Description
Direct from UK warehouse stock at λD 0.031 W/mK and R 0.60 m²K/W, this 20 mm graphite EPS board is the soffit and lintel detailing thickness in the Genderka EPS 031 Fasada Extra Plus range, with 30 boards per pack covering 15 m² of secondary-layer and junction work on a full EWI build-up.
What EPS Grafit 20 mm Does in a UK EWI System
At R 0.60 m²K/W and λD 0.031 W/mK, EPS Grafit 20 mm is the graphite-enhanced polystyrene board specified for soffit insulation, lintel returns, and secondary equalising layers within a UK external wall insulation build-up, certified to EN 13163 and supplied in 1000 × 500 mm panels at 30 per pack. The board sits within the wider graphite EPS insulation range at the natural step above reveal-detailing thickness — thick enough to deliver a meaningful junction R-value, slim enough to fit beneath soffit boards and over concrete lintels without altering the visible head detail. That balance is what makes it the volume detailing thickness across UK domestic retrofit work.
Above the window head, where main-wall thicknesses cannot wrap the lintel without dropping the visible opening, 20 mm gives an R-value comparable to roughly 25 mm of standard white EPS. The result is a continuous insulated plane that closes the dominant cold bridges on a domestic façade without forcing changes to the elevation geometry.
Why Specifiers Choose EPS Grafit 20 mm for UK Soffits and Lintels
- R 0.60 m²K/W in a 20 mm profile: double the junction R-value of the 10 mm board, putting the 20 mm variant in the bracket that satisfies most psi-value targets at soffit and lintel returns under current Approved Document L guidance.
- Thirty boards per pack, 15 m² of detailing coverage: one pack typically covers all soffits, lintels, and ring-beam returns on a three-bedroom semi-detached retrofit with margin for cutting waste at openings.
- Identical mechanical spec across the range: CS70, BS100, and TR100 carry over from every Grafit thickness, so the adhesive bed pattern and fixing schedule used on the main wall transfer directly to the junction layer.
- Slim composite build-ups become possible: bond 20 mm directly onto an existing 100 mm Grafit board at a parapet or column to reach 120 mm total depth, useful where a single board of that thickness is unavailable or impractical to fix at height.
- Graphite technology in a junction format: 20 mm of graphite EPS contributes the thermal performance of approximately 25 mm of standard white EPS, preserving visible reveal proportions and oversill projections on tighter façade geometry.
- UK warehouse stock for next-working-day dispatch: the soffit-and-lintel thickness ships in the same consignment as main-wall boards, so junction material does not stall the programme waiting on a follow-on pallet.
- Full DoP traceability for compliance audits: each batch carries a factory-specific Declaration of Performance referencing Bydgoszcz, Ostrów Mazowiecka, Oświęcim, Brzeziny, or Wschowa — supporting Building Control sign-off and PAS 2035 retrofit audits.
Thermal Specifications — λ, R-Value, Reaction to Fire
| Property | Value |
|---|---|
| Declared Thermal Conductivity (λD) | 0.031 W/mK |
| Thermal Resistance (RD) at 20 mm | 0.60 m²K/W |
| Reaction to Fire (EN 13501-1) | Euroclass E |
| Classification String (EN 13163) | T1-L2-W2-Sb2-P5-BS100-DS(N)2-DS(70,-)2-TR100 |
| Equivalent White EPS Thickness | ≈ 25 mm at λ 0.038 W/mK |
R 0.60 m²K/W places the 20 mm board firmly in the secondary insulation and junction-detailing band rather than the primary main-wall band. Its contribution shows up in the psi-value (Ψ) at lintel and soffit junctions and in the linear thermal transmittance figures used for SAP and PHPP calculations — junctions that, untreated, can account for a significant share of total fabric heat loss even on a fully insulated main wall. The U-value calculation guide for wall insulation thickness covers the calculation method that ties junction insulation to dwelling fabric efficiency.
