Walnut hardwood flooring is offered in two different types: solid hardwood and engineered hardwood. The kind you should choose depends upon your personal preference and in which you intend to install the floor. If you plan to install the floors above grade or at grade, which in this instance is referring to the surface which will be below the ground, you could select either type. But if you plan to install below grade, like in a finished basement, you'll want to prevent solid hardwood and go for the engineered hardwood. This is because of the likelihood of moisture at a below-ground area, which can wreak havoc with strong hardwood flooring and its normal response of contraction and growth. Humidity can cause cracking and warping as a result. The building of engineered flooring can be extremely forgiving to fluctuations in humidity which frequently happen together with the change of seasons. Although it's ideal to keep a similar amount of humidity during your house year round fo...