Updated October 2026
We’ve talked about subfloors previously, and we’ve also talked about fitting strategies (glued or floated..). But what we haven’t flagged is, more often than not, there is a layer between your wood floor and subfloor. It’s the filling in your flooring sandwich, and as with sandwiches, what you choose makes a difference.
Remember, you only get one shot at this – you can’t change your filling once the floor is down!
The short version: which underlay for engineered wood?
- Floated floor on an uneven subfloor: a thicker underlay. We use a 5mm product, which helps the floor mould to the subfloor with far fewer creaks.
- A flat with a strict lease: an acoustic underlay with a spec sheet showing its dB reduction. Higher is quieter.
- Cold floors, such as basement flats: check the tog rating. For wood floors it ranges from about 0.3 to just over 1.
- Damp concerns: a damp-proof underlay or membrane (DPM). It protects the floor, but doesn’t fix the damp.
- Underfloor heating: usually a very thin underlay. Always check with the heating manufacturer.
- Glued floors, like herringbone: you can’t glue to most underlays. Use a special rubber and cork underlay glued to ply.
Do you need underlay for engineered wood flooring?
If your floor is floated (not bonded to the subfloor), yes. The underlay sits between the floor and the subfloor and does several jobs: it smooths out small unevenness, reduces footstep noise, can insulate and can block moisture. If your floor is glued down, you usually don’t use a standard underlay at all, because you can’t glue to most of them (more on that below).
Underlay for floated floors
Here we’re talking about underlays, and, believe it or not, there are many different types.
I had no clue about underlay before we started the business, and it’s the same with most of our clients. Yet, the quality of underlay can make a real difference, and the costs, when set against your flooring budget, often make it a no brainer to upgrade.
Underlay can be used to smooth a subfloor, improve sound proofing, increase heat insulation and create a moisture barrier. Our typical use case for premium underlay is when a client wants less heat loss (think basement flats..) and the subfloor is uneven. Uneven subfloors and floated floors are not a good combination; there’s always a risk of creaks or bounces. To fix this, clients can opt to level the floor with a levelling compound, but that’s expensive. Alternatively, they can use a thicker underlay, which is the next best thing.
Levelling out an uneven subfloor: why 5mm beats 3mm
At Kite, we use a 5mm underlay product made from recycled tyres and cork. We’ve used this product over some pretty uneven subfloors, and the floors have moulded to a perfect fit, with very little creaking or movement. By contrast, we see far more creaks and bounces with thinner products. To upgrade, on a standard flooring project, you’d end up paying around £200 extra, so it’s definitely worth the extra spend.
Soundproofing: what dB rating do you need?
In many flats, leases will stipulate “a premium underlay” must be used for timber floors. Good underlays will have a specification sheet that lists performance, and what you’re looking for is the dB reduction. This relates to footstep sounds on your floor, and a higher dB rating will mean you’ll hear less footsteps beneath your floor. Our entry level underlays have a rating of 17dB, premium underlays can be as high as 28dB. If the underlay doesn’t have a spec sheet steer clear; when you come to sell the flat, a specification sheet is evidence you’ve complied with the lease.
Heat insulation: tog ratings
On the specification sheet, you’ll also see a Tog rating. This is a measurement on how effective your underlay is at insulating heat; the higher the tog rating, the less heat will transfer through your floor. For wood floors, underlays can have tog ratings of anywhere from 0.3 to just over 1.
This product has a high tog and dB rating…. OMG. It’s also called Serenity. Although don’t choose your underlay based on the name.
Blocking moisture: damp-proof underlay
Damp is the nemesis of the wood flooring, and we discover it pretty regularly on our travels across East London, especially in basement flats. A Damp Proof underlay is a low cost tool to protect your new floor against moisture, but note this doesn’t fix a damp problem, it merely stops damp getting to your floor.
Yes. It’s a plastic sheet. But a very thick one. In flooring TPE (Thick Plastic Sheet), doesn’t sell well, so it’s often called a DPM (Damp Proof Membrane)…. or a Vapour Transmission Barrier or Moisture Reduction Enhancer (..we made that one up.._)
Underlay for underfloor heating
Of course there are situations where you need an underlay that transfers heat instead of insulating against it. Normally, this means a very thin underlay, but on some electric underfloor heating systems, you float the floors directly onto them. Our advice is to always check with the heating manufacturer. They are almost always very helpful, and will advise on the best build up strategy. Our guide to wood flooring and underfloor heating goes into more detail.
You often float wood floors directly onto foil, electric underfloor heating systems.
Underlay for glue-down floors (herringbone and chevron)
You cannot glue a floor to most underlays. So, what happens if you want a Herringbone floor (that has to be glued down), but you need sound proofing? This is a common scenario for us in new build developments or leasehold flats with strict leases. Here, if the subfloor is floor boards, typically, 6mm ply will be stapled, and then a special underlay made of rubber and cork is glued to the ply, with the flooring glued to this. There’s a lot of glue, and a lot of material involved, but it gets you the floor you want, and complies with the lease.
Our own underlays are designed for floating our wood and laminate floors: the Wood and Laminate underlay (21dB) and the High performance 5mm underlay (26dB).
Underlay for engineered wood: FAQs
Do you need underlay for engineered wood flooring?
Yes, if the floor is floated. Underlay smooths small unevenness, reduces footstep noise, and can add insulation and a moisture barrier. Glued-down floors usually don’t use a standard underlay, because you can’t glue to most of them.
What is the best underlay for engineered wood flooring?
It depends on the job. For a floated floor on an uneven subfloor, we use a 5mm underlay. For flats, choose an acoustic underlay with a spec sheet showing its dB reduction. For damp, use a damp-proof underlay. For underfloor heating, usually a very thin one, as advised by the heating manufacturer.
Is 3mm or 5mm underlay better for engineered wood?
On uneven subfloors, 5mm. We see far more creaks and bounce with thinner products. On a standard project, upgrading costs around £200 extra, which is usually well worth it.
Can you glue engineered wood to underlay?
Not to most underlays. For glued floors such as herringbone that also need soundproofing, a special rubber and cork underlay is glued to plywood, and the floor is glued to that.
What underlay should I use with underfloor heating?
Usually a very thin underlay that lets heat through. On some electric systems, the floor is floated directly onto the heating. Always check with the heating manufacturer.
What dB rating does my underlay need for a flat?
Check your lease. Entry-level underlays are around 17dB, and premium underlays can reach 28dB, which means you hear fewer footsteps below. Always get a specification sheet: when you sell, it’s your evidence that you complied with the lease.
So, there you have it. A lesson in what you can use between floors. It’s probably not something you thought you would ever have to think about. But it’s really important when choosing a floor. Get it wrong, and you’ll be thinking about it a lot. And you won’t be able to change your flooring sandwich.
Happy project planning.
