Hello!
I am planning to furnish an attic in an old house, and the beams that currently exist are 135*135mm with spacing between 800-1140 mm c/c. I plan to keep the old beams but add new ones in between to level the floor. The span is about 7600mm. Can I use 2 pieces of 145*45 at 3800mm with a nail plate in between, or is 145 too weak? I don't want to build up the floor too much, as it would reduce a lot of the space.
I am planning to furnish an attic in an old house, and the beams that currently exist are 135*135mm with spacing between 800-1140 mm c/c. I plan to keep the old beams but add new ones in between to level the floor. The span is about 7600mm. Can I use 2 pieces of 145*45 at 3800mm with a nail plate in between, or is 145 too weak? I don't want to build up the floor too much, as it would reduce a lot of the space.
Nope! There are no supports at all on the 7600mm. But couldn't you nail 600mm cleats over the nail plate? The span is 7600mm between the outer walls and the 145s I will use are 3800mm.
Couldn't you join 4 pieces of 145s 3800mm with staggered joints, admittedly they will be 45+45= 90mm but can't that work?
Couldn't you join 4 pieces of 145s 3800mm with staggered joints, admittedly they will be 45+45= 90mm but can't that work?
Yes, with sufficiently staggered joints, it is possible. But 600 millimeters is not enough, there will be enormous forces on the joint if you want the joists to bear load. Skip the nail plate and splice end to end with perhaps a two-meter-long piece (or more) on each side of the joint. Difficult to explain in text, but you would need two pieces of 45x145x3800 and two pieces of 45x145x2000 per joist.
But 145 is quite small for such a large span in any case. Don't the joists that are there today sag?
But 145 is quite small for such a large span in any case. Don't the joists that are there today sag?
Do you mean that if you stand in the middle of the existing beams and jump or sway a little, they don't flex? Because even if the width is 140, it's the height that is most crucial. But in any case, as long as you're not planning to have ceramics on the floor, it's just a comfort issue.
Edit: I thought a bit. Almost eight meters is a really long span. I think you will get significant flex no matter what you do with 45x145, and I find it hard to believe that your current joists don't flex. It's probably best if someone else with experience with joists of that span speaks up here, so forget most of what I've said..
Edit: I thought a bit. Almost eight meters is a really long span. I think you will get significant flex no matter what you do with 45x145, and I find it hard to believe that your current joists don't flex. It's probably best if someone else with experience with joists of that span speaks up here, so forget most of what I've said..
I have roughly the same dimension on the intermediate floor, but a 5.3 m span. It flexes quite a bit, if you jump in the right rhythm, the floor really swings. With a 7.6 m span, steel beams are probably needed if you want to avoid significant flexing without having higher beams.
Hans
Hans
Have also thought about it, but since the old floor joist has everything from 600mm to 1400mm in c/c measurements, it won't be easy to get the flooring chipboards to fit... Damn! it seems to be an impossible case to frame up with 145s. If only it could have been possible to create a transition between the new floor joist and the old one somehow and then get a support.
You can also combine both methods.
Align by nailing and add intermediate beams where needed. It will be strong enough if the main load-bearing is on the old beams - you mentioned that it was already strong enough, interesting.
If you want extra assurance that the loads are well distributed, you can use plywood instead of chipboard.
Align by nailing and add intermediate beams where needed. It will be strong enough if the main load-bearing is on the old beams - you mentioned that it was already strong enough, interesting.
If you want extra assurance that the loads are well distributed, you can use plywood instead of chipboard.
I mean, you can definitely make it hold with 45x145, but it will be bouncy. Just like your current floor joists must be if you really feel it. So strength is less of a problem, the floor swaying when someone walks on it is a bigger one. Could making a routing in the ceiling on the floor below not be an option..? Can you live with it swaying?lillenp said: