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Posted by tbasc@bellsouth.net on June 8, 2007, 4:39 pm
> Hello,
>
> I'm adding a staircase to a wood frame house, and since space is
> tight, I'd like to minimize the size of the required opening in the
> subfloor. I've determined where the staircase headroom will start to
> intersect the 2x10 floor joists and framed an opening. However, the
> opening in the subfloor could be smaller than this opening in the
> joists, because of the height of the joists.
>
> Now the typical subfloor won't span the 3' wide opening required for
> the stairs. So what is the best way to support this subfloor
> extension? I have a few ideas below, and I'm looking for guidance as
> to which one(s) would be practical and strong enough.
>
> Thanks, Wayne
>
> (1) Add one or more 2x6, 2x4, or 2x3 headers across the opening, just
> above the required headroom. The 2x6 or 2x4 could be attached
> with joist hangers; not sure how to attach the 2x3.
>
> (2) Cut a bevel on the edge of a 2x10 or 2x12 and install it as a
> tilted header across the opening, following the angle of the
> required headroom. The bevel would allow the subfloor to sit flat
> on the top of this tilted header. For extra support, perhaps
> install mitered blocking between this tilted header and the
> orthogonal header.
>
> (3) Add a subfloor material that can span 3' (such as 1 1/8" plywood
> or a 2x) between the joists up against the existing subfloor.
> This could be supported by stair angles such as Simpson TA.
What ever one does, code requires 80" clearance above the plane
determined by the nosing on the stair.
The use of the area above the stair plays a big part in how you
maintain the 80".
I've seen closets with the floor raised above stairs; walls with the
bottom plate 'echoed' below the sub floor and fastened to support the
sub floor.
T
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