I installed about 750 sq ft of 3/4 x 3 1/4 oak flooring. One room has developed gaps between most of the end joints. There are no gaps between boards. This seems odd to me since wood should expand and contract a lot more across the grain than along the board. I would expect that if the wood has dried out that there would be bigger gaps between the boards than on the ends.

In the rest of the house I see one or two places where the end gaps have opened but in the living rooms it's most of them. Any idea why? The only thing I can think of is the wood has dried out and we stapled the boards so tight we don't see it across the boards.

The only difference is the living room is on a slab. I did the two 1/2 inch pieces of ply on top of plastic, and used staples to attach the floor to the ply.

Immature harvesting.

dont see it that much but I would say if the only room that has that problem is the one thats over concrete then that might be the root of your problem. sounds like the floor is developing a hump. Or like floorguy says it also can be early harvesting of timber. Staples souldnt keep it from gapping if it was a little green. Did you check the m/c before it was installed and have you tested it now? That would be the first thing I would reccomend.

First I've heard of that. Though I don't have any answers to the question, how can cutting down a tree that's 60 years old be different than one that's 30 for example? It's been known to create issues with bamboo but hardwood?

When lumber is being kiln dried, it loses VERY little of its length, if any. I suspect that there may be some vertical flexing of the floor that COULD possibly be a factor in these end joint gaps. Also, in new construction it could happen by "joist pull". But I am not offering either of these two phenomina as the cause. I really dont know with the information at hand.

Vertical flex might explain the one or two gaps on the floor that was installed upstairs but seems a little unlikely for the floor downstairs on ply on a concrete slab.

We did two bedrooms a hallway and then a third bedroom upstairs. There is a little gaping in a few of the ends in that last bedroom. Next we did the downstairs living room. Most of the end joints have opened up. Most of the wood for the living sat on the job site for at least a couple of weeks; though, I did have to get one or two more bundles at some point. (The house has a 45 bend in the middle so lots of rooms don't have parallel walls. Estimating the amount of wood needed was a pain.)

I unfortunately, I don't have any way to get the M/C so I don't have any idea what it was/is. This house is in the San Francisco bay area and the wood supplier told me the wood had been in the area for a while.

Seems like the ply might be the culprit here. No mention of acclimation of plywood or moisture content of it.

But then there would be gapping on side joints as well?

Ken, are you questioning my authority on this matter?

Thats a possibility but perhaps they are not so prevelant. I thought there might be some panelization going on that Tahoe might not see. Engineered panels shrinks which way, both or towards the ends?

I cant help thinking about the floating plywood subfloor. We dont know the mc of the plywood, or the hardwood ,or the slab, in relation to each other. The slab has plastic over it. The hardwood was in SF for a while, and acclimated in the home.
Was the plywood acclimated ? Where was it stored ?
Installation of the floating subfloor... Was the plywood cut into strips? The 2 layers perpendicular to eachother? Was there expansion left around the perimeter, as well as a knife blade width at the seams?
Just seems like subfloor movement to me. I hear you Ken about movement in both directions. But is this theory off the wall? In the same size room, you get more total expansion with a 3" plank compared to a 6" plank. Wouldn't you get more expansion in the narrow width of the ply, then the length? Seems like this could be related to end gapping if the layers were not layed perpendicular to eachother. Or maybe the top layers moving at a different rate? Could be the mc of the bottom layer is different than the top layer, in contact with the hardwood? Was 15lb felt used ? Man, that's alot of question marks, who's on 1st

BUT, this doesn't explain the upstairs. Maybe there's a chance up & down is 2 different issues?

Moisture-Related Dimensional Stability-APA

Here's a pdf link but you need to join to read them, lots of other technical papers on ply and OSB...like tons of them:

http://www.apawood.org/pdfs/managed/TT- ... N=99809542


Here is another similar one written for the layman:

http://www.performancepanels.com/?conte ... p_atr_dim2