How to Lay a Plywood Subfloor Part 1

The floor of any building or structure is its base and one of the most important parts, so when preparing to lay a plywood subfloor there are several things to keep in mind. The subfloor exists for two reasons, to add stability to the floor system and to serve as a base for the finished floor. A level and sturdy subfloor will also help to prevent the finished floor from moving or creaking.

NOTE: This is Part 1 of a 2 part series. To move ahead to Part 2, click here.

The Wood

The first thing to consider is what type of wood to use for the subfloor. Although OSB (orient strand board) is sometimes used, the most commonly used type of wood is C-D grade tongue and groove plywood. The C represents the grade of veneer on the front of the board and the D represents the grade of veneer on the back of the board. C-D plywood is made from thin sheets of veneer that are laminated and then glued together forming a 4 foot by 8 foot sheet of plywood. Plywood comes with two edge options, the square edge and the tongue and groove edge. The tongue and groove edge is more commonly used because the square edged plywood requires underlayment and blocking between the joists. Most types of flooring including wood, floating wood, laminate and carpet can be installed directly over C-D plywood. The 4 foot by 8 foot sheets of plywood are easy to install and cover a large area.

When preparing to purchase the plywood of your choice, you will need to estimate how much wood to purchase. When measuring the area, you should measure all the way to the wall plates in the room.

Preparation and Tips

Plan how you will lay the plywood before beginning the project. When laying a subfloor, the best place to begin is the largest area you can cover before you are required to make a cut in plywood. Typically, most flooring projects will begin toward the rear of the building, house or room. The first piece of plywood you lay needs to have at least two sides of the wood backed against a wall.

After you have decided where to begin, it is best to give yourself a diagram to follow. Using a white piece of chalk to draw an edge line can be helpful, as this line will ensure the plywood remains straight and has not veered into one direction at an angle. In addition, you should sweep and clean the base floor to remove and dust or dirt before laying the subfloor.

When laying cut pieces of plywood it is best to place the cut sides against the wall where possible. When backing the cut side against a wall is not an option, place the cut sides against an uncut side of another piece of plywood.

When laying a plywood subfloor you are raising the height of the original floor. Just keep in mind that the subfloor could cause some doors not to open or close. The doors may need adjustment to accommodate the change to the floor height.