Cold roof - ventilation void size

[SuperJohnG]

I have a SIPS roof coming, which will be slated. 

 

The SIPS roof will have a breathable membrane directly fitted then I had planned to counterbatten using 25x50mm battens then put 22mm sarking over the top, then membrane and slates directly nailed. 

 

However reading the STA guidelines tonight, it says minimum 50mm ventilation gap. So does this mean I need 50 x 50mm roof battens now? 

 

This plays havoc with my combination roof lights with the wall /roof junction. 

 

What's the norm here? 

 

 

[Temp]

50mm is the normal spec for the ventilation gap on a cold roof.

 

Not quite sure why you need sarking boards on a SIP roof? I know they are more common on traditional roofs in Scotland but isn't that for structural reasons? Don't the SIPS already deal with this?

Edited May 7, 2021 by Temp

[Temp]

Deleted.

 

Edited May 7, 2021 by Temp

[SuperJohnG]

35 minutes ago, Temp said:

50mm is the normal spec for the ventilation gap on a cold roof.

 

Not quite sure why you need sarking boards on a SIP roof? I know they are more common on traditional roofs in Scotland but isn't that for structural reasons? Don't the SIPS already deal with this?

Thanks. 

 

The sarking is a preference of the roofers. They aren't in to fitting slates to battens (a few said this) hence seemed  straightforward to add sarking on top of counterbattens. But not so much now if I need a 50mm batten then sarking makes the build quite substantial. 

 

I need to track down others who have done a SIPS roof with slates. 

[Temp]

Ah OK.  I've tiled a small roof onto battens myself and it can be a bit of work planning and setting out the tile battens. I can see it would be easier if you can just nail them on anywhere.

[scottishjohn]

I would have thought 25mm vertical batons to fix sarking boards  or (osb sheeting) to  - and another vapour barrier   between slates and sarking ?- should be fine   ,providing it can vent out of the ridge and bug screen at gutter level 

[SuperJohnG]

1 hour ago, scottishjohn said:

I would have thought 25mm vertical batons to fix sarking boards  or (osb sheeting) to  - and another vapour barrier   between slates and sarking ?- should be fine   ,providing it can vent out of the ridge and bug screen at gutter level 

Thats what I had assumed. I'm just having a wobble as the STA guide says 50mm void and that's what other seems to spec. 

 

My architect also thinks its fine. He also mentioned OSB too as it will be cheaper and easier to fit. But I'm slightly nervous at that not lasting as battens or sarking are obviously treated.

[scottishjohn]

2 hours ago, SuperJohnG said:

Thats what I had assumed. I'm just having a wobble as the STA guide says 50mm void and that's what other seems to spec. 

 

My architect also thinks its fine. He also mentioned OSB too as it will be cheaper and easier to fit. But I'm slightly nervous at that not lasting as battens or sarking are obviously treated.

you fit batons --then clad them with  thick OSB ,then add breathable membrane ,then nail on the slates, needs to be thick OSB to give nails something to fix to -

 If using sarking boards --they must be treated and leave small gaps between them -to allow for movement of wood  as it will grow when damp 

Edited May 7, 2021 by scottishjohn

[SuperJohnG]

1 hour ago, scottishjohn said:

you fit batons --then clad them with  thick OSB ,then add breathable membrane ,then nail on the slates, needs to be thick OSB to give nails something to fix to -

 If using sarking boards --they must be treated and leave small gaps between them -to allow for movement of wood  as it will grow when damp 

I was planning on a membrane over sarking too. 

[eandg]

How are you getting on with your rooflight details? One - of many, no doubt - things I have overlooked today so a very interested observer.