Ledger board to support one end of a half-landing

[dnb]

I've had a request to amend the design for the cupboard space under the stairs. (Apparently my original plan drawing was not understood or I asked for approval when the boss was distracted, so I am therefore wrong and should have known not to do things the easy way...  😉  )

 

The stairs are in a corner of our hallway. The first half flight runs next to an internal structural wall to a half landing that goes out to an external wall. The return flight up to the 1st floor is only suported at each end and is to all intents and purposes in free space both sides. It's probably clearer with a picture - will try to dig one out from us assembling the stair kit.

 

I had planned to build a half-landing height timber stud framework to support the trimmer plate behind the two half flights of stairs. It won't do much supporting of the upper flight because it has newels that reach the floor, but will support one side of the top of the lower half flight (the other side again has a newel that reaches the floor). This is actually next to an internal structural timber stud wall so again not a lot of load will be presented since the stairs are supported by said wall. The half landing would be supported by a simple set of posts where it's easy to demonstrate that there's next to no deflection of the trimmer plate and no issue with any form of loading because there are 4 evenly spaced vertical 4x2 posts at nominal 600 centres to take the load to the floor. The half landing joists would be approx 950mm and attached with Simpsons joist hangers to the trimmer plate at one end and an outer SIPS wall at the other. The trimmer plate and joists will be 2" x 8" C16 timber because I happen to have some handy lengths in the spares pile. Calculations (assisted by timberbeamcalculator.co.uk) suggest it will support much more load than it will ever see and all is easy and good.

 

Now comes the design change... There is a desire to not have the timber studwork wall to support the half landing at the lower flight (or indeed any structure to support the half landing - I was essentially asked why can't it just hover there??). So I am considering if a 2" x 8" ledger board attached to the internal timber stud wall (4x2 studs at least doubled up to support some significant point loads in the house structure at nominal 400mm centres) for one side of the half landing so that I can use a joist hanger on to the ledger board for one end of the trimmer plate (again 2" x 8" timber), and if I am using a ledger plate there, then why can't the trimmer plate be fitted as a ledger plate to the three long newel posts as well in order to achieve the hovering like effect. (The half landing would then use the same joist structure from SIPS wall to timmer plate.) We then had a discussion about who was being unreasonable... Turns out my argument involving numbers and maths wasn't totally convincing (probably valid given I have a bit of a history of overkill)...  

 

So, I need either convinving that a ledger board is a sound idea that won't cost me a load of structural engineering time for both cost and delays and require a load of special BS stamped fixings that need shiny certificates for my new and very keen BCO to examine, or a cunning argument as to why it's not a good idea to do mind changing after the parts arrive on site and it turns out that they're not what the boss believed the plan said that won't get me in too much more trouble...  All this is a little tongue-in-cheek, but I am interested in the answer since I do have a possibly unreasonable distrust of ledger boards, and understanding a bit more about how they work might simplify some other (not BCO controlled) projects on my list even if it doesn't help get the boss her floating half landing. 😉