The secret behind perfect-looking floors is a properly laid subfloor. Most professionals use either OSB or plywood for this. It isn’t an overly complicated project, but it does require some foresight. Using the wrong materials can lead to a floor that sags in between joists and an unhappy building inspector, so it’s extremely important to think this project through before diving in.
What You Need To Know About Laying A Plywood Subfloor
Before making a trip to your local lumber yard or hardware store, you will want to take a few things into consideration in order to save time and money. Skimping here can lead to an uneven floor and having to redo the subfloor. Don’t forget the golden rule of construction, measure twice, cut once.
Flooring Material & Floor Joist Spacing
Although this is a fairly simple project that most laymen can tackle on their own, there isn’t a one size fits all blueprint for materials when laying a plywood subfloor. You must consider the space in between your floor joists and what type of flooring you plan to install on top of the plywood.
Most floor joists span 16 inches from center to center, but not always. A larger span will require a thicker grade of plywood. Furthermore, you can get away with a thinner subfloor if you are going to lay linoleum or carpet on top instead of hardwood or stone.
Fasteners
Both nails and screws will work here. If you want to nail your floors, be sure to use ring-shank nails. They will hold better than a smooth shank nail which will work itself loose in high-traffic areas, causing creaks or dips in the flooring.
Using galvanized screws is another great way to secure your subfloor. Galvanized screws can withstand water corrosion better than a basic steel screw, so they are the way to go, especially for exterior projects that need to stand up to the elements. Not to mention, screws are more forgiving for beginner DIY enthusiasts because they are easier to remove than ring shank nails if you make a mistake.
Local Building Codes
Building codes differ from county to county, and in order to pass inspection, you have to abide by these codes. They may seem like an unnecessary pain in the back, but they ensure the safety and quality of your project. Always check with your local inspection department so that you don’t get stuck with a bunch of material you can’t use. A quick phone call can save you money and a splitting headache in the long run.
Supplies You’ll Need For Laying A Plywood Subfloor
- Tape measure
- Safety glasses
- Plywood (thickness depends on joist spacing and code)
- Framing nailer/hammer (if nailing plywood)
- Ring shank nails (2”-3.5”)
- Air compressor
- Impact driver/screw gun (if screwing plywood)
- Steel/galvanized screws (1.5”-3”)
- Chalk line/reel
- Circular saw
- Construction adhesive/glue
How To Lay A Plywood Subfloor? (5 Steps)
Step 1: Prepare And Measure Workspace
Before you spend your hard-earned cash on materials, take some quick measurements to save yourself from taking multiple trips to the hardware store.
If you are tearing up an old subfloor, it’s a good idea to check the integrity of your old floor joists before getting the rest of your supplies. Make sure they don’t show any signs of sagging or water damage. If they do, you will want to replace them to avoid any bumps or dips in your flooring.
Measure the dimensions of your room so you know how many sheets of plywood to buy. The most common size is 4’X8’ sheets, but some general contractors will use 5’X5’ sheets depending on the spacing between floor joists.
Depending on what type of flooring you plan to install and the local building codes, you will need a minimum thickness of plywood. Most flooring and codes will call for ½”-¾” thick plywood. If this is an exterior project that may get rained on, consider using marine-grade plywood to help prevent warping.
The thickness of your plywood will also determine the length of your fasteners. At a bare minimum, you will want your nail or screw to be 1” longer than the thickness of the plywood. In my opinion, it’s always better to be safe than sorry, so I always use 2.5”-3” fasteners for maximum bite.
Finally, make sure your room is square and level, especially if someone else built it. If I had a nickel for every time I encountered a room that was out of square, I’d be rich. If it isn’t, then you will need to plan ahead so that you can rip down a sheet of plywood to fill in the gaps or adjust the position of your sheets to fit.
Step 2: Mark Your Layout
It can be helpful to make marks on your walls or studs to show where your floor joists are. Once, you lay your plywood, you won’t be able to see them anymore! You can also snap a chalk line as you finish each row of plywood to make their location more visible.
Measure the size of your plywood and snap a corresponding chalk line across the floor joists to ensure that you lay each row straight. This is much easier than ripping small sections or having to pull up your plywood and redo the entire process.
Step 3: Dry Run Your First Sheet Of Plywood
The grain of the plywood should run perpendicular to the direction of your floor joists. In other words, if you are using 4’X8’ sheets, they should run longways across each joist. This maximizes the points of contact where you will fasten the subfloor to the joists.
Depending on the size of your room, you will either run a full sheet or cut it down with a circular saw so that the end of the sheet lays over half of the width of the floor joist. This way, you can securely fasten this sheet and the next sheet in the row to the same joist.
Before applying construction adhesive and nailing/screwing your plywood down, make sure it lines up with your chalk line and breaks in the middle of a joist. If everything looks good, run a bead of adhesive along the floor joist, lay the plywood, and nail/screw it down.
Step 4: Check Your Work As You Go
Continue this process and keep an eye on your chalk line to make sure you are on track. All wood products will expand and contract depending on temperature and moisture, so you will want to leave 1/16”-⅛” of space between sheets to prevent bowing or buckling.
You should put a nail/screw in every 6”-”8” along the edges of each sheet and around every 12” in the middle. Fasteners are much cheaper than tearing up the flooring to fix bumps in the subfloor, so don’t skimp.
Adhesives and glues aren’t usually necessary when it comes to building codes, but they help prevent any creaking that might occur over time. It’s better to take a few extra seconds to apply it than deal with a noisy floor down the road.
The seams of your plywood should line up row to row. You want to stagger these ends as you go to ensure structural integrity and a smooth finished product. If you started your first row with a full 4’X8’ sheet, then make sure your next row doesn’t start with another full sheet. To save material, you can use the remaining sheet from the last piece of plywood that you cut on your first row. If it doesn’t break evenly on a joist, cut it so that it does.
Step 5: Inspect Your Finished Plywood Subfloor
Once you are done laying plywood, make sure that every sheet is securely fastened and they are free from bumps. If you encounter an uneven spot in a sheet that you can’t nail or screw, then feel free to sand it down.
If you feel any movement or hear any creaking in the plywood, add more fasteners to help secure it to the floor joists. Voila! Give yourself a pat on the back and enjoy your beautiful new plywood subfloor!
Final Thoughts On Laying A Plywood Subfloor
Laying a plywood subfloor doesn’t have to be time-consuming or stressful as long as you take the time to plan your project and purchase the correct materials. If you do these and check your work as you go, you will be ready to lay your new flooring in no time!
