OSB is manufactured from rectangular wood strands arranged in cross-oriented layers and bonded with phenolic resin. OSB is stiffer than plywood at the same thickness and roughly 20 to 30 percent cheaper. OSB resists initial moisture penetration longer than plywood but swells permanently at the panel edges if water is allowed to sit. OSB is acceptable under laminate flooring as long as the panels are tongue-and-groove, glued and screwed to the joists, and protected from standing moisture.
Solid plank subfloors are common in homes built before 1965. The planks are typically 1 x 6 or 1 x 8 pine or fir laid diagonally across the joists. Plank subfloors creak more readily than panel subfloors, develop gaps between boards as the wood dries, and rarely meet modern flatness tolerances without correction. A plank subfloor accepts laminate directly only when it has been screwed down at every joist crossing and meets the flatness tolerance; otherwise it is overlaid with 3/8-inch or 1/2-inch plywood to create a uniform surface.
Laminate flooring is a floating floor. Floating means the planks are not nailed, glued, or screwed to the subfloor — the planks lock to each other and rest on the underlayment, free to expand and contract with humidity. A wood subfloor suits a floating laminate installation for four reasons.
First, wood subfloors are warmer underfoot than concrete and produce less condensation, reducing the moisture risk to the laminate’s HDF core. Second, wood subfloors are easier to flatten than concrete because high spots can be sanded and low spots can be shimmed with thin plywood. Third, wood subfloors do not require the heavy 6-mil polyethylene moisture barrier that concrete demands; a standard foam underlayment is usually sufficient. Fourth, fastener-related squeaks in a wood subfloor can be diagnosed and repaired before the laminate is installed, while concrete cracks or moisture vapor problems often cannot.
Every laminate manufacturer publishes a written subfloor specification. The numbers vary slightly between brands, but the four non-negotiable requirements are flatness, moisture content, structural integrity, and cleanliness.
The industry standard for laminate flooring is a flatness tolerance of 3/16 inch over 10 feet, or 1/8 inch over 6 feet. Beyond this, the click-lock joints on the planks are stressed every time someone walks across the floor, and the joints eventually separate or break. Flatness is checked with a 6-foot or 10-foot straightedge laid on the subfloor in multiple directions. High spots are sanded with a belt sander. Low spots are filled with floor-leveling compound or shimmed with thin plywood.
The maximum acceptable moisture content for a wood subfloor under laminate is 12 percent, measured with a pin-type or pinless wood moisture meter. The laminate’s own moisture content and the subfloor’s moisture content should be within 4 percentage points of each other. A subfloor reading of 14 percent or higher signals an active moisture source — a slab leak below, a plumbing drip, an unvented crawlspace — that must be corrected before the laminate goes down.
The subfloor must be firmly fastened to every joist with no deflection underfoot. Loose nails are pulled and replaced with 2-1/2 inch deck screws driven into the joist. Squeaky boards are screwed down before, not after, the laminate is installed. Damaged or rotted panels are cut out and replaced with material of identical thickness.
The subfloor is swept and vacuumed completely. Drywall mud, paint drips, and protruding fastener heads are scraped flush. A single grain of grit between the underlayment and the laminate creates a hard point that telegraphs through the plank as a creak within months.
Plywood is the better subfloor for laminate flooring in any room where moisture exposure is plausible. OSB is acceptable for bedrooms, living rooms, and hallways on a properly conditioned upper floor. The decision rests on three trade-offs.
Moisture behavior is the deciding factor. Plywood expands modestly when wet and shrinks back to its original dimensions when dry. OSB expands at the panel edges when wet and stays expanded — the swelling is permanent. A swollen OSB edge transmits as a visible ridge through laminate within a year. Fastener retention favors plywood as well; plywood holds screws and nails roughly 40 to 60 percent better than standard OSB, which matters in the long term as floors flex with foot traffic.
Cost favors OSB. A 4 x 8 sheet of 3/4-inch OSB costs three to five dollars less than the equivalent CDX plywood, which adds up across a whole-house installation. Stiffness slightly favors OSB, which has higher shear strength at the same thickness.
For laminate in a kitchen, mudroom, or any room where a dishwasher, refrigerator, or washing machine sits on the floor, plywood is the correct choice. For a second-floor bedroom, OSB performs identically to plywood under laminate as long as the panels are tongue-and-groove, glued and screwed to the joists, and the room is climate-controlled.
