How to Choose Underlayment for Pergo Laminate
Choose underlayment by the exact Pergo product, whether its planks have attached pad, and whether the subfloor is wood or concrete. Follow that product’s current instructions for flatness, moisture testing, vapor control, and expansion gaps. Underlayment cannot fix a weak, wet, or uneven subfloor; prepare the surface first, then install only the approved floor system.
A new laminate floor can look ready to install while hiding the problems that cause trouble later: a low spot, a damp slab, or an extra layer of padding that makes the floor too soft. The right underlayment depends on the specific Pergo plank and what lies beneath it. I use a simple order: identify the product, inspect and test the subfloor, then match the approved components to both.
Inspect the Subfloor, Confirm Flatness, and Prepare the Surface
The subfloor is the structural layer beneath the finish floor. Before choosing underlayment, confirm that it is sound, clean, dry, and flat enough for the exact Pergo product. A common Pergo laminate limit is 3/16 inch over 10 feet, but the current installation instructions for your flooring take priority.
Start by finding the full product name and its installation guide. Check whether the planks have attached pad and note the required underlayment, moisture test, and flatness limit. Do not rely on a general laminate rule if the product’s instructions set a different one.
Check for movement, damage, and flatness
Walk the floor and listen for movement or squeaks. Look for loose panels, swollen or delaminated OSB, soft areas, rot, and signs of past or active leaks. Underlayment is not a structural repair: a loose or damaged subfloor needs repair before the laminate goes down.
Check flatness with a long straightedge or level, moving it across the floor in several directions. Measure the largest gap beneath the straightedge and compare it with the product’s limit. The common 3/16 inch over 10 feet is a maximum variation, not permission to leave an unstable or damaged surface in place.
Correct high spots and low areas with products and methods approved for that substrate. Remove debris, fasteners, and old adhesive that would interfere with the flooring system. Do not use a soft underlayment to bridge dips. That can leave the floating planks unsupported and put extra stress on their locking joints.
Decide whether the subfloor is wood or concrete
Wood and concrete need different moisture checks and may need different layers beneath the laminate. On wood, inspect for leaks, rot, loose panels, and moisture concerns. On concrete, check for moisture using the test method required in the Pergo instructions for that product.
There is no single moisture-vapor emission rate (MVER) or in-situ relative humidity (RH) limit that applies to every Pergo floor and underlayment. Compare the test result with the maximum stated in the current flooring instructions. If the result is too high, or moisture is entering the slab, resolve the problem before installation.
Next step: Record the product name, attached-pad status, subfloor type, flatness findings, and moisture-test result. Those details drive the underlayment choice.
Match Underlayment and Moisture Control to the Pergo Product
Underlayment is a layer specified beneath some laminate floors to support the product’s installation system. It is not a leveling compound or a fix for moisture. Choose it by matching the Pergo product’s instructions to the subfloor, and do not add extra cushioning unless Pergo expressly allows it.
| Pergo plank and subfloor | What to check | Underlayment or moisture-control choice |
|---|---|---|
| Planks with attached pad, wood subfloor | Confirm the guide’s requirements and inspect the wood for damage and moisture | Do not add a second cushioned layer unless the guide permits it |
| Planks without attached pad, wood subfloor | Confirm the specified underlayment type and thickness | Use a Pergo-approved underlayment; do not substitute an unapproved product |
| Planks with attached pad, concrete slab | Check the required concrete moisture test and vapor-control instructions | Do not add cushioning; install required vapor control as directed |
| Planks without attached pad, concrete slab | Check the moisture test, approved underlayment, and vapor-control details | Use only the specified system; include required concrete vapor control |
If the planks have attached pad
Attached pad means a cushioning layer is already bonded to the underside of each plank. In that case, do not place another cushioned underlayment beneath it unless the current Pergo instructions specifically allow that combination. Extra resilience can increase movement at the joints and may conflict with the product requirements.
If the planks do not have attached pad
Use an underlayment approved for that Pergo product, with the type and thickness stated in its instructions. Do not choose by thickness alone or assume that an underlayment made for another laminate floor will work. Keep the system to the listed layers; do not overlap or double-layer cushioning unless the specified installation calls for it.
If the subfloor is concrete
Where the Pergo instructions require a vapor retarder, they may call for at least 6-mil polyethylene beneath the flooring or approved underlayment. Follow the specified product and arrangement, including how seams are overlapped and taped. Do not assume that every slab needs the same layer, or that an underlayment alone replaces required vapor control.
A damp slab or active water intrusion is a stop condition. Moisture can contribute to swelling, joint failure, or mold beneath laminate. Polyethylene and underlayment do not correct hydrostatic pressure or an unresolved water source. Find and address the cause, then retest as required.
A practical selection sequence
I use this sequence to avoid buying a layer that the floor cannot use:
- Read the current instructions for the exact Pergo product.
- Confirm whether the planks have attached pad.
- Identify the subfloor as wood or concrete.
- Verify flatness and resolve any structural or surface defects.
- Test moisture as directed and compare the result with the product’s stated limit.
- Select only the approved underlayment and vapor-control components.
Key point: The product guide, not a generic underlayment label, decides which layers belong in the assembly.
