• Solid tongue-and-groove floorboards in good condition — level, secure, no significant gaps, no cupping. Laminate can go directly over these with the right underlay.
• Solid floorboards with moderate issues — some movement, minor gaps, a few loose boards, slight unevenness. Requires preparation before installation can proceed.
• Floorboards in poor condition — significant cupping, large gaps, rot, bounce, structural movement. A plywood overlay is mandatory. In severe cases, the boards may need to be replaced entirely.

The Structural Check: What to Inspect Before Anything Else

Walk across every part of the floor slowly. Listen. Feel. A board that flexes under your foot will flex under laminate. A board that squeaks is one that is moving against a fastener or an adjacent board — and that movement will transmit into the laminate layer above it, causing clicks, creaks, and eventual joint separation.

Check for the following in sequence:

Board Bounce and Deflection

Press down firmly on each board near the centre of the span. Any noticeable spring or bounce indicates that the joist spacing is too wide for the board thickness, or that the boards have thinned over time. Industry standard for laminate installation requires that the subfloor deflects no more than 3/16 inch across a 10-foot span. Floorboards that exceed this will stress laminate locking joints over time.

Cupping and Crowning

Run a long straightedge across the floorboards perpendicular to their direction. Any board where the edges are higher than the centre (cupping) or the centre is higher than the edges (crowning) creates a localised high or low point. These are the spots where laminate planks will rock, fail to lock flat, or create hollow spots that sound drum-like underfoot.

Gap Width Between Boards

Gaps between floorboards are normal and expected in older homes. Seasonal movement causes boards to open and close throughout the year. The problem arises when those gaps are wide enough that a laminate plank bridges the gap unsupported — typically anything wider than 3mm to 4mm becomes a concern. At these widths, pressure on the laminate above the gap causes localised flex, which over time fractures the locking joint system.

Nails and Fixings

Every nail head that sits proud of the board surface is a problem. Laminate underlay is thin. A raised nail head creates a localised hard point that telegraphs through the underlay and prevents the laminate plank from sitting flat. Run your hand along each board edge and across the face. Any raised fastener needs to be punched below the surface with a nail punch before installation proceeds.

How to Prepare Old Floorboards for Laminate Installation

Preparation is not optional. It is the installation. Everything that follows — the underlay, the laminate planks, the expansion gaps — performs correctly only if the subfloor is structurally sound, flat, clean, and dry.

Step 1: Secure All Loose Boards

Every board that moves needs to be screwed down. Use 50mm or 60mm screws rather than nails — screws grip the joist and do not work loose over time the way nails can. Drill a 3mm pilot hole first to prevent splitting, and countersink each screw so the head sits just below the board surface. Pay particular attention to boards near doorways, around the perimeter, and any board that was previously lifted for pipe or cable access.

Step 2: Punch Down All Nail Heads

Use a nail punch and hammer to drive every existing nail head 2mm to 3mm below the board surface. This takes time on an old floor. Do not skip it. A single proud nail head can prevent an adjacent laminate plank from clicking fully into the previous row, creating a visible ridge or a joint that separates under load.

Step 3: Address Gaps Between Boards

For gaps under 3mm, a quality underlay with sufficient density will bridge the gap adequately. For gaps between 3mm and 8mm, fill with a flexible wood filler or thin timber wedges glued into place. For gaps larger than 8mm, or where the gap pattern is widespread across the floor, a plywood overlay becomes the more practical solution than filling board by board.

One method used by experienced fitters for minor gaps: thin strips of wood, slightly tapered, glued into the gap and planed flush once cured. This is slow but effective for heritage floors where disruption needs to be minimised.

Step 4: Sand High Points

Any board that sits proud of its neighbours — even by 1mm — is a high point that needs to be addressed. A belt sander or hand plane works for isolated boards. For widespread unevenness, a floor sander will bring the whole surface to a consistent level faster. The maximum acceptable deviation for laminate installation is 3mm across a 1.8-metre span. Some manufacturers specify tighter tolerances — always check the manufacturer’s installation guide before proceeding.

