Unsupported outside stair stringer flexes too much
Hello all.
Getting ready to insulate and drywall in our home rebuild. I have a few days left to make things as right as they can be. This stair goes from the second floor to the third floor attic area living space. It is less wide than the stair below by design. Walking my 290 lbs up deflects the stair down to the left unsupported side. I was wondering what can be done (other than losing weight and having smaller people visit the third floor) to stiffen the outside stringer. Obviously the stair tread and riser will help with this. Possibilities include:
1. sister in an additional stringer
2. add steel flitch plates to each side of the outside stringer
3. or both 1. & 2. but to the middle and the outside stringer
4. add bridging every two feet between the stringers
Additionally, there are no joist hangers at the top where the stringers are headed off. Should there be for additional strength?
I have included four photos to show the stair framing.
I appreciate the feedback.
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Replies
A few observations
It may be a good idea to double the outboard stringer with something like a syp 2x6, glued and screwed.
Some wedging and construction adhesive in the gaps in framing might improve the situation.
Gluing the risers and treads making the stairs a unit will most certainly improve the stability.
Stairs with temporary treads are notoriously shaky.
2sheps,
syp 2x6 wood certainly be easier than trying to get a full step cut additional stringer sandwiched in.
Could you explain wedging and adhesive? Are you referring to installation of the treads and risers? My stair carpenter is definitely gluing everything. It will stiffen up with that. Just want to give a full measure to that outboard stringer as you call it.
What do you think about adding joist hangers at the head?
Thanks for the reply.
It looked like in the photos that there are some gaps where framing element come together. I'd just like to see really solid contact between stringer and floor framing.
If you can install hangers without splitting or otherwise weakening any lumber, it's probably a fine idea.
Definitely add the 2x6. Unsupported notched stringers usually need some help. A flitch plate would be even better.
Thanks all.
I added the 2 x6 glued and screwed and it had a noticeable effect. Also added hangers to the outboard and middle stringers. Finally, I didn't like the framing and contacts either, so I add some 4 and 6 inch timbertech structural lags. You get one chance before they close it in.
Appreciate the advice.
I'd glue and nail 2x6 on both center and outer stringers. I'd block it every 4' to stop any flex. I guess if it still flexes, add another 2x6 to the other side of the center.