EXTERNAL WALL INSULATION

Where External Wall Insulation Earns Its Place on a UK Building

External wall insulation works as one specified build-up, so the insulation core sets everything above it: graphite EPS boards declared at λD 0.032 W/mK to EN 13163 keep the wall thin enough for tight reveals. Renders World distributes the whole envelope, and the wider render and insulation catalogue sits behind the five collections gathered on this hub.

Each collection here owns one layer of the wall: the insulation core, the adhesive and mechanical fixings that hold it, the reinforced basecoat and mesh, the primer, and the render finish that closes the assembly to weather. Settle the core first and the rest of the schedule follows it, because adhesive type, plug length and render compatibility are all consequences of that one decision.

• Solid-wall retrofit. Pre-1919 brick and stone gains a continuous insulated skin without losing internal floor area or original plaster detail.
• New build and deep retrofit. Fabric targets under current Approved Document L guidance are met by calculation across the whole build-up, not by a board thickness on its own.
• Funded programmes. Measured work under PAS 2035 needs component documentation that matches what was installed, which is a supply-chain question as much as a design one.

Why Trade Buyers Source Whole EWI Systems Here

Buying the envelope from one distributor removes the compatibility guesswork that appears when a core, an adhesive and a finish arrive from three unrelated channels. The points below are the ones trade accounts raise most often.

• Named manufacturers, not re-badged stock: Atlas, Ceresit, Genderka and Rockwool goods arrive with the manufacturer's own declaration of performance behind them, so a specification file can quote the document that was actually issued for the product.
• Board figures you can put in a calculation: the Genderka graphite EPS range declares λD 0.032 W/mK and a declared thermal resistance per thickness, which is the value a U-value calculation needs rather than thickness divided by lambda.
• A non-combustible route where the fire strategy asks for one: Rockwool Frontrock Plus slabs are declared Euroclass A1 for reaction to fire on their own declaration of performance, at slab scope.
• One account across the full build-up: core, adhesive, basecoat, mesh, fixings, primer and finish on a single order, which keeps substitutions off site when a delivery slips.
• Layer-by-layer routing before purchase: this hub sends a project to the collection that owns the layer in question, so the specification is assembled in the right order.
• Stockholding in Southampton: goods ship from the Renders World warehouse by courier or pallet, with orders processed the same day where stock is available.
• Technical reading of the documents: plant scope on a declaration, slab-versus-system fire scope and declared resistance tables are checked against the sheet rather than assumed from a range name.

Choose the EWI Layer Your Specification Starts From

Read the project description on the left, then take the collection that owns that layer. Product-level specification, pack data and pricing live on the collection page, not here.

Specification tier and price per square metre are the bundle collection's own territory, so a budget comparison across tiers is built there rather than on this page.

How the Five Collections Stack Into One Wall Build-Up

The five collections are one wall read in sequence, and the order is fixed by what each layer bonds to. Working outward from sound, dry masonry, the sequence runs adhesive, core, mechanical fixings, reinforced basecoat with embedded mesh, primer, then the decorative render.

• Adhesive to substrate: a cement-based, polyurethane foam or bitumen-dispersion adhesive dedicated to graphite boards, applied to prepared masonry.
• Insulation core by zone: graphite EPS on the main elevation, mineral wool where the fire strategy requires it, hydrophobic boards at the plinth.
• Mechanical fixing: plug length follows surveyed board thickness, and the pattern comes from the system designer's wind-load work.
• Basecoat and mesh: the reinforced layer that gives the render a stable, crack-resistant base.
• Primer and render: a keying coat followed by the finish that closes the wall to weather.

Thickness arithmetic is where the core decision becomes visible. The graphite EPS sheet declares 2.50 m²K/W at 80 mm and 3.10 m²K/W at 100 mm, so 3.10 − 2.50 = 0.60 m²K/W bought by 20 mm of extra depth — and the same 100 mm in Frontrock Plus is declared at 2.85 m²K/W, a slab figure rather than a board one. Neither number is a wall U-value; that belongs to the assembly.

The layer-by-layer build-up guide walks the installer-level sequence, the U-value and thickness calculation method shows how declared resistances combine into a compliant wall, and the fixing pattern and spacing guide covers edge-zone uplift and wind-load zoning.

Where EWI Materials Fit: Retrofit, New Build and Funded Work

Four parties usually touch the same wall — designer, installer, retrofit coordinator and Building Control — and each wants a different document from it. The guides below are the reference points trade customers reach for before the first order, and settling them at design stage is what keeps a programme running to its scaffold dates.

