Description
Rockwool Frontrock Super 120 mm is a dual-density Euroclass A1 stone wool slab supplied 3 slabs per pack covering 1.8 m² — the deep-retrofit thickness in our Super range that retains the standard 1.8 m² pack handling of thinner boards while delivering enhanced U-value performance. It is specified primarily on solid-wall deep-retrofit programmes and mid-rise specifications where 100 mm depth falls short of the target and 160 mm exceeds what the calculation requires.
What Rockwool Super 120 mm Does in a UK EWI System
Rockwool Frontrock Super 120 mm is the deep-retrofit specification thickness in our dual-density Super range — a Euroclass A1 stone wool board delivering λ 0.036 W/mK, R 3.33 m²K/W, and a hardened 150 kg/m³ outer face across a single 120 mm layer. It sits in the broader mineral wool insulation range as the workhorse for grant-funded retrofit and ambitious solid-wall upgrade programmes, supplied 3 slabs per pack covering 1.8 m². The 120 mm depth is the sweet spot in the range: thicker than the standard 100 mm high-rise specification, but retaining the same 1.8 m² pack format and 3-slab handling — so scaffold logistics and storage volume stay consistent with the thinner Super variants rather than dropping to the 1.2 m² format of the 160 mm maximum-depth board.
Why Specifiers Choose Rockwool Super 120 mm for UK Walls
- Deep-retrofit U-value contribution: R 3.33 m²K/W typically achieves a refurbishment wall U-value of approximately 0.28 W/m²K on a 215 mm dense block substrate and around 0.18 W/m²K on new-build steel frame, suiting ambitious retrofit and Future Homes Standard-aligned new build.
- A1 fire classification across the full depth: Non-combustible stone wool maintains the highest reaction-to-fire rating through 120 mm — current Approved Document B guidance typically drives this material-level threshold on relevant buildings.
- Pack format unchanged from thinner Super variants: 1.8 m² per pack at 3 slabs keeps scaffold loading, pack count per square metre, and handling tempo consistent with the 80 mm and 100 mm boards — a workflow advantage over the 1.2 m² format of the 160 mm slab.
- Dual-density mechanical resilience: The 150 kg/m³ hardened outer face carries compressive stress of ≥ 20 kPa, handling wind-load pressures on exposed elevations and point-load impact on ground-floor zones without deforming the render substrate.
- Substrate-compensating inner face: The 80 kg/m³ back layer moulds to masonry irregularities of up to 10 mm, achieving full adhesive contact on the uneven brick and stone typical of pre-1919 retrofit work.
- Vapour-open across the full thickness: μ ≈ 1 maintained through 120 mm of stone wool keeps the dew-point profile inside the insulation, protecting historic masonry from trapped moisture over decades of service.
- Recyclable mineral composition: Manufactured from naturally abundant volcanic basalt, supporting BREEAM and lifecycle-carbon assessments on regulated and grant-funded projects.
Thermal Specifications — λ, R-Value, Reaction to Fire
| Property | Value | Standard |
|---|---|---|
| Thermal conductivity (λD) | 0.036 W/mK | EN 12667 |
| R-value at 120 mm | 3.33 m²K/W | EN 13162 |
| Reaction to fire | Euroclass A1 | EN 13501-1 |
| Water vapour resistance factor (μ) | ≈ 1 | EN 12086 |
| Specific heat capacity | ≈ 1030 J/kgK | — |
The 120 mm depth lifts R-value to 3.33 m²K/W — a 50% improvement on the 80 mm slab at R 2.22 m²K/W — while retaining the same 1.8 m² pack format that keeps site handling consistent across the thinner Super range.
Physical Specifications — Density, Strength, Dimensions
Physical numbers below set the handling reality on scaffold — the 1.8 m² pack format carries through from the 80 mm and 100 mm Super variants, so storage volume per square metre of facade stays flat across the range up to this thickness.
| Property | Value |
|---|---|
| Thickness | 120 mm |
| Slab dimensions | 1000 × 600 mm |
| Density (inner / outer) | 80 / 150 kg/m³ (dual-density) |
| Compressive stress at 10% deformation (CS(10)) | ≥ 20 kPa |
| Tensile strength perpendicular to faces (TR) | ≥ 10 kPa |
| Slabs per pack | 3 |
| Pack coverage | 1.8 m² |
| Pack weight | ≈ 16.2 kg |
| Weight per slab | ≈ 5.4 kg |
Where Rockwool Super 120 mm Performs Best — Buildings & Wall Types
The 120 mm Super slab is the deep-retrofit specification thickness for projects where 100 mm falls short of the U-value target and 160 mm exceeds what the calculation requires — particularly the pre-1919 solid-wall housing stock that dominates UK grant-funded retrofit programmes.
