Roofing. Galv sheeting replacing slates.

[Majimoto]

Hope this isn't repeating any post.

I need to reroof a small leanto. Overhung by another roof .It has slates and underfelt at present.
I have bought polycoated box profile galv sheets for the job.

My question is--- can I screw the sheets to the existing laths (after stripping the slates)?
Or would I need to fit noggins between the rafters to affix the sheets? The rafters are good 2 by 4s.

I have only a 6cm gap for the sheets to fit under the overhang - so not enough space to put new laths.

Grateful for any comments - humorous or otherwise. Especially from anyone who has done this sort of job before.

 

[Ollie78]

If by laths you mean tile batten then it might be OK. The only thing is the roofing tec screws normally used for this roofing are quite thick and may split the battens.
I used this roofing on my shed but I put OSB under it for full support.

Ollie

 

[Bingy man]

I agree with @Ollie78 if possible remove the slates and slats and replace with plywood or osb , as additional protection you could paint the topside of the ply/ osb with bitumen then fix your sheets to the ply or osb. Even if you don’t split the roofing laths I doubt you could exert enough pressure to compress ghe edpm washers. Re: the 6cm gap (150mm ) the depth of the existing laths and the slate thickness wouldn’t be far off 18 mm if I understand you correctly..

 

[Majimoto]

Th

If by laths you mean tile batten then it might be OK. The only thing is the roofing tec screws normally used for this roofing are quite thick and may split the battens.
I used this roofing on my shed but I put OSB under it for full support.

Thanks,Ollie- I hadn't considered the thickness of the screws. Putting an under sheet is something I had thought of-- I'll have to check if I have enough clearance. The galv sheeting is actually quite low profile, so I think there will be room. Thanks again. Now for some decent weather!!

 

[Majimoto]

I agree with @Ollie78 if possible remove the slates and slats and replace with plywood or osb , as additional protection you could paint the topside of the ply/ osb with bitumen then fix your sheets to the ply or osb. Even if you don’t split the roofing laths I doubt you could exert enough pressure to compress ghe edpm washers. Re: the 6cm gap (150mm ) the depth of the existing laths and the slate thickness wouldn’t be far off 18 mm if I understand you correctly..

Thanks - good point about the bitumen.

 

[Spectric]

You want to fix to battens so that there is air flow under the cladding, fixing to boards means a lot of contact.

Why change slates that will last your lifetime to cladding that has a much shorter lifespan, I almost used cladding on my shed but ended up with slates as the better solution.

 

[Bingy man]

Thanks - good point about the bitumen.

Yeah top surface and any edges ( belt and braces approach)

 

[Bingy man]

You want to fix to battens so that there is air flow under the cladding, fixing to boards means a lot of contact.

Why change slates that will last your lifetime to cladding that has a much shorter lifespan, I almost used cladding on my shed but ended up with slates as the better solution.

I’m assuming if it’s profiled sheeting then this would provide airflow but prepared to be corrected..

 

[Spectric]

I’m assuming if it’s profiled sheeting then this would provide airflow but prepared to be corrected..

It will along the raised profile but the valley will be in full contact, any damp will settle.

 

[Bingy man]

It will along the raised profile but the valley will be in full contact, any damp will settle.

I think the bitumen painted on the ply/ osb would suffice for that eventuality but I take your point .

 

[Pedronicus]

Not in a conservation area by any chance are you? If so you may need planning permission to change the roof covering.

 

[Ollie78]

I think the bitumen painted on the ply/ osb would suffice for that eventuality but I take your point .

I put breathable membrane over the OSB on mine. Only because I had some left from doing the sides under the cladding and I thought I might as well.
It does seem to have worked well, no leaks in 6 years or so.

 

[niall Y]

You will need breathable membrane under the profiled sheeting to stop any condensation getting through. On cold and frosty days it can be a real problem,

Corrugated sheeting often goes on roofs that have purlins fixed on trusses. There will be a rail running along the length of the roof at the top at the bottom and at a point mid way, or several points in between,

Where you can't get a fix with the existing timbers you could fix noggins between the rafters beneath the breathable membrane Though it will be less hassle removing the battens, and boarding out the existing roof.

 

[Cobbs]

Why do you need to re-roof?

 

[Majimoto]

Fair point. I won't inquire too closely.

Not in a conservation area by any chance are you? If so you may need planning permission to change the roof covering.

 

[Majimoto]

Why do you need to re-roof?

This area gets a fair bit of traffic - old slate roof above it needs constant access. Ladders are a semi permanent fixture. So slates on the leanto aspect keep getting broken. Utter pain in the *#se.
I lived in Africa for a long time-- nearly all roofs out there are galv sheets - (Bati roofs.) I find them trouble free and permanent. This leanto roof has been redone many times by professional builders, still constantly leaks.
This job will be once and for all. "Probably"

 

[deema]

What about industrial cladding? You can attach it to purlins. I’d get it with insulation ie. Sheet, insulation, sheet. It comes in a wide variety of colours and designs. Look a lot better than galv sheet and a lot quieter when it rains.

 

[Cobbs]

This area gets a fair bit of traffic - old slate roof above it needs constant access. Ladders are a semi permanent fixture. So slates on the leanto aspect keep getting broken. Utter pain in the *#se.
I lived in Africa for a long time-- nearly all roofs out there are galv sheets - (Bati roofs.) I find them trouble free and permanent. This leanto roof has been redone many times by professional builders, still constantly leaks.
This job will be once and for all. "Probably"

Builders or roofers? Not splitting hairs, they're different animals; and being a "professional" only means you get paid for what you do, not necessarily that you know how to do it. Also the roof above looks like it's man made slate, the same as the bit you want to replace, in which case the slates themselves aren't that old, or they'd look it, this sort of slate ages fairly quickly. If you're getting constant trouble with the roof above, I think I'd get it looked at by a specialist roofer, inside and out, just to be sure there are no built-in problems with flashings, tail-lap or whatever.
Did you want to keep the roof-light/Velux in the lower pitch? If you do, that could be a problem with wriggly tin and at the very least will need a new flashing kit, though looking at the picture, it's been bodged already. I think if you're determined to do the metal roofing bit, I'd go the way Deema suggests and use the insulated sheets, they come in a range of thicknesses and do away with problems of condensation, as well as being a lot quieter in the rain. However you go about it, with a roof above at a fixed height and what looks like a box gutter below, as well as an abutting wall with a window in the way, you've got your work cut out.
So, bottom line, first try to find the problem in the upper roof that is causing you to walk all over the bottom one...