All wood flooring (and your cabinets, doors, frames, paint, drywall, etc) have these types of requirements. The "range" is up to the individual manufacturer to specify. I've seen bamboo that has the narrowest requirement of 45%-60%....for good reason. The GLUE that holds bamboo together is RIGID whereas the grass (bamboo is grass) is ABSORPTIVE so it MOVES. Engineered hardwoods are more specific because the layers create layers of glue...and glue acts and reacts DIFFERENTLY from the wood layers. If one expands but the other does not, you get DELAMINATION. The companies have tested their specifications under laboratory conditions and have found the BIGGEST window for "success" with their floors. They have then written those down. As for solid wood floors in old homes, remember this: the wood floors CUPPED and/or CROWNED and/or SEPARATED early on in the life of the floor. It could have taken more than a DECADE for the home to find it's equilibrium. The original owners SIMPLY PUT UP WITH IT (imagine having to 'put up' with crowned floors for 10 years...today's consumer REFUSES to accept this....so we have warranty requirements now that SPECIFY the 'happy place' for each wood product). Once the first sand/refinish occured (25 years later) the "problem" (the visual issues) with the wood were sanded away. One generation later, it looks GREAT. But no one took selfies of the floors in the '60's. And the cuts and widths were different (there is a BIG reason why 2" strip hardwood was sooooooo popular....and it wasn't because it looked good). And the wood was often sourced (and dried/racked) from local mills. And it sat longer on site before it was installed, and, and, and, and....you get the idea.

If you live in a damp area (is that damp soil or is it damp air; as in humid?) I would recommend against wide plank. Even with engineered hardwood, the wide planks are still "less stable" than narrow planks. And to be clear, any install with a wide plank will require adhesive. If you were planning to do a nail-in-place type of installation, you will require a glue-assist with a wide plank (anything 5" or wider). This will drive up the cost of the installation. Maple is pretty but it turns a strong yellow as it ages (it is photosensitive = turns DARKER with exposure to light). Hickory is a lovely product that is stable in sunlight but is LESS stable in the presence of moisture/humidity. As for the core, it is highly dependent on the construction of the plank and the thickness and the adhesives used, etc. If you have links to the products, feel free to add then to the thread. We will have a look at them to see how these things have been constructed. Some of us are/were flooring professionals which means we know WHERE to find these details. They are often hidden or require a very specific search term. Once we have links to the products, we can get cracking on finding out which one *might work better for your situation.

@Kristen Stewart - yes - my sister and I both purchase Woodland Reserve engineered wood floors from F&D (mine are European Oak - I think hers may be white oak ). The floors have held up wonderfully. Have had zero issues with them. She hasn’t has any issues either. Mine look exactly the same as when installed. The upkeep is easy - vacuum and sometimes use a slightly damp microfiber mop. These floors were a great purchase!

Here is a followup to my original posting. Installation of the plank flooring is rather easy but preparing the subfloor is anything but! We are very happy with the final results but getting there wasn’t easy. Some of the SUPERCore Xtreme, Cattanooga Hickory, has been down for more than a year. None of it shows any signs of wear, even when inspected carefully. We vacuum all of the floors in the house every week using 2 inexpensive eufy robo vacs and mop once a month. The color does not show the dirt easily. If you walk on it when it is wet after mopping, it often shows footprints when dry, during certain times of the day when the natural light is just right. I expect the floor to be looking good long after I’m gone. I think the SUPERCore Xtreme, Cattanooga Hickory, is an excellent product. It is really tough. It locks together easily if you follow the directions. Delivery was only one week late; very good considering the supply chain issues at that time. The planks had 5 distinct patterns. I was expecting 6. Bear in mind that the characteristic feature of a pattern, such as a unique knot, can appear on the left side or the right side of a plank and might appear at any location along the length of the plank. So there is a lot of variation among the planks. Before putting them down, I separated a few boxes into 5 different piles of planks, based on the pattern. I installed the flooring in our smallest bedroom first, by myself in November 2021. Waited for spring to resume work. I hired a helper in May 2022 for the remainder after a knee became very painful. My helper connected the planks together and marked the pieces to be cut. I selected the planks from the piles for him to put down and and made the cuts, so I could remain on my feet. I used an electrically powered table saw, jigsaw and a mitre saw to make the cuts. Discovered weeks later that I tore the lateral meniscus in my right knee, probably from getting up and down from the floor so much. Had surgery on the knee in November 2022. Not sure when I’ll start the last small bedroom. All rigid core plank flooring that locks together and floats on top of the sub floor requires a subfloor that is unusually flat. The floor does not have to be level. It does have to be flat. If the subfloor has significant peaks and valleys, (high spots and low spots) the relatively rigid planks will bridge over the low spots, leaving an air space between the top of the subfloor and the bottom of the plank. Stepping on a plank that is bridging over a low spot will cause a popping or snapping sound. You may find the popping and snapping sounds to be annoying. I have learned that most of these noises subside, almost completely, after several months. If the valley is too deep, your weight will stress the tongue and groove locking mechanism too much. Repeated stepping on such a spot will likely cause it to fail. Then the planks may move independently of one another and come apart. That would be a serious problem. Our one story home was built in 2000. It has a concrete subfloor. I have installed the SUPERCore Xtreme, Cattanooga Hickory in one small bedroom, a large bedroom/sitting room and a laundry room. In every room I had to flatten the subfloor before installing the plank flooring. I did the small bedroom first. After watching several Youtube videos, I decided to grind down the high spots instead of filling in the low spots. I bought all new gear to do the job, since I had 950 sq ft of flooring to install. That was a big mistake. Grinding down a concrete floor is an extremely slow, noisy, dirty, dusty, hazardous, and physically demanding job. Here is a photo of the floor in the small bedroom. In subsequent rooms I filled in the low spots with LevelQuik RS Self-Leveling Underlayment, made by Custom Building Products. Mixing and applying this product requires at least 2 people. It’s sold by The Home Depot and others. I did not cover the entire floor with the leveling compound. That would have required about 3 times as much leveling compound and would have raised those floors about ⅛ “ which I didn’t want to do. (Self-Leveling is a misnomer. The stuff is the consistency of thin pancake batter and requires some assistance and tooling to make a smooth flat surface. For the purpose of creating a flat subfloor for plank flooring in a home, I suggest that you add about 10% more water than the directions indicate. Doing so will make it flow better without adversely affecting its performance when cured.) Prior to applying the leveling compound, I applied Multi-Surface Bonding Primer (MBP) to the concrete floor to ensure a tight bond between the original concrete and the leveling compound. (MBP is also made by Custom Building Products.) If you use the MBP you can feather the leveling compound to zero, and don’t have to maintain a minimum thickness of ⅛” over the entire floor. Here are some photos of the floor in the large bedroom completed in June 2022. Finding the borders of the high and low spots is tedious. Next time I will probably pour water in the previously identified low spots of the floor. Then I’ll mark the boundaries of the “puddles” with a large permanent black felt tip maker. Then vac up the water, let dry, apply MBP, and finally the leveling compound. The floor in the laundry room between the garage and the kitchen gets a lot of abuse. It was installed in September 2022. As you can see, the color of the flooring is highly dependent upon the light. That's why it's important to look at samples in your home. Paige; The Flooret Modin Base Soho sample that I tested was more abrasive compared to the SUPERCore Xtreme, Cattanooga Hickory sample. I hope this update is useful for some of you who are considering rigid core vinyl plank flooring.