Underlay Requirements Calculator
Your Results
Complete Guide to Flooring Underlay in the UK
Why Underlay Matters
Underlay sits between the subfloor and the flooring surface, and it performs several critical functions that directly affect the comfort, longevity, and performance of your floor. Without the correct underlay, even expensive flooring will feel uncomfortable, sound hollow, and wear out prematurely. In UK homes, where many ground floors are concrete and the climate creates significant temperature and humidity variations, the right underlay is particularly important.
The key functions of underlay are: cushioning (making the floor comfortable to walk on), sound insulation (reducing both impact noise to rooms below and in-room noise), thermal insulation (keeping the floor warm and reducing heat loss), moisture protection (preventing damp from concrete subfloors from reaching the flooring), and levelling (smoothing out minor irregularities in the subfloor).
Underlay Types for Each Flooring
Each flooring type requires a specific type of underlay. Using the wrong underlay can cause problems ranging from uncomfortable flooring to complete installation failure. Here is what each flooring type needs:
Laminate Flooring Underlay
Laminate needs thin, firm underlay that provides a flat surface for the click-lock joints. The most common options are:
- 3mm foam underlay: The standard choice. Affordable (£1–2/m²), easy to lay, and suitable for most installations. Choose a product with a built-in DPM if installing over concrete. Brands: Mercier, Floorwise.
- 5mm wood fibreboard: Premium option (£3–5/m²). Provides better sound insulation and can smooth minor subfloor imperfections (up to 2mm). Thicker than foam but still within the acceptable range for laminate. Brands: Steico, Fibreboard Direct.
- 2mm XPS foam: Thinner budget option. Provides basic cushioning and a moisture barrier but less sound insulation. Fine for bedrooms and low-traffic areas.
Never use underlay thicker than 5mm under laminate. Excessive underlay thickness causes the floor to flex under foot, stressing the click-lock joints and leading to gaps and squeaks.
Carpet Underlay
Carpet underlay is completely different from hard-floor underlay. It is thick (8–12mm), soft, and designed to provide cushioning and insulation under the carpet:
- PU (polyurethane) foam: The most popular choice in UK homes. 8–11mm thick, good resilience, moderate cost (£3–7/m²). Excellent for living rooms and bedrooms.
- Sponge rubber: Dense and highly durable. Best for hallways, stairs, and high-traffic areas. Maintains its thickness over years of use. £5–10/m².
- Crumb rubber: Made from recycled rubber, very firm. Best for commercial settings or areas with heavy furniture. £4–8/m².
- Felt: Traditional, made from recycled fibres. Good insulation but less resilient. Budget option at £2–4/m².
Wood Flooring Underlay
Engineered and solid wood floors need underlay that provides cushioning and a moisture barrier without being too thick:
- 2–3mm foam: Standard for floating engineered wood. Affordable and effective.
- 3–6mm cork: Premium natural option. Excellent sound insulation and thermal properties. £4–8/m². Ideal for engineered wood over concrete.
- Rubber crumb: Best acoustic performance. Used in flats and conversions where Building Regulations require sound insulation. £6–12/m².
Vinyl / LVT Underlay
Sheet vinyl does not use underlay — it is laid directly onto a smooth subfloor (use levelling compound if needed). Click-lock LVT can use a specialist thin underlay:
- 1–1.5mm LVT-specific underlay: Purpose-designed for rigid-core LVT. Very thin to maintain the stability of the click-lock system. £2–4/m².
Never use standard laminate underlay under LVT — it is too thick and too compressible, which can cause the joints to separate and may void the manufacturer’s warranty.
Moisture Barriers (DPM) — UK Building Regulations
In UK homes, ground-floor concrete subfloors can transmit moisture from the ground below. This moisture will damage flooring over time, causing swelling in laminate, warping in wood, and mould growth under carpet. A damp-proof membrane (DPM) is essential when installing any flooring over concrete.
A DPM is a polythene sheet (minimum 1000 gauge / 250 microns) laid across the entire subfloor with 200mm overlaps at each join, taped with waterproof tape. The DPM should extend up the walls by 25mm (this will be trimmed and covered by skirting boards). Many modern laminate underlays come with a built-in DPM — check the product description before buying a separate sheet.
Timber subfloors in upper-storey rooms do not require a DPM, as they are not in contact with the ground. However, ground-floor timber subfloors with poor ventilation may benefit from improved sub-floor ventilation rather than a DPM.
UK Building Regulations: Sound Insulation
Part E of the Building Regulations (England and Wales) sets minimum sound insulation requirements for floors between dwellings. This applies to flats, maisonettes, and certain house conversions. If you are replacing flooring in a flat or conversion, you may need to achieve specific sound insulation levels, which typically requires acoustic underlay. Check with your local Building Control office for specific requirements.
Underlay Costs in the UK (2026)
| Underlay Type | Thickness | Cost/m² | Roll Size | Roll Price |
|---|---|---|---|---|
| Foam (laminate) | 3mm | £1–£2 | 15m × 1m | £12–£22 |
| Fibreboard (laminate) | 5mm | £3–£5 | 7m² pack | £20–£35 |
| PU foam (carpet) | 10mm | £3–£7 | 15m × 1.37m | £45–£100 |
| Sponge rubber (carpet) | 10mm | £5–£10 | 15m × 1.37m | £75–£140 |
| Cork (wood) | 3–6mm | £4–£8 | 10m × 1m | £40–£80 |
| LVT specialist | 1.5mm | £2–£4 | 10m × 1m | £18–£35 |
| DPM sheet | 250μm | £0.50–£1.20 | 15m × 2.5m | £12–£25 |
Related Calculators
Frequently Asked Questions
Use 3mm foam underlay as standard, or 5mm fibreboard for better sound insulation. Do not exceed 5mm thickness. If the laminate has pre-attached underlay, do not add more — just use a DPM over concrete.
Yes, when installing over concrete subfloors. Use a 250-micron polythene sheet with 200mm overlaps, taped at joins. Many laminate underlays include a built-in DPM. Timber subfloors on upper floors do not need a DPM.
No. Carpet underlay is thick and soft (8–12mm). Laminate underlay is thin and firm (2–5mm). Using carpet underlay under laminate causes the joints to fail. Using laminate underlay under carpet feels hard and uncomfortable.
Calculate room area, add 10% for overlaps and wastage. Divide by roll coverage (commonly 15 m²) and round up. For a 4.5m × 3.5m room (15.75 m²), you need 17.33 m² = 2 rolls of standard 15 m² underlay.
Use the thinnest underlay compatible with your flooring. The combined tog of carpet + underlay must not exceed 2.5. For laminate, use 1.5–2mm low-tog underlay. For LVT, use 1mm specialist underlay. Always check the UFH manufacturer’s specifications.