lowering the ceiling in a small room, some questions

[crobar]

Hi All,

I have a small box room in which I wish to lower the ceiling slightly in order to put in recessed lighting.

The room is about 2.3m wide by 3m long. The two walls at either end which are 2.3m long are drywall, the others are normal walls.

I plan to fit battens around the top of the room, with joists spanning the 2.3m at intervals, and then fit 12.5mm plasterboard. However, I am nervous about attaching anything to the dry walls at either end, can I just fit a joist flush against the wall at either end instead?

Secondly, what spacing must the joists be? I plan to use three sheets of tapered edge 2.4m x 1.2m board. Afterwards I would ideally like to paint straight onto the boards as I understand you can do this, but will I have to screw into the boards halfway along their span to fix them, or just at the edges? How should the screws be hidden if this is the case? Or is this just not the way to do it? I presume the screws at the edges will be hidden by the filler.

Cheers!

 

[fenny666]

hi
how much do you intend to lower the ceiling?

 

[crobar]

Hi,

sorry for the delay, I've been having some trouble accessing the website tonight, I'm going to lower it around 10-15 cm.

 

[fenny666]

personally i wouldn't recommend your suggested method.it just seems a little o.t.t.

what i would recommend is to put in a MF ceiling.this is a simple metal system and perfect for what you are trying to achieve.if you google it there's enough info on how to install it.though if your still not sure just ask.

if you still want to go the joist route - if the joists are adequate to span the room and provide adequate support for the boards then it would be ok to run one along the drywall.

for both methods the way to fix the boards is the same -

for 12.5mm boards the joist/mf5 should be located at max 450mm centres but as you are using 2.4m boards then set them at 400mm centres.

centres increase to 600mm maximum if using 15mm boards

boards must be fixed perpendicular to the joists/mf5.use 32mm drywall screws fixed at 200mm centres across all joists/mf5 and around the room perimeter.

screws should be sunk slightly in to the board(without breaking the paper)
so they can filled.

remember when filling the tapered edge use jointing tape to prevent cracking.

 

[fenny666]

sorry forgot to mention you must stagger the boards as well.for instance if your first board is a 2.4m sheet the next board should be cut down to a different joist/mf5.

 

[crobar]

Thanks for the useful info, I hadn't come across MF ceilings before, I will look into them. That could be much easier.

If using wood, I had also been assuming that I would have the supports running as shown in the first diagram below where the solid lines are the plasterboard sheet and the dotted lines the joists.

[code:1]

1. Plasterboard 2. Room Shape and joists
Support

1200mm _________
{------------} ^ |.........| ^
____________ 1300mm¦ 400mm|.........| ¦
: : |: ^ ¦ {---}|.........| ¦
: : |: ¦ v ____|.........| ¦
: : |: ¦ ^ |..............| ¦ 3000 mm
: : |: ¦ ¦ |..............| ¦
: : |: ¦ 2400 mm ¦ |..............| ¦
: : |: ¦ 1700mm¦ |..............| ¦
: : |: ¦ ¦ |..............| ¦
: : |: ¦ v |______________| v
: : |: ¦ {--------------}
___:____:___|: v ~2300 mm

[/code:1]

Do I though require cross-beams as well? I presume these would be made by nailing/screwing shorter lengths in at intervals between the joists. I was imagining putting in joists as shown in diagram two, where the dotted lines would be the joists, and the plasterboard going in with the long part spanning the room as it is just longer than necessary to do this and would mean only making two joins.

I have also only gone for 12.5mm rather than 9mm as I heard it was stiffer and less susceptable to sagging, is it actually the right choice?

 

[fenny666]

i can see why you want to fix the boards this way to save filling but i can only recommend the correct way which is to fix them across the joists. ultimately it's up to you, however ,bear in mind trying to fit boards in one piece that are cut to the same width as the room is awkward at best.

the joists will require timber noggins, not sure on the maximum centres for these, though i would suggest two noggins per joist split equally over the width of the room.

boards will sag if not fixed at the correct centres in relation to their thickness.
12.5mm boards require max centres 450mm while 15mm boards require 600mm max centres.you could use 15mm boards and reduce the amount of joists needed however this effectively means less support holding a greater mass of board.you'd need to be sure your support is adequate.i wouldn't consider using 9mm boards.