- Solid-wall deep retrofit: Pre-1919 brick and stone homes targeted for ambitious thermal upgrades — see the Victorian solid-wall retrofit guide for whole-elevation detailing context and substrate preparation principles.
- Grant-funded retrofit programmes: The 120 mm depth aligns with the U-value outcomes typically targeted by Warm Homes Plan and successor EWI grant schemes, where measurable thermal improvement per installation visit drives the specification.
- Multi-occupancy and mid-rise with enhanced thermal targets: Where 100 mm is the standard high-rise specification but the project U-value brief calls for more, 120 mm provides the next step up in the range without changing pack format.
- New-build steel-frame elevations: Typically achieves wall U-values around 0.18 W/m²K in a single layer, supporting enhanced-specification compliance pathways under current Building Regulations.
- Exposed and coastal facades on retrofit programmes: The dual-density structure handles wind-load pressures on weather-facing elevations while delivering the thermal depth that exposed sites typically demand from their heating systems.
How Rockwool Super 120 mm Fits Into a Full EWI System
Build-up runs fully vapour-open from substrate to render finish. Bond each slab to prepared masonry with Roker U grey adhesive for mineral wool and EPS, applying a full perimeter-and-centre pattern on the hardened 150 kg/m³ face — branded "THIS SIDE UP" marking outward toward the render. Mechanical fixings from the EWI fixing accessories range apply at a minimum 8 per m² with shaft length sized to clear the full 120 mm board plus substrate embedment.
- Adhesive + base coat: Roker U grey (cementitious, vapour-permeable) — same product bonds the slab and reinforces the base layer with embedded fibreglass mesh.
- Mechanical fixings: 60–90 mm disc washer plugs at 8 per m² baseline; shaft length minimum 160 mm on standard brick to achieve 25–40 mm embedment beyond the 120 mm board.
- Base track: Specify a 123 mm-profile base track (or nearest available standard) from the fixing accessories range to support the full insulation depth at the wall base.
- Reinforcement mesh: Alkali-resistant fibreglass mesh embedded fully in the wet Roker U base coat distributes mechanical loads and resists cracking across the slab face.
- Render finish: Silicone or silicate topcoats keep the system vapour-open from substrate through to surface, in line with the breathing-wall rationale for mineral wool.
How Rockwool Super 120 mm Compares to Sibling Slabs
| Specification | Super 80 mm | Super 100 mm | Super 120 mm (this product) | Super 160 mm |
|---|---|---|---|---|
| Range | Frontrock Super | Frontrock Super | Frontrock Super | Frontrock Super |
| Thickness | 80 mm | 100 mm | 120 mm | 160 mm |
| λ (W/mK) | 0.036 | 0.036 | 0.036 | 0.036 |
| R-value (m²K/W) | 2.22 | 2.78 | 3.33 | 4.44 |
| Density | 80/150 kg/m³ dual | 80/150 kg/m³ dual | 80/150 kg/m³ dual | 80/150 kg/m³ dual |
| Fire rating | A1 | A1 | A1 | A1 |
| Pack coverage | 1.8 m² (3 pcs) | 1.8 m² (3 pcs) | 1.8 m² (3 pcs) | 1.2 m² (2 pcs) |
| Refurb U-value (215 mm block) | ≈ 0.33 W/m²K | ≈ 0.30 W/m²K | ≈ 0.28 W/m²K | ≈ 0.19–0.20 W/m²K |
| Typical use | Entry exposed/impact | Mid-rise specification | Deep retrofit, enhanced U-values | Maximum, near-zero |
The 120 mm slab is the deepest board in the Super range that keeps the 1.8 m² pack format — a workflow benefit on grant-funded retrofit programmes where boarding tempo and scaffold rotation matter alongside the U-value brief.
How Rockwool Super 120 mm Performs in UK Weather — Moisture, Frost, Wind Loads
Deep-retrofit projects on UK solid-wall housing stock — concentrated in northern England, Scotland, Wales, and inner-city brick terraces nationwide — face the dual challenge of substantial thermal improvement while preserving the masonry's moisture-management behaviour. Rockwool Super 120 mm addresses both: the R 3.33 m²K/W resistance reaches a refurbishment wall U-value of approximately 0.28 W/m²K on 215 mm dense block, while μ ≈ 1 vapour permeability allows walls to dry outward through prolonged wet UK weather without trapping moisture at the masonry interface.
