We've had 3 large velux installed above each other up the slope of the
roof above a new staircase.

Between them (horizontally) run the main beams supporting the roof.

the roof has been insulated with 100mm kingspan leaving a 50mm gap to
the felt at the back oif the slates, foilback plasterboarded and
plastered.

Problem :- The beam between the topmost and middle velux has a weepy
wet water mark that doesn't actually drip off but has not gone away
yet (such that we can't varnish that side of the beam or the small
6inch piece of plasterboard that spans between the beam back to the
roof.

The beam between the middle and lower velux has no problems
whatsoever.

The only difference we can see (without starting to rip it all down)
is the lap of the flashings - the problem area has a 2inch lap between
the bottom flashing of the top window and the top flashing of the
middle window, the other velux has a 6inch lap at this area.

Is this the problem i.e. water penetration ? how would I tell if it
were condensation from the inside?
Anyone know the minimum lap for veluxes installed above each other?
Any suggestions for what to do next?


thanks in advance

Jim

jim laid this down on his screen :
The only difference we can see (without starting to rip it all down)
is the lap of the flashings - the problem area has a 2inch lap between
the bottom flashing of the top window and the top flashing of the
middle window, the other velux has a 6inch lap at this area.

If I understand your explanation correctly, a 2" overlap is nowhere
near enough to prevent blown rain entering on a normal roof slope
angle.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

"jim" wrote in message
...
We've had 3 large velux installed above each other up the slope of the
roof above a new staircase.

Between them (horizontally) run the main beams supporting the roof.

the roof has been insulated with 100mm kingspan leaving a 50mm gap to
the felt at the back oif the slates, foilback plasterboarded and
plastered.

Problem :- The beam between the topmost and middle velux has a weepy
wet water mark that doesn't actually drip off but has not gone away
yet (such that we can't varnish that side of the beam or the small
6inch piece of plasterboard that spans between the beam back to the
roof.

The beam between the middle and lower velux has no problems
whatsoever.

The only difference we can see (without starting to rip it all down)
is the lap of the flashings - the problem area has a 2inch lap between
the bottom flashing of the top window and the top flashing of the
middle window, the other velux has a 6inch lap at this area.


you would need at least 100mm overlap for a flashing, 150mm ideally.

Rick Hughes formulated the question :
"jim" wrote in message
...
We've had 3 large velux installed above each other up the slope of the
roof above a new staircase.


you would need at least 100mm overlap for a flashing, 150mm ideally.

I have just checked mine, which I put in 20 years ago. It has 100mm
overlap, and I can see a minimum of two layers at all points in the
flashing.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On 21 Dec, 11:28, Harry Bloomfield
wrote:
Rick Hughes formulated the question :

"jim" wrote in message
...
We've had 3 large velux installed above each other up the slope of the
roof above a new staircase.

you would need at least 100mm overlap for a flashing, 150mm ideally.

I have just checked mine, which I put in 20 years ago. It has 100mm
overlap, and I can see a minimum of two layers at all points in the
flashing.

--
Regards,
Harry (M1BYT) (L)http://www.ukradioamateur.co.uk

hi thanks for thoughts - when you say "two layers" what are those two
layers of?
Presumably velux flashing (from the kit) around the window and what's
the other layer? felt, lead,....?

cheers
jim

jim laid this down on his screen :
On 21 Dec, 11:28, Harry Bloomfield
wrote:
Rick Hughes formulated the question :

"jim" wrote in message
...
We've had 3 large velux installed above each other up the slope of the
roof above a new staircase.

you would need at least 100mm overlap for a flashing, 150mm ideally.

I have just checked mine, which I put in 20 years ago. It has 100mm
overlap, and I can see a minimum of two layers at all points in the
flashing.

--
Regards,
Harry (M1BYT) (L)http://www.ukradioamateur.co.uk

hi thanks for thoughts - when you say "two layers" what are those two
layers of?
Presumably velux flashing (from the kit) around the window and what's
the other layer? felt, lead,....?

cheers
jim

A minimum of two layers of the Velux flashing at all points.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On 21 Dec, 18:47, Harry Bloomfield
wrote:
jim laid this down on his screen :



On 21 Dec, 11:28, Harry Bloomfield
wrote:
Rick Hughes formulated the question :

"jim" wrote in message
...
We've had 3 large velux installed above each other up the slope of the
roof above a new staircase.

you would need at least 100mm overlap for a flashing, 150mm ideally.

I have just checked mine, which I put in 20 years ago. It has 100mm
overlap, and I can see a minimum of two layers at all points in the
flashing.

--
Regards,
Harry (M1BYT) (L)http://www.ukradioamateur.co.uk

hi thanks for thoughts - when you say "two layers" what are those two
layers of?
Presumably velux flashing (from the kit) around the window and what's
the other layer? felt, lead,....?

cheers
jim

A minimum of two layers of the Velux flashing at all points.

--
Regards,
Harry (M1BYT) (L)http://www.ukradioamateur.co.uk

Mmmmmmm....Are yours actually "velux" brand roof windows? Re-did the
offending one today and there were no " two layers" of velux flashing
anywhere!?! Just top flashing of thin "tin" (ali I think - anodised
grey)

(NB how do you tell there are "two layers"?- by looking? (at only one
at a time I presume)....?

Maybe they have changed (economised) things since 20 years ago?

Problem looks like condensation so extra vapour permeable felt lapped
up against top and bottom of the 2 veluxes should cure the
problem ..... fingers X'd....!!!

thanks to all - if it doesn't work I'll post back for usefulness..

Jim