The Best Underlay for LVT on a Timber Subfloor: What Peterborough Fitters Specify

Short answer: on a timber subfloor, the best underlay for click-lock LVT is a thin, high-density LVT underlay of around 1–1.5mm that the flooring manufacturer approves for that range, laid over boards that have been screwed down and, where needed, overboarded with plywood. Glue-down LVT such as most Karndean and Amtico ranges takes no underlay at all: it is bonded to a plywood overlay, never straight onto floorboards.

Timber subfloors are everywhere in Peterborough. The ground floors of Victorian terraces in PE1 and many 1930s semis in PE2 sit on suspended floorboards over a ventilated void, and almost every upstairs floor, whatever the age of the house, is boards or chipboard on joists. Concrete slabs need a different approach, which we cover in our guide to underlay under LVT on concrete. This guide explains what our own fitters specify on wood, and why.

What is the best underlay for LVT on floorboards?

It depends on the type of LVT, and the product's own fitting instructions always have the final say. As a rule:

• Click-lock LVT without a backing: a thin, dense LVT underlay approved by the manufacturer. It smooths out tiny surface differences, supports the locking joints and takes the edge off footfall noise.
• Rigid-core LVT with an attached underlay: nothing extra. The backing is the underlay, and stacking a second layer makes the floor bounce and can void the guarantee.
• Glue-down LVT: no underlay. The boards are overboarded with plywood, the joints and screw heads are smoothed, and the LVT is bonded to the ply.

Manufacturers such as Karndean, Amtico, Moduleo, Quick-Step and Polyflor each publish which underlays, if any, are approved for each range. We check the specific range at the survey so your guarantee stands.

Which underlay goes with which LVT on a timber subfloor?

LVT type	Underlay on timber?	What the boards need first	Watch out for
Click-lock LVT, no backing	Yes: thin, high-density LVT underlay (around 1–1.5mm)	Loose boards screwed down; ply or hardboard overlay if boards are cupped or gappy	Soft carpet or foam laminate underlay, which lets the joints flex and break
Rigid-core LVT with attached backing	No extra underlay	Boards secured and flat within the maker's tolerance	Doubling up underlays, which makes the floor bounce
Rigid-core LVT, no backing	Yes: the manufacturer's approved underlay	Boards secured; overlay where the surface is uneven	Exceeding the maximum underlay thickness the range allows
Glue-down LVT (e.g. Karndean, Amtico)	Never	Plywood overboarding screwed at close centres, joints and fixings smoothed	Gluing straight onto boards, where every gap and joint shows through

You can see the full range we supply and fit on our luxury vinyl tiles Peterborough page, with the glue-down ranges on our Karndean flooring Peterborough and Amtico flooring Peterborough pages.

Do floorboards need plywood before LVT goes down?

For glue-down LVT, always. Floorboards move with the seasons, have gaps between them and are rarely perfectly level from one board to the next. Thin glue-down LVT shows every one of those lines within weeks, so we screw down any loose boards and then overboard the whole area with plywood, laid with staggered joints and screwed at close centres.

For click-lock and rigid-core LVT, it depends on the condition of the boards. Sound, flat boards that have been screwed down can often take an approved LVT underlay directly. Cupped, worn or widely gapped boards need an overlay first, because an underlay is not thick enough to bridge a gap or hide a ridge. We explain the full method in how we fit LVT in older homes without lifting the original floorboards.

On chipboard upper floors, common in newer Peterborough estates, the same thinking applies: the sheets must be fixed tight to the joists, with no movement at the edges, before any LVT or underlay goes down.

Should you put a damp-proof membrane under LVT on a wooden floor?

Usually not. On concrete, a vapour barrier stops moisture rising through the slab. A suspended timber floor works differently: it relies on air moving through the void beneath it, fed by the air bricks in the outside walls. A polythene sheet laid on top of the boards can trap moisture in the timber, so most manufacturers do not ask for one on a wooden subfloor. Where a specific range or underlay does call for a barrier, we follow its instructions.

What matters more is that the void stays ventilated. Blocked air bricks are worth clearing before a new floor goes down, and if you have any sign of damp in a ground-floor room, read our guide to fitting LVT on a floor with damp issues first.

Why can't I use carpet or laminate underlay under LVT?

Because it is far too soft. Carpet underlay is designed to compress, and most foam laminate underlays are thicker and springier than LVT can tolerate. Click LVT is thinner than laminate and relies on rigid locking joints. On a soft base those joints flex every time someone walks over them, and over time they peak, gap or snap. Timber subfloors already have a little natural give, so adding a soft underlay on top makes the problem worse, not better.

If you have spare underlay left over from a carpet job, keep it for the carpet. Our separate underlay page covers the carpet grades.

What underlay works best upstairs and in flats?

Upstairs, the main concern is impact noise travelling through the joists into the room below. Some LVT underlays and attached backings are designed with acoustic performance in mind, and they are worth choosing for bedrooms and landings over a living room. Glue-down LVT on a plywood overlay is also quiet underfoot, because there is no hollow sound from a floating floor.

In flats, check your lease before choosing any hard floor: many set rules on hard flooring or acoustic standards. Bring the wording to the home visit and we will match the underlay and product to it.

Can you fit LVT and underlay over underfloor heating on a timber floor?

Yes, with care. The combined thermal resistance of the underlay and the LVT must stay within the limit set by the heating system and the flooring manufacturer, so a thin, dense underlay is the right choice here too. Surface temperatures also need to stay within the LVT maker's limit. Our guides to R-value and LVT over underfloor heating and the best flooring for underfloor heating go into more detail.

How much does LVT on a timber subfloor cost in Peterborough?

All our prices are supply and fit. From our flooring prices Peterborough page:

Item	Price (supply and fit)
LVT	From £35/m²
Mid-range click-lock and rigid-core LVT	£35–£50/m²
Premium glue-down Karndean and Amtico	£50–£70+/m²
Subfloor levelling (where needed)	£5–£15/m²
Typical hallway and kitchen-diner (25–35 m²)	£900–£2,400

As a worked example, a 14 m² upstairs bedroom in mid-range click-lock LVT would be 14 × £35–£50 = £490–£700. The LVT underlay, any plywood overboarding and any board repairs are itemised in the written quote, so you can see exactly what your floor needs and why.

Book a free subfloor check in Peterborough

The right underlay starts with knowing what is under your current floor. At the free home visit we check the boards for movement and level, and bring LVT samples so you can see them in your own light. You get a written quote within 24 hours, the floor is fitted by our own team, and the workmanship carries a 2-year guarantee. We fit LVT across Peterborough and the PE postcodes from our showroom at The Manor Grove Centre, PE1 5UH, and you can compare every floor we supply on our flooring Peterborough page. Call 01733 924009 to book a free home visit, Monday to Friday 9am–5pm.