Was the HVAC on for a couple of weeks before install? If not, then the home may have been full of moisture from the build and too humid for the install. Once the heat goes on and starts pulling moisture out of the air, the wood does what wood does, and it shrinks. It will expand again in the summer and the gaps will close.

It's a GC issue to solve on a new home, regardless. Call him up and have him do his job.

Seems like a real problem that they didn't get any stain into the cracks, and the sanding job is horrible. Wood movement is normal, but this really looks like the flooring and subfloor were not equilibrated for moisture content before installation. The whole job looks pretty unacceptable.

live_wire_oak: No, i don't think the HVAC was fully operational for two weeks before install. I would guess more like a couple of days.

rwiegand: These were prefinished, so I guess the sanding and stain is more of a manufacturing issue. Although to be fair this product was about $3.75/sq. ft., so I probably shouldn't be expecting perfection. In hindsight, I should not have felt so compelled to stay within my $4/sq.ft. allowance.

Hmmn. Lumber Liquidators. That shines a light or two. I'm seeing the gapping along wall lines in some of the pictures. That to me would indicate there wasn't enough time for the glue to hold the floor together as I'm also going to say this was a glued floating floor.

Or, the installers didn't know how to keep the floor tight around the perimeter. You'll see this mostly with boards that run parallel and not perpendicular to the wall or base. Although I would guess there may be some end gapping here and there.

Could also be some product issues, but it's definitely more installation related. Most guys today use strap clamps to keep floors tight during the installation then temporarily tape them together until the glue bonds and dries.

Here is a link that might be useful:

Is this engineered or solid hardwood? Is it gluedown on slab or nail down on subfloor? There may be some milling issues, but I'd bet installer error though. There are multiple parties at fault though. But it all goes back to your GC on the build. Yell loudly and frequently. It's not a case of a single board replacement. Total replacement is more like it. Kick in some more money and get something with better quality this time.

The question i would like to know is how long ago was the wood installed? And how long after they were installed did you notice this gapping issue?

I thought it was a classic floating floor installation problem. It has all the signs, except I missed the comment about middle of the room.

Likely to be one of these two products...solid, nailed or stapled over a wood sub floor (note basement in photos)

http://www.lumberliquidators.com/ll/s/Cocoa%20Birch

Definitely call the installer back. IâÂÂm finding moisture (shrinkage in winter) not being the issue as itâÂÂs not evident across the entire installation. Just here and there? IâÂÂm guessing this is also out of the GC hands? Floor installed after closing? As far as product problems with LL. Unfortunately thereâÂÂs a long wait there (many don't get resolved) and you may find more peace by handling the problem with the installer. IâÂÂve heard many of the nightmares.

IâÂÂm looking at all angles for you. Any thoughts of wiping some stain into the cracks? It may sound like a cheap fix, but some are fine by it when you weigh all the facts that will also include inconveniences and frustration in replacement. The middle of the room? That canâÂÂt be spot fixed in my opinion, unless the boards affected show a manufacturing problem. Are they narrower in width?

Is the floor nailed, glued or floated?
If it's glued it's possible that the boards either weren't laid tight, they moved just after installation or the installer got a bow in the floor causing gaps. Sizable humps or dips in the subfloor can cause gapping also. You can't cover more floor area with the same number of boards as in an adjacent area.
Some adhesives have "memory". You can push the boards up tight then they ease themselves away from the adjacent board. That's why you'll often see installers putting strips of blue tape on the surface to hold until the glue sets up.
Another possibility is that someone walked on the floor before is cured causing the boards to be displaced.
Without all the facts it's hard to say exactly why this has happened.

gamountains - thank you for your suggestions. I did actually fill in one of the gaps (towards a far wall) with wood filler and applied a stain which frankly looks pretty good. However, it took quite a while to fill, dry, sand, then stain that one gap, so I'm not looking forward to spending hours upon hours fixing the rest, and part of me resents having to do it in the first place.

Anyway, thanks to all of you for your comments. I will raise the issue with my GC -- whether a manufacturing or installation issue, I agree that it is ultimately his responsibility. I mostly wanted to get a sense check that what I am seeing is not in the range of "normal."

The OP still has not told us if this is nail down or glue down.

Also, I miss whether this is solid or engineered. If engineered, it is highly unlikely that product shrinkage is a factor. My guess is engineered that either was defective in manufacture or installation or both. "IF" the product was defective and the installer went ahead and installed it, the responsibility shifts to the installer, as the installer is a professional and should not install a product with an obvious manufacturing defect.

Glenn:

We don't see many gluedowns over basement type home construction. That's why I assumed it was nailed or stapled. It appears to be a 5/8" solid as I was going with the LL name.

It looks like poor installation to me, but we can't see it up close, so we're all just throwing it out there.

Thanks for the clarification re: product type.