• The complete EWI cost guide for 2026 separates material from installed cost, so a budget survives contact with the first contractor quote.
• The day-by-day installation timeline sequences deliveries against the programme rather than the survey date.
• For pre-1919 stock, the Victorian solid-wall retrofit guide covers heritage substrates and the moisture decisions behind a breathable specification.
• The Future Homes Standard guide sets out the tightening fabric targets driving wall specifications on new build and deep retrofit.
• Funded work routes through the grant funding overview and the Warm Homes Plan guide for the current scheme position.
• Consent questions are answered in the planning permission and permitted development guide, which is worth reading before a survey is booked.
• Moisture risk is checked with the dew point and condensation risk guide, and material choice is argued out in the graphite EPS against mineral wool comparison.
• Everything else sits in the rendering and insulation knowledge hub, organised by silo and stage.

Specifier Notes Before the First EWI Pallet Ships

Most of what goes wrong on an insulation order is administrative rather than technical, and four checks catch nearly all of it.

• Confirm the fire strategy before the core: the board class and the slab class are declared on different documents to different harmonised standards, and neither describes the finished rendered wall — so the designer's strategy, not the datasheet, decides the core.
• Check the plant on a declaration of performance: Genderka declares from five production sites, so the document that supports a delivery is the one issued for the supplying plant. Confirming it at order keeps a specification file consistent.
• Survey thickness before ordering plugs: plug length follows the board actually going on the wall, and matching them to a manufacturer's own table beforehand avoids scaffold-level swaps.
• Protect graphite boards from sun on arrival: the manufacturer instructs that the steel-grey surface is shielded from direct sunlight during storage and fixing, which is a stacking decision made on delivery day.

Decide Which EWI Core Fits the Project

Three questions resolve almost every specification on this hub, and each points at one collection.

• Is a non-combustible core required? If yes, the Rockwool slabs are the route and the A1 declaration is read at slab scope. If no, graphite EPS gives more declared resistance per millimetre.
• Does the wall go below DPC? The plinth zone takes the hydrophobic boards, which are declared at 100 kPa compressive strength and 3% water absorption under long-term immersion — the figures that matter where backfill and splash-back meet the wall.
• How much procurement complexity is acceptable? Component-by-component buying suits confirmed quantities; ordering a complete EWI system bundle suits multi-property programmes and first EWI contracts.
• Still weighing the cores? The Renders World technical desk works from the fetched declarations rather than range names, which matters where two slabs share a thickness.

FAQ — Ordering and Specifying EWI Components

Which insulation core suits a standard UK solid-wall retrofit?

Graphite EPS is the usual choice on low-rise domestic work where the fire strategy permits it, declaring λD 0.032 W/mK against 0.035 W/mK for Frontrock Plus, so it reaches a target with less depth at the reveals. Where non-combustibility is required, the stone wool slab replaces it and the adhesive changes with it. The material comparison guide works through both sides in detail.

What does a fire class on a board or a slab actually cover?

A declared class describes the product that was tested and nothing else. The Genderka graphite boards are declared reaction to fire class E to EN 13163, and Frontrock Plus is declared Euroclass A1 on declaration of performance RW-CEE-DoP-0238/BCM/23/w1 issued for the Cigacice plant. A rendered wall carries its own rating under current Approved Document B guidance, assessed as a system by the project's fire engineer.

How many mechanical fixings does a board need per square metre?

Fixing density is a manufacturer and system-design figure taken from the wind-load calculation for the building's height, location and exposure zone, with additional fixings at corners and parapets. No general rule of thumb substitutes for it, which is why this page states none. The fixing pattern guide sets out how the layout is derived.

Can components from different manufacturers be mixed in one system?

Mixing is possible but it moves responsibility for the assembly onto whoever specified it, because a manufacturer's documentation covers its own build-up. The cleaner route on funded or warranted work is a single manufacturer's system, or a bundle assembled to keep adhesive, mesh, primer and render compatible by design. Stone wool in particular takes a dedicated adhesive rather than a polystyrene one.

When can EWI be installed through a British winter?

Temperature and humidity limits are declared per product on its own sheet and differ across adhesives, basecoats and finishes, so the binding limit is whichever component has the tightest window rather than an averaged figure. Shoulder-season work is planned around that component, with cold-weather additives available for the Atlas renders. Programme the render coats to the forecast and the rest of the build-up follows comfortably.

What upkeep does a rendered insulated wall need?

Routine care is periodic inspection of the render surface, the base drip detail and the reveals, plus gentle washing where organic growth appears on sheltered north elevations. Keeping gutters and drips discharging clear of the face does most of the work, and small render repairs are straightforward while they are small.

How do EWI orders ship from Renders World?

Orders are processed the same day where stock is available, with small parcels up to 25 kg on next-day courier and pallets up to 1,200 kg on next-day or two-day economy delivery. All deliveries are curbside only, and pallets are shrink-wrapped rather than weatherproof, so on-site cover matters. Free local delivery covers qualifying orders within 15 miles of the Southampton headquarters, with a per-mile charge beyond that up to 60 miles.