Advice on long loft; load-bearing?

[mucke]

Hi, I am planning to build a loft in my daughter's room, but I'm uncertain about the load-bearing capacity of the construction I have in mind.

The loft will be attached between two concrete walls, and from wall to wall, the length of the loft will be 3.70 meters. The loft will be built (see attached drawings) with 5 longitudinal 45mm x 95mm joists. The question is: are 45 x 95 mm joists too weak for such a long loft?

Edit: Between the longitudinal joists, there will be short cross joists, which will support a flooring made of råspont.

Thanks in advance

M

 

[Stefan N]

Would have gone with the frame and then studs at 150 cc30 instead.

Edit: Or, where are the concrete walls located? Are they on the long sides or the short ones?

 

[mucke]

I would have used the frame and then studs at 150 cc30 instead.

Edit: Or, where are the concrete walls located? Are they on the long sides or short sides?

Hi,

the concrete walls run along both short sides and one long side.

I thought the longitudinal studs would strengthen it, but maybe 150 studs in the frame are sufficient.
I'm just afraid of building too weak.

M

 

[Stefan N]

Yes, then I would have done as you planned.
But can't you go up to 120 on the long one in the front? It should stabilize a bit.

 

[tlundberg]

What will the loft be used for? Will the daughter only sleep up there?

 

[tlundberg]

For floor joists that need to have a span of 3.5 meters, 45x220 is recommended...
http://www.traguiden.se/TGtemplates/popup1spalt.aspx?id=679

But then it's supposed to support a TV sofa with four adults in it. A bed with a little girl in it is much lighter

 

[ArneTW]

I think 45x95 is rather weak, if you want a low construction height you could integrate some HEA-beam, but otherwise, I would definitely increase the dimension. Not only for strength but also for the "sway."

Regarding the weight, it might not normally be much, but suddenly there's a party and the whole bunch of kids decides to see if they can fit in the loft...

/ATW

 

[mucke]

What will the loft be used for? Will your daughter only sleep up there?

Yes, primarily, but since there will be extra space, she'll probably have friends over there too.

M

 

[mucke]

I think 45x95 is a bit too flimsy, if you want a low structure height you could integrate an HEA beam, but otherwise, I would definitely increase the size considerably. Not just for strength but also for the "sway."

Regarding the weight, it might not normally be much, but all of a sudden there's a party and the whole bunch of kids decide to see if they all fit in the loft...



/ATW

It's the sway I'm worried about.
How do you attach an HEA beam and could it be integrated in the middle of the loft frame?

 

[tlundberg]

If you can consider going up to 120mm instead of 95mm, you can screw-glue together six studs, and you'll then have almost the same strength as a 45x220. You also won't need to put noggings between the studs.

 

[mucke]

If you can consider going up to 120mm instead of 95mm, you can screw-glue six studs together, which will give you almost the same strength as a 45x220. Then you won't need to put noggings between the studs.

Hi, just to be sure, but you mean 6 studs that are screw-glued in pairs. That sounds like my solution.

Thanks for all the answers!

 

[tlundberg]

No. Unfortunately I mean six boards that are screwed and glued together into a substantial board that in total becomes 270x120mm. You need three such thick beams. One at the far end, one 60cm in from the outside, and one 120cm in. Up against the wall, a 120x45 is sufficient.

All in all, you will need 19 pieces of 370cm long 45x120 boards.
Then you also need some boards on the short sides to hang the entire loft on.

For fun, I can mention that a single 45x95 board can handle a span of 1.5 meters according to http://www.petersprojekt.se/old/anvisningar/spannviddstabell.xls

 

[tlundberg]

I can't shake off the feeling that it's ridiculously over-dimensioned... You're not going to use it as a living area! A little flex doesn't matter either, right? You're not going to lay tiles on it!

The sizing is done to handle loads at the worst possible spot, right in the middle of the beams. But if you set up a spring mattress measuring 1.20x2 meters, you're moving the loads away from the middle to the edges.

You can attach the entire inner long side to the wall. There will be no flex there at all. This hasn't been taken into account in the dimensioning either.

 

[mucke]

I can't shake the feeling that it seems really over-dimensioned... You're not planning to live on it! A little flex doesn't matter either, right? You're not laying tiles on it!

The dimensioning is done to handle loads at the worst possible place, meaning right in the middle of the joists. But if you set up a sprung mattress measuring 1.20x2 meters, you move the loads away from the middle to the edges.

You can attach the entire inner long side to the wall. So there won't be any flex at all there. This hasn't been considered in the dimensioning either.

Hi, now I get it! 6 joists together as 3 beams. Over-dimensioned, maybe, but I think the solution holds, and it's just as well to have as complete a construction as possible, it mustn't collapse! The only thing is that it will be heavy beams to get up, but that should be resolved somehow, I will have to get some help anyway.

 

[ArneTW]

Now it's starting to get interesting how the plane will be attached to the wall... angle brackets/beam brackets in the studs or a frame with support from the floor?

It's easy to over-dimension what is easy to over-dimension but then forget the weakest link... (wherever it may be hiding?)

/ATW