Cupping stair treads

[CharlieGator]

I recently installed new stairs in my sunroom. After several weeks I noticed that they were starting to cup upward.
I built a 2x6 frame on a concrete slab and added oak stair treads. The treads were laminated, not a solid piece of oak.
They are 1 inch thick.

Any ideas as what is causing the treads to cup?

 

[Henry W]

My guess is air moisture differential - region below is more humid (from concrete?) than the drier air above (in this heating season).
Wait to see what happens when the season changes - and/or get a humidity sensor.

 

[CharlieGator]

My guess is air moisture differential - region below is more humid (from concrete?) than the drier air above (in this heating season).
Wait to see what happens when the season changes - and/or get a humidity sensor.

Thanks

 

[rcarmac]

Is the bottom finished or just the top. When I have done wood steps over some like the concrete, I have to back prime it. Just curious if the back is unfinished wood

 

[CharlieGator]

Is the bottom finished or just the top. When I have done wood steps over some like the concrete, I have to back prime it. Just curious if the back is unfinished wood

Robert,
Just the top is finished with poly.
I thought about this too.
Thanks

 

[Gotcha6]

If you have to replace or can remove existing, put a courtesy kerf cut on the underside about 2/3 to 3/4 the thickness of the tread but not out to the exposed edge. Allow the treads to acclimate if using the old ones. Reinstall with trim screws. I agree with the above answer about the moisture. The boards are going to expand on the moist side and this looks like what happened.

 

[jlwest]

Uneven moisture in the treads.

 

[CharlieGator]

Thanks

If you have to replace or can remove existing, put a courtesy kerf cut on the underside about 2/3 to 3/4 the thickness of the tread but not out to the exposed edge. Allow the treads to acclimate if using the old ones. Reinstall with trim screws. I agree with the above answer about the moisture. The boards are going to expand on the moist side and this looks like what happened.

 

[Wiley's Woodworks]

You've got your answer in the responses above. FYI boards cup towards the drier side or bow on the wetter side. If it's easy enough to remove the treads, your fix may be as easy as flipping them upside down and blowing hot air across underside. You can't apply water to the topside because it's already sealed. If they flatten back out, you will still need to seal the underside and screw them back into place to prevent this from happening again.

 

[CharlieGator]

Thanks to everyone who helped with this issue!
Greatly appreciate your thoughts, knowledge and suggestions.
I will be removing the existing treads, adding a vapor barrier on top of the concrete, filling the frame with insulation and sealing the bottoms with poly!

 

[CharlieGator]

Update on "cupping stair treads" issue.

In addition to the items I mentioned in my last post, I decided to drill 1 1/2 holes through each joist board to facilitate air movement and added two registers to ensure a more balanced air moisture differential!!
Keeping my fingers crossed!!!