Cheers, Carnkie. Yes. of great interest thank you.
Derrickman, thanks for the St. Albans lead. Very interesting.

Regarding sizes and weights/thikness of slates,it is largely due to practical reasons that slate is more popular in thinner sizes.A ton of thin slates ,if all uniform size will cover a greater square area than the same wieght of thicker slates.In other words,1000 thick slates take more space to back,and require more haulage cost than the same number of thin slates.Also for handling,and carrying up a roof you could carry 20 countess`slates up a ladder,but if the same sive slates are say twice as thick you are not going to be so fast.If you are into stone slab roofing,you would only be able to carry 1 up a ladder if it was say 2ft x 3ft.Also lighter slates as opposed to thick slabs,are ideal when british practice is to use as little wood in roof construction:In scotland and america roofs are boarded to carry the weight of snow,where as in england and wales roofs are battened.Generally when slate arrive to a job thy are `sorted into 3 or 4 groups,according to the slight differences in wieght,thus enabling slates to lay flat.If you put a thick slate by a thinner one you have what is known in the trade as a `laugher`.

glancing at the endless 'electric wallpaper' of property programme repeats today, saw one on More4 this afternoon which covered the restoration of a 19th century mill in Huddersfield. Gave a good idea of the flag-slate roof construction, among other things.

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Don't forget Collyweston Slate from Rutland. It is thinly bedded limestone. You see a similar style of roofing in the Yorkshire Dales too.

I guess there's an argument for whether it is a slate or not. I think the locals would claim that it is.

http://en.wikipedia.org/wiki/Collyweston_stone_slate 

Chris.

When I worked as a "River" (slate splitter) at Elterwater in the 1980's the national trust brought slate from the roof of a famous Barn from Wall End Langdale (about a mile away) to be replaced as part of their restoration projects they were about 20 inches by ten with hooked angular tops rather than one nail hole for fixing. Off a large Barn roof only about ten slates needed replacing most due to damage by falling masonry. We used the original as template althought the outside of the slate was weathered dark and moss covered the inside was as new..light green Elterwater. The National trust beleived this slate was original pegged with oak, and therefore at least 400 possibly 600 years old!
the vast majority of this slate went straight back onto the roof again. Also worth remembering how wet Langdale is!

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Could you explain what you mean by,Hooked Angular tops,instead of one hole?

Then you mention NT ,saying these slates were fitted with and Oak peg.

We had similar roofs in South Wales,Oak pegged,but they were Sandstone,there was an old disused quarry on the mountain where i used to live,the rock face,was a series of cracks,rangeing from 1/2in to 1in,
Several of the farms had roofs clad in these.

Wish i could draw them! here goes a description...width of slate about 12 inches flat head of slate about six/seven inches tapering to dressed top "corners" where corners meet slate sides an extra cut into the slate body of about an inch made this I beleive then hung onto the Oak peg. one blow of the hand whittle produced this perfectly.

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