Slating query

Hi, i wonder if i could get a bit of advice from the experts on here.

Next week i`m undertaking a Slate job. Last time i did any slating was a good few years ago and at the time i was just leraning the trade, so i`m not fully experienced in slate roofing.

Now, working the gauge out is not a problem , slate length - headlap divided by 2. My question really is can this gauge be adjusted slightly to account for the roof space, for example, say my set gauge leaves me 5 inch short at the top of the roof, can i adjust it slightly to fit. If not is the best method to "cut" down the top course of slates and top half slates?

Also, i`m not sure if the slates will be pre holed or not, if they`re not, it souldnt be a problem. But if they do come pre-holed whats the best way of coming to the correct gauge for the laths, if the normal gauge formula leaves me miles away from the drilled holes

cut down the top course.

...and don't forget the (if necessary) copper disc rivets.

So cutting down is an acceptable method of fittting the top course then.
Makes life easier.

By all accounts the site agent on the job is a picky so and so. So i wanted to make sure the mehtods i used were correct.

Presentation wise i know i will make a very nice job, i just didn`t want something to come bite me in my arse afterwards.

Right, i`ve just found out the slates on the job will be 500x250.
Also the required headlap is 90 mm.

Now, the thing i can`t get my head round is. The slates come pre holed at 300mm, which as far as i can fathom would give a gauge of 200mm.
but if i were to use the formula of:
Slate - headlap / 2 = gauge
I would get 205 mm. Now i know it`s only a 5mm difference and it shouldn`t cause any problems, but i`m just wondering if it will throw the slates out as i go up the roof.

you are governed by the pre-drilled holes or by gauge formula, i.e. length of tile minus lap divided by 2.

just set a few out dry to the formula and see how it goes.

don't worry about the odd 5 mm set out your battens to the holes and then cut down your eaves course to match.
As Nose says hold up a couple of courses on a dry run to get your gauge.
which ever you do so long as each batten is gauged the same it will stay the same up the roof

Yea, that was pretty much how i was gonna tackle it.

Thanks for the advice.