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Supporting cut joists for staircase.


 
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GCarnegi

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PostPosted: Mon Feb 21, 2011 2:55 pm Reply with quote

I want to put in a staircase in our two storey house up into the loft space, and I realise I'm going to need permissions and building warrant, but regulations aside, I can't seem to get my head around how to support the ceiling (loft floor) once I cut away the joists to get access for the stair.

The stair is going to have to be "L-shaped" with a landing three or four steps down from the top, but it means cutting away the supported ends of about 8 joists (see incredibly poor drawing below). - The stair needs to run "along" the supporting wall.



If the stairs were a straight run, then I could simply put an 8x2 joist across the cut ends of the joists (along the side of the stairs), supported by a granite wall at one end, and a post at the other (which would in turn rest on a supporting ground floor wallhead - that first floor wall is not suitable for load bearing). My problem is that, having an "L" shaped stair means that the "end beam" would have to stop short of the granite wall, with nothing to support it.

The only thing I can think of would be to put a heavy timber "diagonal", bolted to the supporting wall, beneath the landing, somthing like the diagonal on a timber gate, passing the load from the flor above onto the supporting wall 3 ft away! Only thing is that I don't recall seeing many diagonal timbers in housebuilding, so I'm guessing there's likely a better way.

Any suggestions welcome.
kind regards,
Guy[/i]
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Static

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PostPosted: Mon Feb 21, 2011 3:03 pm Reply with quote

This is why most would create the half landing lower down.. can be done with cantilevered steel or cranked steels.. dont think it would be possible in timber..

Would be better to remove the half landing by increasing the stairs riser / decrease going.. or rotate stairs 90deg.. cutting so many ceiling members may be an issue as well.. is the roof traditional or trusses?
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noseall

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PostPosted: Mon Feb 21, 2011 4:58 pm Reply with quote

You will need either a sleeper wall under the half landing or a full height structural newel post.

Or both.
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GCarnegi

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PostPosted: Mon Feb 21, 2011 5:35 pm Reply with quote

Apologies - the picture wasn't very clear and the description wasn't much better! Maybe the below image might be fractionally clearer.



Unfortunately, the width of the bedroom from which I'm stealing space is only about 8ft - not enough for a full run with a landing at the top. Maybe enough for a full run with NO landing at the top, but then I'm stuck on the stairs when I get to the top step - with my nose buried in a block wall icon_wink.gif

Also, I can't extend the stairs the other way (to the right) as this would protrude into the first floor landing/hall which is already less than 3ft wide.

As such, I think I'm stuck with putting some sort of quarter landing in the middle of the stairs. Of course, with this being in a bedroom, I want to keep the "ceiling inlay" (resulting from the underside of the top few steps) against the block wall, meaning I should have a 75cm landing, and about a 165cm run of stairs on the bottom half. Perhaps a winder stair would allow me to get more rise per unit run, but that's not what I'm asking about here.

What I'm struggling with is how to support the ceiling joists cut away to make room for the stair. The drawing shows the supporting walls (thick) and the plasterboard walls (thin). Unfortunately, the apex of the stair will land directly above the middle of my ground floor kitchen, so extending a post down through both first and ground floors is not an option.

To better describe my thoughts stated earlier, the only way I can think of supporting the ceiling joists (ie loft floor) would be by some sort of giant "corner shelf bracket" made from 3x3 steel box sectionor larger, bolted to the two adjoining supporting walls, and supporting a stansion which in turn supports the new load bearing beam.



any thoughts?

ps: should have mentioned, the roof is traditional with two sets of joists , each going from outside walls to middle supporting wall (reducing the span), so there's no "tension" on the joists from a potentially "splaying" roof.

Not sure what a "sleeper" wall is. I'm guessing that it would still be a problem with no supporting structure on the ground floor below?
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noseall

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PostPosted: Mon Feb 21, 2011 7:25 pm Reply with quote

A full length structural newel post at the turn may be the answer.
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GCarnegi

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PostPosted: Mon Feb 21, 2011 7:29 pm Reply with quote

When you say "full length", do you mean right down through the first floor and the ground floor and into the foundation? If so, it would end up about a foot in front of my oven door downstairs. Similarly, wouldn't a sleeper wall need to be sitting on top of something structural?
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noseall

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PostPosted: Mon Feb 21, 2011 7:36 pm Reply with quote

GCarnegi wrote:
When you say "full length", do you mean right down through the first floor and the ground floor and into the foundation? If so, it would end up about a foot in front of my oven door downstairs.
It often pays to read the whole post, i agree! icon_redface.gif

A steel beam or a triple joist could catch the newel bottom, yea/nay?
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GCarnegi

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PostPosted: Mon Feb 21, 2011 8:01 pm Reply with quote

Yes, I think so, but then I'm getting in to chopping into the ground floor ceiling joists as well, which I was hoping to avoid (unless I simply put it on top of them - which I guess I could)
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geraint

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PostPosted: Tue Feb 22, 2011 9:12 pm Reply with quote

GCarnegi wrote:
I want to put in a staircase in our two storey house up into the loft space, and I realise I'm going to need permissions and building warrant, but regulations aside, I can't seem to get my head around how to support the ceiling (loft floor) once I cut away the joists to get access for the stair.

The stair is going to have to be "L-shaped" with a landing three or four steps down from the top, but it means cutting away the supported ends of about 8 joists (see incredibly poor drawing below). - The stair needs to run "along" the supporting wall.



If the stairs were a straight run, then I could simply put an 8x2 joist across the cut ends of the joists (along the side of the stairs), supported by a granite wall at one end, and a post at the other (which would in turn rest on a supporting ground floor wallhead - that first floor wall is not suitable for load bearing). My problem is that, having an "L" shaped stair means that the "end beam" would have to stop short of the granite wall, with nothing to support it.

The only thing I can think of would be to put a heavy timber "diagonal", bolted to the supporting wall, beneath the landing, somthing like the diagonal on a timber gate, passing the load from the flor above onto the supporting wall 3 ft away! Only thing is that I don't recall seeing many diagonal timbers in housebuilding, so I'm guessing there's likely a better way.

Any suggestions welcome.
kind regards,
Guy[/i]



from the top of the stair.. double trim back to the joist over the bottom tread.. triple joist that one and you will have no problems.. the floor will be self supporting. and then just fit the staircase...
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