Subfloor preparation is the longest step in a laminate installation and the step that determines whether the floor lasts five years or twenty-five. The preparation sequence is consistent across plywood, OSB, and overlaid plank subfloors.
The first step is inspection. Walk every square foot of the subfloor and listen for squeaks, feel for soft spots, and look for water staining, rot, or insect damage. Mark every problem area with painter’s tape.
The second step is fastening. Drive a 2-1/2 inch coarse-thread deck screw through the subfloor into the joist at every spot that squeaks or moves underfoot. The joists are usually 16 inches on-center; finding them is easier with a stud finder than by guessing. Loose nails are pulled, not pounded back in — a pounded nail will work loose again within a year.
The third step is flatness correction. A 6-foot straightedge is laid on the subfloor in a grid pattern. High spots over 3/16 inch above the surrounding plane are sanded with a belt sander. Low spots more than 3/16 inch below the plane are filled with floor-patching compound or shimmed with thin plywood. The patching compound must be rated for wood subfloors; concrete-only compounds will crack and fail on a flexing wood subfloor. The full procedure for leveling a wood subfloor for laminate flooring covers both wide-area corrections and isolated dips.
The fourth step is moisture testing. A pin-type moisture meter is pressed into the subfloor at six to ten locations, including at exterior walls, near plumbing fixtures, and in the room’s center. Every reading must come in below 12 percent. If a reading exceeds 12 percent, the source of the moisture is found and corrected before installation begins. Drying a subfloor under laminate flooring is a structured process, and skipping it traps moisture under the planks where it cannot escape.
The fifth step is cleaning. The subfloor is vacuumed thoroughly, including along walls and in corners. Any glue, mud, or paint drip is scraped flush with a 2-inch putty knife.
Underlayment is the thin foam or felt layer that sits between the wood subfloor and the laminate plank. Underlayment serves four functions: it cushions the click-lock joints, it absorbs minor surface imperfections, it reduces sound transmission, and it provides a small thermal break.
Standard 3mm closed-cell foam underlayment is the baseline for a wood subfloor in a climate-controlled room above grade. Felt underlayment, denser and roughly twice as expensive, performs better at sound dampening and is preferred in upstairs rooms where impact noise reaches the ceiling below. Cork underlayment is the premium choice for sound and thermal performance but adds significant cost.
Many modern laminate planks come with the underlayment pre-attached to the back of the plank. Pre-attached underlayment is sufficient over a flat, dry wood subfloor and eliminates a separate installation step. Adding a second layer of underlayment under a plank with pre-attached underlayment voids most warranties — the locking joint is engineered for a specific plank-plus-underlayment height.
A vapor barrier is generally not required between laminate and a wood subfloor on or above ground level. A vapor barrier is required over concrete and is required over a wood subfloor that sits over an unconditioned crawlspace or basement. The distinction matters: a wood subfloor in a sealed, conditioned home does not produce vapor, but a wood subfloor over an open dirt crawlspace does.
Acclimation is the period during which sealed laminate planks adjust to the temperature and humidity of the room before installation. The standard acclimation period is 48 to 72 hours, with the planks left in their unopened boxes, stacked flat in the center of the room where they will be installed. The room must be at its normal year-round temperature — typically 60 to 80 degrees Fahrenheit — and at its normal relative humidity, between 30 and 60 percent.
Skipping acclimation is the single most common cause of laminate floor failure. A plank installed at 7 percent moisture content into a room that runs at 11 percent moisture content will absorb water from the air and expand. Without an adequate expansion gap, the expanding plank pushes against the wall and buckles. Acclimating laminate flooring before installation is not optional for any laminate brand sold in North America.
Laminate flooring on a wood subfloor expands and contracts with seasonal humidity changes by roughly 1/4 inch per 10 linear feet of plank. To accommodate this movement, an expansion gap of 5/16 inch to 3/8 inch must be left between the laminate and every fixed object — walls, doorframes, columns, kitchen islands, hearths, and pipes.
The expansion gap is concealed by baseboard or quarter-round molding installed on top of the laminate. The molding is nailed to the wall, not to the laminate, so the laminate remains free to move. In rooms wider than 30 feet in either direction, an intermediate expansion joint covered by a T-molding is required. The exact dimension varies by brand and plank length, and the maximum expansion gap for laminate flooring is specified in every manufacturer’s installation instructions.
