The roofers who are doing my tiles said the flat dormer rooves was not done very well - and demonstrated it initially by showing me some creative use of felt instead of lead flashing.
So, with some internal grumbling, I asked them to quote and the do the 2 flats, getting some celotex in while they were at it and sorting out the ventilation for the deck.
Just as well - they said it was a "bit saggy". The decking was made of flooring grade chipboard and the last time the roof was refelted, it looks like the men had stuck new felt on the old - came off about 6 layers thick!
Unfortunately, sometimes you cannot easily not have one, eg on a dormer conversion where you cannot go above the ridge (at least not without a huge planning permission exercise).
I discussed GRP and butyl solutions. The result was not as clear cut as I had thought.
My roofers (who have demonstrated competance and diligence beyond doubt - and I've been there with them) said they have come across GRP flat roofs that have cracked. The problem being thermal expansion andthe fact the GRP is bonded to the decking boards so it cannot move. Apparantly you are supposed to have expansion joints. One roof they fixed did and it still cracked and leaked. They had to felt over it.
They had no opinion on butyl sheet but had not used it.
Another roofer who I took quotes from said butyl was prone to tear damage - especially if other people, eg TV aerial folk went over it without care.
Current roofer said that felts had improved and I could expect 20-25 years from the product he used. Oh - and it does not need to be topped with gravel, half of which from the last effort was sitting in my gutter.
So, being a foolish exercise to tell a roofer to use a material he's not got confidence in, I went with felt.
Well yes in theory, but we've uncovered an amazing number of bodges during our re-build exercise, especially in the 2003 extension, which was supposedly building control supervised. The 1650's bit and the 1900 bit were quite sound in construction method by comparison, though admittedly the
1650's bit had suffered not unsurprisingly from the ravages of time. Remarkable what building control didn't spot, and we've had to re-do.
Im a bit surprised they did not suggest Lead, would probably outlast your nice new roof. But im pleased and a bit relived that the roofers seem to be just as professional as when i last had dealings with them. got any photos yet.
The problem with lead is weight and getting it pinched. (The roof has to be made much stronger.) And finding someone that can install it properly. There are other metal alternatives.
Zinc? Doesn't form as readily as lead but light and not attractive to thieves.
A friend has just had a zinc roof fitted in Suffolk. Fitters came from Kent.
Not seen yet it but I understand the technique is to roll form a rib and an upstand from flat sheet held on a roll. The installation is then in long strips with the rib fitting and crimped over the last upstand which has been secured by some folded offcuts nailed to the roof timber.
There was a particularly good demonstration of the techniques in a Grand Designs episode - was it the musicians on the west coast of Scotland where the window got blown in sometime after the program?
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