In article ,
Calum writes:
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?

Difficult to tell.

I bought a couple of those elephant's foot cowls like the one you
have, decided they wouldn't reduce the amount of rainfall going
down the chimney, and took them back. Actually, they may make it
worse by capturing water from a larger area than the original pot
opening, and making it run down the inside of the pot - there's
nothing to make the water running down the outside of the pot
(unless you siliconed it on).
You could repeat the plastic bag test on this flue (but you can't
block the airflow permanently like this).

I then went a bought a couple of these instead:
http://www.brewercowls.co.uk/index.p...tent&Itemid=18
although I fixed them in a different way so the strap isn't visible
http://www.facebook.com/photo.php?pi...&id=1619546457
http://www.facebook.com/photo.php?pi...&id=1619546457

In theory, rain water going in the pot shouldn't cause any problems.
In practice it might because the internal pointing has been washed
away over the years of rain exposure without any heating to dry it.
Also, if the flue isn't ventilated at bottom _and_ top, it will fill
up with condensation, which will soak through the brickwork in time.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]