Step 5: Test Moisture Content

Old floorboards over a suspended timber floor can hold significant moisture, particularly in ground-floor rooms over a crawl space or unventilated void. Use a calibrated moisture meter on multiple boards across the room. Acceptable moisture content for a timber subfloor is typically 8% to 12%, depending on the laminate manufacturer’s specification. Readings above this indicate a problem with subfloor ventilation or rising damp that must be resolved before any flooring goes down.

This is different from a concrete subfloor situation, but the principle is the same — moisture trapped below laminate has nowhere to go and will cause the laminate core to swell, buckle, and separate. For a deeper understanding of how barriers interact with different subfloor types, see our guide on what is the best barrier for laminate flooring.

Do You Need a Plywood Overlay Over Floorboards?

This is the most debated question in this type of installation, and the honest answer is: it depends on the condition of the floorboards and what outcome you are trying to achieve.

A plywood overlay is not always necessary, but it is always beneficial. Here is when it becomes mandatory versus optional:

When a Plywood Overlay Is Mandatory

• The floor has widespread gaps wider than 8mm between boards
• Multiple boards have significant cupping or crowning that cannot be sanded flat
• The floor shows bounce or deflection beyond the 3/16 inch per 10-foot specification
• You want to run the laminate planks in the same direction as the floorboards (this alone justifies an overlay)
• There is evidence of previous moisture damage or localised rot in any boards

When a Plywood Overlay Is Optional but Recommended

• The floorboards are sound but have minor gaps (under 3mm) that you prefer not to fill individually
• You want a completely flat, consistent surface without relying on the underlay to compensate
• The floor has a heritage finish you want to preserve for future use (the ply protects the original boards)

When You Can Install Directly Over the Boards

• Boards are fully secured, flat to within 3mm per 1.8 metres, have no gaps wider than 3mm, and show no moisture issues
• Laminate will be laid perpendicular to the board direction
• A high-density underlay (not thin foam) is being used

If you do add plywood, use minimum 9mm or 12mm structural plywood. Fix it with screws at 200mm centres across the whole sheet, staggering the joints so no four corners meet at the same point. Leave a 1mm to 2mm gap between sheets to allow for movement. Do not use MDF or chipboard — neither handles moisture variation as well as structural plywood.

For context on how plywood performs as a laminate subfloor, see our full breakdown: installing laminate flooring over plywood.

Direction of Lay: Why It Matters Over Floorboards

The conventional rule is to lay laminate planks perpendicular to the existing floorboards. The reason is structural — laying parallel to the boards means each laminate plank spans the full length of each underlying board. Any slight variation in height between adjacent boards creates a waviness that runs the entire length of the room, and the laminate will follow it.

When laminate is laid perpendicular (across) the floorboards, each plank crosses multiple boards simultaneously. This spreads any localised height variation across the width of the plank, which the locking joint and underlay can compensate for much more effectively.

If the room layout makes perpendicular installation aesthetically undesirable — for example, if laying across the floorboards means laying against the length of the room — the solution is to add the plywood overlay first. The plywood creates a uniform platform that removes the directional constraint entirely, allowing you to run the laminate in whichever direction suits the space.

Underlay Selection for a Floorboard Subfloor

Underlay over floorboards needs to do more than it does over a smooth concrete or plywood surface. It must bridge minor surface irregularities, reduce sound transmission (old floorboards over joists can be very acoustically active), and provide thermal insulation if the floor is above a cold crawl space or suspended void.

For a floorboard subfloor, avoid thin foam underlays — typically anything under 3mm. These compress rapidly, provide minimal acoustic performance, and do nothing to compensate for minor surface variation. Instead, look at:

• High-density foam (3mm to 5mm) — good general-purpose choice, compensates for minor irregularities, widely compatible with laminate manufacturer warranties
• Combination foam/film underlays — the integrated moisture film adds protection against vapour moving through the floorboards from below, useful in ground-floor installations
• Fibreboard underlays — excellent acoustic performance, rigid enough to bridge small gaps in floorboards, performs well in upper-floor rooms where noise transmission to the floor below is a concern
• Rubber underlays — premium option, high density, excellent at reducing the hollow sound associated with floating floors over suspended timber subfloors

Check whether your chosen laminate already has an attached underlay layer on the back of the planks. If it does, you cannot add a second underlay below it — the total underlay thickness will exceed the manufacturer’s specification and compromise the locking joint performance. The manufacturer’s guide will specify whether an additional underlay is permitted and, if so, what maximum thickness is allowed.

