The wide boards and narrow boards shrink at the same rate, but if you have narrow boards the gaps are spread out over two boards instead of one board. So instead of a 1/8" gap, you may have two 1/16" gaps instead. Make sense? Another way to go is to use quartersawn wood instead of regular wood. It costs more, but is much more stable. It does not expand and contract nearly as much as plain sawn boards. I installed my hardwood in August with no air conditioning available. I live in South Carolina so it is VERY hunid here. I installed the boards so they were tight with no gaps at all. Now that winter is here and I am running gas heat, I have noticed almost no gaps at all. There are a few, and they are so narrow you can't even stick a piece of paper in them. I am really happy with my wood choice.....3" wide quartersawn white oak.

We have engineered in a country cottage in Ontario Canada, cold dry winters, wet springs, hot humid summers, wood burning and no AC, never have had a single problem in 13 years. The construction of engineered hardwoods lends itself to lesser change due to moisture shifts. I swear by engineered after seeing how it has performed for us.

They both have a point and are likely basing their suggestions on experience. I believe conventional wisdom says that you should have a whole home humidifier to add humidity to the house during the winter. That would keep the wood at a relatively uniform moisture content. If you don't, there's two scenarios I would predict. 1) If you install and finish the floor while the wood is very dry, it will expand when the humidity goes up. Any filler in the cracks will probably be pushed out, the floor may move due to expansion and/or the edges of the boards may get compressed and the cells could get crushed by the force of the expansion. This could also affect the finish at the edges of the boards since the filler is being pushed up and potentially the cells at the edges of the boards are being crushed. When the humidity goes down the floor will shrink and cracks will appear. 2) If you install and finish the floor while it's less dry, it will shrink when the humidity goes down and cracks will appear. If the cracks bother you, they could be filled when this happens. Once the humidity goes up again, the filler would be forced out and the floor would be tight, like when it was new. When the humidity goes down again, the floor will shrink and cracks will appear again. If I was not going to install a whole house humidifier, I think I'd choose scenario #2. Neither scenario is ideal for the floor people since they get blamed either way, for a situation over which they have very little control.

I would purchase a few hygrometers from home depot ($35 each) and place them around the house. I would also place one in the basement. I would then let them settle in for a day or two and then start taking DAILY readings for a week. I would write these down on a piece of paper or a spread sheet (documenting time of day and room location). You would also document the weather OUTSIDE to keep track of any correlation between indoor Relative Humidity and outdoor weather/humidity. Once you have a few points of data, you can then figure out what is going on inside the house. Hickory is dynamic when compared to oak. It likes to stretch it's legs in higher humidity and then shrink up with low humidity. Now for the dehumidifyer in the basement. You mention you are on a lake. Which means ground water is VERY high (the lake is just a large dip in the landscape where ground water has pooled). Add that to porous concrete and you have a very high chance of continuous water vapour (or liquid water) moving into the house through the basement slab. The AGE of the house/slab will tell us if you have a vapour barrier UNDERNEATH the concrete. If you do NOT have a vapour barrier (or it has been compromised = always a possibility) then you will have a concrete slab that is continuously moving vapour into the home. Every day. All day. Day and night. For the entirety of the home's existence. Whew! So much to know, right? First things first: go out and purchase 2-4 hygrometers and set them up around the home. While you are waiting for them to settle in, tell us a bit more about the age of the home and the type of basement situation you have (photos would be SUPER helpful). Tell us how you know there have been seepage issues in the past.