Rafter finish on old stone walls

[heliox]

I want to reslate a very old roof.

Presently it has rafter, purlin and Tied Trusses
It has tonnes of old slate (random sizes bed in lime mortar)
It has several layers of grout,,cement slurry on top of lime slurry.

Basically its stood over a hundred years and is well overdue replacement.
unfortunately last winters real cold has allowed the damp to freeze and has splitting open the ridge. (yes there is some splaying of the walls but structural survey said historical).

I propose to reslate it.
Exisiting timbers are sized:

1, trusses 7x2 3/4"
2.purlins 3 x 2 3/4"
3. Rafters 2x2"

Plan
1. leave trusses
2. upgrade purlins to 8x3"
3. upgrade rafters to 4x2"
4. consolidate random stone wall tops with concrete ring beam
5. install 4x2" wall plate on top.

I am a little stuck at this point, here are some photos
1st one shows eaves detail (or lack of it) i.e slate just protrudes, no rafters showing etc

Untitled

• heliox
• 14 Oct 2011
• 1

2nd the roof weighs alot

Untitled

• heliox
• 14 Oct 2011
• 1

3rd and 4th shows existing timbers.

Untitled

• heliox
• 14 Oct 2011
• 1

Untitled

• heliox
• 14 Oct 2011
• 1

You will see no sign of wall plates, rafters just go into wall, however in another part of the building; were I hacked off, you can see wall plate with birdsmouthed rafters sitting square on inside face,,,another words they dont project to outside of the 700mm thick walls. So I assume the slates are just mortar bedded the rest of the way.

After all that my question is:

Options:
1. If I level walls with a ring beam and I fit a traditional cut roof should I just fix down wall plate to external edge of wall and project rafters using truss clips and create eaves as normal?

2. create ring beam, birdsmouth onto wall plate near external edge and just project slates over similar to existing?

3. create ring beam, build internal leaf one block high, sit wall plate on top and restrain wall plate on inside wall, use truss clips and project through to eaves?

Abit of a conundrum for me really so thought I would put it out here for more heads to look at it.

Many thanks guys.

p.s its only my 3rd post so take it easy, oh and sorry for the long post

 

[heliox]

Hi
I thought I would sketch out exisiting and options to make clearer what I have and propose.

Existing:

Untitled

• heliox
• 14 Oct 2011
• 1

Some Options:

Untitled

• heliox
• 14 Oct 2011
• 1

[/img]

All have concrete ring beam, restraint straps, and truss clips on 1 & 2 but birdmouthed on 3 with a kickout timber nailed alongside to carry slates on?

Any suggestions?

 

[BethesdaSlate]

Wow - interesting old roof, these 'ribbed' roofs are pretty rare now and you may have the conservationists all over this one! This system of vertical ribbing with metal wire and grouting is known as 'Sir Fonio' in North Wales (or 'Anglesey-ing' in English) as it was such a common fix on Anglesey coastal cottages that were originally roofed with low grade slate. Many can be seen on he coasts of Pembrokeshire too and the authorities there will not allow you to touch it without photographing & recording at every stage, and if replacement is deemed necessary then it has to be put back the same (or at least look the same) do you have the same situation where you are? would be interested to know how your going to re-slate it.

As far as you question is concerned I'd go for option 2! , but could you not just use a nice timber rather than the 100mm concrete block?

 

[heliox]

[quote="'ribbed' roofs are pretty rare now and you may have the conservationists all over this one! known as 'Sir Fonio' in North Wales (or 'Anglesey-ing' in English) a[/quote]

Sir Fonio thats interesting:

Your right about conservationists, to be honest I have racked my brain to try and keep the roof but problem is the weight increases over time from subsequent layers. I actually love the roof and will be sorry to see it go.
Its causing localised problems where it has failed altogether and If I leave it any longer its going to go completley one winter. (which I seen go on someone else's house).

Just to clarify this property is not in dorset

Also full residential planning was granted a long time ago and converted very badly, its not listed and they couldn't list if they tried as its been chopped and changed so much.
However, I am reintroducing as much sympathetic material and features as possible and loathe to change the roof as all other local roofs have gone, mine is only one left, but I cant see another way.

