Have a flat roof (standard roofing felt) that meets up with a sloping
slated one. The flat roof is angled slightly so the slate roof takes all
the rain water from it.

The joint between the two is covered in lead.

Even when new, I'd had an occasional problem with a leak which seems to be
from there - but can't be sure as there is plasterboard covering it in the
inside. But when it does leak, water seems to run down one of the joists
for the sloping roof (where you can see them, some way down from that join)

Now lead isn't going to provide a seal against driving rain, so just how
should this joint be constructed?

I'd expect the felt to overlap the slate, and the lead just there to
protect things?

--
*I didn't say it was your fault, I said I was blaming you.

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
Have a flat roof (standard roofing felt) that meets up with a sloping
slated one. The flat roof is angled slightly so the slate roof takes all
the rain water from it.

The joint between the two is covered in lead.

Even when new, I'd had an occasional problem with a leak which seems to be
from there - but can't be sure as there is plasterboard covering it in the
inside. But when it does leak, water seems to run down one of the joists
for the sloping roof (where you can see them, some way down from that join)

Now lead isn't going to provide a seal against driving rain, so just how
should this joint be constructed?

I'd expect the felt to overlap the slate, and the lead just there to
protect things?


One of the problems with lead is that it doesn't work well on long
runs. I believe about 2M is the maximum length. I've had a lead gutter
develop a fatigue crack which i had to bitumen coat to keep waterproof.

On 18/08/2017 13:42, Dave Plowman (News) wrote:
Have a flat roof (standard roofing felt) that meets up with a sloping
slated one. The flat roof is angled slightly so the slate roof takes all
the rain water from it.

Which way round do you mean?

\
\
\_________

or
__________
\
\
\


The joint between the two is covered in lead.

Mine is of the latter form and the slope is the other way so that the
joint is a global maximum and water always wants to run off the lead.

Even when new, I'd had an occasional problem with a leak which seems to be
from there - but can't be sure as there is plasterboard covering it in the
inside. But when it does leak, water seems to run down one of the joists
for the sloping roof (where you can see them, some way down from that join)

Now lead isn't going to provide a seal against driving rain, so just how
should this joint be constructed?

So that each higher part overlaps the lower one (and maybe some soft
mastic water repellent compound between the felt and the lead).
Capilliary action has a bad habit of making water run uphill.
(as does driving rain)

I'd expect the felt to overlap the slate, and the lead just there to
protect things?

If it is how I imagine the lead overlaps the slate and the felt overlaps
the lead. Otherwise there is always a path for driving rain to get in.

--
Regards,
Martin Brown

In article ,
Martin Brown wrote:
Have a flat roof (standard roofing felt) that meets up with a sloping
slated one. The flat roof is angled slightly so the slate roof takes
all the rain water from it.

Which way round do you mean?

\
\
\_________

or
__________
\
\
\

The second, as water tend to flow downhill. ;-)

I do have the first arrangement at the other end of the roof near the apex
of the main roof. That has never given problems.

--
*Warning: Dates in Calendar are closer than they appear.

Dave Plowman London SW
To e-mail, change noise into sound.

On 18/08/2017 17:08, Dave Plowman (News) wrote:
In article ,
Martin Brown wrote:
Have a flat roof (standard roofing felt) that meets up with a sloping
slated one. The flat roof is angled slightly so the slate roof takes
all the rain water from it.

Which way round do you mean?

\
\
\_________

or
__________
\
\
\

The second, as water tend to flow downhill. ;-)

I do have the first arrangement at the other end of the roof near the apex
of the main roof. That has never given problems.

That is what I was trying to determine. Type I is quite common where
there is a ground floor extension whereas type II is loft extension.

Though on mine the flat roof drains away from the apex which is more
reliable in terms getting the lead to seal and avoid leaks.

--
Regards,
Martin Brown

On 8/18/2017 2:44 PM, Martin Brown wrote:
On 18/08/2017 13:42, Dave Plowman (News) wrote:
Have a flat roof (standard roofing felt) that meets up with a sloping
slated one. The flat roof is angled slightly so the slate roof takes all
the rain water from it.

Which way round do you mean?

\
\
\_________

or
__________
\
\
\


The joint between the two is covered in lead.

Mine is of the latter form and the slope is the other way so that the
joint is a global maximum and water always wants to run off the lead.

Even when new, I'd had an occasional problem with a leak which seems
to be
from there - but can't be sure as there is plasterboard covering it in
the
inside. But when it does leak, water seems to run down one of the joists
for the sloping roof (where you can see them, some way down from that
join)

Now lead isn't going to provide a seal against driving rain, so just how
should this joint be constructed?

So that each higher part overlaps the lower one (and maybe some soft
mastic water repellent compound between the felt and the lead).
Capilliary action has a bad habit of making water run uphill.
(as does driving rain)

I'd expect the felt to overlap the slate, and the lead just there to
protect things?

If it is how I imagine the lead overlaps the slate and the felt overlaps
the lead. Otherwise there is always a path for driving rain to get in.



+1 for mastic to "glue the lead down" to the felt.

In article ,
newshound wrote:
If it is how I imagine the lead overlaps the slate and the felt
overlaps the lead. Otherwise there is always a path for driving rain
to get in.



+1 for mastic to "glue the lead down" to the felt.

How about differential expansion? Lead tends to move quite a bit.

--
*All generalizations are false.

Dave Plowman London SW
To e-mail, change noise into sound.