Underlay guide: which type for which floor
Choosing the right underlay for your floor type is as important as choosing the floor itself. A good underlay improves comfort underfoot, reduces noise, aids thermal insulation, and in some cases protects the floor from moisture damage. The wrong underlay can void warranties and cause premature floor failure.
Why Underlay Matters
Underlay sits between the subfloor and the finished flooring and performs several functions simultaneously. It cushions the floor, making it more comfortable to walk on. It reduces impact noise transmission to the room below. It provides a small amount of thermal insulation, which is particularly noticeable in rooms above unheated spaces such as garages. And for wood-based floors, a good underlay helps to accommodate minor subfloor imperfections without transferring them to the surface.
Not all floors require the same type of underlay, and some floors — particularly those that are glued directly to the subfloor or bonded with adhesive — require no underlay at all. Always check the flooring manufacturer's recommendations before purchasing underlay.
Underlay by Floor Type
Different flooring types call for different underlay properties. Here is a guide to matching underlay to floor type:
- Laminate flooring — use a foam or felt underlay with a built-in moisture barrier if laying over concrete. Standard foam underlay is suitable over timber subfloors. Choose an underlay with an appropriate tog rating if acoustic performance is a priority. Many laminate products now come with underlay pre-attached, in which case no separate underlay is needed.
- Engineered wood (floating) — a denser underlay than standard foam gives better support and reduces board flex. A combined moisture barrier and underlay product simplifies installation over concrete.
- Engineered wood (glued down) — no underlay is used. The boards are bonded directly to the subfloor.
- Solid hardwood — typically secret-nailed or glued rather than floated. No underlay in the traditional sense, though some products use an acoustic membrane in specific applications.
- Luxury vinyl tile (LVT) — thin LVT products (under 5mm) are generally glued down without underlay. Thicker click LVT products may float on a specialist thin underlay. Check the manufacturer's specification carefully, as excessive underlay thickness can affect the locking joint integrity.
- Carpet — uses a separate foam or rubber underlay gripped at the perimeter. Thicker, denser underlay improves the feel and lifespan of the carpet.
Underlay and Underfloor Heating
Underfloor heating (UFH) requires special consideration when choosing underlay. All underlay has a tog rating that measures its thermal resistance. The higher the tog value, the more the underlay insulates — which is counterproductive when you want heat to pass from the heating system into the room above.
Most underfloor heating system manufacturers specify a maximum combined tog rating for the floor covering and underlay together. Exceeding this can reduce the efficiency of the heating system and may cause the floor to overheat, which can damage wood-based products. Look for underlay products specifically rated for use with underfloor heating — these typically have tog ratings of 0.5 or below.
Moisture Barriers
Over concrete subfloors, moisture protection is often required to prevent rising damp from affecting wood-based flooring. Many underlay products designed for use over concrete include a built-in polythene moisture barrier. This eliminates the need for a separate damp-proof membrane layer and simplifies installation.
Over timber subfloors, a moisture barrier is generally not needed and can actually be counterproductive — trapping any moisture in the void below the floor rather than allowing it to dissipate. Standard underlay without a moisture layer is appropriate in most timber subfloor applications.
Getting the underlay specification right costs little extra but makes a significant difference to how the finished floor performs and how long it lasts.
