livewireoak is 100% correct...engineered hardwood is real wood, and if your floor is being installed over a slab, you have to go with engineered as solid wood is too unstable. Flooringbro is also 100% correct in stating that a floor is only as good as the installation. We paid a lot of money to upgrade to an 5" wide engineered natural maple floor installed on a slab in our newly contructed home. The floor is beautiful, but just weeks after the install, planks starting coming up all over the place. The problem was that the subfloor was not made level prior to installation. So whatever you choose, please make sure you have good installers who properly prepare the subfloor. Our expensive upgraded floor is an excellent example of that. Good luck to you.

I really appreciate your response. The builder took a look at the floor yesterday and readily admitted that they've never encountered this degree of gapping. He further stated that it was probably due to moisture in either the oak or the subfloor during installation. I'm sure they are going to want to try to repair, but the poly is not going to blend into the rest of the floor. The raised joist runs right through the middle of the kitchen into the great room. As far as using slivers in the other gapping, can you use a sliver when the gap extends the entire length of the house? In other words - you'd have to use really long slivers. Is this doable? I'm going to see if I can find a floor inspector. I really appreciate any help. Thanks.

You should proceed by finding an NWFA certified inspector in your area and paying him to do an inspection. Unless you know the moisture level in the air and wood, and things like nailing schedule, any opinion on what's wrong or how to remedy is strictly a wild guess.

I'm going to disagree with the other opinions in that this could certainly be caused by humidity and acclimation. Every wood pro knows that solid wood will absorb moisture and expand. It's rather unlikely that the boards would be milled to different widths and especially that it would vary in width along a particular board. In general, 4/4 lumber is cut to uniform widths then sent through a machine that mills and kerfs the bottom, mills the top flat and cuts the tongue and groove on opposite sides, all in one machine. Another machine generally adds the end matching. Unless something in the milling machine is moving, or the unmilled boards were too narrow, all pieces will be the same width as they exit the molder. Look at this video at about 1:30 to see the molder in action. https://www.youtube.com/watch?v=wc0N6m4RNdY What you're experiencing is probably the effect of moisture soaking in to parts of boards that were more exposed to humid air. Exposed ends will grow more than centers that are less exposed. Look at the your first full row from the top. On the middle board, the end is wider than the one to the left. In the next row down the opposite is true. It's likely that those ends were exposed to more humid air. The problem is exacerbated when the installer doesn't compensate, since the wide ends can kick the next row out of line, leading to more gaps on the edges and ends. The same thing could happen in very dry air with ends shrinking. Exactly how was the wood acclimated? Was it removed from cartons and wrapping? Was it stacked so air could circulate around all sides of every board? What was the temperature and relative humidity in the space during the acclimation period? What is the current indoor temperature and relative humidity? Is the floor nailed down? I had this happen with a very high quality Canadian solid wood floor. Fortunately mine was dark stained Walnut so once the floor was aligned properly and larger gaps were distributed to make two smaller gaps on each edge, the issue didn't show and once the whole floor acclimated in place there was no issue.