Dimensional stability across the typical UK service range of −10 °C to +35 °C prevents the thermal-expansion movement that thicker uniform-density boards can transmit into the render. The dual-density structure also spreads fixing loads better than a uniform board would at this depth — relevant on exposed retrofit elevations where the original substrate may already show movement-related defects. The Building Safety Act 2026 facade-fire briefing sets out where the A1 classification becomes the specification driver under current Approved Document B guidance on relevant buildings.
Handling and Storage of Rockwool Super 120 mm on UK Sites
- Familiar pack format at deeper thickness: 1.8 m² per pack at ≈ 16.2 kg keeps scaffold logistics consistent with the 80 mm and 100 mm Super variants — the deepest board in the range without dropping to the 1.2 m² pack of the 160 mm slab.
- Cut with a standard long blade: A 150 mm-blade insulation knife clears the 120 mm depth cleanly — place the branded face ("THIS SIDE UP") downward on a flat board, slicing through the softer back layer first to preserve the hardened outer face.
- Confirm fixing shaft length before ordering: A 140 mm plug that works on 100 mm boards leaves only 20 mm in the substrate behind a 120 mm slab — below the minimum for most wind-load calculations. Aim for at least 160 mm shafts on standard brick.
- Orient correctly: Branded face outward toward the render — installing the slab reversed reduces adhesive bond and fixing performance, particularly noticeable on deeper boards where the load profile through the slab is steeper.
- Store dry: Opaque waterproof cover on site; saturated packs handle poorly even though the hydrophobic treatment recovers thermal performance after drying.
Get these five right and the slab arrives at the wall in the same condition it left the pallet — particularly valued on grant-funded retrofit programmes where boarding tempo and pack rotation are scheduled tightly across multiple properties.
Pro Tips From UK Installers Using Rockwool Super 120 mm
A few details separate the cleanest deep-retrofit installs from average — the points below come from EWI installers working on grant-funded solid-wall programmes and enhanced-specification retrofits across the UK.
- Order shaft length to match thickness, not the previous job: 160 mm shafts minimum for 120 mm slabs on standard brick — the most common avoidable rework happens when 140 mm plugs left over from a 100 mm project end up in a 120 mm install.
- Full-bed adhesive on the dense face: Apply Roker U as a full bed to the 150 kg/m³ face — dot-and-dab at this depth leaves the slab vulnerable to drumming, particularly on the exposed retrofit elevations the 120 mm specification is typically chosen for.
- Set fixings flush with the outer face: Drive washer plates so they sit flush with the hardened face, not recessed into the softer back, keeping the load on the high-density side where it belongs.
- Match base track to insulation depth: A 123 mm-profile track aligns with 120 mm slabs — undersizing the track creates a step at the wall base that telegraphs through the render, particularly visible at the bellcast bead.
- Stagger vertical joints on tall elevations: Brick-pattern bond between courses reduces continuous joint lines that could otherwise concentrate movement stress in the base coat over time.
Certifications & Compliance — A1, EN 13162, REACH
- EN 13162: Factory-made mineral wool products for buildings — declared λ 0.036 W/mK, dimensional tolerances, and mechanical properties confirmed for the dual-density construction.
- EN 13501-1: Euroclass A1 reaction-to-fire — the highest reaction-to-fire classification, indicating non-combustible material with no contribution to fire at any stage.
- BS EN ISO 9001: Rockwool manufactures under certified quality management (BSI FM 02262), supporting batch-to-batch consistency across production runs.
- UK REACH compliant: No hazardous classifications associated with the stone wool composition; Rockwool fibres are not classified as possible human carcinogen.
Specifiers and retrofit coordinators routinely cite these certificates as the baseline for non-combustible deep-retrofit specifications — the material-level threshold required by most grant-scheme technical standards and by current Approved Document B guidance on relevant buildings.
Is Rockwool Super 120 mm Right for Your Project?
- Choose this slab if: Your project is a deep-retrofit programme on solid-wall housing, a grant-funded EWI scheme targeting enhanced U-values, or a mid-rise specification where 100 mm falls short of the thermal brief — 120 mm delivers R 3.33 m²K/W and A1 fire safety in the same 1.8 m² pack format as the thinner Super boards.
- Need maximum single-layer depth? The Rockwool Super 160 mm slab at R 4.44 m²K/W targets near-zero and Future Homes Standard specifications, with the trade-off of a smaller 1.2 m² pack and higher per-square-metre material cost.
- Standard high-rise specification? The Rockwool Super 100 mm slab at R 2.78 m²K/W remains the core mid-rise option where the U-value brief is satisfied at 100 mm.
- Entry-level dual-density coverage? The Rockwool Super 80 mm slab at R 2.22 m²K/W suits projects where impact resistance is the driver but additional thermal depth is not required.
