Aperture for stairs

[goodbyegti]

I'm trying to squeeze part of the bathroom below the upper flight of stairs. The design of the stairs can't really change as it's a barn conversion with confined headroom.

 

Here are the stairs:

 

 

 

 

And here are the dimensions of the aperture:

 

 

The upper floor consists of 195mm deep joists at 30mm centres.

 

If I consult a span table like in the attached leaflet 8, I get:

 

Span A = 2230mm

Span B = 825mm

Span C = 2035mm

 

A/B = 0.19

 

The table in leaflet 8 tells me that I can use 2 No. 38 x 195mm joists for a span S of 3.73m. These would actually be 4530mm long in total, supported by a post underneath. To be clear I'm talking about the doubled up joists on the right of the technical drawing (not the horizontal trimmers).

 

The calculations rely on the posts within the stud walls below, supporting the joists above. These posts would be 3 No. 95x45 mm studs bolted together and would form part of the stud walls on the ground floor.

 

To further complicate matters, a stud wall (upstairs) also needs to be supported directly across span S, so I could use 2 No.x 63 x 195 joists instead?

 

Will building control shoot me on the spot? The wife says I should get off the computer and consult an engineer?

Leaflet-8-Timber-trimeer-beans-and-joists-sizes-and-details-for-trimming-around-openings (1).pdf

Edited March 30, 2023 by goodbyegti

[ETC]

Listen to your wife.

[PeterW]

1 hour ago, ETC said:

Listen to your wife.

 +1 to this…

 

lots to consider including the “post” Is probably the newel and is not structurally graded for anything other than holding up the stairs. You’ve got dead loads to consider here and a whole heap of challenges in how you engineer the spans so one for the professionals.

 

[nod]

We’ve an identical stair layout in our previous build Contact the guys that are making the stairs They will feed your measurements into cad Which will work everything out for you and BC

[Pocster]

10 hours ago, ETC said:

Listen to your wife.

First and only time I’ve read that statement.

[goodbyegti]

To follow up on this, I took your advice and asked the engineer. £350 later he said I can use 2 No.x 45 x 195 c24  joists glued and bolted to hang the staircase trimmer off, and 3 studs glued and bolted for the support post. 

 

So all-in-all the end result looks like my drawing above, but I can use 45mm wide joists, rather 63mm. BCO is happy and has accepted, so it will soon be time for some demolition 😁.

Edited March 20 by goodbyegti