Done @Beth!

It can be an humidity issue. Were these gaps present when the flooring was installed? Or did it start showing up later on? What part of Maine is the project located in?

The flooring looks like tongue and groove. What was the installation method? Who was your flooring supplier? We are located in Mass and may know the supplier.

The gaps in front of the stair treads looks more like a installation issue.

Yes it is an unacceptable issue. Yes it can be remedied. Yes that means relaying all the floors. Was the flooring on site, acclimating to the humidity of your space before they began installation? As stated gaps should be along the wall and the baseboard should cover/hide those gaps. I am not sure what you agreed to--no one would want any gaps in the run of the floor.

My guess is the flooring did not acclimate on site for at the very least a week with the heat turned on and a humistat used to check humidity levels

The floors were laid in October. Gapping started before sanding / polying, which only happened last week.

I don’t know the install method. Only that there were nails. I didn’t think they were tongue and groove, but maybe they were. I put pics of the install. (Honestly - I should probably know this, but we have a GC who I trusted.)

It’s on lake Sebago in Maine. I think it was lumber liquidators, but can check.

They let it acclimate for a while, but especially because install was in winter, I am surprised at the gapping.

Are there remedies that wouldn’t require re-laying it?

What is the current indoor humidity level?

Is the image of the installation from October or recently?

Being on the lake, the contractor should have recommended quarter sawn heart pine. That would reduce the shrinking for 5” width.

October was still humid out in our region. With the winter here the flooring has lost a lot of moisture, especially around all the heat sources. You need to bring the humidity level back up to what it was in October. Also, the Flooring would benefit more from a nail assist installation.

We did a 5” red oak live sawn nail assist installation in ogunquit, ME. in September.? It was hot and humid. The house had climate control, though. If, you don’t have a system. You will need one.

You need to find out what the humidity levels are in the home. Order a Hygrometer from Amazon for about $12. Also get a very specific answer to how many days the flooring acclimated and where humidity levels were in the home and flooring prior to installation. Please note wood flooring does shrink during the dryer winter months.

"We chose beautiful 5” Caribbean heart pine for the floors".

I think 50 % of your answer is in that statement. Imported, not dry lumber. "From Lumber Liquidators"

Even a turn of the century Maine Coast cottage might have gaps. I wouldn't use pine for that reason, but clearly your humidity level has dropped significantly. VERY, and is literally sucking the "imported" and install levels right into thinner /dryer air : )