Plasterboard on 600mm centres

[MortarThePoint]

I need to attach plasterboard to the bottom chord of trusses that are on 600mm centres. The plasterboard will then be wet plaster skimmed. The plasterer has recommended adding counter battens (e.g. 22x100) at 400mm centres. That works out as a lot of metres of batten to install. Is his concern reasonable or more based on 9.5mm plasterboard than the usual 12.5mm? I could go up to 15mm if that helps.

[MikeGrahamT21]

Yeah 9.5 is a little on the thin side at the best of times, especially on a ceiling, thicker the better, much like floorboards. The thinner boards you'll end up with ripples over time as it sags slightly.

[Dudda]

I'd add a vapour control layer/airtight layer and then the counter battens. This will give you a service cavity for cables and a recess for spotlights, etc.

This will help a huge amount with heat loss and something I'd do regardless of any plasterboard issue (which should be 12.5mm anyway).

[MortarThePoint]

I wasn't clear in my original post. I was planning to use 12.5mm plasterboard, but wondered if the plasterer's concerns were based on experiences from when plasterboard was more often 9.5mm. Would stepping up to 15mm, from 12.5mm, negate the concern and give a good stiff ceiling?

 

2 hours ago, Dudda said:

I'd add a vapour control layer/airtight layer and then the counter battens. This will give you a service cavity for cables and a recess for spotlights, etc.

 

It's the first floor ceiling and we have attic trusses above with living space. The service gap could be handy for running pipes and electrical cables, but I can route those OK near the eaves on top of the trusses I think.

Edited April 21, 2021 by MortarThePoint

[Mr Punter]

15mm board on ceilings with 600mm centres please.  If you don't, it is nog-tastic.

[MortarThePoint]

56 minutes ago, Mr Punter said:

15mm board on ceilings with 600mm centres please.  If you don't, it is nog-tastic.

 

Would I want this for fire resistance as well? I think 3 storeys requires 30 minutes and on 600mm joist centres the table below says 15mm if using Wallboard. That said, the White Book where that table comes from has lots of different and somewhat confusing tables.

 

I'm going to get bored of carrying heavy sheets of plasterboard through the scaffolding.

 

[Mr Punter]

2 hours ago, MortarThePoint said:

I'm going to get bored of carrying heavy sheets of plasterboard through the scaffolding.

 

It is down to technique.  For the upper floors, can you get a telehandler to lift a pack up so you can drag the sheets off?  You may need the scaffolding gentlemen back to help improve access.

[MortarThePoint]

4 hours ago, Mr Punter said:

15mm board on ceilings with 600mm centres please.  If you don't, it is nog-tastic.

 

The nog-tastic approach has the option of reduce size boards (1800x900) but I expect they are probably expensive compared to the normal sized board

[MortarThePoint]

1 hour ago, Mr Punter said:

It is down to technique.  For the upper floors, can you get a telehandler to lift a pack up so you can drag the sheets off?  You may need the scaffolding gentlemen back to help improve access.

 

I could start a new 'Gym Club'. The rules of which would be:

1. Don't talk about Gym Club
2. Carry these 15mm plasterboards through this cunningly devised assault course

[MortarThePoint]

51 minutes ago, MortarThePoint said:

 

I could start a new 'Gym Club'. The rules of which would be:

1. Don't talk about Gym Club
2. Carry these 15mm plasterboards through this cunningly devised assault course

 

Don't know what I was thinking, it should be called 'Site Club'

[MortarThePoint]

Mounting the plasterboard on Resilient Bar (or Resilient Channel as the US call it) could be a useful approach. It reduces my centres to 400mm or 450mm and also helps reduce sound transmission:

 

I think this may be based on two layers of plasterboard, but one would still give benefit.

 

https://onlineinsulation-sales.com/resilient-bar-rb1-45mm-x-16mm-x-30m-138-p.asp

Edited April 22, 2021 by MortarThePoint

[Russell griffiths]

You won’t be carrying the 15mm boards anywhere on your own, some 15mm acoustic is 45 kg a sheet, as mr punter said either get a pack lifted up with a forklift or get a pack put upstairs with a crane as they are putting the trusses up. 

 

You will I’ll need to plan for this, carrying them through a scaffold maze is a non starter. 

 

And dont even think about smaller boards thats just creating more work. 

[MortarThePoint]

4 hours ago, Russell griffiths said:

crane as they are putting the trusses up.

 

D'oh! Too late for that unfortunately.

[Oz07]

Just go 15mm. I used to go 12.5mm on nogs but 15 is so much easier. I see a lot of jobs where they go 12.5 on 600s with no nogging and all seems to be fine no more or less cracking than any other houses. I wouldn't do it but anecdotally it's not the end of the world.