Slate guage/batten spacing question

[martyc]

Hi there,
Im trying to size up my roof before slating it so that all slates will reveal the same amount from top to bottom and hence look nice and uniform.(dont want a row of really short slates along either the top or the bottom)
Now i know how to set out the spacings by laying the top and bottom lats and dividing the distance between them by the manufacturers guage and rounding up one etc.

However the slates i bought on recommendation already have holes in them 1 @ the top and 2 on the sides.

My question really is...do these holes predetermine the spacing?...im guessing they do as if i use a lesser spacing the holes on the sides of the slates will not be directly over a batten.

Cheers,
Martin.

 

[Roofer]

If your slates have 3 holes in them then they are probably fibre cement (Eternit type) with 2 holes roughly in the middle on each side of the slate (for nails) and 1 at the bottom (for a copper 'rivet')

The gauge is determined by the size of the slate and the pitch of the roof

If your slate is 600x300mm and your roof is 25 degrees or more then the gauge is 250mm (length of slate (600) less headlap (100) divided by 2)

 

[martyc]

Hi Roofer thanks for the info...that is exactly what i have.(slates with holes just off centre on the sides and your right it is the bottom!!)
Slates are as u say 600 by 300.

Now that ive got my head round that that other hole is actually the bottom and not the top i realise that they dont predetermine the headlap as you just pull each slate up to the batten after engaging it with the clip..

However my pitch is ~22 ...so i assume I need a greater headlap?...
Martin.

 

[Roofer]

You need a 110mm headlap so gauge will be 600 - 110 / 2 = 245mm

That is suitable for their minimum recommended pitch of 23 degrees but you should be ok at 22 provided it's not very exposed.

 

[martyc]

Thanks roofer..greatly appreciate the top info,

I actually measured the "exposed" part of the slate on my neighbours new roof which is a similar pitch and it was 225mm...so im guessing his headlap must be 150...that seem excessive??...its not terribly exposed but it is Ireland!!
Cheers,
MArtin

 

[Roofer]

That will give a greater safety margin but new nail holes will need to be formed

 

[martyc]

Cheers Roofer..ill lay out a few slates this eve when i get home and see exactly how they lie.
Thanks for the tips...appreciated.
Martin

 

[noseall]

don't forget the eaves course.

 

[martyc]

eaves course...I take it thats the proper name so for the 250mm slate under 350mm slate...all under a full slate on the bottom course?

Ive one small question.
Im using 2.5 * 1.5 lats...my carpenter spec'd i used them as i am going 600 centres(rafters and joists are all 6*2 and the span is only 10 foot.

Anyway my question is this.
How much higher should the bottom lat be than the others typically?(25mm??)...to kick up the bottom slate?
And also could i omit this bottom lat if i built my fascia taller than the rafters by enough to effectivelty kick up the slates by the same?
Cheers,
Marty.

Edit:
Heres a link that shows a few of the rafters...as you can see I have stopped the rafters and Joists ~3/4 inch before the wallplate edge to accommodate some plywood to support the valley gutter...this is the facia im wondering about making taller to kick the bottom slates.

http://www.4freeimagehost.com/show.php?i=0a80f46a540f.jpg
Cheers!

 

[Roofer]

Eaves course - yes you're right

Battens - should be 25x50mm

Fascia - yes take that up to 30mm above top of rafter (measured perpendicular to rafter) and that will ensure your slates lay nicely

 

[martyc]

Cheers,
If ive got this right so i can omit the bottom batten that the felt would normally lap over.. and just bring my fascia 5mm above where a bottom batten would have been(you say 30mm whereas a regular batten would have been 25..30-25 is 5mm)..seems small!

Also my battens are i think ~35*50 ...any prob with using them?

Also im going to run some ply from the fascia back to the first nailed batten to prevent the membrane from sagging..the membrane im using is called "protect"

Cheers,
MArty.

 

[Roofer]

5mm above level of batten is fine, it will keep it nice and level - you don't want a ski-jump

35mm battens are oversized but ok

The ply felt support is good practice

Is is Protect A1 or VP400 underlay? The vapour permeable one is preferable

 

[martyc]

Perfect thanks a mill...i went with the 35 as the spacing is 600 on the rafters...decided to beef it up a bit mostly for safety whilst slating etc.

Not sure which protect it is...will check when i get home but A1 sounds familiar...was originally going to get "tyvek" i think its called but it was 5 times the price.
If it turns out to be the A1 i will see if i can exchange it for the vapour barrier stuff.
Thanks again,
Martin.

 

[martyc]

The "protect" i have is the A1 unfortunately
... ill be going to the builders providers tomorrow so ill try change it...if i cant get it will the A1 be OK or should i splash out another €150 for the tyvek?(€200 a roll V 45!!..thank god i only need one roll)
Also the A1 i noticed has a shiny side and a dull side...is there a right side up?
Cheers,
Marty.

 

[vinty]

Hi there,
Im trying to size up my roof before slating it so that all slates will reveal the same amount from top to bottom and hence look nice and uniform.(dont want a row of really short slates along either the top or the bottom)
Now i know how to set out the spacings by laying the top and bottom lats and dividing the distance between them by the manufacturers guage and rounding up one etc.

However the slates i bought on recommendation already have holes in them 1 @ the top and 2 on the sides.

My question really is...do these holes predetermine the spacing?...im guessing they do as if i use a lesser spacing the holes on the sides of the slates will not be directly over a batten.

Cheers,
Martin.

IF your slates have three holes in them, the two on the side are for the nails, the single hole is at the bottom not the top, it is for the copper rivet, they are probley fibre cement and the nail holes are pre drilled for 10 inch centres on your battens or the nearest metric equivalent. If you don't want a short course at the top you will have to measure the rafter divide it by the number of courses so that each course is equal.