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Discussion in 'Layout Progress' started by Pencarrow, 1 March 2016.
I'd say it was unnecessary Chris.
Yes, you need to maintain the lap or the roof will leak. The top course would be a bit over half the length of the rest of the slates so they lap over the fixing pegs (or nails) in the course below the final full course. The visible part of the slate will be about the same length as on the rest of the roof.
Often the top course only just came out of the ridge tile.
I would agree with Phil, can you provide us with a preview of what you intent to use as a ridge please.
You do ask difficult questions. Haven't decided yet.
Think I might leave further roof work for today. Too hot. If I take the top off the solvent I suspect it will all evaporate.
Thanks for all the input though. Old stone roofs isn't something I know much about.
Right then, you know when you're in bed and it suddenly comes to you.....Well, last night I remembered this building in Tintagel ( Cornish ...Tick ) and it has a stone roof ( tick ) which has been restored to as original as possible, that said, here a a few "doctored" photos that may give some idea as to the ridge finish.....Oh! and its all wonky too (tick).....
Nice shots there G Bloke, cheers for posting.
I remember that! I think I remember that.....
Plenty of photos on Flickr. Search for Old Post Office Tintagel.
It's when you wake up in the middle of the night and tell the wife you have to get up and go home. Something comes to you then.
Thats more or less what I did and these are some of the images that give some reasonable shots of it.
Alan Downes has made a model of Tint-a-gull Post Office, no idea what his roof was like though.
A simple explanation of how slate should be laid -
In Cornwall the roofs would be slate. Cornish slates are usually thicker and coarser than Welsh slate, and the colour is blue/grey which ages to a silvery grey. Two quarries still produce Cornish roofing slate, Delabole and Trevillett (near Tintagel). There is also an Argentinian slate imported as an alternative to Cornish slate. A Chinese slate was promoted in Cornwall during the 90s with pretty disastrous results.
While slate is a rock the particular characteristics resulting from the metamorphic process compressing siltstone to form slate make it easy to split into thin layers of great strength, a slate roof would not usually be referred to as a stone roof. Stone roofs are different, either large sandstone flags (eg Pennines) or smaller stone tiles (usually limestone, eg Cotswolds). Stone tiles are usually laid in a similar manner to slate, but pegged with oak pegs instead of nails. Pegs were also used with the coarser Cornish slate, hence peggies being the name for the random sized and thickness slates in Cornwall. A stone roof would usually have more mortar used to keep it weather proof, back to parging mentioned previously. Stone roofs are much more localised than slate as the material was heavier and bulkier to transport, as well as more difficult to work with.
If anyone is interested in learning how the buildings they are modelling fit in a broader context there are a number of good books. Try 'Illustrated Handbook of Vernacular Architecture' by R. W. Brunskill and 'The Pattern of English Building' by Alec Clifyon-Taylor as a starting point.
Sorry to bore people but my work involves spending a fair amount of time documenting and inspecting slate roofs. I have a site meeting on Monday morning to work out how to fix a slate roof on an ex-church which was relaid a few years ago using nonstandard details and now leaks at all the abutments. Of course, when making models you can do whatever you wish.
Not boring at all, Fraser (and I can recommend Brunskill in particular. Some nice, clearly labelled drawings and projections and accessible, well-written text. Needless to say, I'm reasonably sure that my copy is on the shelf at work...
Always good to use a modelling project to learn a bit more about various subjects. For me it's what makes the hobby interesting. Every day is a school day, always happy to learn and be corrected.
Very informative. For a set size of slate, how are the lap and gauge determined? Are they a function of pitch??
The steeper the pitch, the smaller the slate that can be used. It is all based on how far the rain water will track under the slate at each joint. The nail holes in the course below need to be in the area that will always stay dry, one reason old slate roofs leak is the nail holes get bigger over time due to movement of the slate with temperature changes and wind so the hole ends up in the wet area. There are tables listing the pitch suitable for each slate size in most of the old text books, probably also available somewhere on the internet. You might also need the list of the names of the sizes to work out that a Duchess is 24"x12" etc. The tables are nearly always for Welsh slate as it was sold all over the world. Cornish slate was much more localised and one size of slate on a roof was less common. The pitch tables don't work for diminishing course roofs and the roofs are more prone to leak near the ridge unless they are parged on the underside. A load of differing sized slate was cheaper than one size if the quarry was local. Railway stations and government buildings usually have single size slate roofs.
On stone as in Purbeck rooves mostly common pitch 45° or steeper. We would like to get 4" of cover at least for a nail, peg. That is the course with the nail was covered by the next layer but the cover was the course above this being over the hole by the 4". On a strip and relay you tended to by what the gauge was and adjust for breakages and or better cover. As for parging it was more to give the tiles a soft bed, and to even out the levels due to varying thicknesses. Purbeck rooves were often pointed in for neatness rather than waterproofing. In fact the national mistrust stopped the pointing at one time.
Likewise also interested in these details. My father-in-law was a plumber (trained under Tom Finney - for those that have knowledge of football history and Preston North End). In addition to the plumbing he specialised in leadwork for roofing and was part of the maintenance team for the Preston Royal Infirmary. When he retired I managed to grab many of his leadworking tools which included his book "The Plumbers Handbook" published in 1960. Which has several interesting pages on gutters and ridge / hip rolls.
However I thought this @1960 was too "modern image" for this thread.