Different wood subfloor conditions require slightly different preparation. The principles are consistent — flat, dry, fastened, clean — but the path to those four conditions changes with the starting point.
A new plywood subfloor needs the least preparation. The panels are tongue-and-groove, glued to the joists with construction adhesive, and screwed at 6-inch intervals along the panel edges and 8-inch intervals in the panel field. Flatness is verified with a straightedge. Moisture content is measured. Underlayment is rolled out, and laminate installation begins.
An old plank subfloor — common in homes built before 1965 — is rarely flat enough for laminate on its own. The plank gaps, the cupping of individual boards, and the diagonal orientation of the planks create flatness deviations well beyond the 3/16-inch tolerance. The standard correction is to overlay the plank subfloor with 3/8-inch or 1/2-inch underlayment-grade plywood, screwed through the planks into the joists. The overlay follows a specific sequence, covered in the next section, to avoid telegraphing the plank seams through the new plywood.
OSB is acceptable under laminate as long as the panels are tongue-and-groove, fastened correctly, and free of edge swell. Any OSB panel with visible edge swell is sanded flush with a belt sander before laminate installation. Laminate flooring over OSB subfloor is a routine installation in modern construction and rarely causes problems when the OSB has stayed dry.
Existing hardwood, engineered wood, or even an older laminate floor can serve as the substrate for new laminate, provided the existing floor is firmly attached to the subfloor and meets the same flatness tolerance. Loose boards are screwed down. Damaged sections are replaced. The expansion gap is measured from the new laminate, not the old floor.
Laminate can be installed directly over old floorboards or a plank subfloor when the boards are at least 3/4 inch thick, screwed down at every joist, flat within 3/16 inch over 10 feet, and below 12 percent moisture content. When any one of these conditions fails, a plywood overlay turns the boards into a single flat plane before the underlayment goes down.
Old floorboards fall into three condition classes, and each class sets the preparation path:
Square-edge boards open wider seasonal gaps than tongue-and-groove boards because nothing locks adjacent boards together, so square-edge plank subfloors are usually overlaid.
Each defect in a floorboard surface has a specific correction:
Laminate installed directly over floorboards or a plank subfloor must run perpendicular to the boards, crossing them at 90 degrees. Laid parallel, each laminate joint sits above a subfloor seam, the planks rock on the seam ridges, and height differences between adjacent boards create a waviness that runs the length of the room; installers who ignore this rule typically see rocking, joint disengagement and gaps within the first 12 months. Laid perpendicular, each plank bridges several boards and spreads the variation across its width. The subfloor direction overrides the usual longest-wall or light-direction preference; a plywood overlay removes the rule and lets the laminate run any direction.
A plywood overlay is required over floorboards or a plank subfloor in six situations:
The overlay is 3/8-inch or 1/2-inch structural plywood, laid with its long dimension perpendicular to the boards. The sheets are glued and screwed with 1-1/4 inch screws every 6 inches along the edges and every 8 inches in the field, seams are staggered so no four corners meet at one point, and a 1/8-inch gap is left between sheets for expansion. MDF and particleboard are not used as overlays because neither handles moisture variation as well as structural plywood. An overlay is also worth adding over sound boards with a heritage finish, because it protects the original floor for future use.
8mm laminate is the practical minimum over a well-prepared floorboard subfloor, and 10mm to 12mm is the better choice when small gaps or slight board-to-board variation remain. Thicker planks are more rigid, bridge minor imperfections, and reduce flex at the locking joint. Over floorboards, thin foam underlayment under 3mm is avoided; high-density foam at 3mm to 5mm, fiberboard, or rubber underlayment compensates for the uneven surface and reduces the hollow sound of a floating floor over a suspended wood deck.
Three failure modes account for most laminate-over-wood problems, and all three trace back to the subfloor.
Squeaks under laminate flooring almost always come from the wood subfloor below, not the laminate itself. The plank moves vertically against the underlayment or against a high spot in the subfloor, generating friction that produces noise. The fix is to identify the squeak before installation by walking the bare subfloor, screwing down every loose section, and re-checking. After installation, fixing a squeak requires lifting the laminate, which is why pre-installation diagnosis matters.