Install the Floating Floor, Transitions, and Expansion Gaps
A floating floor is connected plank to plank but is not fixed to the subfloor. It needs the clearances specified by its manufacturer so it can move as conditions change. Install the approved underlayment and vapor-control layers as directed, then protect the perimeter gap and avoid pinning the floor with trim or fixed objects.
Lay the underlayment and vapor control as specified
Follow the product instructions for the direction of installation, seam placement, and edge details. If a concrete vapor retarder is required, use the specified material and tape or overlap seams as directed. Keep layers smooth and free of folds, debris, and gaps that conflict with the system instructions.
Do not add a second cushion layer to an attached-pad plank unless Pergo expressly approves it. Do not use underlayment to hide a low area, and do not overlap separate cushioning layers unless the instructions require that arrangement. Extra material is not a substitute for a flat, sound base.
Leave room for floor movement
Maintain the perimeter and fixed-object clearance stated in the current instructions. Three-eighths of an inch is common, but it is not universal; follow the specific product guide. Keep the required space around walls, pipes, cabinets, and other fixed objects, and do not fill the gap with hard-setting material.
Fit transitions and moldings so they do not clamp the floating floor to the subfloor. A trim piece may cover the clearance, but it must not pin the laminate. Check doorways and adjoining flooring as you work so transitions cover the required gaps without blocking movement.
Two illustrative inspection scenarios
These examples show how the decision process works; they are not a substitute for the product guide or a report of a particular installation.
- Attached-pad planks over wood: The installer finds a loose OSB panel and a noticeable low spot. The right first move is to secure or repair the panel and correct the flatness issue. Adding a second cushion would not fix either defect and may conflict with the Pergo instructions.
- Planks without attached pad over concrete: The installer confirms the product’s approved underlayment, tests the slab by the required method, and compares the result with the stated limit. If the instructions require a 6-mil polyethylene vapor retarder, the installer includes it and treats seams as directed. If the slab is damp beyond the limit or has active water intrusion, installation waits.
Next step: Before laying planks, check the approved layers, the prepared surface, and the expansion clearance. A correct underlayment choice still depends on correct installation.
Protect the Floor: Moisture, Cleaning, and Long-Term Care
Long-term performance depends on keeping moisture out and allowing the floating floor to move as designed. Underlayment can be part of the specified system, but it cannot stop an active leak or repair a damaged subfloor. Follow the Pergo care and installation instructions, and investigate any new moisture or movement promptly.
Keep water from reaching the floor through leaks, spills, or wet cleaning beyond what the product allows. If you find a damp area, swollen plank edges, or a musty smell, look for the source rather than assuming the underlayment will contain it. A vapor retarder is not a cure for water entering under pressure.
During installation, protect the perimeter space beneath trim and around fixed objects. Later, avoid adding fasteners through the floating floor or changing trim in a way that clamps it. If the floor begins to lift, separate at joints, or feel unusually soft, check for a moisture problem, movement, or a blocked expansion gap.
Conclusion: The dependable choice is the Pergo-approved system for the exact plank and subfloor, installed over a sound, flat, dry base. Confirm attached-pad status first, follow the product’s moisture and vapor-control rules, and preserve the specified expansion space.
Frequently Asked Questions
These answers cover the most common choices that affect Pergo laminate underlayment. Product instructions vary, so use the guide for your exact flooring when it differs from a general rule. The short answer is to verify the plank, subfloor, moisture requirements, and approved installation layers before starting.
Can I add underlayment beneath Pergo laminate with attached pad?
Not unless the current Pergo instructions expressly allow it. A second cushion layer can make the floor more resilient and may stress the locking joints or conflict with product requirements.
Does Pergo laminate always need underlayment?
No. The answer depends on whether the planks have attached pad and what the product instructions require. Use only the specified system for that floor and subfloor.
What underlayment should I use over a wood subfloor?
Use the type and thickness approved for your exact Pergo product if the planks need a separate underlayment. First repair loose, damaged, or uneven wood; underlayment cannot correct those problems.
Do I need a vapor barrier over concrete?
Follow the current Pergo instructions for the specific laminate and slab. Where they require a vapor retarder, use the specified system; at least 6-mil polyethylene may be required, with seams treated as directed.
What moisture test should I use on concrete?
Use the test method required by the current product instructions. Compare the result with that product’s stated maximum; there is no one MVER or in-situ RH limit for every Pergo floor.
How flat must the subfloor be?
A common Pergo laminate limit is 3/16 inch over 10 feet. Confirm the exact flooring guide, then correct high and low areas using methods compatible with the subfloor.
Can underlayment level an uneven floor?
No. It should not bridge dips or replace proper surface correction. Prepare the subfloor to the flooring’s flatness limit before laying the underlayment and planks.
How much expansion space should I leave?
Use the gap in the current Pergo instructions. Three-eighths of an inch is common, but the required clearance can vary. Keep the gap around fixed objects and do not fill it with hard-setting material.
What if my concrete slab is damp?
Do not cover a moisture-compromised slab. Resolve active water intrusion or excess moisture, then test again as required. Underlayment and vapor control do not fix hydrostatic pressure or an unresolved source of water.
(This article was written by one of our staff writers, Thomas Whitaker. Visit our Meet the Team page.)
