Engineered wood flooring consists of two or more layers of wood adhered together to form a plank. Typically, engineered wood flooring uses a thin layer (lamella) of a more expensive wood bonded to a core constructed from cheaper wood. The increased stability of engineered wood is achieved by running each layer at a 90° angle to the layer above. This stability makes it a universal product that can be installed over all types of subfloors above, below or on grade. Engineered wood is the most common type of wood flooring in Europe and has been growing in popularity in North America[4]. Denver Hardwood Flooring
"Click" or Woodloc systems: there are a number of patented "click" systems that now exist. These click systems are either "unilin" or "fiboloc" A "click" floor is similar to tongue-and-groove, but instead of fitting directly into the groove, the board must be angled or "tapped" in to make the curved or barbed tongue fit into the modified groove. No adhesive is used when installing a "click" floor, making board replacement easier. This system not only exists for engineered wood floors but also engineered bamboo and a small number of solid floors (such as "parador solido click") and is designed to be used for floating installations. It is beneficial for the Do-It-Yourself market. Hardwood Floor

Generally, hardwood floors need to be buffed every 3–5 years. The process usually takes about one day. Buffing refers to the process of using a stand up floor buffer. The floor is abraded with 180 grit screen on the buffer. This allows for the new coat of finish to mechanically adhere to the floor. This process works with great results as long as the floor hasn't had any waxes or synthetic cleaners. Denver Hardwood Floor
Tongue-and-groove: One side and one end of the plank have a groove, the other side and end have a tongue (protruding wood along an edge's center). The tongue and groove fit snugly together, thus joining or aligning the planks, and are not visible once joined. Tongue-and-groove flooring can be installed by glue-down (both engineered and solid), floating (mostly engineered only), or nail-down (not recommended for most engineered). Denver Hardwood Flooring
It is difficult to compare solid wood flooring to engineered wood flooring due to the wide range of quality in both product categories, particularly engineered. Solid wood has some limitations. Recommended maximum widths and lengths are typically 5" / 127mm wide and 7' / 2100mm long. Solid hardwood is also more prone to "gapping" (excessive space between planks), "crowning" (convex curving upwards when humidity increases) and "cupping" (a concave or "dished" appearance of the plank, with the height of the plank along its longer edges being higher than the centre) with increased plank size. Solid wood cannot be used with underfloor radiant heating.[5] However extra care is necessary with the planning and installation of the heating system and the wood flooring, such as limiting the temperature to 85 °F (29 °C), avoid sharp temperature fluctuations, utilizing an outdoor thermostat to anticipate heating demands, and monitoring the moisture content for the subfloor before installation. Hardwood Floor