Suspended ceiling made with 4x2s

[akist]

I am building a suspended ceiling over a small bathroom. I have opened pigeon holes on opposing walls to fit C24 4x2 joists laid on their flat side, not on their edge. The clear span is 1800mm and the bearing into the walls is 95mm. I have spaced the 4x2s 195mm apart (100mm gaps between joists). The floor above will be either 18mm or 25mm ply.

Could someone please tell me if I have enough support for the floor above, or better what is the permissible load?

PS I could replace one joist with a concrete lintel if needs be.

 

[foxhole]

How is it a suspended ceiling if it’s supporting a floor?

 

[robinbanks]

laid on their flat side

Why?

 

[Dereekoo]

Your floor will take a standard live load of 0.25kn/m2 and standard dead load of 1.5kn/m2, defelction will be at the maximum allowance of 5.5mm

 

[akist]

How is it a suspended ceiling if it’s supporting a floor?

It is a platform on which I will install a staircase quarter landing. As the staircase passes over a small ensuite bathroom, I will fix plasterboards on the underside of the joists.

The width is about 1.2m, the span 1.8m.

Why?

Because I want to maximise the ceiling height below and minimise the quarter landing level height above (need to reach it in 12 steps).

Your floor will take a standard live load of 0.25kn/m2 and standard dead load of 1.5kn/m2, defelction will be at the maximum allowance of 5.5mm

Hmm, thanks for the calculations. The floor will be the base for a staircase, 1.26m2 quarter landing plus two more steps. If you have a couple of people on it it might exceed 150kg.

So it seems I need to strengthen it a bit, here are some photos.

I could replace the first 4x2 with a concrete 65x100 lintel, that would hold the edge of the platform and on the other side there is a wall we are sitting on...

 

[robinbanks]

So the platform is the quarter landing of a staircase? or it supports a quarter landing of a staircase?

 

[akist]

I think it supports the landing, I will finish in 18mm or 25mm ply. The staircase man will add a 25mm-32mm "redwood" or some other material on it. I think on one side, that which is over the door as in the photo, it will be my platform taking the load.

 

[robinbanks]

So you'll have 2 inch of joist, 1 inch of board, and 1.5 inches of board again..

And you're striving for minimal height build up, but really, if you turned the 4x2 the other way and ditched the board you were going to fit, and fit the board the stair man will fit, your buildup is just one inch higher, and significantly stronger

Do you really need that inch? I mean, really?

 

[akist]

No, you are right. And the 4x2 on its edge will be stronger. I am going on site now to take a look.

 

[akist]

I pulled myself up on that single 4x2 on the photo, and yes it flexes I'd say 10mm at least, I am 83.5kg. But it is a C16, tomorrow I am getting some C24 to see what difference it might make.

 

[Dereekoo]

I pulled myself up on that single 4x2 on the photo, and yes it flexes I'd say 10mm at least, I am 83.5kg. But it is a C16, tomorrow I am getting some C24 to see what difference it might make.

On average 2 to 3mm but all depends on what quality the c16 and C24 actually used is as the the strength in different pieces of c16 or c24 varies quite a bit hence wood strength in structural design is based on the lower probability values

 

[oldbutnotdead]

4 x 2 at 1800 span will still be 'bouncy' when you walk on it, even with the timbers the conventional way up.
Which might be undesirable on a staircase

 

[akist]

4 x 2 at 1800 span will still be 'bouncy' when you walk on it, even with the timbers the conventional way up.
Which might be undesirable on a staircase

Yes it did bounce terribly with a man weighing just 62kg on it!

So I have turned the 4x2 on their narrow edge, but have not tried them with a live load yet. As you said, I do not expect miracles and still expect bouncing, even with noggins and with the coverings on ( a sheet of ply and the staircase's own landing ).

There are 6 joists in the distance of 1.2m which is the landing width. I am thinking of putting a concrete lintel 65x100 (or maybe two lintels) in between those joists to take most of the weight.