# Warping oak stair treads



## J WILSON (Feb 25, 2013)

As a contractor, I recently built a stairwell transition between a garage and the basement/main floor of the house. A stair company built the stairs. The top three treads of stairs leading to the basement began cupping, so I replaced them myself with the homeowner staining and sealing before installation. Now the top two treads are warping again. No sign of moisture. Both entrances to upper and lower levels to the house are cased openings. What could cause this?


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## DannyT (Apr 26, 2011)

were the bottom and the ends sealed also?


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## Keith Mathewson (Sep 23, 2010)

Is there a difference in which spaces are heated?

I'm guessing that these are not housed stairs.


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## scsmith42 (Jan 24, 2011)

Cupping in dry wood is typically caused by differences in RH% on each side of the wood. You can minimize it by finishing both sides of the board. Additionally, it sounds like the basement may be more humid than the rest of the house.


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## Brian T. (Dec 19, 2012)

Air dried outdoors under cover, the equilibrium moisture content should be in the 12-15% range.
Indoors in service, that MC can drop as low as 4-5% and movement is probable. Particularly if the wood was cut tangentially, parallel to the plane of the growth rings.
The only fix that I've ever see was a set of ripping cuts, hidden on the underside of the wood, maybe 1/2 the thickness of the wood. That appeared to do a good job of alleviating the cupping movement.
A glue-up of narrow pieces works for this as well.


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## J WILSON (Feb 25, 2013)

DannyT said:


> were the bottom and the ends sealed also?


Yes, the homeowner sealed both the top and bottom.


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## J WILSON (Feb 25, 2013)

Keith Mathewson said:


> Is there a difference in which spaces are heated?
> 
> I'm guessing that these are not housed stairs.


The transition stairwell is heated. Obviously, the adjacent garage is not. Both levels of the house have open entryways.


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## scsmith42 (Jan 24, 2011)

If they are cupping "towards the bark", then it sounds like the lumber was not properly dried. It is the natural tendency for the growth rings on lumber to "try to straighten out" during the drying process.

On the other hand, if they are all cupping the same direction, irrespective of the orientation of the growth rings, then it sounds like there is a problem in RH% on one side of the board. 

Lumber will cup towards the dry side.


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