In fact the local authority used to insist on keeping them until someone pointed out that it is unenforceable, so they dont anymore.

re; the concrete block, that will be rough rendered to match existing internal, will be lime washed too. you wont know its there. in fact I was thinking of insetting the beam and block a few inches and lay another course of stone clad in front, like I will on external leaf.

Re: Options, yes, Option 2 looks most likely.

Thanks for comments its all welcome and I hope more solutions pop up.

 

[heliox]

Bethesda slate? the penny didnt drop when I replied earlier.

My intention 2 years ago was to remove the worse section 8 linear meters, upgrade the timbers and recover in reclaimed welsh slates, which I bought, in fact they are purple welsh 9x9 and I was going to blend it in over a party wall then install ribs and grout to match.

With the ribs, they use barbed wire and in effect they become lintels. Albeit not horizontal.

I was going to lay the roof uneven to blend further and when all finished regrout the whole lot.

Well as mentioned its looking like it all needs to come off, there are good sections but it will be a mammoth task to repair as is.

So my latest plan is forget the purple heathers and go for 6000 16x8 welsh reclaims and do the whole 20 metres. basically I will end up with a aged roof but no grouted roof anymore. there is no point grouting a brand new 16 x8 slated roof because its not original and the ones that I have seen done; you know they have been done.

There is only one way I would go for a regrout and that is to do it exaclty as original, i.e lime bed each random slate then grout the lot afterward.

At least that way although a new roof, the result is that it is exactly as it was layed originally. so its very sympathetic and after a few years you would be hard pressed to tell the difference.

I have the skills to do it, Problem where do I get around 150m2 of random slate?

Even If I strip the existing roof I cant reclaim the slate (actually maybe some) the problem is its not north wales welsh slate its the softer welsh cousins, hence the problem roof in areas. So I would have to source the slate, well I dont need to tell you that the original slate was used as a cheap alternative. Well the irony is things haven't changed its about cost, I have been offered 14x8 welsh reclaims at 40p each.

I haven't bought them yet, I am still planning out how to change it all in one go, That's why I intend consolidating the wall tops, the fact the ridge has opened up means I HAVE to do something.

 

[BethesdaSlate]

If it were me and I had the budget I'd redo it in small randoms something like 16s down to 12s, peg fixed and top bedded. That would be as original and look great in my opinion.

However this would be expensive, especially in labour cost, I reckon the next best option would be small Randoms as above but centre nailed into modern battens, and thirdly 14x8 reclaimed they could look great too.

There are many people involved in conservation and planning departments in Carmarthenshire that have insisted that grouting a newly laid roof is the right thing to do in the conservation areas- whereas myself and other heritage minded slate people are of the opinion that grouting, (and ribbing for that matter) would have happened during the life of the roof to try to prolong its life and never was an original method of roofing. To completely grout a newly laid roof in my opinion is wrong - I've seen so many of modern grouted roofs fail, which they obviously will as soon as frost gets under it.

A compromise I have seen working (if it is a requirement to keep the ribs), is just to fit the barbed wire ribs and grout over these as traditional repair and just have some light grouting on the slate, but not enough to cause damming up all the perps and laps and certainly not layers of mortar which will inevitably end up coming off in sheets every spring. I believe the only reason older grouted roofs seem to have lasted so long compared to modern attempts to replicate them is because it was done partially, bit by bit, over many years - this would have allowed previously laid mortar to have had the chance to have completely keyed and set before more was applied anywhere near it.

I was quite surprised when I thought that roof was in Dorset! - I'm guessing it must be west Wales somewhere then?

Jeez -apologies for the long post, I've been interested in this types of roofs for a while!

 

[heliox]

When you say

I'd redo it in small randoms something like 16s down to 12s, peg fixed and top bedded.

I assume 16" long and 12" long? by what widths?
1. Or do you mean any random width with all slates 16" and 12" long?
2. Or random widths and random lengths between 16 and 12?

I think you mean 1. with alternating courses i.e row of 16 random widths then 12 randome 16,12,16,12 etc?

Labour is not an issue for cost as its my own time. any idea on the cost of random slates those sizes? and how do I work out the m2 coverage for ordering if all random?

