joist size for loft conversion

[xdrive]

hi

doing hip to gable with dormer conversion very soon hopefully.

Need to get right length for joists and rafters.

Firstly what would be the dead load as the span table varies.

I've read usual live load will be 1.5kN/m2 for domestic. Table gives value for dead load only.

It will be used as 2 bedrooms and one bathroom eventually.

I am trying to use smaller depth joist because I want to maximise height space. I'm hopefully looking for around 2.3m height by bringing my first floor ceiling down by 100mm.

I've gone with the following direction for joists. I did intend to use 8x2 but hoping to get away with 7x2 c24 or less

For the extension roof I was hoping to use 6x2 as rafters. Will have a couple of velux windows. Angle is around 15.2 degrees.

Because I want to keep a vaulted ceiling I'm assuming I can't use purlins as it would spoil the "look" internally.

Cheers

 

[tony1851]

Your dead load will be in the range 0.25 - 0.5 kN/sq. m.

On the 3.9m span, 7x2 C24 @ 400 c/s might be a bit bouncy, consider putting them at 350 centres or even a little closer.

 

[xdrive]

Your dead load will be in the range 0.25 - 0.5 kN/sq. m.

On the 3.9m span, 7x2 C24 @ 400 c/s might be a bit bouncy, consider putting them at 350 centres or even a little closer.

Is the floor span 4m (0.05m on each bearing)
Also can stud wall act as support?

 

[tony1851]

The old tables I use go by the clear span; other tables might go centre-of-bearing to centre-of-bearing.
A stud wall can certainly act as support to a floor, as long as the stud wall itself is well-supported.