EPS INSULATION BOARDS

Genderka EPS 031 Fasada Extra Plus graphite boards run from 10 mm to 200 mm, declaring λD 0.031 W/mK to EN 13163 and a declared thermal resistance of 3.20 m²K/W at 100 mm. Renders World holds the thickness range in Southampton stock for UK retrofit and new-build programmes.

Where Graphite EPS Boards Perform Best on UK Walls

Graphite EPS insulation boards UK specifiers fix to solid masonry declare λD 0.031 W/mK to EN 13163:2012+A1:2015, delivering 3.20 m²K/W at 100 mm and keeping reveal depth close to the original facade line. The manufacturer scopes these boards to render systems bonded directly to the wall, and they sit inside the wider external wall insulation build-up as the thermal core.

The declared use list on the technical sheet is narrower than general-purpose polystyrene, which is what makes the range predictable on facade work. Genderka names four applications that matter to a render contractor:

• Walls in bonded render systems — the primary case, boards adhered and mechanically fixed before a reinforced layer.
• Lintels and window reveals — the thin end of the range wraps openings so the insulation line stays continuous.
• Soffits from below in bonded render systems, including exposed floor edges.
• Walls with cladding and a ventilated cavity, where the board insulates behind a separate rainscreen.

Depth follows the target, and the target is a calculation rather than a board choice. A declared resistance is a board property; the wall figure that Building Control reads comes from the whole build-up, so the U-value and thickness calculation method is where a thickness gets justified.

Why Specifiers Pick Graphite Boards for Render Systems

Six things separate this range from general polystyrene on a facade schedule, and all six are readable on the manufacturer's documentation rather than inferred from it.

• λD 0.031 W/mK declared, not nominal: the graphite content lowers declared conductivity against standard white expanded polystyrene, which is the whole reason the range exists and why a target is reached at less depth.
• A declared resistance table per thickness: Genderka publishes RD against every thickness, so a calculation uses the declared value rather than thickness divided by lambda — the two differ by rounding and only the declared figure appears on the declaration of performance.
• BS100 and TR100 mechanical grades: bending strength at or above 100 kPa and tensile strength perpendicular to the faces at or above 100 kPa, the properties that decide whether a board survives handling at scaffold height and holds an adhesive bond under wind uplift.
• Tight dimensional tolerances: thickness held to ±1 mm and length and width to ±2 mm, with flatness to ±5 mm, so courses close without shimming and joint gaps stay small enough for the basecoat to bridge.
• One material specification across the range: every thickness carries the same conductivity, mechanical grades and reaction-to-fire class, so an elevation mixing reveal strips with field boards behaves as one material.
• Plant-specific declarations of performance: Genderka declares this product separately from five production sites, so the evidence pack for a job can name the document issued for the plant that actually supplied it.
• Stock and technical reading in the UK: Renders World dispatches from Southampton and reads the declarations rather than the range name, which matters where two similarly named Genderka lines carry different figures.

Match Board Thickness to Declared Thermal Resistance

Read the project on the left and take the declared resistance on the right into the wall calculation. Eight of the range's thicknesses are shown, spanning reveal strips to maximum depth; the intermediate 20 mm, 90 mm and 160 mm boards sit between neighbouring rows and behave as the rows around them.

The steps between rows are what a specification argument turns on. Moving from 90 mm to 100 mm buys 3.20 − 2.90 = 0.30 m²K/W; moving from 100 mm to 150 mm buys 4.80 − 3.20 = 1.60 m²K/W for 50 mm of extra build-up. Renders World will price the alternatives side by side where a reveal or a boundary line makes the deeper board awkward.

How to Fix Graphite Boards Into a Render Build-Up

Fixing sequence is set by the manufacturer, and two of its instructions carry hard timings. Boards are bonded with an adhesive dedicated to grey graphite board, and mechanical fixing follows no earlier than 24 hours after bonding — driving plugs into a green bed disturbs the contact the bond depends on.

• Prepare and prime the substrate: sound, dry masonry, with defects made good before any adhesive goes on the wall.
• Choose a permitted adhesive: the sheet allows cement-based adhesives, polyurethane foams, or water-dispersion bitumen compounds, taken from the EPS adhesives basecoats range. Solvent-bearing products attack the bead structure and are excluded outright.
• Rasp the bonding face: Genderka recommends abrading the board immediately before bonding to raise adhesion, which is the single cheapest step in the sequence.
• Fix mechanically after 24 hours, using plugs from the insulation fixing accessories range. Density and plug length come from the system designer's wind-load work and the plug manufacturer's own table, not from a rule of thumb.
• Build the reinforced layer: the sheet requires a reinforced coat over the bonded boards, embedding alkali-resistant rendering mesh in fresh basecoat before priming and finishing.

