cowl top.


Personally I would scaffold up, or whatever, and demolish the stack top,
and start again and build a new top, done properly.

I take it the flat roof is part of the new conversion? If so its been
badly done.

It should be redone in conjunction with the chimney.







Thanks for your thoughts
Calum