Stair tread deflection

**John Arnold** · 09-12-2013, 11:39 AM

Newly rehabbed row home in Philadelphia has stairs with open risers. Builder added some ugly partial risers, to cover himself for the 4 inch rule, probably thinking the new owner would just remove them after moving in.

Anyway, the treads have no riser support, are only supported on the sides, and deflect about 1/4 inch when normal sized people step on them.

Is there a max allowed deflection? The treads are one inch thick, and also overhang the side supports by about 3 inches. They are not solid wood. Appears to be plywood of some kind with veneer.

Photos shows stairs from behind.
risers.jpg

**Billy Stephens** · 09-12-2013, 06:51 PM

Originally Posted by John Arnold

Newly rehabbed row home in Philadelphia has stairs with open risers. Builder added some ugly partial risers, to cover himself for the 4 inch rule, probably thinking the new owner would just remove them after moving in.

Anyway, the treads have no riser support, are only supported on the sides, and deflect about 1/4 inch when normal sized people step on them.

Is there a max allowed deflection? The treads are one inch thick, and also overhang the side supports by about 3 inches. They are not solid wood. Appears to be plywood of some kind with veneer.

Photos shows stairs from behind.
risers.jpg

Yes there is a deflection limit. STRUCTUREmag - Structural Engineering Magazine, Tradeshow: Wood-framed Stair Stringer Design and Construction

**John Arnold** · 09-13-2013, 03:57 AM

Originally Posted by Billy Stephens

Yes there is a deflection limit. STRUCTUREmag - Structural Engineering Magazine, Tradeshow: Wood-framed Stair Stringer Design and Construction

Billy, Thanks for that, but it appears to be about stringer deflection. In my case, all the deflection is taking place at each individual tread.

**Billy Stephens** · 09-13-2013, 04:37 AM

Originally Posted by John Arnold

Billy, Thanks for that, but it appears to be about stringer deflection. In my case, all the deflection is taking place at each individual tread.

OK,

link is for Fiberglass treads and deflection scale is Span/150. Wood Standard I think is Span/240.

http://www.fibergrate.com/media/4068/treadload.pdf

**John Kogel** · 09-13-2013, 06:53 PM

Slippery and Fugly to boot.[

]

**Michael Chambers** · 09-22-2013, 12:14 PM

Originally Posted by Billy Stephens

Yes there is a deflection limit. STRUCTUREmag - Structural Engineering Magazine, Tradeshow: Wood-framed Stair Stringer Design and Construction

I admittedly just briefed through it, but it appears that the article Billy provided the link to just addresses stringer construction and deflection, and says nothing about stair tread deflection.

My resource is a deck construction guide, but I think the stair construction guidelines would be the same for interior stairs. It calls for no more than 18" between stringers if cut stringers are used, and no more than a 36" span if solid stringers are used, but then 2x4 ledgers have to be installed under the stair tread ends. It also cites a maximum individual stair tread deflection of length/288 with a 300 lb. concentrated load. In the case of a 36" wide stair, this would be 1/8" maximum deflection.

Here's a link to the deck construction guide. I'm citing info from the bottom of page 17.

http://www.awc.org/publications/DCA/DCA6/DCA6-09.pdf

**Frank Norman** · 09-28-2013, 10:42 PM

[QUOTE=Michael Chambers;231984] ...
.. stair construction guidelines would be the same for interior stairs .. no more than a 36" span if solid stringers are used, but then 2x4 ledgers have to be installed under the stair tread ends.
/QUOTE]
Agree the ends of of the treads have to be securely supported where they meet a solid stringer, but saying this has to be provided by a 2x4 ledger assumes only wood is used. The photo shows what might be steel angle supports or joiners.

**Michael Chambers** · 09-29-2013, 05:48 PM

[QUOTE=Frank Norman;232207]

Originally Posted by Michael Chambers

...
.. stair construction guidelines would be the same for interior stairs .. no more than a 36" span if solid stringers are used, but then 2x4 ledgers have to be installed under the stair tread ends.
/QUOTE]
Agree the ends of of the treads have to be securely supported where they meet a solid stringer, but saying this has to be provided by a 2x4 ledger assumes only wood is used. The photo shows what might be steel angle supports or joiners.

Yea, I spotted the same thing after I posted my comments. It would make more sense to just say the treads would have to be securely supported from underneath the ends, but of course I was citing a source provided by the American Forest and Paper Association which does specify 2x4's for this. They probably only think in terms of wood. Go figure!