Setting out slate battens

[robinbanks]

So, of the few resources I've found around the web about laying out a slate roof, some discuss battening out to the ridge, but the advice doesn't make sense to me:

1) Full slate on the eaves, 50mm ish overhang to the gutter
2) Set the first batten so the nail holes are central
3) Next batten up (ignore the short course at the eaves for now) positioned so the top of the slate is just less than central (so the overlapping slate's nail holes are central)

I'm ok with that, but then:

4) measure the batten gauge
5) measure to where the top batten will go
6) divide the distance by the gauge
7) round up
8) divide the distance by the rounded up value; that's your actual gauge

Er, but say if the gauge is 200mm, and the distance to the ridge is 2040mm that gives 10.2 courses, round up to 11, 2040/11 is 185mm, but that's dropped 15mm off the gauge, which means the nails of the slate on row 3 probably end up punching through the slate on row 2..

So am I right in thinking that for pre-holed or reclaimed slates, your batten gauge is set/dictated by the holes; if you want a wildly different gauge you re-hole the slates, or you put up with the top course landing wherever it lands?

 

[datarebal]

Gauge on a pre holed slate is set , you don't open or close the gauge . Top batten comes where it comes at the ridge. Cut as you need .
Pitch and head lap dictate hole position .

Most tiles on the other hand can be adjusted

 

[robinbanks]

I guess the only adjustment then is where you start the first batten, which may be the only recourse to reducing some ugly two inches wide ribbon at the top on preholed slates; shoot it over a bit extra at the bottom and trim so the top and bottom margins are the same?

Like tiling a bathroom wall, you don't start with a full tile at the bottom and get to the top and need a 2 inch sliver all round, you set a half tile plus an inch at the bottom so it comes to need a half tile plus an inch at the top, as it were

 

[datarebal]

Apart from you do start with a whole slate .and you could never end up with a 50mm cut.

 

[oldbutnotdead]

Are these real slates or fibre cement? If fibre cement you don't start with a full slate at the eaves- can't remember the details, think it's 300 headnailed then 450 in premade holes then full slate. Similar at the ridge. Marley guide is pretty good

 

[datarebal]

The first visible course will be a full slate . Eave courses cut to size based on slate used. Cement fibre require two cuts , one picks up the cdr the one above that does the weathering