The Expansion Gap: More Critical Over Floorboards Than Almost Any Other Subfloor

Floorboards move seasonally. Laminate moves seasonally. When both are present in the same floor assembly, you have two layers of movement occurring simultaneously, and they do not always move in the same direction or at the same rate.

This makes the expansion gap around the perimeter of the room non-negotiable. The minimum gap for most laminate manufacturers is 10mm to 12mm from every fixed object — walls, door frames, pipe collars, hearths, and built-in furniture bases. In rooms over 8 metres in length or width, check the manufacturer specification for whether intermediate expansion joints are required.

Do not fill this gap with silicone or caulk after installation. It must remain free to allow movement. Cover it with skirting board or beading instead. When skirting is refitted, fix it to the wall — never to the laminate floor surface itself.

When laminate is prevented from expanding — either by a gap that was left too small or by being pinned by a heavy object — it buckles upward at the joints. Understanding why this happens, and the physics behind it, is covered in detail in our article on why laminate flooring expands.

Acclimatisation: Why Floorboard Subfloors Require More Attention Here

Laminate planks must be acclimatised to the room before installation — this is standard practice. Most manufacturers specify 48 to 72 hours in the room, flat-stacked with the boxes open or the planks separated to allow air circulation.

Over a floorboard subfloor, the reason for acclimatisation is more acute than over concrete. The floorboards themselves hold moisture and release it into the room air. If the laminate is installed before it has adjusted to this moisture environment, the planks will continue to absorb moisture post-installation and expand beyond the allowance of the expansion gap. The result is buckling — and it typically appears within the first few weeks, especially if installation happens in autumn or winter when indoor heating begins drying the air.

Specific Problems That Appear After Installation and What Causes Them

Hollow Sound Underfoot

The characteristic drum-like sound of laminate over a suspended floor is caused by the air gap between the underside of the laminate system and the floorboards below. This is amplified where floorboard gaps are present, where underlay is thin, and where the overall floor assembly has significant void space beneath it. A denser underlay and a more thorough preparation of the floorboard surface (filling gaps, securing boards) reduces this significantly but may not eliminate it entirely — it is an acoustic characteristic of all floating floors over suspended timber subfloors.

Clicking and Squeaking After Installation

If the floor develops a squeak or click that was not present immediately after installation, the source is almost always one of three things: a board that was not fully secured before laminate was laid and has begun to move; a raised nail that has worked up through the underlay over time; or a laminate joint that has partially separated due to subfloor movement. The first two can often be addressed without removing the laminate — drilling and screwing through the laminate surface at the affected point, countersinking the screw and filling the recess. The third requires local plank replacement.

Gapping Between Laminate Planks

Gaps appearing between individual laminate planks after installation indicate that the floor has contracted — the humidity in the room has dropped, the laminate has dried and shrunk, and the joints have opened slightly. This is more common over floorboard subfloors because the wood beneath also contracts, potentially pulling the underlay and laminate system downward at the edges. Ensure room humidity is maintained above 40% throughout the year. Persistent gapping that does not close when humidity is restored may indicate that the expansion gap was undersized, causing the floor to be mechanically compressed and then unable to return to its full dimension. See our detailed troubleshooting guide on how to fix gaps in laminate flooring.

Planks That Will Not Click Together

If you encounter laminate planks that resist locking during installation over floorboards, the cause is almost always a high point in the subfloor. The plank cannot lie flat enough for the locking profile to engage. Get down and look along the floor surface at a low angle. The high point will be visible. Address it before attempting to re-engage the joint. Forcing laminate joints together over a high spot damages the locking profile permanently — the joint will never hold correctly, and that section will require replacement.

More on diagnosing and solving this during installation: why your laminate flooring won’t click together.

Choosing the Right Laminate Thickness for a Floorboard Subfloor

Thickness matters more over floorboards than over concrete. A thicker laminate board has more inherent rigidity — it is less likely to flex independently across a gap in the subfloor below and more likely to bridge minor imperfections without transmitting stress to the locking joint.

