Don't use slate and a halves? Or use them but with thicker slates?

[Black Timber]

Hi all

I've got some repair work to do soon on a single storey roof that abuts a gable end wall. The leadwork was pretty shoddy before and needs replacing with proper lead soakers and flashing. As such, a couple or rows of slates will be coming off.

I've heard it's best to use slate and a halfs where possible, rather than thin width sections of slates. But upon enquiring it seems you don't really get slate and a halves in reclaimed Welsh slates. So that leaves me two options...

1. Forget about slate and a halves, use thinner width slates as needed, and carry on.

2. Use larger format but thicker slates. One rec yard has 30" x 20" slates which could be cut down to almost slate and a half (24" x 20"). The existing slates are 24"x 14". The trouble is that these slates are quite thick compared to the existing. I've never done and am no expert on roofing so am not sure whether the slates being thicker would cause more problems than I'm trying to solve?!

Any thoughts gratefully received!

Many thanks

 

[stuart45]

When slating a roof you normally sort out the slates into 3 different thicknesses, and start off using the thickest at the bottom. Having a thicker slate in the same course means the slates don't sit as well.
If the half slates are next to an abutment, it isn't such an issue. It's on the verge where the wind can lift them, although it's more of a problem with smaller slates.

 

[Black Timber]

Many thanks. That's good to hear. Mine are quite big - 20x12 (500x300) at the back and 24x14 (600x350) at the front. The only issue is that they aren't half slates where they meet the abutment; more like think slivers of slate in some places.

But I hope I can make it work because I've had no luck at all finding reclaimed slate and a halfs. I have found new ones at 500x450 (couldn't find anything bigger) but they come in at minimum £25 per slate!

My other idea to get around this was to:

a) Use wider soakers. Perhaps get 225 or 240mm lead, with a 75mm upstand, leaving 150-165mm for the horizontals.

b) Use a Z shaped cover flashing - i.e. lead in the cut chase of the wall, cover flashing over the soaker upstands, and a horizontal cover over the slates. I was thinking this would add an additional line of defence against water even getting to the abutment and soakers in the first place. But I've asked around about this Z shaped flashing idea and responses on the whole have said it isn't a great idea and/or wouldn't be beneficial. Any thoughts on that would also be great.

Thanks again

 

[Stevers]

My slate roof from around 1879 was relaid in 1997 using hooks and too many of the old perished slates. Because of the hooks it isn't in too bad a shape apart from the verges. These I relaid with the half slates nailed top and centre using heavy gauge copper nails. To increase my chances of success, I only used completely sound slates, and drilled and countersunk the fixing holes with masonry bits. My slates were 10"x20" and the gauging was a bit random resulting in some narrow half slates. I made sure that any replacement slates were at least 5" and narrowed the next slate where necessary to give a consistent overhang to the verge whilst also making sure that I maintained an adequate sideways lap all the way up, swapping the hooked slates around to achieve this since not all the existing slates were 10" wide.

Any sample of existing natural slate roofs will show extensive use of half slates and I am convinced that use of 'slate and a halves' is modern good practice rather than being essential or done often historically. A sound half slate nailed top and centre is not going anywhere. If half slates on a verge were only top nailed, then I can definitely see that as a weakness though. The half slates that I had lost or were insecure prior to the repair, were perished and were only centre nailed in holes made with a pick fastened with a lighter weight copper nail. I did the verge on the north gable two years ago, and the south gable last year and so far it's all good up there. The original roof used half slates and lasted for over a hundred years in an exposed location, and I'm confident that my repaired roof will see most of us out quite comfortably.

 

[Black Timber]

Wow, that's a super helpful response, thank you very much.

I went up onto the roof to measure things up yesterday but haven't had time to put together the info to post it here. I'll hopefully do that later or over the weekend.

In the meantime, may I ask - do you just have verges at your house or are there any abutments or similar?

Thanks again

 

[Stevers]

There is slating up against our chimneys, full slates only on the outside but half slates on the inside faces. The chimney bases are random stone so the flashing is set in a groove at the same angle as the roof about 4" up rather than stepped. Under the Code 4 flashing are Code 3 soakers. The poor workmanship is really a reflection of a lack of access to this area in 1997, due to the builder's scaffolding being only on front and back of the house.


This is the view before I'd deepened the groove and hacked off the remains of the original mortar flashings. The bottom of the each soaker was aligned with the bottom of the slate. I had to add a missing soaker, and one of the flashings wasn't quite deep enough to tuck into the new deeper groove so is new. Basically I just reworked what was already there, and didn't as it turns out take nearly enough photos!



