Extending above stairway

[_me_]

I'm hoping to create an internal extension above the stairway to make the bathroom a little bigger.

Pics and quick sketches are shown below to give an idea. Essentially I want to extend above the stairway by about 2.5ft, which will make a big difference to how I can layout the bathroom (shown in before and after sketch)

Due to the headroom above the steps, I can't just extend with the same floor. To bear the load, I was thinking of fixing a beam to the party wall which will run horizontally to sit on top of the existing floorboards (shown in the cross-sectional sketch). The fact that it will sit on top of the existing floor by a couple of inches won't matter as the new space will house a shower so will be raised anyway.

Has anyone done/seen anything similar?
Any tips for the best way to bear the load? (Wood / steel? single beam or structure?)
Will I need formal structural calcs for it to be passed by building control?
Any general tips welcome!

Thanks

 

[_me_]

 

[Tigercubrider]

You have to have 2 metres headroom minimum when going up stairs.

I am not qualified but considering that the rest of the house won't have a steel in to support the stairs/ landing, I would have thought that timber would be fine. Although a steel might allow the "step" to be lower?

Whatever the step is, will be reflected in loss of headroom in the shower

 

[_me_]

Thanks, appreciate the quick response!

May look at using timber for it then as I'll probably do as much as I can myself and it'll be easier to deal with.

Anyone know whether I'll need to have structural calcs done for this?

Also - what's the best way to connect to the party wall? Will I need to bore into it or can I just connect using plates? (I'm guessing the latter will be easier to do and also easier legally) any recommendations of how to connect it are welcome!

Thanks again

 

[big-all]

you can gain a few inches in length/height by fixing the floor with the last joist on top off the floor height forming part off the end stud wall over the stairs
in other words the flooring will screw up into the last joist/stud wall
assuming a 42% slope you will gain about 90-95% off the joist depth
now this may technically breach a reg or two i dont know but can make the difference where it wont be quite enough otherwise

 

[chappers]

4x2 will be more than adequate, you can double up the beam across the stairwell for completeness, just hang it off the party wall with a masonry joist hanger/shoe. You won't need any structural calcs. What head height will you have over the stairs and what head height do you have over the stairs with the existing setup.

 

[_me_]

Thanks - this does actually help as it will allow me to go above the next stair slightly (by a few inches) to make the new wall flush with the existing wall. I guess I could always just support the wall separately if needed - ie, have the new floor structure and the horizontal beam at the bottom of the new wall fixed to the party wall separately

 

[_me_]

Hi Chappers - thanks that's reassuring I won't need to go through the hassle of that. Assume it's still notifiable to building control though?

Current headroom in that part if the stairs is just under 5m. Will be changing it to just over 2m

 

[chappers]

I suppose technically yes aa its a structural element/bathroom fit. But personally I wouldnt bother.
If youve got over 2 m at all points then happy days