Screwing slates to battens

[Andy R]

I'm getting my house re-roofed...

It has an original slate roof - circa 1840 - but every year, a few slates fall off, due to the nails failing.
I've decided to bite the bullet and have them all taken off - and the roof felted and re-battened.
the plan would be to re-use as many of the old saltes as possible - and source a few 'new' ones to cover breakages etc.

I've found a builder who is prepared to do the work (he has done work for me in the past).
He's not a roofer - but he's worked on plenty of roofs in the past, including on listed buildings.

I plan to source the materials for him - and he's asked me to get screws to attach the slates to the battens.
I was expecting to be sourcing copper nails - but he says he would rather use screws...

Should I be concerned about his plan..?!

Thanks.

 

[vinn]

Its a strange "builder" who asks the customer to source his materials.
How do you know that this "he's not a roofer" has done any roofing at all in the past?

Screwing down slates is rarely done except for very particular conditions.
Copper nails are excellent & commonly used fixings.

Removing old slates needs gentle handling as the in-situ slates are lifted - otherwise you will be paying out for possibly expensive unnecessary replacements that careless handling has caused.

To re-slate requires many details that are second nature to a roofer - its far more than just taking them off & putting them back on.

 

[datarebal]

Oh dear.. Copper nails is the way forward.
got a feeling about this one... horses for courses..

 

[^woody^]

Why not screws? Still secure and less vibration when fixing. Must be stainless steel though.

 

[datarebal]

horses for courses...
jack of all trades.. master of none

 

[Doggit]

If he's suggesting screws, then he's definitely not a roofer. Stainless steel screws will cost an arm and a leg against copper or galvanised screws, and the heads will cause the next row of tiles to sit proud, and there's more danger of breaking the tiles as the head screws down too much.

Roofings not complicated, but as Vinn says, there is detailing work that a roofer will find second nature, and they'll also know the right roofing membrane to use, rather than just "felt". You've got to know how to start off the first couple of rows, and then set the battens from that, and then finally finish off at the top, so check if he does know enough to do the job, as using screws, suggests he doesn't.

 

[vinn]

Takes longer to fix with screws & if the correct laths are fixed with correct fixings at correct centres then a little vibration is irrelevant to the experienced worker.
The clout heads on roofing nails have a wider hold-down without the need to take too much out of the slate.
Screw heads are more prone to being too proud.
SS screws are more expensive than cu nails.
Screws can snap while fixing.
Removing screws with a slate ripper can be extremely fiddly & is more open to cracking the slate or possibly leaving in a stub of thread.

Anyway, thats all that occurs to me for now - I've only used screws for particular purposes, & I've never seen any roofers using them to fix a whole roof.

 

[Andy R]

Thanks for the replies guys – it’s appreciated…

I do think that he’s a ‘jack of all trades and master of non’ – but that doesn’t mean he can’t do a reasonable job on my roof.

I know he’s got plenty of experience working with slate roofs – including listed buildings – so I have no reason to think he’s not up to the task.

It was just the suggestion of using screws that concerned me.
I’ll question him on his reasons.

As Woody implies – I was really asking ‘why not’: and Vinn and Doggit have given some valid reasons (though it does strike me that it’s not a totally ridiculous suggestion – more of a non standard one).

I’ll feedback on the outcome of the discussion !

Thanks again for the thoughts…

 

[^woody^]

I've never seen any roofers using them to fix a whole roof

You've never worked on a roof with thin rafters and a delicate plaster ceiling on the other side then?

 

[Andy R]

I’ve had a chat with my builder/roofer and he’s happy to use copper nails for the majority of the slates – which I feel is good news !

The next bone of contention is the roofing felt…

There’s nothing there currently - and he’s suggesting using bitumen roofing felt.

I was in favour of a breathable membrane to prevent condensation – but he’s saying you don’t get condensation issues with bitumen felt…

Any thoughts/comments…?!

 

[^woody^]

but he’s saying you don’t get condensation issues with bitumen felt

He's certainly wrong about that one.

You can get condensation with breathable membranes too though, so if there is a risk you should use an 'air open' product.

You and your builder should also be aware of the need to eaves trays, eaves and ridge ventilation, and this work will require a notification to building control in respct of Part L1 - thermal insulation.

 

[Doggit]

With roofing felt, you risk getting condensation inside the loft space, because there's no where for the moisture to go. Not all breathable membranes are actually breathable, they're just marketed as such, so ventilation between the membrane and the slates is important.

 

[freddiemercurystwin]

Hmm I wonder how lofts used to work before breathable membranes were invented. There's nothing wrong with using felt if the ventilation is adequate.

 

[Andy R]

Hmm I wonder how lofts used to work before breathable membranes were invented. There's nothing wrong with using felt if the ventilation is adequate.

I think that’s a very fair point…

The chances of making my loft air tight, must be next to non existent !

I’m sure that things will improve, wrt to drafts, when the slates are all positioned correctly – but simply, the building has too many imperfections, for there to be no air flow.

Provided he can work out the placement of the eave slates – and has calculated the headlap correctly, I’m now optimistic that it all will work out OK !! (I’m a glass half full kind of guy )

 

[^woody^]

Not all breathable membranes are actually breathable,

Those ones are black, smell of tar, and tend to be known as "rolls of felt".