How wide are the floor strips and how wide are the gaps?

In a correct install they should be relatively small and uniform gaps that change throughout the years as you change from heating (dry air shrinks the strips) to cooling (cooler air has higher RH and the strips swell).

the wider the strips are the more change in dimension there will be.

If the wood is mixed flat, rift, and quarter sawn the changes may be different between the various grain styles making the gaps slightly less uniform.

Brickeyee - thanks for responding. The floors are narrow common red oak. The gaps run the entire length of the house and they are random ranging from 2, 3, 4, 5 feet apart. There doesn't seem to be any consistent pattern. The gaps range in size from the thickness of a dime to the thickness of 2 quarters. Most are the thickness of one quarter, you can throw in some nickels too. I don't know how else to explain the size of the gap, so forgive my lack of technical jargon.

Any advice will be greatly appreciated.

You need to find out what went wrong with the original install. Fix it? Maybe. I had to fix a job that went bezerk many years ago and I used a wood epoxy compound and wood slivers to do that. I couldn't tear it all out, because fancy cabinetry and trim work was installed on the floor. In your case a complete tear out may be what you want to do. Difficult to say without inspecting the floor.

But you do need to find out the cause. Hire a certified independent flooring inspector to do that.

You can let the builder and the installer attempt to repair your floor, of course with the understanding that everyone goes back to square one if the results are unsatisfactory.

Good luck.

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 can repair flooring in the manner I described. A skilled craftsperson can blend almost anything if the same products are used to do the repair as used in the original install; it's doable but can take days to accomplish; that is why the 5 day estimate.

A flooring inspector's report may likely state the probable cause as what the builder suggests. If this build was the typically 'fast track'...then there can be problems with wood flooring as a result of not waiting for the moisture difference between the subflooring and the flooring to become acceptable.

Good luck.