We've got a woodburner in an outbuilding which I'm currently
refurbishing. Whether the stove itself's ever really been used since it
was installed out there, I have no idea - probably not, or very little.

The roof on the building's recently been replaced with plastic-coated
steel sheet (instead of asbestos cement sheet). I'm in the throes of
ripping down the old plasterboard and insulation, and replacing with more
insulation and thin wood cladding.

The flue comes out the back of the stove and goes straight up through the
roof. There's a couple of brackets holding it to the wall along the
length. The bottom foot or so's single-skin, the rest is double-skin
insulated.

I've had a fire in it this morning, stoked right up, to see what the
external temps on the flue got to. The stove itself saw 400+degC. The
uninsulated single-skin got to 300degC (and has gone a lovely dark straw
colour...). The outside of the double-skin got to about 70degC. I know
I'm going to need to allow about 50mm around the double-skin as it goes
through the ceiling, and was going to box that off before stuffing the
rest with insulation. The hole through the ceiling timber's going to be
finished with a stainless finisher.

What did alarm me a bit, though, was looking at the outside of where the
flue comes through the roof, with it all at the hottest. There must have
been about an inch clearance between the metal flashing and the roof
skin, due to expansion of the flue. Now it's all cooled down, it's back
to flush. It's towards the edge of the roof slope, and the side of the
flashing's tucked under the finishing piece for the roof edge - which
bent up slightly as a result.

Should I be concerned about that expansion and do something about it...?
Should the flashing be free to move on the flue? The top of it's
underneath a rain collar on the uppermost section of flue, with a "hat"
on the whole thing.

On 06/06/2014 14:11, Adrian wrote:
We've got a woodburner in an outbuilding which I'm currently
refurbishing. Whether the stove itself's ever really been used since it
was installed out there, I have no idea - probably not, or very little.

The roof on the building's recently been replaced with plastic-coated
steel sheet (instead of asbestos cement sheet). I'm in the throes of
ripping down the old plasterboard and insulation, and replacing with more
insulation and thin wood cladding.

The flue comes out the back of the stove and goes straight up through the
roof. There's a couple of brackets holding it to the wall along the
length. The bottom foot or so's single-skin, the rest is double-skin
insulated.

I've had a fire in it this morning, stoked right up, to see what the
external temps on the flue got to. The stove itself saw 400+degC. The
uninsulated single-skin got to 300degC (and has gone a lovely dark straw
colour...). The outside of the double-skin got to about 70degC. I know
I'm going to need to allow about 50mm around the double-skin as it goes
through the ceiling, and was going to box that off before stuffing the
rest with insulation. The hole through the ceiling timber's going to be
finished with a stainless finisher.

What did alarm me a bit, though, was looking at the outside of where the
flue comes through the roof, with it all at the hottest. There must have
been about an inch clearance between the metal flashing and the roof
skin, due to expansion of the flue. Now it's all cooled down, it's back
to flush. It's towards the edge of the roof slope, and the side of the
flashing's tucked under the finishing piece for the roof edge - which
bent up slightly as a result.

Should I be concerned about that expansion and do something about it...?
Should the flashing be free to move on the flue? The top of it's
underneath a rain collar on the uppermost section of flue, with a "hat"
on the whole thing.

You probably need some on site advice from a heating engineer who has
the appropriate professional qualification. If you don't then expect
your insurance to be invalid if the worst happens.


--
Peter Crosland

Reply address is valid

Adrian wrote:
We've got a woodburner in an outbuilding which I'm currently
refurbishing. Whether the stove itself's ever really been used since
it was installed out there, I have no idea - probably not, or very
little.

The roof on the building's recently been replaced with plastic-coated
steel sheet (instead of asbestos cement sheet). I'm in the throes of
ripping down the old plasterboard and insulation, and replacing with
more insulation and thin wood cladding.