Physical Specifications — Density, Mechanical Strength, Dimensions
| Property | Value |
|---|---|
| Manufacturer | Genderka Sp. z o.o. |
| Product Range | EPS 031 Fasada Extra Plus |
| Thickness | 20 mm |
| Board Dimensions | 1000 × 500 mm |
| Coverage per Board | 0.50 m² |
| Boards per Pack | 30 |
| Pack Coverage | 15.0 m² |
| Density | 15 kg/m³ |
| Compressive Strength (CS) | ≥ 70 kPa |
| Bending Strength (BS) | ≥ 100 kPa (BS100) |
| Tensile Strength (TR) | ≥ 100 kPa (TR100) |
| Dimensional Stability — Normal | ± 0.2 % (DS(N)2) |
| Dimensional Stability — 70 °C | ≤ 2 % (DS(70,-)2) |
| Colour | Steel grey (graphite) |
| Standard | EN 13163:2012+A1:2015 |
Where EPS Grafit 20 mm Performs Best — Soffits, Lintels, Secondary Layers
The 20 mm board earns its place in four specific zones of a UK EWI build-up, each of them characterised by depth constraints and outsized influence on junction performance. Soffit returns top the list: the horizontal masonry plane above window heads meets the underside of any lintel or projecting course, creating a continuous edge that needs insulating to keep the envelope unbroken. The 20 mm thickness fits beneath soffit boards and around lintel projections without interfering with rainwater goods or the visible head detail above the opening.
Lintel and ring-beam returns follow the same logic. Exposed concrete lintels behave as thermal short-circuits through an otherwise insulated wall — their localised U-value can sit around 3.5 W/m²K before treatment. Wrapping these elements with 20 mm of graphite EPS drops that localised value substantially and brings the junction back into psi-value compliance for the dwelling fabric calculation.
- Soffit insulation: closing the horizontal cold bridge between main-wall insulation and the underside of soffit boards or roof-edge zones.
- Lintel and ring-beam returns: wrapping exposed structural concrete so dense elements no longer act as heat-loss short-circuits through the insulated envelope.
- Secondary equalising layer: bonded over an uneven render carrier or rough masonry to create a flat surface for basecoat or for a thicker primary insulation board.
- Composite thickness build-up: laminated onto a 100 mm Grafit main-wall board at parapets and column edges to reach 120 mm total depth where a single board of that thickness is unavailable.
How EPS Grafit 20 mm Fits Into a Full EWI System
Within the layered build-up, the 20 mm board installs after the main-wall boards are bonded — either as a separate junction layer at soffits and lintels or laminated onto a thicker primary board for a composite assembly. Apply adhesive from the EPS adhesives and basecoats range full-bed to the back face — perimeter-and-dab gives unreliable bond at this profile — then press onto the prepared soffit, lintel, or substrate surface with tight butt joints between adjacent boards. On horizontal soffit work, temporary propping until adhesive cure (typically 24 hours) prevents the board sagging away from the substrate.
Once bonded, the basecoat reinforcement layer wraps continuously from the main wall face around the soffit or lintel return with embedded alkali-resistant fibreglass mesh, creating a monolithic crack-resistant surface across the junction. The full layer-by-layer sequence is covered in the complete EWI system build-up and layers explained guide. For the fixing pattern that secures the main-wall boards above and below the 20 mm junction layer, the insulation board fixing pattern and spacing guide sets the densities most UK installers work to. Where mechanical retention is specified at exposed soffits, a short plug from the fixing accessories range handles the duty.
How EPS Grafit 20 mm Compares to Sibling Thicknesses
| Property | 10 mm Grafit | 20 mm (this board) | 30 mm Grafit |
|---|---|---|---|
| Thickness | 10 mm | 20 mm | 30 mm |
| λD | 0.031 W/mK | 0.031 W/mK | 0.031 W/mK |
| RD | 0.30 m²K/W | 0.60 m²K/W | 0.95 m²K/W |
| Boards per Pack | 60 | 30 | 20 |
| Pack Coverage | 30.0 m² | 15.0 m² | 10.0 m² |
| Typical Use | Reveal returns, narrow junction strips | Soffits, lintels, secondary layer | Cost-effective entry thickness, deeper overlays |
All three slim-band thicknesses share graphite bead technology and identical mechanical properties — the choice comes down to depth available at the junction and the R-value the psi-calculation calls for. The 20 mm board wins on soffits and lintels where 10 mm undershoots the junction target and 30 mm overshoots the available depth; the 10 mm variant fits tighter reveal returns; the 30 mm steps up where geometry allows a more substantial overlay.
