During a Scottish Area Group (ScOONs) Zoom meeting on 16 August, one of our group asked what happens at the ridge of a slate roof and what happens when a slate roof slopes down to a vertical wall. As it happens two other participants are architects (one actually a former architect - me). One of the delights of a Zoom meeting is that while discussion is going on, you can Google for information and then share your screen when you find it. We felt that it might be of wider interest to share what we came up with in this forum.
I'll look at the ridge first. There are essentially two ways of doing a ridge on a slate roof. One is to use clay tiles bedded in mortar in exactly the way that you would with a tiled roof. (And on a prestige building, these can be quite fancy decorative tiles.) The other way, which was the more relevant one for a fairly modest building in south-west Devon, is to use lead.
The picture below (shamelessly stolen from the internet) shows an identical detail used for both the ridge and hips of a roof. It is formed around a wooden rail up to about 3 inches in diameter nailed to the top of the ridge pole and hip rafters. Flat lead sheet is then dressed over that by a lead worker to fit snugly around the wood and over the adjacent slates. The undercut on either side of the wooden rail allows the lead to grip on to it without using nails (which would compromise its watertightness). Lengths of lead sheet are simply overlapped to achieve the length needed. Water can't accumulate on the top of the roof, so it doesn't compromise keeping the rain out.
If you notice the small tabs holding the lengths of lead down, these are clips to help secure it. They are actually strips of lead laid across the wooden rail and nailed to it. Once the lead ridge has been formed, the ends are simply folded over as you see in the photo.
Note that the lead is dressed snugly down over the slates, so that on the hip detail, you can still see the slate courses through the lead.
(A zinc ridge is similar, but being stiffer, pre-formed lengths are used and the galvanised steel clips go on top of the zinc, not under as with lead.)
Ian
When a slate roof meets a wall, you need a gutter. See the pictures below for the appearance. The gutter is lead on wooden boarding. The lead goes quite a long way up the stone wall and is dressed into a groove chased into the stonework. It also goes a correspondingly long way up under the slates. Water doesn't necessarily drain away quickly here (think snow accumulation or wet leaves), hence the effective depth of the gutter.
About every 10 feet or so, the lead needs a joint and this is achieved with one of the steps in the gutter that you can see. A simple overlap won't so, because of the risk of standing water. The step down is at least 3 inches, often a bit more. The lengths of gutter in between are not quite level. 1 in 30 is a common slope to use, which may be ignorable on a model.
Note that because of the geometry of the situation, the gutter gets narrower at each step. The minimum width needs to be 9 to 12 inches, basically so someone can stand there with a broom to remove those wet leaves.
Where two slate roofs slope down to a valley, you get essentially a double-sided version of the same arrangement.
As an aside, notice the colour that the wooden door has weathered to and the way the iron hinges have rusted - definitely a challenge to capture!
Also the second picture shows some of those fancy ridge tiles I mentioned (the building is a church).
Ian
Thanks - that was an excellent impromptu tutorial last night! :)
I mentioned the other extreme - fancy ridge tiles. As you say it applies to more prestigious buildings and I guess it was a sign of wealth or at least aspiration and genteelness as seen in urban Victorian 'villas'. I think the word I was looking for was pierced detail. More of it here than you can shake a stick at -
http://www.rooffinials.co.uk/brux-lodge-ridge-tile-restoration.html (http://www.rooffinials.co.uk/brux-lodge-ridge-tile-restoration.html)
Sorry - the image is not embedding as it is http and not https
http://www.rooffinials.co.uk/images/stories/roof%20finial%20work/Brux_Lodge/Brux_Lodge_Ridges_and_Finals.jpg (http://www.rooffinials.co.uk/images/stories/roof%20finial%20work/Brux_Lodge/Brux_Lodge_Ridges_and_Finals.jpg)
Something else occurred to me but I could not find it last night that might help Paul. Another good source for architectural detail is to track down building conservation websites.
This one is for Scottish roofing, but there are almost certain to be similar sites for other locations, particularly if they relate to National Parks or conservation areas.
https://www.buildingconservation.com/articles/scottish-slate-roofs/scottish-slate-roofs.htm (https://www.buildingconservation.com/articles/scottish-slate-roofs/scottish-slate-roofs.htm)
I mentioned I looked out for old slated roofs around here that still had variable sized slates. No - it is not a very wide roof and perspective foreshortening!
