Tray ceiling - timber choices

[Mjward]

Hello

I am looking to build tray ceilings in several rooms that will have an LED ring around the internal perimeter as well as house several downlights.
I've not managed to find much online about the structure behind these but think I've got a fairly good idea now, attaching studs to existing joists to form a "box", adding vertical noggins before replicating the "box" and attached to the bottom of the noggins before finally securing all sides to studs attached to the wall.
This will then be clad in MDF (lighter than plasterboard and doesn't require plastering).

From the resources out there, I've seen some well followed home cinema companies make the stud frame out of 25x50mm (1x2s) and just wanted to sanity check that is sufficient (there is no sag potential across the span given multiple fixes to existing joists plus only real load is the frame itself plus MDF cladding).

Secondly, any strong views about 6mm or 9mm cladding for this? I don't know if the weight benefit of the 6mm is offset by the potential for it to suffer sagging or unlikely if supporting studs/noggins are space max every 600mm for example.

 

[Bingy man]

I would say at 600mm centres the 6 mm will likely sag asp in time but 9 mm will give you a better chance , mdf loves moisture and will swell if it’s given half a chance ,, MDf sealer will help prevent this and it can be overpainted with varnish or paint .you could reinforce the stud frame with the type of wires and fixings used in suspended ceilings or builders metal straps for additional strength.

 

[Mjward]

I would say at 600mm centres the 6 mm will likely sag asp in time but 9 mm will give you a better chance , mdf loves moisture and will swell if it’s given half a chance ,, MDf sealer will help prevent this and it can be overpainted with varnish or paint .you could reinforce the stud frame with the type of wires and fixings used in suspended ceilings or builders metal straps for additional strength.

Thanks for this, will go the 9mm route. I've not checked weight differentials yet but will also look into moisture resistant MDF.

Like for like ply seems to be 3x the weight which rules it out for this purpose

 

[Mjward]

MR MDF might be way forward, 19.9kg Vs 16.6kg for 2.44x1.22x9mm sheet i.e. not a significant load addition

 

[Bingy man]

Thanks for this, will go the 9mm route. I've not checked weight differentials yet but will also look into moisture resistant MDF.

Like for like ply seems to be 3x the weight which rules it out for this purpose

Also probably 3 times the cost of your mdf - good luck and a few pics of your progress would be good

 

[Mjward]

Will definitely get updates going on here with pics once I get started in coming weeks. Thanks for your help

 

[Jameshow]

Thanks for this, will go the 9mm route. I've not checked weight differentials yet but will also look into moisture resistant MDF.

Like for like ply seems to be 3x the weight which rules it out for this purpose

Not at all ply weighs less than mdf.

https://www.travisperkins.co.uk/plywood/structural-hardwood-plywood-2440mm-x-1220mm/p/9000189655

 

[Mjward]

Not at all ply weighs less than mdf.

https://www.travisperkins.co.uk/plywood/structural-hardwood-plywood-2440mm-x-1220mm/p/9000189655

You're absolutely right, not sure what I was looking at before but just checked and the equivalent sheet from my local yard is 18kg ie all the same ballpark.

Now what I don't understand is that they are now pricing the same 9mm sheet as 24.75 (ex vat) in ply but 26.95 (ex vat) in MDF. Given I will be painting this and want it to blend in with the surround plaster on walls and ceiling, would ply or MDF be preferable? As without that factor I would always choose ply over MDF every day of the week

 

[Garden Shed Projects]

If you are buying material metal ceiling stud work would be cheaper and lighter for the frame. Your choice of MDF to avoid plastering? How do you intend to deal with the joints to avoid cracking?
Plasterboard with tape and joint would likely look a better finished product. Tape and jointing is a faf but can be learned fairly quickly with a bit of youtubery.
That is how I’ve seen it done.

 

[Mjward]

If you are buying material metal ceiling stud work would be cheaper and lighter for the frame. Your choice of MDF to avoid plastering? How do you intend to deal with the joints to avoid cracking?
Plasterboard with tape and joint would likely look a better finished product. Tape and jointing is a faf but can be learned fairly quickly with a bit of youtubery.
That is how I’ve seen it done.

I think I'm just reticent about metal stud work as I have zero experience with it and I've priced up the studs in CLS/carcassing timber and its less than 200 pounds.

With regards to MDF/ply to panel the stud frame, my intention was to butt the joints as close as possible and use wood filler/sanding to blend them. I'm not wholly against PB with tape and jointing filler but like for like I believe the 9mm boards to be 40% heavier than MDF/ply. Additionally after boarding out several rooms I really don't find it a nice material to work with and certainly would get nice edges without the addition of beading etc.

 

[rafezetter]

You're absolutely right, not sure what I was looking at before but just checked and the equivalent sheet from my local yard is 18kg ie all the same ballpark.

Now what I don't understand is that they are now pricing the same 9mm sheet as 24.75 (ex vat) in ply but 26.95 (ex vat) in MDF. Given I will be painting this and want it to blend in with the surround plaster on walls and ceiling, would ply or MDF be preferable? As without that factor I would always choose ply over MDF every day of the week

I saw that mself at another suppliers MDF being more expensive than plywood - I cannot understand how this is either. Plywood will be very hard to get a very smooth "plaster like" surface on. I made a ply box years ago and it took multiple layers of primer and sanding back to get rid of the grain - all in all it must have had 5 coats all sanded back, which is just not feasable for a ceiling.

I would also go for 450 centres as thin mdf will sag even over a 600mm distance, I've seen it, and UK humid days may also be a factor so seal BOTH sides.

For something this decorative and impossible to "fix" once done, you should do all you can to "belt and braces" the various parts.

