Installing Hardwood Floors Over Different Subfloors
Plywood and OSB come in 4’ x 8’ sheets that are either 5/8” or ¾” thick. Plywood should be fastened with 2-1/2” long deck screws every 8 inches along the floor joists below. To prevent squeaks and noise later on, apply adhesive caulking on top of the floor joists before laying the plywood sheet.
¾” Thick Solid Wood floors can be installed directly over 5/8” or ¾” plywood subfloors. As well, engineered hardwood and laminate floors can also be installed over 5/8” or ¾” plywood.
Laying the boards along the long length of the room will make the room appear larger.
If the subfloor is old or weak and flexes when walked on, it is recommended to add an additional layer of plywood 3/8” or ½” thick using glue adhesives and screwed down to add dimensional stability over the weak subfloor – this adage applies to all hardwood and laminate floorings whether the installation method is glue down, nail down or floating floor system.
Laminate flooring can only be installed using the floating method over plywood subfloor with a recommended underlayment pad between the laminate flooring and the subfloor.
If the subfloor is old or weak and flexes when walked on, it is recommended to add an additional layer of plywood 3/8” or ½” thick using glue adhesives and screwed down to add dimensional stability over the weak subfloor. As well, humidity levels fluctuate constantly and ground water table (The level below which the ground is completely saturated with water) so depending where you live, it is recommended to lay 15lb. felt underlayment paper over the subfloor to contain the moisture transfer which may rise up from damp crawlspace and basements and possibly affect the dimensional stability of the floor system.
Plank subfloors are usually found in older homes and the nails on the plank boards will loosen from the boards expanding and contracting over time. Using 2-1/2” deck screws re-secure the planks to the floor joists below, as loose or damaged boards will affect the dimensional stability of the finished floor.
3/4" Thick Solid Wood Flooring must be installed perpendicular to the plank subfloor boards (at a 90 degree angle). Otherwise, if it is installed parallel to the direction of the plank subfloor, the newly installed hardwood flooring could gap and pull apart if the plank subfloor expands or contracts. If you want the floors to run parallel to the subfloor, make sure to add an additional layer 3/8” or ½” thick plywood underlayment over the plank subfloor.
Less than 1/2" thick Engineered, Solid Wood or Floating can be installed over a wood plank subfloor as long as the 3/4" plank subfloor is flat. The hardwood flooring must be installed perpendicular to the subfloor boards (90 degree angle). If the subfloor shows any deflection when walked on, it is recommended to add an additional layer of 3/8” or ½” plywood underlayment over the plank subfloor. The added dimensional stability allows you to run your new wood flooring in any direction desired.
9/16" (0.5625”) or thicker Floating Engineered Wood Floors can be installed on plank subfloor. The hardwood flooring must be installed parallel to the subfloor boards (at a 90 degree angle). If there is any deflection in the wood plank subfloor when walked on it is recommended to add an additional layer of 3/8" or 1/2" thick plywood underlayment over the plank subfloor to add dimensional stability to weak subfloors. The added dimensional stability allow you to run your new wood flooring in any direction desired.
Concrete slabs are usually 4-6” thick and the moisture content of concrete never dries out. It will “sweat” for the life of the slab, producing moisture vapors and depending on the time of the year, emit higher than normal (more than 4%) moisture vapors depending on the ground water table. Moisture testing must be performed. Tape 2’ x 3’ sheets of plastic over couple of areas of the slab. Wait 24-48 hrs and see if the plastic collected any moisture. Plastic 6 mil thick moisture barrier, moisture resistant adhesive glue, 15 lb. felt underlayment paper and plywood are some of the options used to correct the excessive moisture levels.
3/4" Thick Solid Wood Flooring first lay 6 mil plastic vapor barrier over the concrete slab. Then lay 2 layers of ½” thick plywood over the plastic vapor barrier. For glued down engineered wood, it is recommended to use an adhesive that is water resistant.
Floating Engineered Wood Floors were designed for installing over concrete and really work the best. These hardwood floors can simply be installed using their 1/8" thick padding directly on the concrete slab over a 4-6 mil plastic.
Laminate Flooring can simply be installed using their 1/8" thick padding directly on the concrete slab over a 4-6 mil plastic.
Concrete slabs need to be flat. Use a self-leveling cement type floor leveler to fill any depressions within the slab and allow to dry before installing any flooring.
Particle Board – Underlayment
Particle boards are unsuitable for nail down or glue down hardwood installations. They are brittle – nail fastened will loosen over time and cause movement and noise. For hardwood nail down or glue down, particle boards must be removed prior to installation.