The flue comes out the back of the stove and goes straight up through
the roof. There's a couple of brackets holding it to the wall along
the length. The bottom foot or so's single-skin, the rest is
double-skin insulated.

I've had a fire in it this morning, stoked right up, to see what the
external temps on the flue got to. The stove itself saw 400+degC. The
uninsulated single-skin got to 300degC (and has gone a lovely dark
straw colour...). The outside of the double-skin got to about 70degC.
I know I'm going to need to allow about 50mm around the double-skin
as it goes through the ceiling, and was going to box that off before
stuffing the rest with insulation. The hole through the ceiling
timber's going to be finished with a stainless finisher.

What did alarm me a bit, though, was looking at the outside of where
the flue comes through the roof, with it all at the hottest. There
must have been about an inch clearance between the metal flashing and
the roof skin, due to expansion of the flue. Now it's all cooled
down, it's back to flush. It's towards the edge of the roof slope,
and the side of the flashing's tucked under the finishing piece for
the roof edge - which bent up slightly as a result.

Should I be concerned about that expansion and do something about
it...? Should the flashing be free to move on the flue? The top of
it's underneath a rain collar on the uppermost section of flue, with
a "hat" on the whole thing.

No, the flashing should remain stable on the roof, the top hat is to prevent
rain hitting the uppermost section of flue, that is to say, there should be
a few mm gap around the flashing and the flue, if it's too tight a fit, this
is what happens

/ . If you don't then expect your insurance to be invalid if the worst happens./q

Woe woe & thrice woe......

Jim K

How far above the roof is the "top hat"?

Jim K

On Fri, 6 Jun 2014 13:11:21 +0000 (UTC), Adrian wrote:

What did alarm me a bit, though, was looking at the outside of where the
flue comes through the roof, with it all at the hottest. There must have
been about an inch clearance between the metal flashing and the roof
skin, due to expansion of the flue. Now it's all cooled down, it's back
to flush. It's towards the edge of the roof slope, and the side of the
flashing's tucked under the finishing piece for the roof edge - which
bent up slightly as a result.

Doesn't sound right. I'd expect the flashing to stay with the roof
and be slighly clear of the flue. Attached and sealed to the flue is
a storm collar that overlaps the top of the spigot of the flashing.

http://www.bes.co.uk/products/172a.asp

Scroll down to the flashing kits at the bottom of the page.

--
Cheers
Dave.

On Fri, 06 Jun 2014 12:16:24 -0700, JimK wrote:

How far above the roof is the "top hat"?

And this is the point where photos would be REALLY useful, isn't it?

External overview (cold) -
https://farm4.staticflickr.com/3841/...611f14_o_d.jpg

External closeup (cold) -
https://farm4.staticflickr.com/3891/...6211e7_o_d.jpg

External closeup (hot) -
https://farm4.staticflickr.com/3891/...3cc9db_o_d.jpg
At that point, the double-skinned outer wall just inside the roof was
about 70degC. The outside of the stove was near-on 400degC - I'd
deliberately provoked it into blast-furnace mode, to get a worst-case
situation. The uppermost section of the single-skin was about 200degC.

Inside view -
https://farm4.staticflickr.com/3906/...10d291_o_d.jpg
It's 1750mm from the one and only support bracket up to the roof skin, btw
- the bracket's on the double-skinned flue

Are you in a smokeless area, I saw on the tv the other day a guy was
informed that due to it not being designed to pass smoke free legislation
he could only burn smokeless fuel on his woodburner, which kind of defeated
the object of having it in the first place!
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Adrian" wrote in message
...
We've got a woodburner in an outbuilding which I'm currently
refurbishing. Whether the stove itself's ever really been used since it
was installed out there, I have no idea - probably not, or very little.

The roof on the building's recently been replaced with plastic-coated
steel sheet (instead of asbestos cement sheet). I'm in the throes of
ripping down the old plasterboard and insulation, and replacing with more
insulation and thin wood cladding.

