alternate tread stair question

hi,
Alternate tread stairs are for steep applications, such as to a loft. I was asked to build a set for someone. The tread width is 24", the depth for the wide half is 10", reducing to 4" for the narrow half. Thickness spec'd at 1 1/16". Housed in the stringers (1 1/2" thick). Material to be ash, maple, or birch...
My question is: Due to the depth of the tread, I would need to glue up narrower boards to make up the 10". As the front of the tread is only supported on one side, I am concerned that someone stepping on the tread could snap it off at the glue joint. I have heard "the glue is stronger than the wood", but it still is a concern to me.
Any opinions or experience with this?
A picture of a similar stair can be seen at http://www.tradestairs.com/acatalog/birch_24_spacesaver.html
mine will have no risers...
thanks,
david
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david blumberg wrote:

That could be why the manufacturer, in the example you cited, uses 24 mm Birch plywood for the treads.
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says...

In a situation like a stair tread that's unsupported one side, I'd worry about shear forces on the glue joint, not so much the strength of the glue per se. Since you're housing the outside end, twisting forces should be mostly taken care off. Insert a bisquit or a spline into the equation and you'll be much better off, i.m.o. but then risers _would_ make it structurally much stronger again.
Also safer: We have a riser-less steep stair (used to be a ladder for a high bed) going up to the loft in the barn where my wife has her wool studio and she's twice nearly put her leg through the gap when carrying bulky things that obscure her vision.
-Peter
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david blumberg wrote:

I wouldn't worry about the glue...I'd worry about the wood itself snapping along the grain. This is probably why the one you linked to used plywood.
I've seen a version of this where they had a third stringer down the middle of the stair, and each stair was only 12" wide but staggered (ie. no "narrow half").
Chris
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Double or triple your tread thickness.
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You could always incorporate a third stringer, similar to a ships ladder, or even a wood shelf support in the center using the same type of wood.
If you must glue a few pieces together to make your treads the biscuit idea would work the best I picked up biscuit joiner at Lowes for about $100.00 versus the dewalt for $190.00 is not a bad deal if you only use it a couple of times a year.
Dave FL
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Tom Silva used the Miller Doweling System to repair a broken tread that exhibited the very symptom you are concerned about. Perhaps you could use these to prevent, as opposed to repair, breakage along the grain.
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Thanks for all the replies...I remember seeing the show with the dowel repair...I did not notice that the treads in the link I posted are plywood. I can get 1" maple plywood here, so I will see if the interested party would consider that...
david
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says...

You can also make your own 'ply' by using 2@3/4" boards on top of each other with the joint staggered horizontally: ________________ |___________+___| |___+___________|
then cut your treads out of that --- that should be quite strong. Laborious though.
-P.
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http://www.stairplan.com/spacesaver.htm The glue probably won't fail, the wood will fail somewhere. Seasonal changes will exacerbate the situation with solid wood treads. Either use a center stringer, use plywood, laminate solid wood to make your own plywood, or use through-bolts to reinforce the freeboard end.
R
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