- Low-rise where fire strategy permits combustible insulation? Browse the graphite EPS board range at λ 0.032 W/mK for higher thermal resistance per millimetre at reduced material cost.
All values stated are based on manufacturer-declared data from Rockwool and remain subject to confirmation through project-specific assessment. Specifications may be updated by the manufacturer without prior notice — verify against the current Declaration of Performance before specifying.
What to Order Next — Pack Sizes, Lead Times, Compatible Components
Each pack of Rockwool Super 120 mm covers 1.8 m² (3 slabs at 1000 × 600 mm). For full-system ordering at this thickness, the slab quantity must be paired with thickness-appropriate base track, mid-length mechanical fixings, and a matched run of Roker U adhesive — components specified for 100 mm boards will not carry over directly.
- Adhesive & base coat: Roker U grey adhesive 25 kg — calculate 4–5 kg/m² bonding plus 3–4 kg/m² for the reinforcement layer.
- Mechanical fixings: Select from the EWI fixing accessories collection at 160 mm-plus shaft length to achieve 25–40 mm substrate embedment beyond the 120 mm board, at a baseline 8 per m² adjusted upward per project-specific wind-load calculation.
- Base track: Specify a 123 mm-profile base track (or nearest available standard) from the fixing accessories range to support the full insulation depth.
- Lead time: Full-pack orders confirmed before the daily cut-off ship on the next UK working day.
FAQ — Rockwool Super 120 mm Coverage, Compatibility, Ordering
How many square metres does one pack of Rockwool Super 120 mm cover?
Each pack contains 3 slabs of 1000 × 600 mm and covers 1.8 m² laid flat — the same pack format as the 80 mm and 100 mm Super variants. Order quantities should include 5–10% allowance for cuts at reveals, returns, and parapet detailing, with extra on irregular elevations where multiple board cuts are required.
What U-value does 120 mm Rockwool Super typically achieve?
On a 215 mm dense concrete block refurbishment substrate, 120 mm of Frontrock Super typically achieves a wall U-value of approximately 0.28 W/m²K, based on Rockwool's published U-value tables. On a new-build steel frame with cement particle board sheathing, the result is typically around 0.18 W/m²K, subject to project-specific calculation. The U-value calculation guide walks through the thickness selection method against current Approved Document L guidance.
How does Super 120 mm compare to Super 100 mm in practice?
Both share dual-density construction, A1 fire classification, and 1.8 m² pack coverage. The 120 mm steps R-value from 2.78 to 3.33 m²K/W — a meaningful U-value improvement of around 0.02 W/m²K on typical refurbishment substrates. The additional thickness sits in the softer inner layer rather than the dense outer face, so render-substrate behaviour is unchanged. Choose 120 mm where the U-value target or grant-scheme specification calls for the deeper option.
What fixing shaft length do I need for 120 mm slabs on brick?
For a 120 mm slab on standard brick, select fixing plugs with at least a 160 mm shaft — this provides the full board penetration plus 25–40 mm minimum embedment into the substrate. A 140 mm plug designed for 100 mm boards leaves only 20 mm in the masonry, typically below the minimum for reliable wind-load resistance. Use 60–90 mm disc washers at 8 fixings per m² baseline, adjusted per project wind-load assessment.
Does Rockwool Super 120 mm meet A1 requirements for relevant buildings?
The slab carries Euroclass A1 reaction-to-fire under EN 13501-1 — the highest classification, indicating non-combustible material. Where current Approved Document B guidance requires A1 or A2-s1,d0 insulation in the external wall construction of relevant buildings, this product meets the material-level threshold; the overall system specification remains a project-specific matter for the building designer.
Is 120 mm Rockwool Super suitable for grant-funded retrofit?
The 120 mm depth aligns with the U-value outcomes typically targeted by Warm Homes Plan and successor EWI grant schemes on solid-wall housing stock, and the A1 fire classification satisfies the non-combustible material requirements that grant-scheme technical standards routinely specify. The 1.8 m² pack format keeps installation tempo consistent across multi-property programmes where boarding tempo and scaffold rotation are scheduled tightly.
Is this slab a sustainable specification at 120 mm depth?
The slab is manufactured from naturally abundant volcanic basalt with no blowing agents carrying ozone-depleting or global-warming potential, and off-cuts can be returned to Rockwool's recycling programme. At 120 mm the lifetime energy savings from a wall U-value around 0.28 W/m²K offset the embodied material impact within the early years of service, supporting BREEAM and lifecycle-carbon assessments on regulated projects.
Technical Documentation — Rockwool Super 120 mm TDS & Datasheets