(https://www.buildingconservation.com/articles/scottish-slate-roofs/scottish-slate-roof.jpg)
This is more along the lines of what might be relevant to Paul for his Baskerville layout. It is not a record of historical buildings but what it contains might give an insight into what is regarded as being common vernacular styles. I guess there is always the danger of finding a particular example building in an area being modelled and using that as the basis for construction only to find it is atypical of the area. Something like a conservation guide should hopefully give a broader idea of what is typical (or at least what looks the part given modern ideas of comfort and hygiene!)
https://www.dartmoor.gov.uk/__data/assets/pdf_file/0026/74771/14781_111109_Dartmoor-Design-Guide.pdf (https://www.dartmoor.gov.uk/__data/assets/pdf_file/0026/74771/14781_111109_Dartmoor-Design-Guide.pdf)
Thank you - that's very interesting - and useful.
Then there's the whole thing about slate sizes (and their names!)
and on some roofs I think they get smaller near the ridge? (At least that's what I have done on Angst)
And here's the hip detail done with zinc. (It's North Berwick Lifeboat Station - I was waiting for a lift just across the road from it this morning and spotted the photo-opportunity.) In 4mm scale, it's pretty much indistinguishable from lead. There are a couple of give-aways, though:
The clips are galvanised steel (and rusty by the seaside) and on top of the flashings.
The metal is pre-formed and quite stiff, hence the kink where it has been bent to accommodate the change in pitch just above the eaves (known as sprocketing in the trade).
Also because the metal is stiff, it doesn't conform to the individual slate courses as lead would.
Ian
Quote from: hughn on August 17, 2021, 11:22
Then there's the whole thing about slate sizes (and their names!)
and on some roofs I think they get smaller near the ridge? (At least that's what I have done on Angst)
As Graeme pointed out, it's a feature of some old slate roofs. Note also on Graeme's picture, the widths of the slates are random. The reason for that is so that as the slates get smaller towards the top, you don't end up with the gaps between slates in successive courses lining up with each other (and letting the rain through). You do occasionally see roofs where the depths but not the widths diminish as you go up the roof (so the widths can all be the same), but that's rarer.
Ian
Quote from: hughn on August 17, 2021, 11:22
Thank you - that's very interesting - and useful.
Then there's the whole thing about slate sizes (and their names!)
and on some roofs I think they get smaller near the ridge? (At least that's what I have done on Angst)
I was aware of some of the names, but not the origin -
http://www.penmorfa.com/Slate/sizes.htm (http://www.penmorfa.com/Slate/sizes.htm)
One might need to be careful in speaking some of the names in polite company, e.g. "Broad Duchess" ;D
At the opposite extreme to what look like almost playing card sized slates on some old roofs there are the buildings in Yorkshire that look like they are roofed in paving slabs.
https://vimeo.com/78715268 (https://vimeo.com/78715268)
And then there is just showing off -
(https://dmduncanandsons.files.wordpress.com/2013/02/20130206-194155.jpg)
https://dmduncanandsons.wordpress.com/
I had no idea my question would cause this much discussion, but I'm glad it did. This is very useful information, and I thank you all. Now I just have to try to model it with my very limited skills!
Quote from: GraemeD on August 17, 2021, 13:07
At the opposite extreme to what look like almost playing card sized slates on some old roofs there are the buildings in Yorkshire that look like they are roofed in paving slabs.
They pretty much are! There are such things a "stone slates".
Technically, it's when you use a sedimentary rock (sandstone or limestone) rather than actual slate which is metamorphic (it's basically squashed clay). It's a geologically inaccurate term as the stone used very specifically ISN'T slate.
You can use any sedimentary rock that can be split reasonably easily along its bedding planes and is both waterproof and robust enough not to crumble. They are much thicker and heavier than actual slate and need a massive roof structure but still thrived as a traditional building material in some parts of England.
More information than you could possibly want here: https://historicengland.org.uk/advice/technical-advice/buildings/building-materials-for-historic-buildings/stone-slate-roofing/ (https://historicengland.org.uk/advice/technical-advice/buildings/building-materials-for-historic-buildings/stone-slate-roofing/)
Ian
Living south of the border I've found this thread informative and interesting but have been reluctant to intrude. However, now the subject has widened slightly to stone roofing I will presume to make a small contribution.
Here on the Isle of Purbeck limestone with mostly flat bedding planes is plentiful and stone roofs common. The extension at the back of our house has what I believe is termed a catslide stone roof:
(https://live.staticflickr.com/65535/51386804545_7515b5993b_b.jpg) (https://flic.kr/p/2mhSNGH)r1 (https://flic.kr/p/2mhSNGH) (https://www.flickr.com/photos/92012779@N06/),
and at the front there are two eaves courses of stone which is also a common feature hereabouts.
