Counter batten/service cavity below posi

[junglejim]

I’m going to be adding battens to the underside of posi joists to ensure a flat surface and additional service cavity. I’m wondering the best size to use (was thinking 25x50) and also trying to work out hope to finish the edges where they overhang the joists to the wall. Any photos of similar appreciated.

 Thanks 

[crispy_wafer]

used 22*100 rough sawn here, 22*75 may have been better, but it gave plenty of scope for board ends...  Other thing I'd note would be working out lamp, mvhr duct, aircon, speaker placement beforehand to eliminate any potential clashes.

[JohnMo]

I used 45 x 50. But it depends what you need to run in the cavity. Our ceiling lights needed just under 50mm to get the ballast in. If it's just cables 25mm will be fine.

 

But if doing again I would use a wider section of wood so less likely to split near ends.

 

Also consider the spacing between battens and what plasterboard you use. I did 600mm centres and then had to add additional to support the plasterboard correctly.