Wall for floating staircase?

[flanagaj]

We are planning on having a floating staircase and the TA has not made any mention in the drawings to BC.  I assume it will require a SE to see what make up the wall which the treads will be mounted to, needs to be.  Just not sure whether a single skin 7N block wall would suffice or even a single skin brick wall.  I want the stairs cantilevered from the wall as opposed to having a single central spine below the treads.

Has anyone installed such a staircase and if so, how was the mounting wall constructed?

[crispy_wafer]

Nice idea, yeah I'd run it past your SE for peace of mind, or even @Gus Potter might lend an ear for his thoughts.  I cant help too much, because I've gone with central spine, however when time comes for manufacture, assuming you don't fabricate it yourself, don't be afraid to look up local fabrication firms and joiners for treads.

[Russell griffiths]

Whatever you think it needs over engineering Massively 

I witnessed a large  staircase that had a complex curve in it nearly twist off the wall as the temporary bracing was removed. 
 

there are some serious forces at play with cantilevers, and there would be nothing worse than a bouncy staircase. 
 

steel support structure buried in the wall for me, or a 140mm solid block wall. 

[markc]

A lot depends on the balustrade. If the handrail and infil (assuming glass) is designed as load bearing the cantilever is drastically reduced and a block wall would be ok. If the treads are true single cantilever’s then you are into reinforced wall territory. A bespoke stair company will have SE’s they work with regularly.

[Nickfromwales]

Defo 120x 50mm steel box section uprights into a 5” ‘stud’ wall, with same for header and footer, if you want longer treads and for it to be bombproof.

 

Glulam or 3” trimmer for head of stairs can be swapped out for a steel, if it isn’t already spec’d in steel for eg, to allow this to all be welded / mechanically connected so the best result of all.
 

We’ve had an excellent steel fabricator and welder on site this week sorting a knackered roof out, and the results are fantastic and quite cheap for what you get. Day rates for a welder vs chippy aren’t wildly far apart (max £100 a day difference) and they get a lot done quite quickly by getting stuff cut and made up off site, then it’s just install / clamp / weld / bingo bango. 
 

Steel is not super expensive, so worth finding out what it would cost to do this in metal afaic, and then know you never need to worry / revisit ever again.

Steel opens up an entire new world of possibilities, where’s other materials such as wood have huge limitations; a lot of wood finished stairs need metal spines anyways. 

 

[flanagaj]

Thanks all.  I am planning on working with a local steel fabricator for the steel aspects and will manufacture the treads myself.  Fortunately, I can manufacture the treads as I baulk at the £200 / tread that people on eBay are charging.  One option would be to have steel rods for the balustrade, which are threaded and connect each end of the treads to a steel beam in the ceiling. 

[Nickfromwales]

If anyone wants the details of a fantastic mobile fab / welder who travels nationwide, pm me.

 

Been a great few days with this chap and he’s proper old school (let’s get it done) with 35+ years on the stick. 

[Tony L]

6 hours ago, flanagaj said:

Has anyone installed such a staircase and if so, how was the mounting wall constructed?

 

No, but I'm planning this (that's if I have any money left when the build nears completion). I discussed my plan with my SE, & my drawings show standard 7N blocks laid flat - so my wall that the stairs will hang off is 215 thick (+ finish) rather than 100.

[Gus Potter]

17 hours ago, flanagaj said:

We are planning on having a floating staircase and the TA has not made any mention in the drawings to BC.  I assume it will require a SE to see what make up the wall which the treads will be mounted to, needs to be.  Just not sure whether a single skin 7N block wall would suffice or even a single skin brick wall.  I want the stairs cantilevered from the wall as opposed to having a single central spine below the treads.

Has anyone installed such a staircase and if so, how was the mounting wall constructed?

What a lovely proposal. This floats my boat as an SE.

 

I imagine you have seen a "floating" stair in say a tenement (Scotland) or a traditonal town house in Bath.  I'll try and explain how these roughly work. 

 

Each tread is not a cantllever. It is supported by what can be a thin wall at the inner edge.`

 

Simplisticaly the way we design these is to let the outer side of the tread rest on the one below and to make it work this has to continue all the way down.  The treads are actualy, in torsion so where they are built into the wall the wall has to be designed to resist the tread torsion,  so you need a good weight of wall above. By default the treads need to have torsional resistance. A traditional stone stair tread has enough beef to satisfy. 

 

You find more detail on the theory on the internet. 

 

It's not a design job for the faint hearted but most SEs can handle it.. but you'll need a good height of blockwork above (to provide ballast weight)  and maybe some engineering brick round about the tread end where they run into the wall to take the local torsional stress. 

 

 

 

 

[JohnMo]

So glad I built single storey - one or two levels of thought process deleted.