POLYSTYRENE EPS GRAFIT 20mm

Graphite EPS earns its keep at the head of an opening, where a lintel or soffit runs straight through the insulated plane. This board is the step above reveal thickness in the Renders World graphite EPS insulation boards range, sized for the returns a main-wall thickness cannot wrap.

What the Grafit 20mm Board Closes at Soffits and Lintels

Polystyrene EPS Grafit 20mm is a graphite-enhanced expanded polystyrene board declaring a thermal resistance of 0.60 m²K/W at 20 mm under EN 13163:2012+A1:2015, fitted at lintel returns and soffits where a main-wall board would drop the visible head detail. That resistance belongs to the junction, not to the wall.

The manufacturer's technical card names the duties this board is made for, and they map closely onto UK detailing work. Fitting to that list keeps the specification defensible when Building Control asks what the strip is doing there.

• Lintel and reveal returns — the card lists thermal insulation of lintels and reveals as an intended application, which is the head-and-jamb work around every opening.
• Soffits from below — insulating floor and roof soffits from underneath within a render system, where 20 mm clears rainwater goods and trim.
• Ring beams as permanent formwork — closing the beam line under render, another application the card states directly.
• Secondary equalising layer — bonded over rough masonry or an uneven carrier to bring a face back into plane before basecoat.

Why Installers Fit Graphite EPS Rather Than a White Board

The reason is continuity of material rather than headline performance. Keeping the same grey board at the junction as on the main wall means one adhesive family, one rasping habit and one finish across the elevation.

• Declared resistance at 0.60 m²K/W: both GENDERKA declarations read this session agree exactly at 20 mm, so this is the one figure on the page that carries no scope dispute.
• Twice the 10 mm resistance in the same detailing band: 0.30 to 0.60 m²K/W, which is what makes 20 mm the working choice once depth allows it.
• Grey-board adhesives already on site: the card restricts fixing to cement-based, polyurethane foam or water-dispersion bituminous adhesives, the same families the main-wall boards need.
• Plant-level paperwork: GENDERKA declares from five production plants, so the Declaration of Performance can be matched to the batch that arrives rather than to the range in general.
• Supplied beside the main-wall thicknesses: Renders World lists the detailing boards in the same range, so junction material can go on one order.

Declared Specifications — Two GENDERKA Documents, Two Scopes

Two GENDERKA declarations are open against this board and they are not the same range. The record points at EPS 032 Fasada Extra; the document published on this page until now is the EPS 031 Fasada Extra Plus declaration. Both were fetched this session, so both appear with their scopes.

Declared property	EPS 032 Fasada Extra	EPS 031 Fasada Extra Plus
Thermal conductivity λD	0.032 W/mK	0.031 W/mK
Thermal resistance at 20 mm	0.60 m²K/W	0.60 m²K/W
Bending strength	≥ 75 kPa	≥ 100 kPa
Tensile strength, perpendicular	≥ 80 kPa	≥ 100 kPa
Compressive strength at 10 %	no performance declared	no performance declared
Reaction to fire	E	E
Harmonised standard	EN 13163:2012+A1:2015	EN 13163:2012+A1:2015

 

Specify on the stricter column and the detail holds whichever board is delivered: take 0.032 W/mK, ≥ 75 kPa bending and ≥ 80 kPa tensile, then confirm the range and plant against the delivery note. Neither document declares a compressive strength at all — both record it as no performance declared — so a load-bearing duty for this board is agreed with the designer rather than read off a sheet. For turning a declared resistance into a wall figure, the U-value and insulation thickness calculation guide works through the build-up properly.

Reaction to Fire, at Board Scope

Both declarations give the board a reaction-to-fire class of E, declared under EN 13163:2012+A1:2015. That is the board alone and not the rendered build-up around it, whose rating belongs to the complete specified system; the elevation's fire strategy is settled with the designer and the system holder, and the board is specified inside it.

Water Absorption and Dimensional Stability

The EPS 032 card carries the designation T1-L2-W2-Sb2-P5-BS75-DS(N)2-DS(70,-)2-TR80, where the water-absorption class W2 and the stability limits sit: ± 0.2 % in normal laboratory conditions and ≤ 2 % under the elevated temperature and humidity test. Those tolerances are what hold a soffit strip flat once the reinforcement layer has locked it in.

How to Install the 20mm Board Overhead and at Returns

Two instructions on the card do most of the work here, and both are easy to honour. The rest is sequencing around the fact that this board often goes on overhead.

1. Use a dedicated grey-board adhesive — cement-based, polyurethane foam or water-dispersion bituminous, per the card, and per the adhesive maker's own sheet for open time. Options sit in the EPS adhesives basecoats range.
2. Rasp the face immediately before bonding. GENDERKA recommends abrading the board surface just before adhesive contact to raise adhesion, and on a strip this size it costs seconds.
3. Butter the full back face at this profile, then press onto the prepared soffit, lintel or beam line and check the strip against the main-wall plane.
4. Hold overhead work until the adhesive takes. The card sets mechanical fixing no earlier than 24 hours after bonding, so a horizontal board wants support through that window rather than a plug driven early; where the detail calls for a fixing, it comes from the insulation fixing accessories range, with layout logic in the board fixing pattern and spacing guide.
5. Wrap the reinforcement layer continuously from wall face to return, embedding fibreglass mesh without breaking the lap. The card is explicit that a reinforced layer follows bonding, and the full order is in the EWI system build-up and layers guide.