And prior to the (new longer) ridge tile going back on. The use of half slates wouldn't change anything as you'd just top and centre nail them as you go. The side tingles (formed with a suitable drip under) are 'insurance' and not really needed! ;-)

For background we'd lost the lid of one those clay elephant feet chimney cowls - blown clean off I kid you not! I got the scaffolding in to glue and pin that back on since water would be running down that chimney pot and flue - although luckily it never showed up inside. Whilst up there, I tackled a plastic stone repair to the chimney and painted those fancy bargeboards. Only when I got up there to do all that, did I realise with a sinking feeling that the verge on the north end would need re-doing this time, so I had to get the scaffolders back to extend the scaffolding both sides. They were pretty good about it at the time, although I did get my leg pulled when they came to scaffold the other end which I already knew was in a very poor state!

 

[Black Timber]

Sorry, back onto this a bit later than I'd hoped...

I think I may have mostly found what I need. I can get some slate and a halfs for the back of the house where the slates are a bit smaller. And I will try to cut the slates to roughly follow the contours of the wall.

For the front, I have now measured up... Using what I can get, in the worst case scenario the slate will stop an inch short, so leave an inch gap (maximum) between the side of the slate and the wall. Is this acceptable or an absolute no no? To help mitigate, I plan to use soakers with a 165mm width across the tops of the slates

For the flashing I'm back to thinking to just use it vertically as that seems to be standard practice and the wider soakers will hopefully be more beneficial.

Many thanks

 

[Black Timber]

Sorry to be a pain, but wondered if anyone has any thoughts before I go ahead and get this done?

The main question is - is it ok to have a one inch gap between the side of the slates and the abutment wall? Soakers will have a width of 165mm.

Many thanks

 

[Stevers]

Slates should have a small gap between them and spreading the slates slightly in the row might allow you to close the up to 1" gap. It's debatable though whether slate and a half with an inch gap would be better than a half slate with a lesser gap, when there is a historical precedent for the extensive use of half slates on verges and abutments. I found that the key for my satisfactory use of half slates was to top and centre nail them.

 

[malcolm]

It's an abutment to a wall. The closest I've been to that is where a roof meets a chimney. It's well worth a search for chimney flashing to get thoughts about how that is done and where the tiles need to be.

Tile and a half is normally reserved for the roof projecting over a gable so you can get a bit more overhang than they could achieve with a half tile. If you are not overhanging I can't see a half tile being an issue.

 

[Black Timber]

Hi

Many thanks for the helpful replies @Stevers and @malcolm

The issue with spacing out adjoining slates in the row is that the plan was just to re-do the leadwork. As such I'm planning to strip a couple rows vertically. Stripping back more rows would make it a much bigger job, which I'd really prefer not to.

Thanks for the suggestion RE looking at chimney flashings. I have actually had a look and it seems to be the same deal with abutments. And the ideal is to get the tiles pretty close, which unfortunately I can't for the reasons given above.

It's debatable though whether slate and a half with an inch gap would be better than a half slate with a lesser gap

Tile and a half is normally reserved for the roof projecting over a gable so you can get a bit more overhang than they could achieve with a half tile. If you are not overhanging I can't see a half tile being an issue.

Funnily enough and contrary to standard practice, after having a re-measure it turns out my need for slate and a halfs is more where the full slates abut the wall, not the half slates. So for example on the front, the width required at the abutment for the full slate row is 15", but the slate is only 14" wide.

I found that the key for my satisfactory use of half slates was to top and centre nail them.

Thank you for that tip, which I'll look to follow when I do the job.

Cheers


PS - interesting in the chimney photo that the flashing is going over the slates. I enquired about this previously (and a little above in this thread) and the consensus was that it is not needed, and that the flashing only ever needs to be vertical. Was there a specific reason for it covering the tiles as well? That's presuming it's your photo!
Flashing over slates

 

[Stevers]

Running the flashing over the tile may be a pantile thing perhaps due to there not being soakers. My understanding is that for slates and plain tiles there should be soakers with the flashings just covering the upstand of the soakers.

 

[stuart45]

The lead can be dressed over a single lap, profiled tile, as spoakers can't be used. A soaker needs a double lap tile or slate, so it's sitting on a tile below.
Nowadays, you can get abutment soakers, or secret tile gutters for use with single lap tiles, especially plain single lap with no profile to dress the lead over.

 

[Black Timber]

Thanks again for your replies and help, much appreciated.