When going over 4" wide (or even over 3" if you're conservative), it is best to blind nail and glue to prevent later squeaks or pops. There is not enough holding strength across the whole width of the board with blind nailing alone to have a perfectly noise free floor over time. It can be mostly noise free, but not perfect due to wood changing with humidity. When using nails and glue, you will need to have a subfloor that is flat without above-panel correction so that the glue can attach. This is not as common as you might think due to the popularity of carpets over the last 40 years which allows for sloppy floor construction standards. It might be possible to use a poured floor leveling compound that is properly dried and then just glue the hardwood to the flat subfloor. This is not so commonly done due to the large cost and effort involved and having to use many clamps to keep the boards together while the glue sets. If going this route, engineered hardwood flooring would probably be better than solid due to greater uniformity and stability.

417.5 Shower floors or receptors. Floor surfaces shall be constructed of impervious, noncorrosive, nonabsorbent and waterproof materials. 417.5.1 Support. Floors or receptors under shower compartments shall be laid on, and supported by, a smooth and structurally sound base. 417.5.2 Shower lining. Floors under shower compartments, except where prefabricated receptors have been provided, shall be lined and made water tight utilizing material complying with Sections 417.5.2.1 through 417.5.2.4. Such liners shall turn up on all sides at least 2 inches (51 mm) above the finished threshold level. Liners shall be recessed and fastened to an approved backing so as not to occupy the space required for wall covering, and shall not be nailed or perforated at any point less than 1 inch (25 mm) above the finished threshold. Liners shall be pitched one-fourth unit vertical in 12 units horizontal (2-percent slope) and shall be sloped toward the fixture drains and be securely fastened to the waste outlet at the seepage entrance, making a water-tight joint between the liner and the outlet. 417.5.2.1 PVC sheets. Plasticized polyvinyl chloride (PVC) sheets shall be a minimum of 0.040 inch (1.02 mm) thick, and shall meet the requirements of ASTM D 4551. Sheets shall be joined by solvent welding in accordance with the manufacturer’s installation instructions. 417.5.2.2 Chlorinated polyethylene (CPE) sheets. Nonplasticized chlorinated polyethylene sheet shall be a minimum 0.040 inch (1.02 mm) thick, and shall meet the requirements of ASTM D 4068. The liner shall be joined in accordance with the manufacturer’s installation instructions. 417.5.2.3 Sheet lead. Sheet lead shall not weigh less than 4 pounds per square foot (19.5 kg/m2) coated with an asphalt paint or other approved coating. The lead sheet shall be insulated from conducting substances other than the connecting drain by 15-pound (6.80 kg) asphalt felt or its equivalent. Sheet lead shall be joined by burning. 417.5.2.4 Sheet copper. Sheet copper shall conform to ASTM B 152 and shall not weigh less than 12 ounces per square foot (3.7 kg/m2). The copper sheet shall be insulated from conducting substances other than the connecting drain by 15-pound (6.80 kg) asphalt felt or its equivalent. Sheet copper shall be joined by brazing or soldering. SECTION P2709 SHOWER RECEPTORS P2709.1 Construction. Where a shower receptor has a finished curb threshold, it shall be not less than 1 inch (25 mm) below the sides and back of the receptor. The curb shall be not less than 2 inches (51 mm) and not more than 9 inches (229 mm) deep when measured from the top of the curb to the top of the drain. The finished floor shall slope uniformly toward the drain not less than 1/4 unit vertical in 12 units horizontal (2-percent slope) nor more than 1/2 unit vertical per 12 units horizontal (4-percent slope) and floor drains shall be flanged to provide a water-tight joint in the floor. P2709.2 Lining required. The adjoining walls and floor framing enclosing on-site built-up shower receptors shall be lined with one of the following materials: Sheet lead; Sheet copper; Plastic liner material that complies with ASTM D 4068 or ASTM D 4551; Hot mopping in accordance with Section P2709.2.3; or Sheet-applied load-bearing, bonded waterproof membranes that comply with ANSI A118.10. The lining material shall extend not less than 2 inches (51 mm) beyond or around the rough jambs and not less than 2 inches (51 mm) above finished thresholds. Sheet-applied load bearing, bonded waterproof membranes shall be applied in accordance with the manufacturer’s instructions. P2709.2.1 PVC sheets. Plasticized polyvinyl chloride (PVC) sheet shall meet the requirements of ASTM D 4551. Sheets shall be joined by solvent welding in accordance with the manufacturer’s instructions. P2709.2.2 Chlorinated polyethylene (CPE) sheets. Nonplasticized chlorinated polyethylene sheet shall meet the requirements of ASTM D 4068. The liner shall be joined in accordance with the manufacturer’s instructions. P2709.2.3 Hot-mopping. Shower receptors lined by hot mopping shall be built-up with not less than three layers of standard grade Type 15 asphalt-impregnated roofing felt. The bottom layer shall be fitted to the formed subbase and each succeeding layer thoroughly hot-mopped to that below. All corners shall be carefully fitted and shall be made strong and water tight by folding or lapping, and each corner shall be reinforced with suitable webbing hot-mopped in place. All folds, laps and reinforcing webbing shall extend not less than 4 inches (102 mm) in all directions from the corner and all webbing shall be of approved type and mesh, producing a tensile strength of not less than 50 pounds per inch (893 kg/m) in either direction. P2709.2.4 Liquid-type, trowel-applied, load-bearing, bonded waterproof materials. Liquid-type, trowel-applied, load-bearing, bonded waterproof materials shall meet the requirements of ANSI A118.10 and shall be applied in accordance with the manufacturer’s instructions. P2709.3 Installation. Lining materials shall be sloped one-fourth unit vertical in 12 units horizontal (2-percent slope) to weep holes in the subdrain by means of a smooth, solidly formed subbase, shall be properly recessed and fastened to approved backing so as not to occupy the space required for the wall covering, and shall not be nailed or perforated at any point less than 1 inch (25.4 mm) above the finished threshold. P2709.3.1 Materials. Lead and copper linings shall be insulated from conducting substances other than the connecting drain by 15-pound (6.80 kg) asphalt felt or its equivalent. Sheet lead liners shall weigh not less than 4 pounds per square foot (19.5 kg/m2). Sheet copper liners shall weigh not less than 12 ounces per square foot (3.7 kg/m2). Joints in lead and copper pans or liners shall be burned or silver brazed, respectively. Joints in plastic liner materials shall be jointed per the manufacturer’s instructions. P2709.4 Receptor drains. An approved flanged drain shall be installed with shower subpans or linings. The flange shall be placed flush with the subbase and be equipped with a clamping ring or other device to make a water-tight connection between the lining and the drain. The flange shall have weep holes into the drain.

