What Is R-Value & Why Does It Matter for LVT Over Underfloor Heating in a PE Postcode Home?

Short answer: R-value is how strongly a floor resists heat passing through it, measured in m²K/W, and for LVT over underfloor heating lower is better. Glue-down LVT on its own usually adds very little resistance, often around 0.01–0.03 m²K/W, which is why it is one of the best floors for underfloor heating. Click LVT with an underlay adds more, so the underlay choice matters as much as the floor.

We regularly fit LVT over underfloor heating in Peterborough homes, from new builds with screeded ground floors and air-source heat pumps to older terraces where an electric mat has gone into a bathroom or kitchen. The question we are asked most at the free home visit is simple: will the heat still come through? R-value is the number that answers it. This guide explains what it means, how to read it on a data sheet, and how we use it when we specify LVT across the PE postcodes.

What is R-value in flooring?

R-value is thermal resistance: a measure of how much a layer slows heat moving through it. It is written in square metres kelvin per watt (m²K/W). A higher number means the layer acts more like insulation; a lower number means heat passes through more easily.

For underfloor heating you want the opposite of what you want in a loft. Everything you lay over the pipes or cables (the floor finish, any underlay and any rug) sits between the heat and the room. Each layer adds its own R-value, and the totals add together:

Total floor-covering R-value = floor finish + underlay + anything else on top

You can estimate a layer's R-value from its thickness in metres divided by its thermal conductivity. As a worked example, a 2.5 mm glue-down LVT with a conductivity of around 0.25 W/mK gives 0.0025 ÷ 0.25 = 0.01 m²K/W. That is why thin, dense LVT performs so well: there is very little material to slow the heat down.

How does R-value relate to tog?

Carpet and underlay are usually rated in tog rather than R-value. They measure the same thing on a different scale: 1 tog = 0.1 m²K/W. So a combined carpet and underlay of 2.5 tog has an R-value of 0.25 m²K/W, and a floor with an R-value of 0.15 m²K/W is 1.5 tog.

R-value (m²K/W)	Tog	What it usually means over underfloor heating
0.01–0.05	0.1–0.5	Very low resistance: typical of glue-down LVT and sheet vinyl laid directly on a prepared subfloor
0.05–0.10	0.5–1.0	Low: typical territory for click LVT, laminate or engineered wood with a thin underlay made for underfloor heating
0.10–0.15	1.0–1.5	Moderate: around the figure many heating designers work to, especially for low-temperature heat pump systems
Up to 0.25	Up to 2.5	The long-standing upper guide for carpet and underlay combined over underfloor heating

Treat these bands as a guide to how floors compare, not a specification. The exact figure for your floor comes from the product data sheet, and the figure your system can accept comes from your heating designer.

Why does R-value matter for LVT over underfloor heating?

Underfloor heating is designed to deliver a certain amount of heat at a certain water or cable temperature. Add too much resistance on top and three things happen:

• The room takes longer to warm up, because heat is held back in the screed.
• The system has to run hotter to reach the same room temperature, which costs more to run and works against the efficiency of a heat pump.
• The floor surface can get hotter than it should in some spots, which matters because LVT ranges from Karndean, Amtico, Moduleo, Quick-Step and Polyflor are generally approved for underfloor heating only up to a floor surface temperature of 27°C.

Keep the total R-value low and the heating does what it was designed to do, at the temperature it was designed for.

Does glue-down or click LVT have a lower R-value?

Glue-down LVT is almost always the lower of the two. It is thin, dense and bonded straight to a smoothed subfloor, with no air gap and no underlay. Click and rigid-core LVT is thicker and normally sits on an underlay, and that underlay can add more resistance than the plank itself.

Option	Typical build-up	Effect on R-value	Supply-and-fit guide
Glue-down LVT	LVT bonded to a smoothed, levelled screed	Lowest: very little between heat and room	Premium glue-down Karndean and Amtico £50–£70+/m²
Click or rigid-core LVT	Planks over a thin underlay approved for underfloor heating	Low, provided the underlay is a low-resistance type	Mid-range click-lock and rigid-core £35–£50/m²
Click LVT on the wrong underlay	Planks over a thick, soft acoustic underlay	Higher: the underlay can hold back heat	Not something we would specify over underfloor heating

Our click-lock vs glue-down LVT guide covers the other differences, and you can see the full range on our LVT flooring Peterborough page.

