If you're already fitting a new wood floor, that's genuinely the easiest and most cost-effective moment to add proper insulation underneath it, since the underlay simply becomes part of the normal installation sequence rather than a separate, disruptive job later. Uninsulated suspended timber floors can account for a significant share of a property's total heat loss, so it's worth getting right the first time.
Understanding Tog Rating
Underlay is rated using a Tog value, the same measurement used for duvets, and it works the same way: the higher the Tog rating, the more thermal resistance the underlay provides, meaning better insulation against heat loss through the floor. Thickness, density, and the specific material all factor into a given underlay's Tog rating, so two products of similar thickness can still perform quite differently depending on what they're actually made from.
For a standard room without underfloor heating, choosing a higher Tog rating genuinely makes sense, since the priority is stopping heat escaping downward through the floor.
If You're Fitting Underfloor Heating, This Changes Things
This is where it's easy to get the choice backwards. If underfloor heating is part of the plan, you actually need a low Tog rating, typically 0.5 or below, since the goal here is the opposite of standard insulation: you want heat to pass upward from the heating system into the room as efficiently as possible, not get trapped or resisted by the underlay beneath the boards. Using a high-Tog underlay over underfloor heating effectively blocks a meaningful portion of the heat you're paying to generate, making the whole system less efficient and slower to warm the room.
If you're planning underfloor heating, it's worth confirming the Tog rating of any underlay before it goes in, rather than assuming a "better insulation is always better" approach applies here, since in this specific case it works against you.
What Layering Looks Like During A New Fit
For a typical new installation, the sequence generally follows a consistent order:
- Subfloor preparation, making sure the surface is clean, level, and structurally sound before anything else goes down.
- A damp-proof membrane, where needed, particularly over concrete subfloors prone to rising moisture.
- The insulation or acoustic underlay layer, chosen for the room's specific priorities, thermal performance, sound reduction, or underfloor heating compatibility.
- The wood flooring itself, fitted on top once the layers beneath are properly prepared and settled.
Getting this sequence right matters more than it might seem, skipping or rushing the subfloor preparation stage undermines everything laid on top of it, regardless of how good the insulation itself is.
Suspended Timber Vs Solid Subfloor: Different Approaches
The right insulation approach depends heavily on what's beneath the floor. Suspended timber subfloors, common throughout London's Victorian and Edwardian housing stock, typically use mineral wool fitted between the joists themselves, addressing the unheated void directly beneath the room. Solid concrete subfloors call for a different approach entirely, usually rigid insulation boards or a suitable underlay combined with a damp-proof membrane, since there's no joist void to work with and moisture management becomes the more pressing concern.
Getting this distinction right at the planning stage avoids specifying the wrong product for your actual subfloor, which is a genuinely common and avoidable mistake in DIY insulation projects.
New Wood Floor Insulation: Common Questions
What Tog rating should I choose for a standard room without underfloor heating?
Generally, a higher Tog rating is the right call here, since the priority is maximising thermal resistance and reducing heat loss through the floor.
Why does underfloor heating need a low Tog underlay instead of a high one?
Because the goal is the opposite of standard insulation. You want heat to pass upward into the room efficiently, and a high-Tog underlay resists that heat flow, making the underfloor heating system work harder and less efficiently than it should.
Does the insulation approach differ between a suspended timber and a solid concrete subfloor?
Yes, significantly. Suspended timber floors typically use mineral wool fitted between the joists, while solid concrete subfloors generally need rigid insulation boards or underlay combined with a damp-proof membrane instead.
Is it worth adding acoustic underlay at the same time as thermal insulation?
Often yes, particularly in flats where noise transfer between floors matters. Many underlay products are designed to address both thermal and acoustic performance in a single layer, which is more efficient than treating them as separate jobs.
Call us on 020 7036 0625 or request a free site visit and we'll advise on the right insulation approach for your specific subfloor and heating setup.
