Tue, 19 Dec 2023 07:05:56 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303808#Comment_303808 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303808#Comment_303808 Sun, 08 Oct 2023 10:39:21 +0100 greenfinger
(Background first - the room has a vaulted ceiling (so no loft), is not currently heated, and is only used by one person. There's no kitchen.)

I've stripped some slates off my roof over the weekend to do a repair. Most of the slates are quite damp on the underside (a few are even wet, I'd say). They are also a bit flaky - still sound, but with a thin-ish layer flaking off the surface. This is both on the underside and on the top where the slate was covered by the slate above.

First and foremost, is this normal and to be expected? If it is, then great :) I'll replace the bad ones and get on with it. If it's a sign of a problem, what's the most likely cause and - dare I ask - remedy?

If it is a potential problem, there are a few factors which might be contributing and which might also solve the problem once put right. The trouble is, with the slates back on I'm not going to know in the future whether there's been an improvement. Here's those factors:

- There is currently no ventilation. The make up from inside is: plasterboard, rockwool/glassfibre, no air gap, sarking boards, felt (1f), battens, slates. I'll be putting in ventilated soffits and vented ridge, a 50mm airgap between the sarking and top of insulation, and replacing the insulation with PIR. But will adding ventilation beneath the sarking boards and felt do anything to help ventilate above the sarking boards and felt?

- Only horizontal battens were used. No vertical counterbattens beneath. So any water that makes it passed the slates has no path down to the gutters. That being said, the felt was pretty much all dry and and the battens look fine. But I didn't know if this was significant from a ventilation point of view (or whether there even needs to be ventilation between the sarking boards and slates?).

- There has been a section of plasterboard ceiling (10 foot wide 3 foot long) missing for the last year or two, along with 10" a hole in the sarking and felt. So from inside you can see the underside of the slates through that hole (the hole is from a removed flue). Given that the hole is only 10" and the removed plasterboard 10x3, could this contribute to the much larger area outside where the slates are damp/wet underneath?

Sorry for the length of the post. Any thoughts - as ever - would be most welcomed and appreciated.

Many thanks]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303815#Comment_303815 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303815#Comment_303815 Sun, 08 Oct 2023 16:32:33 +0100 tony
IMO nothing can prevent it and not worth preventing.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303822#Comment_303822 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303822#Comment_303822 Mon, 09 Oct 2023 08:10:30 +0100 greenfinger
So would you say that ventilation between the insulation and underside of the sarking is important? 50mm I'm aiming for.

But that ventilation between the top side of the sarking (and the felt) and the underside of the slates is not needed? Even if condensation is inevitable - which makes sense as you describe - is the air gap not required to help dry out the condensation rather than to keep things moist under there semi-permanently? Just thinking aloud...

Also, is flaking on the underside of the slates a problem or to be expected, and can they be re-used if the flaking is a thin layer?

Many thanks]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303826#Comment_303826 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303826#Comment_303826 Mon, 09 Oct 2023 15:20:23 +0100 tony
I don’t worry about ventilation between the slates and the sarking layer. As soon as the sun comes out the slates get warm and moisture is driven away.

Between the insulation and the sarking, follow the regs. I suspect that the gap is over egged and 25mm would be ok, I have seen less without problems, don’t quote me though.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303827#Comment_303827 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303827#Comment_303827 Mon, 09 Oct 2023 20:49:38 +0100 greenfinger
I guess what it comes down to then is how bad the flaking is on my slates. They are Welsh. It's actually worse on the upper section of the topside (the sections covered by the slate above). I'll attach some photo examples, and wondered if you or anyone else can say whether they look bad and if so whether that is likely caused by lack of ventilation.

I should add that the battens all seem fine. Would they not show signs of mould or rotting if lack of ventilation was a problem?

Cheers

Link to photos. Sorry, they're not the best. Can take more if needed.

https://drive.google.com/drive/folders/1qlaU8o5W_reDlT86soxY7D3n9w5GTaO2?usp=sharing]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303839#Comment_303839 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303839#Comment_303839 Wed, 11 Oct 2023 18:10:08 +0100 greenfinger
Many thanks]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303844#Comment_303844 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303844#Comment_303844 Thu, 12 Oct 2023 06:59:14 +0100 tony http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303852#Comment_303852 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303852#Comment_303852 Fri, 13 Oct 2023 12:36:36 +0100 cjard
Try breaking it over your knee or hit it more than once with a hammer - the worse flaky ones will break apart or the thud sound changes as the layers are coming apart from each other. Good slates will carry on ringing the same, as you hit them.

Other problems also show themselves when you hit a slate, if there is a hairline split soemwhere the slate will have a rattle sound as well as the thud or ring. I've reinstalled flaking slates before but only as a last resort, and I put them near the ridge of the roof so I don't have tens of rows to strip and re-lay if they do start breaking in years to come

If a slate is holed in the wrong place, you can usually re-hole it further in towards the centre, or some small distance away from the existing hole; you're more likely to run into problems if you have to re-hole further up as the lower hole will be closer to the wind drive line or the runoff fan-out line (more on those below) as these parts of the slates get wet from rain during normal operation. Note that those cyan and green lines are just estimates/guides and in severly exposed locations could be very different

Generally if a slate is damaged above the nail holes you may choose to use it if it's in otherwise good condition, but do remember that the area of slate above the holes contributes to the double lapped nature of a slate roof

In the attached diagram (borrowed from fixmyroof and added to) I've added a red dotted outline to describe the outline of the slate with the faint "y" on it. The yellow area is the area of that slate that is above the nail holes, and you can see that it is required to carry water from the gap between the two green lines. The green lines are the "fan out" line and the cyan dotted line is an example wind-drive line
If there were a hole or some damage where the blue X is, wind driven rain could easily leak there. If the slate were re-holed or had old holes too close to the fan out or drive lines, they could let through (and then they have their own fan-out)

..so be cautious, especially if youre installing a slate with a missing bottom corner etc above a slate with damage above the nail holes - you might have to maintain awareness of defects in what's already laid and defects in the slate youre installing as you go]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303884#Comment_303884 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303884#Comment_303884 Tue, 17 Oct 2023 11:15:21 +0100 greenfinger
And thanks for all the other replies too.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303895#Comment_303895 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303895#Comment_303895 Wed, 18 Oct 2023 06:14:32 +0100 cjard http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303903#Comment_303903 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17989&Focus=303903#Comment_303903 Wed, 18 Oct 2023 11:55:53 +0100 greenfinger
I also noticed that some slates have what look like cracks going across them, but they aren't - they are more of a kind of vein maybe? Can't think of what the right word would be. There's a fair few like that on the roof, so I wasn't able to test them. The few I had like that off the roof I tried bending and they were sound so I think they're not a problem.

Have you come across similar?

Thanks again for all your help]]>