How EPS Grafit 20 mm Performs in UK Weather — Moisture, Frost, Wind
The board's W2 water absorption classification and DS(70,-)2 dimensional stability mean it holds declared performance through UK seasonal cycling, where wind-driven rain and freeze-thaw stress concentrate at soffit and lintel edges. The closed-cell graphite EPS matrix absorbs negligible bulk moisture, and the BS100 bending strength accommodates thermal movement between summer surface temperatures and winter night-time lows without cracking at the joint with main-wall boards.
One UK-specific handling note matters at this thickness. The 20 mm profile is thin enough to flex under its own weight when carried flat over distance, so store packs on a level surface rather than leaning them against a wall. The steel-grey graphite finish also absorbs solar radiation faster than white EPS — keep packs under opaque sheeting until needed and fix boards to the wall the same working day they are unwrapped, protecting the bead-layer adhesion key against cumulative UV softening.
Pro Tips From UK Installers Using EPS Grafit 20 mm
Five habits separate a clean soffit-and-lintel install from one that generates callbacks at the junction. None of them appear on the technical data sheet, and all of them come from the way experienced UK applicators sequence the work on multi-property programmes.
- Pre-cut soffit and lintel strips at ground level: measure each opening, then cut the full allocation on a labelled jig at scaffold base before lifting boards to the platform. On-scaffold productivity rises sharply and waste drops on multi-property runs.
- Full-bed adhesive, never perimeter-and-dab: at 20 mm, partial-contact patterns leave voids that telegraph through the basecoat and finish. Butter the entire back face for reliable contact across the full board area.
- Prop horizontal soffits until adhesive cures: light timber battens or push-stick props hold the board firmly against the underside for the 24-hour cure window, preventing sagging that would otherwise compromise the bond before fixings (if specified) go in.
- Long-blade Stanley knife in a single pass: a sharp blade taken cleanly through in one stroke gives a square cut edge that maximises adhesive contact at the next board joint. Score-and-snap produces a ragged surface that reduces effective bond area.
- Wrap mesh continuously across the junction: embed the same fibreglass mesh used on the main wall around the soffit or lintel return without breaking the lap — this is the detail that prevents micro-cracking at the corner where the two planes meet.
Handling and Storage on Site
Stack packs flat on a level surface rather than leaning them against a wall — at 20 mm the boards flex under their own weight and propped stacking introduces a permanent bow over a few days. Keep packs under opaque sheeting or inside covered storage until needed, both to prevent UV softening of the graphite surface and to keep boards at ambient temperature for predictable adhesive open-time. Lift packs by the strapping or by supporting the long edges rather than the short ends to avoid creasing the outer boards in transit from delivery point to working platform.
Certifications and Compliance — EN 13163, Euroclass E
- EN 13163:2012+A1:2015: the harmonised European standard for factory-made expanded polystyrene in buildings, covering declared thermal conductivity, dimensional tolerances, mechanical strength, and water absorption.
- Reaction to Fire — Euroclass E: typically suitable for use within EWI systems on residential buildings below 18 metres, where the project fire strategy permits Euroclass E with approved fire-barrier detailing under current Approved Document B guidance.
- CE Marking and Declaration of Performance: each production batch carries a DoP referencing the specific Genderka factory of origin (Bydgoszcz, Ostrów Mazowiecka, Oświęcim, Brzeziny, or Wschowa), supporting traceability for Building Control inspections and PAS 2035 retrofit audits.
- Junction Detailing Under Part L: insulating soffits and lintels with graphite EPS supports the linear thermal transmittance (psi-value) calculation at critical junctions under current Approved Document L guidance and the conventions set out in BR 443.
Is EPS Grafit 20 mm Right for Your Project?
- Specify EPS Grafit 20 mm for soffit, lintel, and ring-beam returns on EWI build-ups using graphite EPS on the main wall area, where the junction R-value target sits above what a 10 mm reveal strip can deliver but below the depth available for a main-wall thickness.
- Drop to the 10 mm Grafit board for reveal returns where only 10 mm of clearance exists between the insulated wall plane and the window frame.
- Step up to the 30 mm Grafit board for cost-effective entry-thickness overlays on deeper junctions, or for secondary layers where the geometry allows a more substantial contribution.
- Switch to mineral wool slabs where the project fire strategy requires non-combustible A1-rated insulation across the whole build-up, typically on residential buildings above 18 metres.