(https://live.staticflickr.com/65535/51386536404_118cfcd02a_b.jpg) (https://flic.kr/p/2mhRqZA)r2 (https://flic.kr/p/2mhRqZA) (https://www.flickr.com/photos/92012779@N06/),
I've always worried about the sheer weight of tiled and stone roofs – especially as most tiled roofs are effectively double layer – although slate would be significantly lighter, I imagine. Certainly even relatively thin stone is much thicker than slate, as you can see from the photos. (When we renovated this house the stone roof at the back was sagging noticeably so we put in an RSJ to help support it.)
Note how well the guttering, which I imagine contains asbestos, blends with the stone... :)
David.
Thanks David. I think that far from being unwanted it addresses a point that came up in the original online discussion about local materials and styles of architecture. It also illustrated a specific question that Paul had on lead flashing. A good example can be seen of a valley construction in your photo. Clearly this is more obvious than on a grey slate roof due to the colour contrast and thickness of the roofing material but it illustrates the point. Perhaps something to note is how wide or narrow the gap bridged by the lead is on a particular building. Apart from regional variation I suspect the age of the building or at least the time of the last re-slating plays a part. I get the impression that perhaps in general more recent roofing has wider gaps. On many of the Victorian slate roofs (I guess Welsh slate) in Aberdeen the gap is almost non-existent. In fact I even wonder if it was a matter of the slater's pride in making an almost perfect butt joint.
Here's another photo of a valley with thinner roofing material (indirect image link via Google as the original website is http not https.)
(https://lh3.googleusercontent.com/proxy/cAjPLfbQMYjdiZfr4JtYI9QJGl3JHZ5edQ1Vq4ZTwRRaqQ0ijm1JplYu0qFLPzEp3Fv9Ydhtol-UohlL_PTudXZV6aoOMZwJXMgw4Ja7dauqDsQtk3hbqOB3XXim4HiXBMetT1yznB2q75mZdkEo-x09S6lD5ycYcWpxSYZ_V85sISt65AJWVroI7rnrGTyXWeYkwJ5Q)
http://www.sigaslate.co.uk/knowledgebase/material-advice/replacing-a-scottish-slate-roof/ (http://www.sigaslate.co.uk/knowledgebase/material-advice/replacing-a-scottish-slate-roof/)
In my case the valleys also make a useful path for broadband cabling (RH wall, >gutter > valley > over the other side)! The ridge on the extreme left is of an extension added about twenty years ago, which necessitated cutting into the stone of the main roof, so the valley is fairly recent.
I wonder whether the rather elegant 'feathering' on the lower edges of the slates are an added feature, an inevitable result of dressing the slates, or maybe both?
David.
Having attempted to size and shape a couple of slates myself, I'd say there was a certain inevitability about it ;) but watching the Yorkshire stone roofing video it did mention doing something similar in order to create a sharp edge to shed water, though clearly the stone is a lot thicker and perhaps more likely to wick water back up the underside.
With slate slates the cutting is done with a hammer over a sharp anvil-like edge so the underside can or should be quite neat but it flakes off at the top. I had an opportunity to examine the tools when our house was re-slated but had to improvise when I tried it myself. I much admit cheating and using a hacksaw for most of the re-sizing once I got a reasonable edge for the visible edge. My application was a rather twee slate cill for the replacement cast underfloor air vents I put in after the originals rusted away.
Like you, I have tried cutting slates in the past but the results were... er unpredictable, shall we say?
I imagine granite is not much use for roofing!
David.
I was looking for something on roofing in Dartmoor for Paul, but came across this instead. The search link said South and West England, but turned out not to be South and West enough, but relevant to many NG layouts.
https://www.spab.org.uk/sites/default/files/SPAB%20Technical%20Advice%20Note_Slate%20and%20Stone%20Roofing%20in%20Wales%20and%20the%20Marches_0.pdf (https://www.spab.org.uk/sites/default/files/SPAB%20Technical%20Advice%20Note_Slate%20and%20Stone%20Roofing%20in%20Wales%20and%20the%20Marches_0.pdf)
One could really Geek-out on modelling roofs! I guess it is a pretty prominent part of a model building.
That looks like an entire OU course!
David.
P.S. Why can't I see the 'like' button any more? Where's it gone (if it has)?
The detail shown on the horizontal box gutter where the pitched slated roof abuts a wall is quite common but incorrect.
There should be a cover flashing over the upstand from the gutter and it is this that is chased into the wall and not the upstand to the gutter which should be free to move with expansion and contraction; failure to provide the cover flashing may lead to failure of the joint due to thermal movement with consequent ingress of water behind the lead cuasing damp in the internal wall and possible dry rot in timbers in contact with it including boarding to the gutter . Not good.
Sorry to be so pedantic but I spent my working life reporting upon building defects!
Playing trains is much more fun.