This article is a DIY guide for the homeowner that covers finding, removing, and replacing damaged plywood subflooring. It also contains a tool and material list.
Repairing Your Plywood Subfloor
If your home has a basement or is built off the ground with post-and-pier supports, you probably have some plywood subflooring. 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? Why not repair your plywood subflooring yourself?
In most cases the whole subfloor doesn't need repair, only limited areas. To determine this you will have to remove your current finish floor, whether it's sheet vinyl, carpet, or something else. It's a great time for remodeling anyhow.
But prior to doing anything, give your homeowner insurance agent a call to review your situation and file an insurance claim. If you're covered and you do the repair yourself, you'll save all the labor costs that will they will pay you for.
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.
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. When you've found the bad spots that need repair, strike chalk lines so you'll know where to cut.
Keep two things in mind: the spots marked off must be square. Use the 3-4-5 rule to ensure this. Secondly, any cut you make parallel to a floor joist must be down the nearest joist's 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 plumbing. Set your blade cutting depth just one 1/4” deeper than the damaged plywood subfloor.
When you close in on a wall you'll find that the bottom plate of your circular saw will prevent you from reaching the wall. It's time to use your hammer and chisel.
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 you'll need to buy. Plywood is sold in 4' X 8' sheets so you'll 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. In the old days, subfloors were were nailed down but nails work loose.
Today, responsible building contractors apply construction adhesive to the floor joists before screwing.
When you're done, putty the gaps.
You might need to scrape or sand your old subfloor. Now it’s time to install the new finish floor... but that's another project!
The copyright of the article Repairing Your Plywood Subfloor in Home Flooring is owned by Kelly Smith. Permission to republish Repairing Your Plywood Subfloor in print or online must be granted by the author in writing.
You should use decking screws to fasten the subfloor, not drywall screws.
Drywall screws tend to break and the plywood will loosen over time.
Dec 6, 2008 4:38 PM
Guest :
I would encourage the use of construction adhesive under the plywood to
eliminate squeaks. I would also encourage this time to consider adding
bracework between the floor joists if not already there
Dec 29, 2008 1:07 PM
Guest :
In a number of your articles you mention the 3-4-5 rule. Could you explain
that or refer me to another article. Thanks
Dec 30, 2008 9:52 AM
Kelly Smith :
Thanks for the suggestion. I just posted an article explaining the 3-4-5
rule and linked to it!
Feb 2, 2009 12:06 PM
Guest :
My rotten subfloor is built over dirt. When I fix the flooring, I would
like to put material between the dirt and wood to protect it... what should
I use?
Feb 24, 2009 12:16 PM
Guest :
I need to cut a hole in my floor to reach my basement drain. The plywood
is sitting on 2x3's I believe. anyway, when using a circular saw, do you
need to somehow make an opening before using the saw or do you just start
it up and cut your hole? Thanks
Jul 1, 2009 4:13 PM
Guest :
I have a strange situation. I have two layers of plywood for my floor
separated by black plastic (looks like black trash bags). Previous
homeowners put in carpet in the bathroom (underneath the toilet). Wax seal
broke. Leakage. Septic tank backed up and totally saturated the upper layer
of plywood. The vanity is built in over the plywood and can't be moved. One
and a half of the top layer of plywood sheets are damaged. It's so bad I
can't really tell what the thickness of the plywood is. Some of it I was
able to get out, and other parts I can't seem to removed (I'm trying not to
damage the plastic and lower layer). I need to replace the damaged parts
and then put down linoleum. I'll have to do it by myself and I am not very
coordinated or strong (My father was going to help but he passed away
suddenly), but I am the only one in the house who is halfway decent at
carpentry. I can't afford to hire a professional for the job, and if
I could afford it, there aren't any that would be willing to come out to my
area as it is remote. Once I replace the damaged top layer, should I
spray the wood with anything to prevent moisture damage? Should I put
something underneath the linoleum as an additional moisture barrier? Any suggestions?
To the person who wants to cut a hole to
reach the basement drain- I would drill a few holes just in case to get a
look at how thick the wood is and make sure you aren't going to hit
anything else when you cut, but that's just me.
Jul 2, 2009 7:21 AM
Kelly Smith :
If it was me, I would remove all the subfloor and start from scratch. That
part about the vanity would worry me too. Chances are that water leeched
under it. Eventually that will end up with mildew and rot, both of which
are big problems.
Jul 3, 2009 12:41 AM
Guest :
Thank you. I'm still trying to figure out how to remove the top layer
without ripping the plastic or damaging the floor underneath. I've been
keeping a dehumidifier in the room to keep the floor dry. When I initially
had to clean up the raw sewage that filled the room I got very sick,
despite using a mask. I still wear a mask, gloves, and eye protection
whenever I go in there to try to figure out how to get the damaged part
out. I'm thinking of spraying the new subfloor with Killz once I get it put
in. The floor underneath the plastic feels sturdy. The spot that my
father patched in the other bathroom (that did not have plastic between
layers) will have to be fixed after that. My father tried to patch it but
there are gaps and the wood putty fell out leaving a hole which lets air
from under the house come in. Not really his fault as he was suffering from
nerve degeneration and it was a quick fix to be able to put the toilet back
in (the toilet fell through the floor with my brother on it). If I could
say something to the builders of this house I would ask why the hell they
put carpet in the bathrooms...
Aug 9, 2009 9:35 PM
Guest :
I am going to replace a bathroom subfloor. I know that there is water
damage around the bathtub and toilet. Will there be a sub floor under the
tub? If so do I need to replace it if the damage is not too bad? [I don't
relish the idea of moving a cast iron tub.]
I know there is
also damage to the walls but I am comfortable removing ceramic wall tiles,
old drywall and replacing that with greenboard or a better material and
retiling. If I find damage to the joists I will call a pro.
Aug 10, 2009 6:18 AM
Kelly Smith :
What's under your tub probably depends on your home's age and your local
building code. It's one of those situations where you don't know until you
look.
For the walls, I'd go with Hardi backerboard or something
similar. Greenboard is falling out of favor in most places.
Aug 28, 2009 7:50 PM
Guest :
We purchased a home that has a two story addition. (main living level and
basement level.) Unfortunately, they built the upper room on the main level
two inches lower than the rest of the main level, so when you walk from the
dining room into the addition, you have a half step, or a tongue biter...
We are raising the floor on the main level and part of this involves adding
joists so we have to take the subfloor up. Most of the plywood subfloor
comes up easily, but my husband says that we have to cut the subfloor next
to the walls because the plywood subfloor is wedged under the framing. He
is using a 1 and a half inch blade on a dremel tool to cut the plywood
along the wall. This takes forever and is noisy. There has got to be a
better way or better tool! Do you know what it is?
Aug 28, 2009 7:51 PM
Guest :
We purchased a home that has a two story addition. (main living level and
basement level.) Unfortunately, they built the upper room on the main level
two inches lower than the rest of the main level, so when you walk from the
dining room into the addition, you have a half step, or a tongue biter...
We are raising the floor on the main level and part of this involves adding
joists so we have to take the subfloor up. Most of the plywood subfloor
comes up easily, but my husband says that we have to cut the subfloor next
to the walls because the plywood subfloor is wedged under the framing. He
is using a 1 and a half inch blade on a dremel tool to cut the plywood
along the wall. This takes forever and is noisy. There has got to be a
better way or better tool! Do you know what it is?
Aug 30, 2009 5:29 AM
Kelly Smith :
I would try using a sawzall. The blade is long enough that you might be
able to cut very close at an angle.
Jul 22, 2007