The flue comes out the back of the stove and goes straight up through the
roof. There's a couple of brackets holding it to the wall along the
length. The bottom foot or so's single-skin, the rest is double-skin
insulated.

I've had a fire in it this morning, stoked right up, to see what the
external temps on the flue got to. The stove itself saw 400+degC. The
uninsulated single-skin got to 300degC (and has gone a lovely dark straw
colour...). The outside of the double-skin got to about 70degC. I know
I'm going to need to allow about 50mm around the double-skin as it goes
through the ceiling, and was going to box that off before stuffing the
rest with insulation. The hole through the ceiling timber's going to be
finished with a stainless finisher.

What did alarm me a bit, though, was looking at the outside of where the
flue comes through the roof, with it all at the hottest. There must have
been about an inch clearance between the metal flashing and the roof
skin, due to expansion of the flue. Now it's all cooled down, it's back
to flush. It's towards the edge of the roof slope, and the side of the
flashing's tucked under the finishing piece for the roof edge - which
bent up slightly as a result.

Should I be concerned about that expansion and do something about it...?
Should the flashing be free to move on the flue? The top of it's
underneath a rain collar on the uppermost section of flue, with a "hat"
on the whole thing.

Adrian wrote:
On Fri, 06 Jun 2014 12:16:24 -0700, JimK wrote:

How far above the roof is the "top hat"?

And this is the point where photos would be REALLY useful, isn't it?

External overview (cold) -
https://farm4.staticflickr.com/3841/...611f14_o_d.jpg

External closeup (cold) -
https://farm4.staticflickr.com/3891/...6211e7_o_d.jpg

External closeup (hot) -
https://farm4.staticflickr.com/3891/...3cc9db_o_d.jpg
At that point, the double-skinned outer wall just inside the roof was
about 70degC. The outside of the stove was near-on 400degC - I'd
deliberately provoked it into blast-furnace mode, to get a worst-case
situation. The uppermost section of the single-skin was about 200degC.

Inside view -
https://farm4.staticflickr.com/3906/...10d291_o_d.jpg
It's 1750mm from the one and only support bracket up to the roof
skin, btw - the bracket's on the double-skinned flue

It seems the flashing is attatched to the flue, or the outer flue.

Looking at the inside view, I seriously doubt if any water could get through
that, certainly not when it's cold otherwise you would have noticed it by
now, and when it's hot, the flashing will also be hot, given that no rain
can actually drive onto it with the cowl and the lower collar, the only rain
to hit it would evapourate fairly quickly, so short answer; ignore it and
forget about it.

On Sat, 7 Jun 2014 17:10:40 +0100, Phil L wrote:

Looking at the inside view, I seriously doubt if any water could get
through that, certainly not when it's cold otherwise you would have
noticed it by now,

Agreed.

and when it's hot, the flashing will also be hot, given that no rain
can actually drive onto it with the cowl and the lower collar,

Er the corrogated flashing in the best part of an inch above the
corrogated roof. You must live somewhere where the rain only ever
falls near vertical, up here it frequently falls near horizontal so
much so that vertical is note worthy. B-)

Half decent bit of wind and rain blowing up that roof will get in
through that huge gap.

... the only rain to hit it would evapourate fairly quickly,

The roof will be pretty cool.

so short answer; ignore it and forget about it.

No, the flashing up stand needs to be freed from the flue with as
little clearance as possible and all the flashings put back down
properly and snugly. The storm collar then needs to be positioned
just above the top upstand with the system cold.

--
Cheers
Dave.

On Sat, 07 Jun 2014 12:20:05 +0100, Brian Gaff wrote:

Are you in a smokeless area

I very much doubt it. Rural Herefordshire.

