Advice re. timber lining board ceilings / walls

Hi all,

I hope everyone is going okay with the lockdown! I'm after some advice, I'm building my own house in NZ and I'm trying to work out the best way to go about installing the timber lining boards on the ceilings and walls. I'm not a buider, just an enthusiast, so forgive me if some of these of these questions are a little basic.


The first problem: as the internal finished surface is 9mm thick T&G rimu lining boards and as the ceiling is a barrel vault we are considered higher risk for condensation issues in the roof. Therefore in accordance with BRANZ guidelines we'll install a vapour barrier behind the timber lining boards which will stop internal moisture penetrating into the roof space. However I'm not sure where the best place to install the vapour barrier is. Originally I was planning on attaching the lining boards directly to the ceiling battens using construction adhesive & brads through the tongue, however if I install the vapour barrier on the battens first (ie directly behind the boards) then I'm not going to be able to use construction adhesive to fasten the boards.

Alternatively, I could install the vapour barrier on the battens and then fasten say a 10mm thick strip of timber on top, ie fastened through the vapour barrier back to the battens. I can then install the lining boards directly to this 10mm strip using construction adhesive and brads. The problem I have with this solution though is that I'll then end up with a 10mm air gap between the lining boards and the vapour barrier, which I suspect will just end up becoming damp due to all of the internal moisture that can get into that space.

So as I see it my two options are either:

• Install lining boards directly on top of the vapour barrier, which means I can only fasten the boards using brads and not adhesive;
• Install lining boards on a spacer, leaving an approx. 10mm air gap between the boards and the vapour barrier.

Do you guys have any thoughts about what approach is best? Would you ever install lining boards using only brads or is construction adhesive necessary?

Additionally, I tested my 16 gauge paslode bradder on the tongue of the 9mm lining boards and it had a tendancy to split or break off. I'm looking to get an 18 gauge air powered bradder and I'll see if I can find / modify a tip so that I can get the brads accurately into the right part of the board. Any suggestions as to what might work or how best to avoid splitting?

Lastly, I want to avoid wasting any more material than I need to and as such I want the joints between the ends of the boards to be able to be located anywhere on the wall, rather than just where I've got a stud or a batten. So I was thinking I could use the router to make a T&G joint on the ends of the boards, which means that when the timbers expand or contract the ends will still be okay. The problem is I can't seem to find a T&G router set that would be suitable for a 9mm board, they all seem too big. So what I was thinking of doing instead is using the router to make a 'shiplap' style joint so that the end of one board could overlap the other. What do you reckon, would that work?

Thanks in advance for your help!

Cheers,

William