Buckling is the upward bowing of laminate planks in the field of the floor and is caused by the laminate expanding into a space where there is no room to expand. Buckling traces back to two pre-installation failures: an expansion gap smaller than 5/16 inch, or laminate installed at too low a moisture content for the room’s actual humidity. Wood subfloors do not cause buckling on their own, but a damp wood subfloor accelerates it by raising the laminate’s moisture content from below.
Gapping is the visible separation between adjacent planks and is the opposite of buckling. Gaps appear when laminate installed in summer humidity dries out in winter and contracts. A 1/8-inch gap that appears in winter and closes in summer is normal and self-correcting. A gap that persists year-round indicates a broken click-lock joint, usually caused by an out-of-flat subfloor that stressed the joint until it failed. The remediation steps for fixing gaps in laminate flooring depend on whether the joint is intact or broken.
Laminate sounds hollow over old floorboards because of the air gap between the floating floor and a suspended wood deck, amplified by board gaps and thin underlayment. Filling gaps, securing every board and using a denser underlayment reduce the drum-like sound, although no floating floor over a suspended subfloor eliminates it entirely.
A click or squeak that appears after installation comes from one of three sources: a board that was not fully secured and has begun to move, a nail that has worked up through the underlayment, or a laminate joint that has partially separated from subfloor movement. The first two can often be fixed from above by screwing through the laminate into the joist, countersinking the screw and filling the recess; a separated joint requires local plank replacement. Planks that refuse to click together during installation indicate a high point in the subfloor, visible when sighting along the floor at a low angle. Forcing the joint over a high spot permanently damages the locking profile. Seasonal gapping over floorboards is reduced by keeping indoor relative humidity above 40 percent year-round.
Laminate flooring requires underlayment between the plank and the wood subfloor unless the plank has underlayment pre-attached. Installing bare laminate directly on a bare wood subfloor voids the warranty and produces a hollow, hard-sounding floor that wears unevenly.
The minimum acceptable plywood or OSB thickness for a wood subfloor under laminate flooring is 5/8 inch over joists spaced 16 inches on-center, and 3/4 inch over joists spaced 19.2 or 24 inches on-center. Thinner subfloors deflect under foot traffic and stress the laminate’s click-lock joints.
Laminate flooring is a floating floor and does not transfer load to the joists, so the plank direction relative to the joists is an aesthetic choice rather than a structural requirement. The exception is laminate laid directly over old floorboards or a plank subfloor, which must run perpendicular to the boards unless a plywood overlay is installed first. Most installers run the planks parallel to the longest wall or toward the room’s primary light source.
A wood subfloor on or above ground level in a climate-controlled home does not require a separate vapor barrier under laminate flooring. A wood subfloor over an unheated crawlspace or unconditioned basement does require a 6-mil polyethylene vapor barrier, just as a concrete subfloor would.
A wood subfloor adhered or fastened to a concrete slab is not an ideal base for floating laminate flooring because it traps any moisture rising from the slab between two impermeable layers. The recommended approach is to remove the wood layer and install the laminate over the concrete with a proper vapor barrier, or to verify that the slab below is fully dry and sealed before proceeding.
Laminate flooring on a wood subfloor is the most predictable and forgiving combination available to a residential installer. The preparation work — verifying flatness, measuring moisture, fastening loose sections, cleaning the deck, and acclimating the planks — does not change with the brand of laminate or the species of wood pictured on the plank. The work changes only with the condition of the subfloor.
A laminate floor installed over a flat, dry, well-fastened wood subfloor with proper underlayment, an adequate expansion gap, and acclimated planks performs for 15 to 25 years with no surprises. A laminate floor installed over a subfloor that fails any one of those conditions begins showing problems within the first year. The variable that matters most is not the laminate. The variable that matters most is the wood underneath it.
James Miller is a seasoned flooring contractor with years of hands-on experience transforming homes and businesses with high-quality flooring solutions. As the owner of Flooring Contractors San Diego, James specializes in everything from hardwood and laminate to carpet and vinyl installations. Known for his craftsmanship and attention to detail, he takes pride in helping clients choose the right flooring that balances beauty, durability, and budget. When he’s not on the job, James enjoys sharing his expertise through articles and guides that make flooring projects easier for homeowners.
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