Under laminate flooring you typically need a smooth, dry subfloor plus a suitable underlayment layer, which changes slightly depending on whether the base is concrete or wood.

Quick Scoop: What Goes Under Laminate Flooring?

1. The Layers, From Bottom to Top

  1. Structural subfloor
    • Concrete slab, plywood, or OSB (or old plank boards in older houses).
 * Must be solid, clean, fairly level, and dry.
  1. Moisture/vapour barrier (when needed)
    • On concrete or any area prone to damp, a plastic vapour barrier or an underlay with built‑in moisture barrier goes directly on the slab.
 * Protects laminate from warping and swelling caused by moisture rising through concrete.
  1. Underlayment (the main “pad”)
    • A thin, resilient sheet laid over the subfloor before the laminate “floats” on top.
 * Materials include foam, polyethylene, cork, felt, or rubber; foam is common and budget‑friendly, cork/rubber/felt are more premium.

 * Some laminates already have this pad attached; in that case you usually only add a separate moisture barrier over concrete, not another full pad.
  1. Laminate flooring
    • Click‑lock planks that float over the underlay instead of being nailed or glued.

“What goes under laminate flooring?” → Subfloor + (moisture barrier if needed) + underlayment pad, then the laminate itself.

2. What Kind of Underlayment Do You Actually Need?

For concrete subfloors (basements, slabs)

  • Underlay with built‑in moisture barrier is the safest default.
  • Often a 2‑in‑1 or 3‑in‑1 foam pad: cushion + sound control + vapour barrier.
  • In very damp areas, people may use a separate plastic vapour film plus an underlay on top.

For timber/wood subfloors (plywood, OSB, planks)

  • Standard foam underlayment usually works well if the subfloor is dry and mostly flat.
  • Fibreboard or cork can help even out minor imperfections and improve sound and thermal comfort.
  • You generally don’t need a separate vapour barrier unless there’s a moisture risk from below.

3. Why Underlayment Matters (And Why You Almost Always Need It)

Most modern laminate installations should not go directly on the subfloor without some kind of underlay.

Main jobs of underlayment:

  • Moisture protection
    • Underlays with vapour barriers block moisture from concrete and help prevent swelling, cupping, and mold.
  • Sound reduction
    • The pad absorbs impact noise (footsteps, dropped objects) and reduces echo in the room below.
  • Comfort and insulation
    • Adds a bit of “give” and warmth underfoot, making laminate feel less hard and cold.
  • Protection from friction and minor subfloor flaws
    • Foam acts as a buffer so the laminate can expand/contract as a floating floor without rubbing directly on the subfloor.

4. Common Types of Underlayment (Mini Guide)

  • Standard foam underlayment
    • Basic, budget option for flat, dry wood subfloors.
  • 2‑in‑1 vapour underlayment
    • Foam + integrated moisture barrier; common over concrete where you need simple moisture protection.
  • 3‑in‑1 or “silent” underlayment
    • Thinner or denser pads that combine moisture protection, better sound deadening, and a bit of levelling.
  • Cork underlayment
    • Natural and hypoallergenic, good for sound and thermal insulation, also used under click‑lock vinyl or engineered wood.
  • Rubber or felt pads
    • More premium sound control and comfort, often used in multi‑storey homes or apartments.
  • Vapour block film only
    • Plastic sheet used where the laminate already has a pre‑attached pad, so you only need moisture protection.

5. What You Might Find Under Existing Laminate (Forum‑Style Curiosity)

Real‑world posts often show surprising stacks under laminate:

  • Old hardwood or plank floors under a pad and laminate.
  • Vinyl sheet or other “remnant” flooring used as a layer between subfloor and top floor, sometimes causing soft spots if not removed.
  • Mixed layers: shiplap subfloor, tongue‑and‑groove wood, old underlayment fabric, then laminate.

These stories are a good reminder: if you’re replacing laminate, inspect each layer so you’re not building over a problem like rot, soft subfloor, or trapped moisture.

6. Simple Decision Checklist (If You’re Installing Now)

  1. Identify your subfloor
    • Concrete → plan on a moisture barrier (either separate film or built into the underlay).
 * Wood → usually foam/fibreboard/cork without a plastic barrier, unless moisture is a concern.
  1. Check your laminate product
    • If it has an attached pad, do not add another full foam pad; only add vapour film over concrete if required by the manufacturer.
  1. Choose the underlay based on:
    • Moisture risk (basement vs upstairs),
    • Need for noise reduction,
    • Budget and comfort level.

Bottom line: what goes under laminate flooring is not just “whatever is there already” but a deliberate stack—subfloor, the right moisture protection, and a suitable underlayment pad—so the floor stays flat, quiet, and dry for years.

Information gathered from public forums or data available on the internet and portrayed here.