Suspended Ceiling joists sizes - any joiners?

[Mr Bump]

My tame joiner is coming to see me tomorrow eve for a chat but just wanted to gain a bit of info prior.

I have a back room in our house that is approx. 5mx5m so a pretty big room.
It has a very knackered old ceiling which I want to make good.
I have looked at over boarding and replastering but the old ceiling has a few sags and I think it could make things worse.
I also want to put in a layer of insulation as the room is very tall (old Victorian terrace) and has two outside walls.

I am happy to lose the height it wont make any difference.

my thoughts are to install a floating suspended ceiling using the soild brick walls and joists going across the 5m span, I will then install 10cm kingspan and plasterboard.

and voila we should have a nice dropped insulated flat ceiling that doesn't impact on the old one.

question is given 5m span what joist size is probable and how often would you space them considering the will be also battened in between to keep from warping etc?

 

[bass_junkie83]

Assuming the space above will never be used as a usable loft space/storage then something like a 47x225 C16 @ 600mm centres would probably be about right. A SE should really confirm though.

Something else worth considering is the insulation, I assume by kingspan insulation you mean their rigid board product which will sit between joist. If you have ~200mm deep joists and 100mm insulation, then each joist is effectively a thermal bridge through the insulation which will limit it's thermal performance. If there is no insulation there currently then this will still be a good improvement, but if it were me I would use a mineral wool insulation to fully fill the depth of the joists and then run a further 100mm of mineral wool on top covering the joists running in the other direction.

 

[Mr Bump]

Yeah the project is purely to create an insulated ceiling there will be no load at all on the joists.
looking on an engineering website it says 150mmx47mm is well within for 5m and will see what joiner says.

I like the kingspan as it is very light and really easy to install and manage.

 

[bass_junkie83]

There will still be loads applied, though the weight of insulation, plasterboard and finishes so that needs to be confirmed.
The spacing could be reduced to 400mm centres and increase the timber grade to a C24 may allow for shallower joists.

 

[Mr Bump]

reducing the centres is fairly likely I suspect, good info ta

 

[gerry s]

150x47 is fine but just screw a bracket to the ceiling at about half way, just find a friendly positioned joist in the original ceiling. Ask the plasterer what centres he needs just in case he uses smaller boards and would want 450mm.

 

[Mr Bump]

150x47 is fine but just screw a bracket to the ceiling at about half way, just find a friendly positioned joist in the original ceiling. Ask the plasterer what centres he needs just in case he uses smaller boards and would want 450mm.

To be honest I don't want to touch the original ceiling I know it is stable but I want to just leave it alone.
Also I will be doing all the plaster boarding myself once I have chatted to my friendly joiner. I will probably use small boards and insulate as I plod along.

 

[joxby]

I'm confused by the suspended ceiling bit, it sounds more like just a plasterboard ceiling, no suspending.
The options for a suspended ceiling are varied, but for an ordinary plasterboard to joist/batten, Kingspan is a good choice but its not cheap, then there's the skimming/taping/filling/painting?
6x2 timbers over 5m for a ceiling seem pretty adequate though..

 

[Mr Bump]

Yeah it is not really suspended. Wrong choice if words. It will be a new ceiling below the old one supported on a new set of joists.