I would more than likely go for centre nailed as it will be recovered internally with membrane and insulation etc.
It was covered over in tongue and groove, rockwool, until I ripped it all out to make repairs.



re: your comment:

I agree totally, and if anyone thinks it was done from day one they are guessing, it certainly around here was done during the life of the roof, with subsequent coats every so many years, I know as I have talked to the elderly gentleman who grew up seeing his grandad doing it. and it was purely as you say to prolong the life. However having said that I assume the fact they were just cheap outbuildings for the poor that when they laid the roof they would not have been bothered on the finished look, it would be all about practicality. SO, on those lines when they laid it there would be mortar everywhere, because of bedding in and the randomness of the slate sizes etc, so from day one no doubt they would have dried out fairly white looking until rain cleaned it. later layers were just repair.

re; your comment "A compromise I have seen working etc....and why lasted so long compared to modern attempts to replicate them .........
I agree totally, I have seen a few attempts, most look o.k and sympathetic, but you know they were done yesterday.

I am going to have another long look at this as like you I am interested in these roofs and the whole simplicity of how people lived, hard life but content to provide for their families.

I'll tell you how hard a life, a spring used to come up in what is now the middle of our living room (its been bypassed by land drains now)

well the family that were farmer tenants here in the late 40's were evicted due to the farm being sold as part of inheritance by auction, when the buyer went to let them know they would have to leave; three or four of the family were huddled around the coal fire, with wellies on and water from the intermittent spring filling the whole ground floor 6-8 inches deep, and whilst they were being told a bone whale corset belonging to the farmers wife drifted out of a cupboard and floated across the room!

It must have been absolutely dire conditions!

Anyhow, I am going to have another look at this as I want to keep what I can, problem is though as it was subsequent layers over a very long time and the later layers cement based the weight up there doesn't bear thinking about. In one part where there were childrens bedrooms the trusses had rotted out completely and the cowboys put some 3x2 cross ties in and tongue and grooved the lot! I nearly had an heart attack when I seen what one section is being supported by!

I would love to know where the building inspectors were that day!

I got new oak timbers ready to put new trusses in when I remove that section, I'll enjoy making those up.

 

[BethesdaSlate]

What I meant by 'Randoms 16s down to 12s' was random width slates of varying lengths, 16" being the longest.
You would start the roof at the eaves with the longest slates, working down to shortest near the ridge.

These days we normally use even nr lengths i.e 16s, 14, 12s etc, but when using reclaimed it just depends what you can source and use what you get, they could be 16s,15,14,12,11 for example so you need to be able to work with what you get (as they would have done originally).

The key to Random slating is getting it all sorted before you start! sort all slates into their lengths on the ground and work out how many courses of each size you can manage (make sure you've always got a few left over of each size) then batten accordingly.

You would normally buy reclaimed randoms by the tonne, on average a tonne will cover about 17m2 and can cost anything from £200 - 700 per tonne.

If you're doing it yourself you'll need to accept it will take a lot of time and will require much patience and study, there is a lot more to random slating than most people think, but don't let that put you off!

 

[heliox]

If you're doing it yourself you'll need to accept it will take a lot of time and will require much patience and study, there is a lot more to random slating than most people think, but don't let that put you off!

O.K I wont let it put me off

In the last few days I have been quite fortunate, I have just been given as much random slate as I want to salvage from this pile!

And its only 2 minutes away, builder was going to use it as hardcore!

Here are just 4 I picked up to show randomness.

Then this afternoon chatting with my mate and he tells me he may be able to give me 3 or 4 tonne he sorted and stored at someones barn when his brother was renting it. He is gong to see if they are still available and if they are there I can have them.

So I have had a rethink again! (your fault Bethesda)

(this part I was going to do as temp fix)
I have just bought expanding foam and am going to fill in all the ridge, around 8-15m of cracks upto 3"wide!

Then I will trim externally and give a 6" coat either side of ridge (over the foam) with "Roofix 20/10" http://www.newventureproducts.co.uk/Roofix_2010.htm

I have had a tin on the shelf for over a year.
That will keep the water out until spring and hopefully there wont be any significant movement over winter. (depending how cold it gets)

By Spring I will have a big pile of sorted random slate from the pile above and if my mate comes up trumps on another load.
(I also have already a pallet of random from neighbours house I have had awhile)

I will then remove my roof, do all the wall consolidation (ring beam) then install all cut roof timbers and breather membrane. watertight again.

at this stage I should have a good idea how much I have salvaged from my roof, and combined with what I should have sorted by then, I should have more than enough to redo.

