Small unsupported area of mezzanine

[buffster]

I'm looking to add a small mezzanine to a house but the stair configuration I need to use will have a winder box in the corner of the room, then 1 additional tread. This means the first joist is further into the space than I'd like, as effectively the mezzanine is smaller by the width of that tread.

Is it possible to reclaim that lost space by, for instance, doubling or even trebling up the first joist and then bolting additional joists to them which could be supported from one end but not the other (to effectively fill the blue area on the drawing)? The strip I would like to add is approximately 250mm wide by 2600 long. Joists are 147mm by 75mm. I know I'm not explaining myself very well, hopefully the attached drawing will show what I'm trying to accomplish.

 

[freddiemercurystwin]

Is the stair existing or new?

 

[buffster]

It will be a new stair, just serving the mezzanine.

 

[tony1851]

In theory you could bolt joists together, one after the other. But in practice there will be a twisting-effect on the end (full-length) joist.
To comply with Building Regs (if that's your intention), the floor has to be capable of supporting a point load of 1.4kN (approx 300 lbs) at any
position. I suspect 147 deep joists would not be easy to brace against the twisting force if that sort of load was applied at the edge. It might work if you underboarded the soffit with something rigid, such as 18 thick ply or OSB.

 

[buffster]

Thanks for your replies. Twisting was the thing I was most concerned about, I did wonder whether it was viable to bolt the extra joists not only to the first joist/doubled joist, but also through to say the next joist or 2 across, with noggins (?) between the joists to help prevent twisting.

 

[freddiemercurystwin]

He knows the answer really .......

 

[buffster]

To be honest I know that a supporting post is the obvious solution, but I'd really rather avoid having to use one if I can.