Using 600mm slates next to 500mm slates

[rreanor]

I have a single pitched roof on a garage I need to reslate, right next to it is the same but with 500mm slates. I can get hold of new 600mm fibre cement slates very cheaply, and they look identical to the adjacent slates, but is it possible to blend in these different length slates with thr old ones which are next to it?

Alternatively I could trim each cement slate so they're the same length/width but it seems you only get them in 600mm and I'm wondering if they're meant to be trimmed shorter.

 

[Mrs Ten Names]

I have a single pitched roof on a garage I need to reslate, right next to it is the same but with 500mm slates. I can get hold of new 600mm fibre cement slates very cheaply, and they look identical to the adjacent slates, but is it possible to blend in these different length slates with thr old ones which are next to it?

Alternatively I could trim each cement slate so they're the same length/width but it seems you only get them in 600mm and I'm wondering if they're meant to be trimmed shorter.

It may be possible align the bottom edges of your slates with the adjoining slates by having a greater headlap on your roof.
This site gives minimum headlap for various sizes and various conditions:

What is the minimum headlap for fixing slates? | Cupa Pizarras

The headlap is determined by considering the roof pitch, wind uplift, and exposure to driving rain.

www.cupapizarras.com

It should be possible to increase the headlap of your slates, so that the bottom edges align with the adjoining slates.
Where they join, it may be necessary to position battens to accommodate both sizes.

Or you could use a bonding gutter:

 

[datarebal]

You'd need to re hole , and they likely not sit good. And you would need to cut to get the bond .
Bonding strip would work .
You can get cement fibres in 250 x 500