Roof battens and counter battens

[S1llyB1lly]

Hello folks

Just been looking into roof construction and sometimes I see that the construction involves battens and counter battens, while at other times, I see battens only?

I am planning to use natural slate, about 8mm thick. Under what circumstances should I have counter battens + battens and under what scenarios should I have battens only?

As an example, the attached image shows only 1 layer of battens...

 

[S1llyB1lly]

But then on this installation they use battens + counter battens...

 

[^woody^]

When you are insulating the top of the rafters, and water needs to drain and air needs to flow under the tile laths

 

[S1llyB1lly]

Ok, so I only need 2 x layers of battens if I am insulating over the rafters, otherwise just the 1 x layer is fine?

 

[^woody^]

Insulation or something similar such as a ridgid board. Anything that stops water draining beneath the laths

If you are tiling staight on to rafters, then just the horizontal battens in the normal way.

 

[S1llyB1lly]

Hi Woody, thanks for your input.

In terms of rafters, they will be 200mm in size, I'm going for in between the rafter insulation only, and sealing it all up from underneath using Tyvek AirGuard, just before the ceiling plasterboard is fixed on.

So in terms of layers, it will be:

1. Slate
2. Battens
3. Breathable membrane (I'm using Tyvek Supro)
4. Rafters with Celotex in between each one
5. Tyvek AirGuard
6. Plasterboard

Hopefully that will be fine?

 

[^woody^]

As long as you have an air gap above the celotex, into which the membrane can sag. IIRC, the air gap does not need to be ventilated with Tyvek