- Confirm thickness against the dwelling target using the Future Homes Standard 2026 insulation requirements guide for new-build work and Approved Document L for retrofit programmes.
Declared thermal values (λD, RD) are stated per EN 13163 and the Genderka manufacturer technical data sheet. Actual installed performance depends on substrate condition, adhesive coverage, and the complete EWI system build-up. Verify current data with the manufacturer or the project energy assessor before specification.
What to Order Next — Pack Sizes, Lead Times, Compatible Components
One pack of 30 boards covers 15 m² of soffit and lintel detailing — typically enough for all junction zones on a three-bedroom semi-detached retrofit with 5 to 10 % cutting margin. Pair the order with the matching adhesive from the EPS adhesives and basecoats range and the appropriate short fixing plug from the fixing accessories range if the specification calls for mechanical retention at exposed soffits. UK warehouse stock supports next-working-day dispatch on full-pack quantities ordered before midday, so the junction material arrives with the rest of the EWI consignment rather than as a separate delivery.
FAQ — EPS Grafit 20 mm Coverage, Compatibility, Installation
How many 20 mm boards are in a pack, and what area does one pack cover?
Each pack contains 30 boards, each measuring 1000 × 500 mm, giving a total pack coverage of 15.0 m². For soffit and lintel detailing on a three-bedroom semi-detached retrofit, one pack generally provides enough material for all junction zones with a 5 to 10 % allowance for cutting waste around complex profiles and service penetrations.
Does a 20 mm soffit board need mechanical fixings, or is adhesive enough?
For horizontal soffit applications, full-bed adhesive supplemented by temporary propping until cure (typically 24 hours) is usually sufficient — at approximately 0.15 kg per board, gravity load on a horizontal joint is minimal. Where the project specification or Building Control calls for mechanical retention at exposed soffits, a short fixing plug installed after adhesive cure handles the duty, provided the substrate behind the board offers adequate embedment depth.
Can the 20 mm board be combined with thicker boards for a custom total depth?
Composite build-ups are an accepted EWI detailing technique. Bond the 20 mm board to the face of the thicker primary board using a thin bed of compatible adhesive, then apply the reinforcing basecoat and mesh across the entire composite surface as a single continuous layer. The approach is particularly useful at parapets and column edges where the total required depth falls between standard board thicknesses in the range.
How does the 20 mm compare to the 10 mm and 30 mm Grafit variants?
All three share λD 0.031 W/mK and identical mechanical properties (CS70, BS100, TR100). The difference is R-value and pack count: the 10 mm variant gives R 0.30 m²K/W at 60 boards per pack for reveal returns, 20 mm doubles to R 0.60 at 30 boards per pack for soffits and lintels, and the 30 mm variant reaches R 0.95 at 20 boards per pack for deeper overlays. Choose by depth available at the junction and the R-value the psi-calculation requires.
Can the 20 mm board be used as primary wall insulation?
At R 0.60 m²K/W, the 20 mm board is a junction and secondary-layer product rather than a primary insulation layer. Approved Document L wall U-value targets (0.26 W/m²K for new build, around 0.30 W/m²K for retrofit where feasible) require substantially thicker insulation across the main wall area — typically 80 mm to 160 mm of graphite EPS depending on the existing wall construction. The 20 mm board performs best as a junction layer complementing those main-wall thicknesses.
What is the best way to cut a clean edge at 20 mm thickness?
A sharp long-blade Stanley knife taken in a single steady pass gives the cleanest cut at this thickness, producing a square edge that maximises adhesive contact at the next board joint. Score-and-snap can leave a ragged surface that reduces effective bond area, so avoid it on edges destined to butt against the next board. A hot-wire cutter works well for repetitive soffit strips when fed at a steady rate.
What fire classification rules apply when specifying 20 mm graphite EPS in the UK?
The board carries a Euroclass E reaction-to-fire classification under EN 13501-1 and is typically suitable for residential buildings below 18 metres, where the project fire strategy permits Euroclass E with approved fire-barrier detailing in accordance with current Approved Document B guidance. For taller buildings or higher-risk façades requiring non-combustible A1-rated insulation, mineral wool replaces EPS across the build-up. Confirm the classification with the designer and Building Control at design stage to avoid substitutions on site.
Technical Documentation — EPS Grafit 20 mm TDS, DoP, Certificates