On Sat, 07 Jun 2014 23:44:03 +0100, Dave Liquorice wrote:

and when it's hot, the flashing will also be hot, given that no rain
can actually drive onto it with the cowl and the lower collar,

Er the corrogated flashing in the best part of an inch above the
corrogated roof. You must live somewhere where the rain only ever falls
near vertical, up here it frequently falls near horizontal so much so
that vertical is note worthy. B-)

Half decent bit of wind and rain blowing up that roof will get in
through that huge gap.

That was my thought... Fortunately, the prevailing weather tends to come
from the west, the side that's tucked under the roof edging.

No, the flashing up stand needs to be freed from the flue with as little
clearance as possible and all the flashings put back down properly and
snugly. The storm collar then needs to be positioned just above the top
upstand with the system cold.

Thanks. Time to get up onto the handily-placed shed roof (right next to
that flank of the building, and solid enough to walk on).

In message , Adrian
writes
On Sat, 07 Jun 2014 23:44:03 +0100, Dave Liquorice wrote:

and when it's hot, the flashing will also be hot, given that no rain
can actually drive onto it with the cowl and the lower collar,

Er the corrogated flashing in the best part of an inch above the
corrogated roof. You must live somewhere where the rain only ever falls
near vertical, up here it frequently falls near horizontal so much so
that vertical is note worthy. B-)

Half decent bit of wind and rain blowing up that roof will get in
through that huge gap.

That was my thought... Fortunately, the prevailing weather tends to come
from the west, the side that's tucked under the roof edging.

No, the flashing up stand needs to be freed from the flue with as little
clearance as possible and all the flashings put back down properly and
snugly. The storm collar then needs to be positioned just above the top
upstand with the system cold.

Thanks. Time to get up onto the handily-placed shed roof (right next to
that flank of the building, and solid enough to walk on).

From the photos, the shed has been re-roofed, retaining the chimney
flashing.

As has been said, there should be a gap between the sleeve and the flue.
Maybe the flue has also been re-newed and forced to fit.

--
Tim Lamb

On Sun, 8 Jun 2014 10:00:45 +0000 (UTC), Adrian wrote:

Half decent bit of wind and rain blowing up that roof will get in
through that huge gap.

That was my thought... Fortunately, the prevailing weather tends to come
from the west, the side that's tucked under the roof edging.

I guess down there you don't get fine dry powder snow. That's right
******* stuff for getting in. It gets carried on the airflow(*) and
as the inside of a building tends to be at a lower pressure than the
outside when the wind blows due to venturi effects it gets drawn in
rather than blown.

(*) So can follow quite long and twisty paths.

--
Cheers
Dave.

On Sun, 08 Jun 2014 12:03:14 +0100, Dave Liquorice wrote:

I guess down there you don't get fine dry powder snow.

No snow at all last winter - our first one here. But nothing would
surprise me about the climate here.

On Sun, 08 Jun 2014 11:46:23 +0100, Tim Lamb wrote:

From the photos, the shed has been re-roofed, retaining the chimney
flashing.

Yep, early this year, replacing knackered asbestos-cement corrugated
sheet.

As has been said, there should be a gap between the sleeve and the flue.
Maybe the flue has also been re-newed and forced to fit.

The flue's not been touched since installation, somewhere between '98 and
'05 or so.

On Sun, 8 Jun 2014 11:15:32 +0000 (UTC), Adrian wrote:

From the photos, the shed has been re-roofed, retaining the
chimney
flashing.

The flue's not been touched since installation, somewhere between '98
and '05 or so.

The flashing will have been. How did they get that new roof sheet in
place without taking off the flashing and possibly the top section of
flue?

Suspect when they put the flashing back they formed it tight to the
flue or perhaps even sealed it with silicone...

--
Cheers
Dave.

On Fri, 06 Jun 2014 19:12:51 +0100, Phil L wrote:

Should I be concerned about that expansion and do something about
it...? Should the flashing be free to move on the flue? The top of it's
underneath a rain collar on the uppermost section of flue, with a "hat"
on the whole thing.