OK...let me get this straight. You have a plywood subfloor. That means there should be no NEED for a vapour barrier. The vapour barrier will be BELOW the plywood (somewhere in the basement or somewhere in the crawl space). If there isn't one, then there can be issues. If you are over a crawl space, you can do yourself a favour by looking to see what type of barrier is there. Vapour barriers are not allowed to be used over top of plywood sheathing. It creates more problems than it solves. The best you can hope for is a moisture retardant membrane (allows some moisture to move through slowly). With hickory - which is a hardwood that likes to move...A LOT - in a 4" wide plank, you would do VERY WELL with a glue-assist method. Technically a "wide plank" is anything 5" or WIDER. But hickory is such a dynamic wood that it can be ranked as "wide plank" in the 4" width. This is the fun of working with hickory. It takes MORE EFFORT to keep it happy. And happy starts when it is acclimating. And keeping it happy once it is installed means keeping the humidity in a tight range. You do not want SWINGS. You want to stick to a 10% range (ie. 35% - 45%; or 45% - 55%) throughout the lifetime of this floor. Hickory is beautiful. It is a diva. And like all Divas it takes a bit more care and attention to details.

You will need to deal directly with Home Depot for any/all of your warranty needs. The subcontractors used by HD will try their best to wiggle out of this. It is between you and HD. The FULL contract is with HD. That means HD (and anyone they subcontract the work to) are fully responsible for this job. The home's internal living conditions are your responsibility. That's why we are encouraging you to find out what your home's humidity levels are. That means you will need a hygrometer (can purchase one through Home Depot for about $30). When you drop in to speak with the flooring department at HD, feel free to purchase a hygrometer on your way out. If you have multiple floors, you can purchase one for EACH LEVEL of your home. Once you have your handy-dandy-trusty-dust hygrometers in hand, you can place them around the house. You can then start your readings the next day (let the meters settle in...just like wood). You will document date/time of day/weather/location for each hygrometer. You can do this twice a day for a few weeks. Once you have created your OWN data sheet, you can use this to PROVE your home has adequate humidity. The humidity inside a home can be VERY different from outside humidity. Especially in the winter months. Winter is the DRYING time (home heating systems dry out the air = low/very low humidity levels). You will have to prove that your home's humidity is NOT the reason for the issues described in your photo.