If your home has a basement or is built off the ground with post-and-pier supports, you probably
have some plywood subflooring.
Moisture Leads to Plywood Subfloor Repairs
The usual culprit causing rotted plywood subflooring is water damage. Given that fact, you would
expect it in your kitchen or bathroom. Do you find yourself in this unlucky position? How about
repairing your plywood subflooring yourself?
Tool and Material List
Pry bar (for old tack strips if you have them)
Screws and/or nails
Plywood or OSB as needed
Should You Use Plywood or OSB?
The choice really boils down to personal preference; each material has its pros and cons. Both plywood and oriented strand board (OSB) are about equal in strength and durability. Building codes generally recognize both plywood and OSB to be alike in their properties and use the phrase "wood structural panel" to describe them. But, plywood subfloors are stiffer than OSB by about 10%.
Keep in mind that if you live in one of those currently-popular tiny houses, the building codes have been somewhat amended since they are not full-size structures. Before beginning any work, check your local codes and pull building permits as applicable prior to beginning any work.
Depending on the scope of your flooring project, OSB is cheaper than plywood by about $3 to $5 per panel. OSB is known to be less water-resistant; it swells in thickness when exposed to moisture. OSB has has more decay resistance than plywood.
OSB Subflooring with a Vapor Barrier.
Many contractors find OSB easier to work with on larger projects because usually the sheets have a grid pattern inked on them, almost eliminating the need for carrying around a T-square. But on simple repairs, who cares? Given all these factors, it really boils down to budget and environment.
Remove the Current Finish Floor
In most cases the whole subfloor doesnt need repair, only limited areas. To determine this
you will have to remove your current finish floor, whether its sheet vinyl, carpet, or something
else. Its a great time for remodeling anyhow.
If carpet is what you have and it still has some life left, you can undo it from the tack strip and
roll it up to reuse. If not, just get rid of it and the padding.
Important Step: Get Your Homeowners Insurance Agent Involved
Prior to doing anything further, give your
agent a call to review
your situation and file an insurance claim. If youre covered and you do the repair yourself,
youll save all the labor costs that will theyll pay you for.
Take Note of your Damage and Prep the Area
Now take a look at your plywood subfloor. Make a note of which areas need repair. Do a visual
inspection and poke it with something sharp to test for mushy spots.
Plywood is an
engineered wood product
that holds up well, but too much moisture will break it down.
Everytime you find a spot, mark it with spray paint. When you've found all the bad spots
that need repair, strike chalk lines so youll know where to cut.
The Good Old 3-4-5 Rule
Keep two things in mind: the spots marked off must be square. Use the
to ensure this.
Secondly, any cut you make parallel to a floor joist must be down the nearest joists center line.
Strike your chalk line centered on the existing nail heads.
Cut Out the Damaged Subfloor
Use an electrical circular saw to remove the damaged spots. Prior to cutting, look at the underside
of your subfloor if you can, from the basement, to prevent cutting through electrical wiring or
Set your blade cutting depth just one 1/8 inch deeper than the damaged plywood subfloor.
When you close in on a wall youll find that the bottom plate of your circular saw will prevent
you from reaching the wall. Its time to use your hammer and chisel.
As an alternative to hammer and chisel, an effective power tool is one of the new
oscillating tools like the Rockwell SoniCrafter, Dremel Multi-Max, or Fein MultiMaster.
Replace the Damaged Plywood
Now that the bad plywood is gone you can install the new. There are two things to consider:
the thickness of the existing plywood and the amount of new plywood youll need to buy. Plywood
is sold in 4 X 8 sheets so youll need to buy a little extra to account for scrap.
When you get the new plywood home the rest is easy: taking measurements, cutting the sheets,
and installing them. Drywall screws with coarse threads are good for this project.
But before you lay any plywood on the floor joists, lay down a bead of construction adhesive on the
joists. Use a green building product like Bostik Home Heavy Duty Construction Adhesive.
Its developed especially for subfloors, stair treads, and decks. Back in the day, the subfloor
was simply nailed down. But the nails would soon work loose and cause squeeks. When youre done,
putty the gaps.
In years past, plywood subfloors were nailed down. The problem is that after a few years, the nails
would work loose. What a pain to have to pull carpet or other finish floor to stop the squeeks! The thing
to do now is to apply glue and to use screws rather than nails.
You might need to scrape or sand your old subfloor. Now its time to install the new finish
floor and install baseboards... but thats another project!