 

[Garden Shed Projects]

I think I'm just reticent about metal stud work as I have zero experience with it and I've priced up the studs in CLS/carcassing timber and its less than 200 pounds.

With regards to MDF/ply to panel the stud frame, my intention was to butt the joints as close as possible and use wood filler/sanding to blend them. I'm not wholly against PB with tape and jointing filler but like for like I believe the 9mm boards to be 40% heavier than MDF/ply. Additionally after boarding out several rooms I really don't find it a nice material to work with and certainly would get nice edges without the addition of beading etc.

CLS will be fine for the frame but natural expansion and contraction will cause your filler to fall out leaving cracks visible on the mdf sheets. You could make a feature of it and chamfer any butt joints if that the look your going for.

You will need paper tapes for the flat joints and beads fo any corners in PB but it more likely look as a single built item more than a number panels fixed together.

Is weight an issue?

 

[Mjward]

I saw that mself at another suppliers MDF being more expensive than plywood - I cannot understand how this is either. Plywood will be very hard to get a very smooth "plaster like" surface on. I made a ply box years ago and it took multiple layers of primer and sanding back to get rid of the grain - all in all it must have had 5 coats all sanded back, which is just not feasable for a ceiling.

I would also go for 450 centres as thin mdf will sag even over a 600mm distance, I've seen it, and UK humid days may also be a factor so seal BOTH sides.

For something this decorative and impossible to "fix" once done, you should do all you can to "belt and braces" the various parts.

Suspected this was the case when the videos I saw all used MDF. Pricing is a win for plywood cabinet makers but alas not me in this instance, will stick to MDF.

With regards to sealing, I'm guessing it's cheaper to seal standard MDF than pay the 25% extra for moisture resistant MDF but how does it compare performance wise or given fact it's bedroom not bathroom/kitchen I shouldn't be overly concerned?

 

[Mjward]

CLS will be fine for the frame but natural expansion and contraction will cause your filler to fall out leaving cracks visible on the mdf sheets. You could make a feature of it and chamfer any butt joints if that the look your going for.

You will need paper tapes for the flat joints and beads fo any corners in PB but it more likely look as a single built item more than a number panels fixed together.

Is weight an issue?

Certainly sounds like i need to give further consideration to both. Just seeing so many high end/professionally built cinema rooms built with tray ceilings consisting of simple stud and MDF I made the assumption the movement must be so negligible to not cause cracks.

For PB if I can just filler/joint tape and bead then why do people ever plaster? Genuinely curious

 

[Garden Shed Projects]

I have no experience of building cinema rooms but are you sure they are mdf. Mdf has low resonance and they do build speaker boxes out of it. Maybe that’s why. Can’t see how you butt joint it without cracking though.

Plastering is a much better finish than T&J but it needs a skilled man to do it and they are few and far between since we stopped training people. T&J is fairly easy to learn and like artexing is often done by a painter.

 

[Bingy man]

Reading all the replies above it certainly gives you multiple options, it seems to me wether you use p/b or MDf or plywood there will be the obvious issues of the joints expanding and contracting with any fillers used cracking and falling out . All solutions are labour intensive and or potentially expensive. Imo I would consider using a decorators flexible caulk applied with a profiling tool or just seal the chosen surface and then use flat wallpaper ( not the cheap lining paper) but a lightly embossed vinyl that can be painted in your chosen colour-maybe a combination of the two above methods. As per above post I have no experience of cinema rooms but cracks in ceilings look unsightly and will annoy you. I imagine advice from a professional decorator would help you .

 

[Doug71]

The best examples I've seen have been plastered but I can see why MDF is appealing. I was working in a house last week which had a very obvious DIY MDF version with some lovely big cracks where the joints were, it looked awful.

If you do go down the MDF route I would definitely use MR MDF as it is less prone to move than normal MDF. Think about how much warmer a room is at ceiling level when the heating is on or you have the fire lit, you can see why cracks would appear and joints open up.

I'm no structural engineer but I wouldn't see the weight as a massive issue,. If you used 2 sheets of 18mm MDF you would only be looking at about 70 kg (the weight of a person) and I presume it would be just around the edges of the room with the weight spread over many joist?

Take all this with a pinch of salt as I have never done a tray ceiling, I am just being one of those people who give advice on something they don't know anything about

 

[Spectric]

Your choice of MDF to avoid plastering? How do you intend to deal with the joints to avoid cracking?

You could cover them with trim.

I'm no structural engineer but I wouldn't see the weight as a massive issue,

It really depends upon the structure, a traditional house would probably be fine but a modern build where they use cheap lightweight wood may cause issues.

 

[pip1954]

Having been in the building trade all my life, I would NOT use MDF ! it will crack unless you put some sort of moulding over the cracks but I think you are after a flat ceiling I would think of more framing than less to make stronger put joists closer to make a better job.
Also if you do not intend to plaster make sure the frame is spot on other wise the board(which ever you use) will follow the frame and look a mess.
Take your time to get the frame right first good luck I have always wanted to do this myself but the look is in the finish .

 

[Terry - Somerset]

I don't think weight is an issue.

Assuming a room size of (say) 4x5m (perimeter 18m) and 500mm frame centres = around 36 "frames" each secured by probably two screws. Even if the total weight of frame, MDF/ply/plasterboard, light fittings was as much as 200kg, this would averagely be a 3kg load per screw - trivial.

If a perimeter frame is fixed to the wall this would limit any movement and sag on the wall edge. The exposed edge has an "upstand" - if this was part of the frame to which the boards are fixed it would limit sag on the open edge.

The best finish would probably be with plasterboard and plaster skim. However MDF will probably work if any joins were screwed (and glued) into a batten to avoid movement.

Other considerations - ensuring access for bulb replacements, occasional repainting, and that lighting is fixed the "right" distance from the open edge..