Double up joists in loft

[messimagician]

I'm want to put bigger joists in the loft. These will be independent from the ones already in place.

I have a question which I'm sure someone will be able to help with.

Where the bedroom door is is a timber frame which I believe would not be suitable to hold the weight of a floor so I think I need to change the direction of the joists at that point and run smaller joists perpendicular above the existing ones instead

The joists im using are c16 175x45, now the new joist which will be closest to the door frame would then have the smaller joists coming off it which would make it a supporting beam. Would this require doubling up the joists to make 175x90?

What fixings would this require in this instance as I'm not entirely sure.

The new joists will span 2.4m which will run parallel with the existing loft joists

The perpendicular joists would need to span 1.2m so could I get away with using 4x2?


Thanks

 

[John D v2.0]

4 by 2 is fine for a short span but you also need to think of the extra load on the joist they are hanging off. Not just double up blindly but also how about the bearings for that.
You can look at the trada span tables for assistance, but if you want it up to scratch you'll likely need an SE input.

 

[messimagician]

Thanks John, I did look at the trada table for spans and the 4x2 would be adequate

I have been looking online and I believe what I've been looking at are called trimmers.
On the councils website they have two examples. The layout I require is like fig1 and I'm assuming this is to a standard floor 0.25-0.5

Over the small bedroom the span of the new joists would span 2.4m from eaves to load bearing wall. I then need to span from this wall to the eaves at the front of the house which is 3.6m.

Can someone just double check this would be ok. 175x75 c24 doubled up spanning 3.6m with a Ioaded length 1.1m. I would not be boarding right to the very end of the eaves anyway

Thanks

 

[Jonathan1111]

Do you have a sketch of what you trying to do? I am somewhat confused, how this is going together. Are you going to split the joists over the internal wall?

 

[messimagician]

Here is a quick sketch. The joists will have to split as the spans are different so will require larger size joists. These will sit next to each other on the load bearing wall

The trimmer joists which wasn't too sure about would be seated near to the doors on the wall and another set of trimmers on each side of the steel beam using hangers. These would have 4x2 joists spanning 1m perpendicular

 

[Jonathan1111]

What centres are you planning for the main 3.6m joists? If you are using 600 centres, then your trimmers are "replacing" one joist, if 400 centres, then "replacing" 2 joists. so doubling up on either side should be fine.

 

[messimagician]

Hi Jon

That's great, thanks for the help. I was intending on using 400 centers for the main joists on both 2.4m and 3.6m spans.

 

[michaelscad]

you can get metal web posi/easi joists span well up to 8 metres
sit 150mm over existing they come with the calcs from the suppliers
tske out a couple rows of tiles and slide them in

 

[michaelscad]

this might help

 

[freddiemercurystwin]

I don't know what the OP is actually trying to achieve? Have I missed it?

 

[cdbe]

Surely it just needs a length of timber to span the gap over the door frame? Also you will probably need a trimmed opening for the hatch, which would usually go in the landing, so you should be able to do it all in one go.