Hi there

I’m hoping to install a ventilated ridge soon and after reading up there’s a few things I’m unsure about. I wondered if anyone could help please?

The roof is Welsh slate and has stone/concrete ridge tiles (not sure which m but they are the old type). There is ventilation already at the soffits. In case it’s relevant, the roof has sarking boards, and the felt is the old style black stuff (1f?) laid directly onto the boards.

1. Should slates be cut flush to or proud of the top battens? Strangely, at the moment the slates are cut flush on one side, but on the other they overshoot the batten by around 75mm.

2. What is a good size gap to have between the top battens at the ridge? Currently they are 105mm apart. Does that sound ok?

3. How much do ridge tiles need to overlap the slates by? The current overlap is 97mm on one side (where the slates are cut flush) and 155mm on the other (where the slates overshoot).

4. The existing felt fully crosses over at the ridge. I’m presuming this would need to be cut to create an air gap, but am I right? If so, how much to cut and remove?

5. And finally, any recommendations for a good ventilated ridge system? I want something that is effective but also that won’t look too out of place on an old house with Welsh slate. Obviously it will need to fit/overlap the slates sufficiently, given the above dimensions. And also, because we live in a very rural area, it would need to keep vermin and insects out!

Happy to upload photos and get any more details that might help with the answers.

Thanks a million for reading. I’ve been trying to answer these questions as best I can but not having much luck, so any help would be fantastic.

Do you have a problem in that you want to put in a ventilated ridge?
What is the context of doing this work?
Slate particularly welsh slate which varies in thickness is in itself allows good ventilation between the slates.
One thing you should be aware if you do not already know is, that the regs now require that the ridge tiles be mechanically fixed. Mortaring them in place will not do any more. Certainly is the case for a new roof, a repair might be different but worth a check.

I would prefer more headlap for the ridges 95mm too tight

Ideally 25mm gap at the ridge

Ridge overlap - I like 150mm but 100mm might be ok depends on the pitch

Many thanks for the further replies.

Posted By: tonyI would prefer more headlap for the ridges 95mm too tight

Sorry to be thick, but not sure what you're referring to here and how it differs to the "ridge overlap". Out of my numbered points above, which one are you referring to RE 95mm headlap? Sorry to be a pain.

Posted By: tonyIdeally 25mm gap at the ridge

OK, so 25mm from the top edge of the slate to the centre of the ridge? And the same both sides, giving a 50mm gap all together? Having thought about that a bit more, if the gap is 50mm, once the batten(s) for fixing the dry ridge are put in place, that would leave next to no space for ventilation. Would that be a problem? Also, is the 105mm total gap between the battens as it is now problematic enough that I need to remove and replace the top battens to change that gap?

Posted By: tonyRidge overlap - I like 150mm but 100mm might be ok depends on the pitch

The pitch is 9/12 (36.5 degrees approx.).

Thanks again

Posted By: tonyI don’t think there are requirements for ridges to be mechanically fixed yet apart from on new houses

"Today, mechanical ridge fixing is required by the building regulations for both new-build and refurbishment projects. Updates to BS 5534 in 2014 effectively banned the use of mortar as a primary fixing, leading to the need of additional mechanical fixings, while further updates to the standard in 2018 provided clarification on the scope of the standard and requirements for compliance." according to https://www.marley.co.uk/blog/how-to-fix-ridge-tiles-to-a-roof

Similar also on https://www.labc.co.uk/news/code-practice-bs5534-spells-changes-roofers

Hi folks

If anyone has any thoughts on my points in the OP, I'd love to hear from you :)

Many thanks

Thanks Jonti. And sorry for the delay - I've been away.

Interestingly, I came across these articles which discuss what to do with slates at the ridge, and they seemed to be against overshooting the last batten due the fulcrum point it creates and problems with wind up lift. Their suggestion is to add a second higher (and slightly thicker) batten so that the last slates head has something to rest on. Or to cut the corners of the last full slate ("shoulder"), and then nail the last slate in the gaps created. Or to use hooks. Explained a lot better in the articles! Would you consider it overkill?

https://www.roofconsult.co.uk/articles/tiling/tips82.htm

https://www.roofconsult.co.uk/articles/fixslate.htm

Cheers