Storage and Handling for Grey Boards

One line on the card is unambiguous: because of the steel-grey colour, the surface must be protected from direct sunlight, briefly as well as long-term. Keep packs sheeted until the working face is wanted and the adhesion key stays intact. The card also keeps boards away from fire sources, from organic solvents and from their vapours, and asks for protection against mechanical damage in transport and storage — which for a 20 mm strip means stacking flat rather than leaning it against a wall.

How the 20mm Board Compares With the 10mm and 30mm

Board	Declared resistance	Where it belongs
EPS Grafit 10mm	0.30 m²K/W	Tight reveals and narrow strips
Grafit 20mm (this board)	0.60 m²K/W	Soffits, lintels, ring beams
EPS Grafit 30mm	0.90 m²K/W	Deeper returns and overlays

 

All three take the same adhesive and the same rasping habit, so the choice is depth first and resistance second. The 10 mm and 20 mm figures are identical across both declarations; the 30 mm cell carries the stricter 0.90 m²K/W, because the two documents part company at that thickness while agreeing below it.

Choosing Between the Slim Detailing Thicknesses

• Drop to 10 mm where clearance behind the frame is the binding constraint and the strip still has to take basecoat and finish.
• Stay at 20 mm for soffits, lintel returns and ring beams, where the depth exists and the extra 0.30 m²K/W is worth having at the junction.
• Move to main-wall thickness such as the 50mm Grafit board for the primary insulated plane, and treat the wall target as a build-up calculation rather than a thickness.
• Check the dwelling target first on new build with the Future Homes Standard 2026 insulation guide, then size the detailing boards around the main-wall decision.

Price, Availability and Kerbside Delivery

The listed figure is £1.60 per board, read from the product endpoint in August 2026. No VAT label was shown alongside it, so treat the figure as displayed and confirm the tax position at checkout. Board format on this listing is 1000 × 500 mm, which is 0.5 m² per board, so £1.60 ÷ 0.5 m² = £3.20 per m² of board at that price.

The listing showed as not available to order at the same fetch. That is a snapshot rather than a permanent state, and the quickest route is a stock enquiry, since the published policy is that the team confirms restocking times or alternatives on anything out of stock. Boards per pack and pack coverage are confirmed at order rather than quoted here, for the reason set out in the report.

• Processing: same day where stock is available.
• Transit: parcels to 25 kg next day; pallets next day, or two business days on the economy option.
• Local delivery: free by company van within 15 miles of the Southampton base on qualifying orders, then a per-mile charge to a 60-mile limit.
• On arrival: kerbside only, and pallets are shrink-wrapped but not weatherproof — for grey EPS that means cover and a second pair of hands at the kerb, planned in advance.

FAQ — Quantities, Compatibility and Compliance

How do I work out how many boards a soffit run needs?

Each board covers 0.5 m² at the 1000 × 500 mm format, so a run is total return area ÷ 0.5, plus a cutting allowance for corners and service penetrations. As an example, 12 m² of soffit and lintel returns comes to 12 ÷ 0.5 = 24 boards before waste. Pack quantities are confirmed with the sales team at order.

Which adhesive suits a grey board overhead?

One from the three families the card permits — cement-based, polyurethane foam or water-dispersion bituminous — applied to the full back face at this profile. The range of adhesives and basecoats for insulation boards covers all three routes, and the adhesive's own sheet governs open time and coverage.

How does 20 mm differ from the 10 mm board in practice?

Declared resistance doubles from 0.30 to 0.60 m²K/W, and material, adhesive and fixing logic are unchanged. Available depth behind the frame or under the soffit usually settles it before the numbers do, and the 10mm Grafit board takes over once clearance runs out.

Can it serve as primary wall insulation?

At 0.60 m²K/W it belongs at the junction rather than the main wall, where a far higher resistance is needed. Main-wall thicknesses in the same range handle that duty, and the wall figure is always established by build-up calculation rather than by a board property.

What does the class E reaction to fire mean when specifying?

It describes the board as declared under EN 13163:2012+A1:2015 and says nothing about the finished wall, whose rating belongs to the complete system. The route through is to confirm the fire strategy and system specification with the designer at design stage, and specify the board within it.

Technical Documentation

• GENDERKA EPS 032 Fasada Extra — technical card (PDF)
• GENDERKA EPS 032 Fasada Extra — Declaration of Performance, Bydgoszcz plant (PDF)
• GENDERKA EPS 031 Fasada Extra Plus — Declaration of Performance, Wschowa plant (PDF)

The declaration matching the batch supplied, and the plant that issued it, is confirmed at order.