Floor joist specification

[macadonald]

Oldun or anyone else. I thought I'd best place another post rather than carry on from the roof post. Should open the advice up to anyone searchign in future.

I have the plans that my 'architects technician' drew up and reading the spec for the floor joists, he has suggested 95 x 47 joists at 400 centres, with a max span of 1.5m. This requires a sleeper wall over 2.7m obviously. He suggested 95 x 38 wall plates to hang these off.

How does all this sound. I'm still a little surprised that I need the sleeper wall, but happy to build it if necessary. May come down to the requirement of a gap of at least 150mm below the joist to oversite that will mean my timbers would be too big to avoid a sleeper wall.

How does the above sound to you? I plan to place 18/22 mm ply on top of these joist to bring up to internal floor board level and then solid wood flooring on top of that.

Many thanks

Mac

 

[Deluks]

Sounds good, don't forget insulation.

 

[macadonald]

Thanks Deluks. So sleeper wall with these joists is best, not larger joists, without a sleeper wall?

 

[theoldun]

Once again Mac, you have made a c*ck up from word go. Either you do not read your drawings correctly or your architect is as much good as frog with no back legs.
How ever there are ways round every thing, but it is going to cost you a lot more money now for insulated suspended floor.
Need to know the depth from existing house floor to existing sub ground in extension. Needs to be accurate and not a guess.
Will also put some more information on your roof for you over next couple of days
Regards oldun.

 

[macadonald]

Oldun,

Thanks for that, I think.

Will get the dimensions to you asap. Not sure how asking if the joist size I was specified is ideal is a c*ck up, but no doubt you will elaborate. Unless you are saying this because I have chosen suspended timber rather than solid concrete slab. If so, long story short, I wanted suspended timber to give me flexibility with laying pipes services etc. Building this myself, I know that if I had poured concrete, I would have realised I wanted something somewhere else at a later date and been stuck...

 

[^woody^]

I can't understand why you would want to build a sleeper wall when the floor could be constructed without one

 

[macadonald]

Okay, dimensions for walls are the same as for ceiling, i.e. 5.7m from outside to outside minus 600mm for walls. The projection outwards is 3m to the outside wall, minus 300mm for the wall.

The depth to sub ground is tough as the sub ground is up and down at the moment. That's this weekends job to level that out and possibly pour oversite concrete.The depth from internal floor level to external ground level, which my top of oversite cannot be lower than is 40cm.

I hope this helps and more so hope it's not a cock up. Can't see why it is though.

 

[macadonald]

Woody, I really don't want to build a sleeper wall. That is my question here. The architect has specified timber dimensions with a sleeper wall. I want to know if I can increase the timber dimensions and avoid. Guessing from your answer that I can.

Cheers

 

[tony1851]

If you have 40cm floor-to-ground level, you have sufficient clearance to have full span joists without a sleeper wall. It would be easier for you to install the floor with joists in one span rather than messing about getting a sleeper wall level.

 

[theoldun]

Both woody, his mate Dave from Lincoln and Tony are correct. You do not need sleeper walls. Your architect is a bell end.
Firstly. Your P/A ratio is 0.8, therefore you will require 75mm of insulation with a lambda value of 0.022 between the joists to achieve current U value of 0.22W/m2K. We use Celotex FR4000.
Second to span 2700 C16 47x150 regularised to 145 at 400 centres will suffice. These will support imposed load of 1.5kN/m2 and a dead load up to 0.5kN/m2.
You will need one row of herring bone strutting or solid bridging down the centre.
You will need 150mm clear air space below bottom of joists and over site concrete. Over site concrete to be minimum 75mm thick, membrane below and minimum 75mm consolidated MOT.
Total of 458 mm below finished floor level and sub ground.
You should have or will require 2 number 75x225 cranked air bricks on each flank end. 675 in from the corner and 450 out from existing house. Or there abouts.
Joists. Either cut slots for standard masonry to timber hangers and where patio door is, knock couple of course of brickwork of footings and sit on internal skin with dpc below, or bolt47x145 plate to walls and use timber to timber long leg hangers. Ply for the floor is costly 18mm P5 chipboard is plenty good enough.
Before Dave from Lincoln sticks his beak in , regulations for timber suspended floors are not he same in regard to sub ground covering as to for block and beam.
You have all you need to know.
Regards oldun