Duquesa roof slate failure rate...?

65mm nails are to big for slates, most likely have been used to secure the battens as this is the most used size.

The extra battens may have been needed if the gutter was installed before the re-roof, sometimes a fillet or cant strip is installed at the bottom row to keep the tiles in alignment, or re just resting on the slightly raised fascia board.

 

That extra batten is known as a counter batten. & used as Jit mentioned.

Would have puncture roofing membrane.

Nails far too long,many years ago, old roofer told me nails length should always be two slates thick plus 20mm- 25mm in length.

Looking at photo slates look like they are not sitting flush with previous slate, might be just camera angle.

 

Stop talking about ridge tiles, folks - it's got now't to do with this...

The proper copper nails were used for the actual tiles - not 65mm jobbies - you can see a pack in post #17.

Aren't these additional battens used to set the correct slope of the tiles so that the subsequent layers above also lay flat on the ones below?

JoHo, I forget the make of slate tile we had fitted to our place around 10 years ago, but they were Spanish too, look very similar to yours and were the same as used on many Tesco stores etc.

I have to say that our job doesn't look as neat as yours - ours don't lie as neatly flat over eachother, and there is some rattling when the wind blows. And, lordie, the wind blows up here (North Devon) - it took a tree down right outside our front door a couple of weeks ago.

Lost slates? Ooh, around 3 or 4 over a period of a decade. And I put these failures down to a non-professional roofer who either over-whalloped a few, or possibly stood on them during the job. As far as I am concerned, it isn't normal to lose slates at all - our old family house on the Isle of Lewis (you want wind...?!) hasn't lost a slate since it was built in the late 50s.

It simply cannot be reasonable to expect to lose 6-odd slates per year. That's nuts.

 

Looking at post 17,the pack has 65mm on it.

 

Really? Blimey

I couldn't read that - I was going by what looked strongly like ~40mm length nails.

65mm? That's some clouting required. And it would be very hard to judge when to 'stop'...

 

Using photoshop, I measured a nail, near enough 65mm, far too long, probably too large in diameter, so stressing hole in slate.

 

A 65mm copper clout nail is 3.35mm diameter, fixing slate the nail should be 3.20 - 3.25mm diameter, so I presume nails are too tight,iif 65m nails used, so slate can't move, it then fails, hence slates coming adrift.

Even some shorter nails , like 38mm are 3.35mm diameter.

EDIT: Well, I just had a read of brochure, they suggest 3.00 – 3.35mm diameter nails, so that theory sunk!

 

Joho, before starting the repairs, I would suggest doing some research on the tiles that you used - you might have already done it, but try to look for some reviews online. Maybe some other people had the same problem and it's not the builder but the tiles.

 

Now't wrong with Cembrit Duquesa slates, used on many jobs domestic & commerical up & down the UK without problems, has to be down to the fixing/installation.

http://www.cembrit.co.uk/Duquesa_slates_give_historic_cottage_a_brand_new_look-32928.aspx

 

In this case, it's the installation. It's unacceptable for them to cause you problems after only one year.
I wish you good luck with this! What did the builder say?

 

Cembrit were at the Homebuilding Show, they said that all natural slates have to be graded.

The thicker ones need to be laid at the bottom course and thinner one to the top, this stops slats sticking out.

Glendyne slate which is Canadian apparently comes already sorted as they use lasers to measure thickness of the slates.