For a well-prepared floorboard subfloor, 8mm laminate is the practical minimum. For a subfloor with residual minor irregularities — small gaps, slight variation between boards — 10mm to 12mm is the better choice. The additional thickness distributes the load across a wider area and reduces the flex at the joint line.

AC rating also plays a role in how the floor wears over time in residential versus high-traffic areas of the home. A full comparison of thickness specifications and what they mean in practice is covered in whether to use 8mm or 12mm laminate.

Installing Laminate Over Floorboards: Step-by-Step Summary

1. Inspect the entire floor. Walk, press, listen. Identify all loose boards, raised fixings, gaps, cupping, and high/low points.
2. Secure every loose board. Screw down with countersunk screws at every joist crossing. Punch all nail heads below the surface.
3. Assess whether a plywood overlay is needed. If gaps are widespread, boards are cupped, or you want directional freedom, install minimum 9mm structural plywood across the whole floor.
4. Fill remaining gaps. Use wood filler or thin timber wedges for gaps up to 8mm. Sand or plane any high points to achieve a maximum 3mm variation per 1.8 metres.
5. Check moisture content. Use a moisture meter. Resolve any readings above the manufacturer’s specified threshold before continuing.
6. Acclimatise the laminate. 48 to 72 hours flat in the room with adequate airflow around the planks.
7. Lay the underlay. Use a high-density product appropriate for a timber subfloor. Butt edges — do not overlap. Tape all seams.
8. Install perpendicular to the floorboards unless a plywood overlay has been installed, in which case direction is a design choice.
9. Maintain the full expansion gap. Minimum 10mm from every fixed perimeter structure throughout the installation.
10. Undercut all door frames. Use a flush-cut saw or multi-tool to remove the bottom of door architraves so the laminate slides underneath — this gives a professional finish that does not require beading at transitions.

For a complete visual and detailed walkthrough of the installation process from start to finish, see our main guide on how to install laminate flooring.

Frequently Asked Questions

Can I install laminate directly over old floorboards without removing them?

Yes, provided the floorboards are structurally sound, secured, flat within tolerance, and free from significant moisture issues. The boards do not need to be removed. They function as the structural subfloor — laminate is installed on top of them with underlay in between.

Do I need a moisture barrier over floorboards?

Over a ground-floor suspended timber floor with a void beneath it, a vapour control layer is advisable. Cold air circulating through the void carries moisture, and in certain conditions this can condense on the underside of the floorboards and migrate upward. A combination underlay with an integrated moisture film, or a separate vapour control layer laid before the underlay, addresses this. On upper floors over a heated room below, a separate moisture barrier is generally not required.

In what direction should laminate be laid over floorboards?

Perpendicular to the existing floorboards is the standard recommendation. This ensures each laminate plank crosses multiple boards, distributing any height variation rather than running parallel to it. If you want to run the laminate in the same direction as the boards, install a plywood overlay first.

How do I deal with squeaky floorboards before laying laminate?

Locate the squeak precisely and screw the board down firmly into the joist below. If the squeak is between boards rather than between board and joist, a small amount of dry lubricant (talcum powder or specialist floor squeak spray) worked into the gap can eliminate friction-based noise. Do not lay laminate over an unresolved squeak — the noise will transmit clearly through the laminate system and be amplified by the resonant space below the floating floor.

What thickness of laminate is best over floorboards?

A minimum of 8mm for well-prepared floorboard subfloors. 10mm to 12mm for subfloors with residual minor irregularities. The additional thickness provides greater rigidity across the span and reduces flex at the locking joints.

Can I lay laminate over tongue-and-groove floorboards?

Yes. Tongue-and-groove floorboards are generally more stable than plain-edge boards because the interlocking profile resists differential movement between adjacent boards. They still need to be checked for security, nail heads, and levelness — but as a subfloor they are well-suited for laminate installation.

Installing laminate over floorboards is one of the most common renovation projects in older homes, and when done correctly it produces a floor that is durable, visually consistent, and significantly easier to live with than worn or painted original boards. The preparation is the project. Every hour spent securing, levelling, and assessing the subfloor pays for itself in the performance and longevity of what goes on top.