No, the flashing should remain stable on the roof, the top hat is to
prevent rain hitting the uppermost section of flue, that is to say,
there should be a few mm gap around the flashing and the flue, if it's
too tight a fit, this is what happens

I've finally got round to climbing up there and having a good look.

The rain collar is firmly glued to the flue using a grey sealant/mastic
of some kind. The bead above has been nicely smoothed in, so it almost
looks like a weld.

There's also a sodding great big bead below, which does a great job of
firmly attaching the flashing to the flue, too. rolls eyes

On Thu, 12 Jun 2014 07:35:00 +0000 (UTC), Adrian wrote:

The rain collar is firmly glued to the flue using a grey sealant/mastic
of some kind. The bead above has been nicely smoothed in, so it almost
looks like a weld.

There's also a sodding great big bead below, which does a great job of
firmly attaching the flashing to the flue, too. rolls eyes

There's the problem, but how to get that freed off? No doubt the
collar was nicely fitted after they'd done a good job gooping up the
top of the flashing spigot. As that's tucked up under the storm
collar a right B to get at.

Or do you mean there is a bead of sealant underneath where the collar
meets the flue? It might be possible to get a sharp knife and cut
through the bits that are stuck to the flashing. Maybe also along the
slope of the storm collar then pull it out. Depends how much of this
selant bead is stuck to the flashing.

Or take a hacksaw to the whole lot just below collar and replace the
top section of flue and fit new storm collar.

--
Cheers
Dave.

On Thu, 12 Jun 2014 09:29:23 +0100, Dave Liquorice wrote:

The rain collar is firmly glued to the flue using a grey sealant/mastic
of some kind. The bead above has been nicely smoothed in, so it almost
looks like a weld.

There's also a sodding great big bead below, which does a great job of
firmly attaching the flashing to the flue, too. rolls eyes

There's the problem, but how to get that freed off? No doubt the collar
was nicely fitted after they'd done a good job gooping up the top of the
flashing spigot. As that's tucked up under the storm collar a right B to
get at.

Or do you mean there is a bead of sealant underneath where the collar
meets the flue?

I do.

It might be possible to get a sharp knife and cut
through the bits that are stuck to the flashing. Maybe also along the
slope of the storm collar then pull it out. Depends how much of this
selant bead is stuck to the flashing.

Reminder of the view...
https://farm4.staticflickr.com/3841/...611f14_o_d.jpg

Or take a hacksaw to the whole lot just below collar and replace the top
section of flue and fit new storm collar.

That's kinda tempting. There's a joint between flue sections just below
the roof.

I'll pull it off, get it down to ground level, and have a rummage.

On Thu, 12 Jun 2014 10:58:57 +0000, Adrian wrote:

The rain collar is firmly glued to the flue using a grey
sealant/mastic of some kind. The bead above has been nicely smoothed
in, so it almost looks like a weld.

There's also a sodding great big bead below, which does a great job of
firmly attaching the flashing to the flue, too. rolls eyes

There's the problem, but how to get that freed off? No doubt the collar
was nicely fitted after they'd done a good job gooping up the top of
the flashing spigot. As that's tucked up under the storm collar a right
B to get at.

It might be possible to get a sharp knife and cut through the bits that
are stuck to the flashing. Maybe also along the slope of the storm
collar then pull it out. Depends how much of this selant bead is stuck
to the flashing.

Reminder of the view...
https://farm4.staticflickr.com/3841/...611f14_o_d.jpg

I'll pull it off, get it down to ground level, and have a rummage.

Don't black tin roofs get warm in direct sunshine?

So I went around the collar with a Stanley knife, and freed it. Then
between flue and flashing with the knife, and freed that. A good bead of
sikaflex around the flue, just above the flashing, and lower the collar
to that. Then a bead around the top, and smooth. The flue still moves
relative to the flashing, and it looks like it should be watertight.

I'll give it 24hrs, then fire it up and see what happens...