Answer - A violin is meant to be bowed; a floor is not. It seems that the living room floor has settled around the perimeter. Less so in the middle. Not exactly ideal for a game of marbles or snooker. Or laying hardwood flooring.
Leveling the house is out of the question. Friends had a horrible experience with their plaster walls cracking all over the place.
K was initially concerned the difference might be as much as an inch. In reality, it’s only about a ¼". I thought that maybe we could plump up the edges with padding. Guess not. An installer guy was here yesterday to have a look. He suggested sawing a bit off the joists. What joy.
I really wanted to buy the flooring this weekend.