Any advice re supporting a spiral stair. The stair will be quite large
(Class C diameter approx 1900mm) and likely to be a steel
construction.

I was planning to just span 3 joists with 18mm ply and 1 1/4" floor
boards on top in a square 900mm (which would make up the height i need
to be flush with the final floor) Joists are approx 7" x 2" and at
450mm centres.

But belt and braces... should I be thinking about putting in a
concrete footing between 2 bridled joists. Since most (all?) the
weight is on the central colomn.

Timber domestic floor designs are usually based around a 150Kg per sq
metre static loading. I'd imagine a steel spiral staircase would be
more like 1000Kg.

Haven't you/your structural engineer had to specify the supporting
structure (with detailed calculations) to Building Control?

wrote:
Any advice re supporting a spiral stair. The stair will be quite large
(Class C diameter approx 1900mm) and likely to be a steel
construction.

I was planning to just span 3 joists with 18mm ply and 1 1/4" floor
boards on top in a square 900mm (which would make up the height i need
to be flush with the final floor) Joists are approx 7" x 2" and at
450mm centres.

But belt and braces... should I be thinking about putting in a
concrete footing between 2 bridled joists. Since most (all?) the
weight is on the central colomn.

Is it starting on the ground floor? Is that solid or suspended? The base
of the staircase will be where the load in concentrated.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 5 May, 23:41, John Rumm wrote:
wrote:
Any advice re supporting a spiral stair. The stair will be quite large
(Class C diameter approx 1900mm) and likely to be a steel
construction.

I was planning to just span 3 joists with 18mm ply and 1 1/4" floor
boards on top in a square 900mm (which would make up the height i need
to be flush with the final floor) Joists are approx 7" x 2" and at
450mm centres.

But belt and braces... should I be thinking about putting in a
concrete footing between 2 bridled joists. Since most (all?) the
weight is on the central colomn.

Is it starting on the ground floor? Is that solid or suspended? The base
of the staircase will be where the load in concentrated.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/


The stair will start on the ground floor. Its a timber suspended
floor - though its not really suspended more 7" x 2" joists laid on
bricks every metre or so directly on the solum.

wrote:

The stair will start on the ground floor. Its a timber suspended
floor - though its not really suspended more 7" x 2" joists laid on
bricks every metre or so directly on the solum.

It sounds like there that you will need to focus your efforts then, make
sure the floor at that point is strong enough to carry the stair. It
might be that you need to strengthen the floor, or alternatively find a
way to transfer the load to the sub floor/brickwork. Do you know how
much the complete stair will weigh?

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/