What R-value should I aim for with a heat pump?

Air-source heat pumps run at lower water temperatures than gas boilers, so they have less heat in hand to push through a floor. That makes R-value more important, not less. Heating designers commonly work to a total floor-covering resistance of around 0.10–0.15 m²K/W (1 to 1.5 tog) for these systems, and some design for less.

Many newer homes around Peterborough are built with screeded ground floors and low-temperature heating. If yours is one of them, ask your developer or heating installer what floor-covering resistance the system was designed for before you choose a floor. With that figure in hand, LVT is one of the easiest floors to keep inside it. Our new-build flooring guide for Cardea and Stanground South covers other things to check when you get the keys.

Is the underlay or the LVT more important?

Over underfloor heating, the underlay is often the deciding factor. A plank of click LVT adds a modest amount of resistance; a thick foam or acoustic underlay can add much more. That is why we only fit click LVT over underfloor heating on a thin underlay that the manufacturer approves for it, usually with a vapour barrier where it goes over screed.

Standard underlay in Peterborough starts from £4/m² supplied and fitted, but a specialist underfloor-heating underlay is specified for the job and itemised in the written quote. If you live in a flat, the building may also require a minimum acoustic rating, so we check both requirements together rather than trading one off against the other.

How do PE postcode homes differ?

We see three common set-ups across Peterborough and the surrounding PE postcodes:

• New builds with wet underfloor heating in screed. Often paired with a heat pump. The screed must be fully dry before any LVT goes down, and the heating is brought up gradually afterwards. Glue-down LVT or click LVT on a thin approved underlay both work well.
• Extensions and kitchen-diners in older homes. Underfloor heating is often added to the new floor only. We check that the old and new floor levels meet cleanly and that the heated area has the right build-up.
• Bathrooms with electric mats. Often added during a bathroom refit in terraces and semis. The cables need to be properly covered and levelled before LVT goes on top; our guide to LVT in bathrooms explains the rest.

Whatever the set-up, the subfloor has to be flat and dry. Subfloor levelling is typically £5–£15/m² where needed, and in older Fenland homes we test moisture first; our moisture-testing guide explains why.

How do we check R-value before we fit?

At the free home visit we ask what heating you have, look at the subfloor and, where you have them, read the heating installer's notes. We then check the data sheet for the LVT and underlay we are recommending and add the two R-values together, so you can see the total compares with the figure your system was designed for. If a combination does not suit, we change the underlay or move you to glue-down rather than fit something that holds back the heat.

For a wider comparison of every floor type over underfloor heating, including engineered wood, laminate and carpet, read our best flooring for underfloor heating guide. You can also see engineered wood flooring in Peterborough and vinyl flooring in Peterborough if you are weighing other options.

What does LVT over underfloor heating cost in Peterborough?

LVT is supplied and fitted from £35/m². Mid-range click-lock and rigid-core LVT is £35–£50/m², and premium glue-down Karndean and Amtico is £50–£70+/m². As a worked example, a 30 m² kitchen-diner in mid-range click LVT at £35–£50/m² comes to 30 × £35 = £1,050 up to 30 × £50 = £1,500, before any levelling or specialist underlay, which are itemised in the written quote. The full table is on our flooring prices Peterborough page, and the Karndean ranges we fit are on our Karndean flooring Peterborough page.

Book a free home visit

We are local flooring fitters in Peterborough, with a showroom at 4 The Manor Grove Centre, Vicarage Farm Road, Peterborough PE1 5UH, and our own team does the fitting, backed by a 2-year workmanship guarantee. You will find coverage details on our carpets and flooring in Peterborough page.

If you have underfloor heating and want LVT that lets the heat through, call our team on 01733 924009 to book a free home visit, Monday to Friday. We will bring samples, check the build-up and send a written quote within 24 hours.