TL;DR
The window between old carpet coming out and new carpet going in is the only time anyone sees the subfloor, and it is worth using properly. The essential work is removing every staple and debris, checking moisture, dealing with any odor at its source, fixing squeaks, and confirming the deck is sound. Almost all of it is faster and cheaper now than later.
Why This Matters More Than It Looks
A subfloor is not just something to staple carpet to. Anything left on it telegraphs upward. A stray staple creates a visible bump. Debris under new carpet is felt underfoot for years. Odor in the deck passes straight through new pad and new carpet as if they were not there.
The prep is also nearly free relative to the job, because the floor is already exposed and the crew is already there. Coming back to fix any of it later means pulling up new carpet.
Step One: Staples, Nails, and Old Tack Strip
Old carpet is held to the pad and the deck with staples, and a room can hold hundreds. Every one has to come out or be driven flush, because a raised staple wears through new pad and eventually shows.
Tack strip is inspected rather than automatically replaced. Strip that is intact, dry, and firmly fastened with sharp pins can stay. Strip that is rusted, split, loose, or has dull pins gets replaced, since it is what holds the carpet's tension for the next decade.
Step Two: Vacuum, Then Vacuum Again
The deck gets vacuumed thoroughly, not swept. Sweeping moves fine debris around and leaves it in the seams between panels. A shop vacuum with a brush attachment gets into the panel joints and the perimeter where debris collects.
Pay particular attention to the edges, corners, and closet thresholds. Those are the areas installers work around quickly and the areas where a missed screw or chunk of old pad tends to survive.
Step Three: Check for Moisture
This one is not optional, especially over a slab or in a basement. New carpet installed over a damp deck traps that moisture and creates exactly the conditions that support growth.
On a concrete slab, a simple check is to tape a square of plastic sheeting tightly to the surface and leave it for a day or two. Condensation underneath means the slab is passing moisture and the cause needs addressing before flooring goes down. On a wood deck, a moisture meter reading compared against an unaffected area in the same building is the equivalent test.
Source: IICRC S500 water damage restoration standard
What If the Subfloor Smells?
Odor in a deck almost always means residue is still present, most often pet urine that soaked through the old pad. Cleaning the surface and applying an enzyme treatment appropriate to the residue is the first step, followed by full drying.
Sealing comes only after that, on a dry deck, and only when odor persists. It blocks what remains from passing through, but it is a barrier rather than a treatment, and sealing over untreated contamination usually leads to the odor returning later. Sealing a subfloor after a water loss covers when it is appropriate.
Step Four: Squeaks and Fasteners
A squeak is almost always a panel moving against a joist or a fastener working loose. With the deck exposed you can find the joist, drive a screw through the panel into it, and the squeak is gone permanently.
This takes minutes now and is impossible without pulling carpet later. Walk the entire floor slowly before anything goes down, mark every squeak with tape, then fix them all in one pass.
Step Five: Flatness and Damaged Panels
Carpet is forgiving about minor variation but not about everything. Ridges at panel edges, high spots from previous flooring adhesive, and dips will show through, especially with a thin dense pad.
Soft, swollen, delaminating, or water damaged panels get cut out and replaced rather than covered. That is a structural question, not a cosmetic one. Deflection you can feel underfoot when walking is worth having someone look at before new flooring hides it.
Step Six: Do the Other Jobs Now
The exposed deck is the moment for anything that involves the floor. Running low voltage or network cable, adding an outlet, insulating a floor cavity, or addressing an HVAC register all get easier.
The same is true of painting. Baseboard and wall painting is much simpler with the floor bare, and a fresh cut line at the base looks better against new carpet than an old one. Planning a carpet replacement step by step covers where these sit in the overall sequence.
What Not to Do
Do not wet mop a wood subfloor. Plywood and oriented strand board absorb water readily, swell at the edges, and take days to dry. Vacuum and spot clean instead.
Do not paint a deck with ordinary paint hoping to block odor, since standard paint is not a stain and odor blocker. Do not lay new pad over an old one. And do not deodorize a smelling deck instead of treating it, which is the same trap covered in deodorizer versus true odor removal.
FAQ
Do you need to clean a subfloor before installing carpet?
Yes. Every staple, nail, and piece of debris left behind eventually telegraphs through new pad and carpet, and any odor in the deck passes straight through new flooring. It is the only time the deck is accessible, and the work is cheap while it is exposed.
How do you remove old carpet staples?
With pliers, a staple lifter, or a floor scraper, working systematically across the room rather than randomly. Staples that will not pull can be driven flush with a hammer. A room can hold hundreds, so budget real time for it.
Should the subfloor be sealed before new carpet?
Only when odor or staining remains after the deck has been cleaned, treated, and fully dried. A clean dry deck needs no sealer. Sealing damp wood traps moisture inside it, which causes the problem it was meant to prevent.
How do I check a slab for moisture before carpet?
Tape a square of plastic sheeting tightly to the concrete and leave it a day or two. Condensation underneath means the slab is passing moisture and the cause needs addressing first. On wood, use a moisture meter compared against unaffected material.
Can I fix floor squeaks before new carpet goes in?
Yes, and it is the ideal moment. Locate the joist, drive a screw through the panel into it, and the squeak is gone. Walk the whole floor and mark every squeak with tape before the new flooring covers them.
Does old tack strip need to be replaced?
Not always. Strip that is dry, intact, firmly fastened, and has sharp pins can stay. Rusted, split, loose strip or strip with dull pins gets replaced, since it holds the carpet's tension for the life of the installation.
Where the carpet needs more than spot work, professional carpet cleaning covers the full job.
Subfloor prep is the least visible part of a carpet job and one of the few parts that is genuinely permanent, since everything done here gets covered for a decade or more. Every home is different, so what the deck needs depends on what comes off it. Get a quote and we will walk you through it.