"Roly" wrote in message
m...
The current position is that the lady isn't convinced by the advice not
to use foam. She asks for specific reasons why it's not a good idea. At
the moment I can understand her point that it could mostly be a gut
reaction against getting foam. The only valid reason so far was about
timber not being able to dry out. Any other reasons ?

She's quite impressed by the fact that some prestigious clients appear
to have had this sort of work done, including the National Trust. They
try to look after their buildings, so she feels that they wouldn't botch
things.

Once again, I know nothing of such things and would welcome any advice.

Spraying the inside under any roof covering is an absolute no no. Its use is
only for short term for a complete re roof .
There is no ventilation for condensation and if the roof as to be repaired,
its a nightmare to get access to find where the ingress of water in coming
from. You just cant remove any of the roof covering to replace tiles or
slates without cutting away the foam from the underside for about 2 feet or
600 mm area just to replace one slate or tile. Any ingress of water will
just spread and rot any timbers. I'm not convinced that the National Trust
still use this method. Once a roof as been sprayed none of the slates or
tiles can be reused, this stuff sticks to every thing. The cost of a re
roof will be double of an ordinary re roof. I very much doubt if 100% of the
underside is covered right down to the eaves. All the underlay has to be
taken off from ridge to fascias, any leaks made watertight and rotting
timbers replace with new or treated to stop further decay.

From what I read its the valley section that's causing the trouble. If the
roof cover is of the single lap concrete tile type with concrete valley
trough, this is a common problem with this type of roof. Theses valley
trough lay direct on to the underlay felt. Over the years, due to the
trough condensation, this rots the underlay, then the valley rafter. Also
the mortar bedding disintegrates and sucks water in and contributes to the
problem and eventually cause timber rot and wet ceilings.
The cure is to get the valley trough taken out, re felted and GRP valley
section fitted and the tiles reinstated, re aligned bed and pointed. If the
valley it of Lead construction, simple have it renewed with new lead lining.

I have done this many times. I have photos but don't know how to put them
on the group for you to see how its done. If any member knows how to put
theses pics on a site for viewing, please advise

K Spencer.