Board format affects the fix as much as thickness. These are 1000 × 500 mm boards, half the width of the 1000 × 1000 mm format, so a course closes with twice the vertical joints and staggering them properly matters more. The full installer-level sequence, layer by layer, is set out in the EWI system build-up guide.

Installer Habits That Keep a Board Fix Moving

Three of the four habits below come straight off the technical sheet and are routinely skipped; the fourth is ordering discipline that pays back across repetitive elevations.

• Sheet the packs on arrival. Genderka instructs that the steel-grey surface is protected from direct sun, brief exposure included, because the colour that delivers the low lambda also absorbs radiation. Opaque cover from the moment the pallet lands keeps the bonding face in good order.
• Keep solvents off the stack. No substance containing organic solvents goes near the boards, which quietly rules out some site sealants and cleaning products stored on the same scaffold lift.
• Treat the 24-hour cure as a programme item, not a guideline — plan the bonding day and the plugging day as separate visits to the same elevation rather than chasing both before the scaffold moves.
• Order by pack coverage, not board count. Boards per pack falls as thickness rises, so a mixed order of reveal strips and field boards produces very different pallet volumes from similar-looking quantities.

One specification point is worth knowing before a structural query arrives: the designation for these facade boards carries bending and tensile grades but no compressive strength term. Compressive strength is not a declared property of this product, so plinth, floor and trafficked applications belong to a board that declares one.

Which Insulation Core Should You Order?

• Order graphite EPS where the project fire strategy accepts a reaction-to-fire class E board within the build-up and the priority is the most declared resistance per millimetre. The class belongs to the board, and the finished wall is assessed as a system by the project's designer under current Approved Document B guidance.
• Switch to mineral wool insulation where the strategy calls for a non-combustible core, or where a vapour-open assembly is the point. Note that stone wool takes a wool-compatible adhesive rather than a polystyrene one.
• Confirm the thickness by calculation, using the declared resistance from the table above rather than a thickness that worked on a previous job, and check the regulatory direction in the Future Homes Standard guide.
• Confirm the plant at order. Because the declaration of performance is issued per production site, the Renders World trade desk matches the document to the supplying plant before dispatch so an evidence pack stays consistent.

FAQ — Thickness, Fixing and Fire Classification

How many packs does a measured wall area need?

Work from pack coverage and add for waste. On a surveyed 100 m² of net wall area in 100 mm boards, 100 ÷ 3.0 m² per pack = 33.3, and adding 10% for cutting around reveals and service penetrations gives 37 packs. The same area in 200 mm boards runs 100 ÷ 1.5 = 66.7, so 74 packs with the same allowance. Always order against a measured survey rather than a plan take-off.

What does stepping up one thickness actually buy?

The declared resistance table answers it directly: 90 mm declares 2.90 m²K/W, 100 mm declares 3.20 and 150 mm declares 4.80. So the 90 to 100 mm step adds 0.30 m²K/W for 10 mm of depth, while 100 to 150 mm adds 1.60 for 50 mm. Whether either step changes the wall's compliance position depends on the rest of the build-up.

Which adhesives are permitted on graphite boards?

The technical sheet names three families: cement-based adhesives, polyurethane foam adhesives, and bitumen compounds based on water dispersion, each used according to the adhesive manufacturer's own instructions. Anything carrying organic solvents is excluded because it damages the bead structure. Abrading the bonding face immediately before adhesive is the manufacturer's recommendation for better adhesion.

How long after bonding can plugs be driven?

Mechanical fixing is carried out no earlier than 24 hours after the boards are bonded, giving the adhesive time to develop before the board is pierced and clamped. The reinforced layer follows the fixing, not the bonding. Where weather stretches the cure, the sequence waits rather than compresses, and the elevation is none the worse for it.

What does the reaction-to-fire class cover?

Genderka declares reaction to fire class E for the board itself, on both the technical sheet and the declaration of performance, to EN 13163:2012+A1:2015. That class describes the board as tested and is not the rating of a rendered wall, which is assessed as a complete system. The height threshold, cavity barriers and any requirement for a non-combustible core are decisions for the project fire strategy under current Approved Document B guidance.

How much dimensional variation should a fixer expect?

Thickness is declared to ±1 mm, length and width to ±2 mm, squareness to ±2 mm per metre and flatness to ±5 mm. Dimensional stability is declared at ±0.2% under normal laboratory conditions and within 2% under the specified temperature and humidity conditions. In practice that means courses close cleanly and the reinforced layer bridges the joints it is designed to bridge.

How do board orders ship?

Orders are processed the same day where stock is available, with pallets up to 1,200 kg on next-day delivery or two business days on the economy option, and small parcels up to 25 kg next day. Deliveries are curbside only and pallets are shrink-wrapped rather than weatherproof, so on-site cover and unloading arrangements are worth confirming when the order is placed.