Wanted: plan for single spine wooden staircase

[mattcz]

The title sort of says it all.

thanks.

[Gaza]

as in one housed stringer or central stringer under center

[mattcz]

a what what what?????

Ok - I imagine a single very large old beam. Stick it on a diagonal between floors. Cut into beam to hold steps. Insert rustic wooden steps. While I have no idea, this logically sounds like a single stringer under centre.

I know it sounds as though I just 'designed' it but I am sure there is more to it than this.

Thanks!

[watson]

How wide is the beam Matt?? Might need something else in addition to a cut-in.

[mattcz]

I am in the design stage at the moment but thinking of 16 x 16cm. perhaps sitting (as it were) on it's corner (though flattened - if you get the picture). Would like any additional supports to be as hidden as possible. BTW, I am in Czech Republic so I can get away with anything that is logically safe (ie no handrails :) ).

[watson]

So roughly speaking something like this.........


79817

[mattcz]

yep...that's it

[watson]

Is either side against a wall or is it in the centre of an area?

[mattcz]

watson - the top step will need a small beam to slot into the exposed ceiling beams that run parallel to the stairs. That is, the stairs run up in the space between two beams. Those beams will provide the support for the stairs. Clear as mud? :)

[watson]

Beauty..........clear as.
So you could go up to the beams from the steps with steel rod or similar ....with some artistic imbellishment of course.
So, I don't reckon you need plans.....just the nominal charts for height of steps etc..which will designate how far the staircase extends into the room.......especially as there doesn't appear to be much OHS interference from the local authorities.
It sounds like a good project....in amongst all else that you've got going on.

[mattcz]

so....if I cut half way into the beam to slot in each step...how big would the beam need to be to support (or is that what you mean about the metal support)?

I would just have a stab at it but hate destroying useful old wood as a part of my learning process :)

[watson]

Yep....that's why I'm off looking for a reasonable set of tables that will give you the requirements for the cuts and the step ratio against step depth or width (whatever they call it).
So if we start with the beam for the riser.......we need the width and the depth of the beam....and its length....so that its not buggered up by testing.
I'll get some more drawings (rough) to determine what you need to know .
Oil be bach......or Handel....or whoever.

[watson]

here's what we've gotta find out.


79818

[mattcz]

ok - length of the beam is 3800mm

Rise (correct term??) from floor to ceiling is 2400mm

Size of beam, as mentioned, is somewhat variable. I have 160mm x 160mm now so, if it won't collapse, that size would be my preference. Otherwise, I will ask around for a bigger beam.

Thanks for all your help.

m

[watson]

just some further thoughts


79819

[Bedford]

Matt, are you calling the bottom of the ceiling joist (beams) ceiling height?

I could be wrong here, but I think it has to be worked out as an overall height from floor to floor, not floor to ceiling, as this could result in an uneven rise at the top step.

I think you need to add the the thickness of the beams and floor boards into the calculations, if you haven't already.:)

[mattcz]

hmmmm...... if the step was thick enough, it wouldn't wobble! (Do NOT pay any attention to me, I do NOT know what I am talking about).

Wasn't seeing supports.

Are you telling me that if I am imagine something that appears to defy physics that it probably won't? Bugger.

[mattcz]

Matt, are you calling the bottom of the ceiling joist (beams) ceiling height?

I could be wrong here, but I think it has to be worked out as an overall height from floor to floor, not floor to ceiling, as this could result in an uneven rise at the top step.

I think you need to add the the thickness of the beams and floor boards into the calculations, if you haven't already.:)

yep, that was in original calculation. but thanks for checking

[watson]

Now we need some 14 yr old kid with a calculator that can do square root.

That's to find how far the beam will come out on the floor from the 2.4M height.
That will tell you the angle that the complete staircase will be using that beam.

[mattcz]

3m :)

I based it on the dimensions of the stairs from ground floor to first (these stairs are from first to loft)

[mattcz]

...but the angle? Buggered if I know....too long since I was 14

[watson]

I've got a calc up in the shed.....so I'll work it out in the morning.....currently 8:30 PM. So I'm just trying to find out how steep the stairs would be.
More to follow.
A bit of fun though.

[watson]

Found it....33.8º

[mattcz]

:2tsup: Excelent

[Master Splinter]

Blocklayer's site has a calculator for that sort of stuff....

http://www.blocklayer.com/stairs/default.aspx

[mattcz]

That is so helpful and confusing at the same time. More helpful than confusing but...am I to understand that the uncut portion of the supporting beam needs to be a minimum of 147mm (on the diagram, the 'throat')?

Or - due to the fact that my plan is for a single spine - this particular figure doesn't relate to my design.

I really hate asking people to hold my hand - sorry.

[Master Splinter]

Typically a stinger is about 300-400 deep, and the most common material I've seen is 32mm MDF (which is not exactly noted for its strength).

However, using a single 160mm square beam would be a bit on the dodgy side - once you cut into it to take the treads, there will be precious little left! Then, you have the problem of mounting the treads to it, solidly enough so that some 150kg person standing on the far edge won't cause nasty things to happen. I've only ever seen single string stairs done with a metal stringer. Not saying that wood is impossible, but it's getting to the realm of reaching for an engineer. They also need pretty hefty treads - 40-50mm thick - to prevent deflection.

[mattcz]

my (ridiculous) idea is, rather than lay the spine beam on one face and cut half way through, to lay the spine on one of it's corners and cut halfway through. So the cuts would be diagonal from one corner to the other

ouch - hefty treads

I am beginning to understand why I can't find a picture of this idea on the net.

[Master Splinter]

The problem with having the cuts on the diagonal is that you'll have even less material where you need it for strength - instead of the most highly loaded area (the underside of the stringer) being a large flat surface, it's going to be a narrow point, which is a textbook definition of a stress riser (http://en.wikipedia.org/wiki/Stress_concentration). (listen closely and you can almost hear it calling out "I'm going to fail here!")

Draw a cross section to scale, at the point of the deepest cut, and see if you think that amount of timber would hold a decent amount of weight!. I work it out as 80mm thick....that doesn't inspire confidence in me!

[mattcz]

ow.........this is not looking good

but I bet the guy who came up with this idea (http://1websurfer.files.wordpress.com/2009/03/staircase-10.jpg) never gave in

what if I put a sign saying "NO FAT KIDS"

bugger...thanks for all your help (all of you). Please be aware that some stairs of some sort will have to go in and these figures will be used to construct them. So it is not all in vain.

[Master Splinter]

Assuming you have two 160x160mm beams of sufficient length, you could cut them in half to give you four 160x75ish mm beams and join them together to give you two 320x75 beams. Plenty of meat there, and you could then put in a hefty 20mm rebate to take the steps. Would have a nice, solid rustic farm appeal....

[mattcz]

NOW YOUR TALKING......!

I am on my way out the door but will run around with measure later...

crate of beer here for you....:)

[jago]

Get one of your drunken neighbours to pick a good tree .... TIMBERRRRRRRRRRR
away you go .