An underlayment is recommended for hardwood floors to help prevent moisture from seeping up under the floor. Some underlayments also provide a cushion for the floor.
An underlayment is a thin barrier between the hardwood floor and the subfloor, and they can range in composition from thin black felt paper to cork. It is a good idea to use underlayments for hardwood floors regardless of whether they are nailed down, stapled or a floating installation. Nailed and stapled floors usually get a thin underlayment, such as felt paper, while thicker underlayments, like cork and foam pads, are more useful for floating hardwood floor installations.
Padded underlayments cushion floating floors and help even out any minor imperfections or warping in the floorboards. These underlayments may also come with a waterproof backing to keep moisture from seeping up into the floating floorboards. When using an underlayment that doesn't have waterproof backing, a second protective layer of plastic sheeting is required before installing the underlayment and flooring.
Manufacturers usually produce an underlayment to use with their brand of hardwood flooring. This makes it easy to find the best type of material to use with the flooring. These materials are sold in rolls a few feet wide and up to dozens of feet long.