Once the joists and HVAC ducts were installed, I was ready to install the subfloor. The subfloor is the smooth layer that goes under the actual flooring. In my case, I am using tile (thanks to a house full of elderly dogs with elderly bladders). With tile, the subfloor needs to be flat and smooth. Today’s post explains how to install subfloor for a tile floor. The full vision for my project is here.
Rating (decode with the handy-dandy guide here):
- Time
- Money
- Tools
- Experience
- Strength
- Risk
- Suckage
Tools:
- Measuring Tape
- Circular Saw
- Impact Driver/Cordless Drill/Corded Drill (in preferred order)
- Chalk Line (or a very long straight edge and a pencil)
- Caulk Gun
- Hammer/Mallet
- Level (the bigger the better)
- Scrap 2×4 (~8″-2′ long)
- Safety glasses/Ear Plugs/Gloves/Knee Pads/
Supplies:
- Subfloor
- More subfloor adhesive than you think you could possibly use
- Deck screws
Step 1: Plan Your Room
The first thing I did was measure the room and determine how many sheets of subfloor I needed. It’s easy to fall into the trap of taking the square footage and dividing by 32′ (a standard sheet of plywood is 4′ x 8′). However, this doesn’t account for any weird cuts you’ll have to do, and doesn’t always let you line your seams up the way you need to.
The first thing you need to understand in order to plan your room is how the boards are built. You’ll install tongue and groove plywood or OSB for your subfloor. The tongue and grooves are on the long side only. Therefore, you want all of your short side seems to line up with a joist so they have something to rest on instead of being cantilevered off. Here is an example of how I did it. See how the seam lines up on one of my joists?
Another rule of laying subfloor is staggering your corners. You don’t want to lay it out in a grid, because this makes all your corners line up in one place, creating a weak spot. I stagger by half a sheet when I can, but sometimes that’s not possible. I try to make it so my seams are at least 2 joists away.
Step 2: Dry Fit the First Row
Once you open your subfloor adhesive you’re on limited time to get the floor down. This makes it very important to dry fit each sheet before applying the glue.
Start by using your chalk line to mark 4′ rows perpendicular to the joists. This is the width of the sheet lumber and gives you a guide when you’re applying the adhesive. Next, lay your sheet lumber and line it up with this mark. You’ll want the edge to be over half of the joist (like the diagram above). You’ll want to go start to finish with each sheet before moving on to the next one (you’d be surprised how long it takes to drive screws across an entire sheet of plywood).
Lastly, you’ll want to be prepared before you open your adhesive. Have your drivers charged and ready to (I like my impact driver myself). Get your screws ready too, and your tool belt loaded if you’re choosing to use one.
Step 3: Apply the Glue
Stand up the first sheet of subfloor along the long edge so that it just flips down close to where it needs to be. You have a little wiggle room, but don’t want to have to slide the subfloor anymore than an inch or so in any direction once the adhesive is applied.
Now that you’re confident in the placement of your subfloor, load your caulk gun. I attempted to use the 1 quart size of subfloor adhesive, but my hands are too weak to use that. I switched to the typical size caulk gun instead for the rest of the subfloor. Run a good size bead across all of the joists that will be in contact with the first sheet of subfloor. Your chalk line will help you know where to run adhesive. Remember on the end joists that you need to put the adhesive towards the side the sheet will sit on. For single 2x joists you can run a single bead, but for doubled up joists you’ll want to put it on in a squiggle so the whole face ends up covered.
Step 4: Screw Down the Floor
Once your joists are glued, flip the sheet of subfloor down and begin screwing. The corner can have a screw 3/4″ away, and then screw every 4-8″ down the joist. Repeat for every joist until the sheet is fully secured.
Step 5: Repeat Down First Row
Repeat steps 3 and 4 until the first row is complete.
Step 6: Install the Next Row
Now the installation gets a bit trickier. Now that your first row is installed, you’ll need to install the tongue (or groove depending on how you oriented your floor) into the groove of your first row. However, don’t get crazy with a hammer. You NEED to use a wood block to distribute the force through the edge so you don’t bang up your tongue and groove. You’ll glue in the same manner as the first row, except before you screw down you need to get the tongue and groove seated.
Once you flip your plywood down (so tongue and groove are lined up), work your way along the outside long edge. Use a wood block (scrap 2×4) and lay it against your edge. Hit your hammer against this block, not the side of the wood. Work your way back and forth across the long edge until the tongue and groove are seated. This is the part of the project that raised the suckage level to by the way. If I were to do it again, I’d make ti so I was hammering the groove edge, instead of the tongue edge.
Once the tongue and groove are sufficiently seated (doesn’t need to be perfectly flush, but should be within 1/4″), screw down the subfloor along each joist (just like step 4!)
Repeat step 6 until all your floor is installed. Use your level as you go to check for any abnormalities.
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