So I need to ask a few questions:

1. I know it will be slow process, and how long is a piece of string, but how long per m2 should I allow approx? (Is 3 m2/day reasonable?)

2. You mentioned pegging and bedding in top, I assume oak treated pegs? I have a stack of cedar here but suppose too soft for pegs? no problem using Oak I got stacks of green and semi seasoned, cedar wouldnt need treating I was thinking, but if I use oak then just soak in preservative yes?

3. bedding in method: I assume when you say top, you mean outside face, i.e (A)butter the inside bottom 1/4 of the slate and just press into position? and smooth excess with brush? or (B) butter top 1/4 of last laid slate and press on new (like laying bricks)? I think B.

4. the pegs how much should protrude through top of slate? i.e clout nails are flat but pegs wont be, so slate will sit proud not flat albeit mortar will fill the gap the peg makes between slates. 5mm? 10mm?
I couldnt see on my existing but noticed that in one room there was pegs on one elevation with split branch battens (hazel or oak?)

on the opposite face it was partly nailed and partly pegged but the battens were plastering lathes softwood, so I think that elevation has previously been redone, albeit a longtime ago.

5: bedding in mortar: 1:3 hydraulic lime, sharp sand?
This site looks interesting:
http://www.collywestonstoneslaterstrust.org.uk/specificationguide2.htm
It mentions bedding in too, but top of slate, I haven't read completely but it looks like its the top of the slate you just laid then place new on top.

long post (again), hope not too boring for readers, hope it helps others if they come across this kind of problem grouted roof.

any suggestions most welcome. many thanks.

 

[BethesdaSlate]

Not sure I'd describe that pile as 'fortunate' personally, think I'd be with the builder on that one and treat it as hardcore!

Regarding your questions:

1. Remeber that more than 50% of your time will be taken up in 'not laying' the slates ie, cleaning, sorting into sizes, holing the slates, making pegs(?), battening (battening for randoms is quite complicated) stacking, sorting (again!) - then you get to lay them. - You should be happy with actually laying 3m2 a day I guess.

2. Oak pegs would be best if you're pegging, seasoned preferably.

3. Difficult to describe without showing, but I'll try; By 'top' I mean 'head' of the slate as opposed to the bottom or tail. For your project I'd recommend head bedding, that is laying the slate onto a mortar bed on the top of the two slates below, but you need to be quite particular how this 'bed' is shaped in order not to block the perps and kick the slates up to much, this comes with experience in doing it. So yes more like 'B'

4. The Pegs will protrude 'slightly' as long as they fit snug in the hole and hold then thats fine, 10mm protruding would be too much though for sure. As you say, have a look at the originals.

5. Yes - Hydraulic Lime and sharp sand mix is fine for bedding.

Suggestions - find some better slates if you can!

 

[heliox]

Not sure I'd describe that pile as 'fortunate' personally, think I'd be with the builder on that one and treat it as hardcore!

I must admit the picture looks horrendous, but the slates are absolutely sound, and the pile is massive, but I agree I need to source slates and have ready before I start. So will be on the lookout for some, I seen some randoms being sold by a company on eBay but they are huge slates so I need to shop around.

re:bedding in and not blocking perps here is a sketch with perps filled between two slates at heads and under the top slate, is this what you mean? i.e perps are clear on the exposed parts of slates but filled by bedding in on the hidden part of perps, yes?

Untitled

• heliox
• 24 Oct 2011
• 1

[/img]

Also is it possible to do this method on a warm room with insulation over rafters?

Many thanks again

 

[BethesdaSlate]

Yes, something like that, although the tails of the second course will be much lower down in reality as they will be double (possibly even triple) lapped.

And yes, this method is fine whatever is going on underneath. But it seems extremely labour intensive for something that can never be identified as being done (as you're boarding the underside) - it would be a lot less hassle nailing and would look the same.

 

[heliox]

Many Thanks Bethesda

If it helps anyone in similar situation there are some videos by English Heritage one on Collyweston Slating and the other Swithland slating.

The give a good overview of the techniques used and I believe similar to what we have been talking about.

http://www.youtube.com/watch?v=NAxeOk_j9bI&feature=related

 

[BethesdaSlate]

Those videos give some good advice. I have been working with the maker of those videos for English Heritage, we hope to have one available soon showing Welsh Random Slating, just waiting for the right job to film on!

Good luck with the project.