Insulated Rendering Systems That Cut Your Heating Bills and Transform Your Property.
BBA-certified external wall insulation installed by specialists with 25 years of experience. Warmer walls, lower energy bills, and a render finish that lasts — all in a single installation.
ECO scheme compatible · Fully insured · Written guarantee on all EWI work
What Is Insulated Rendering and Who Should Consider It?
Insulated rendering — also known as External Wall Insulation (EWI) — combines rigid insulation boards fixed to your external walls with a protective render finish on top. It wraps your home in a continuous thermal blanket, eliminating cold bridges and drastically reducing heat loss through the walls.
EWI is ideal for solid-wall properties (pre-1930s homes without cavity walls), homes with high heating bills, properties with penetrating damp caused by exposed masonry, and homeowners looking to improve their EPC rating. It's also the most effective way to insulate a property without losing internal floor space — unlike internal wall insulation, which reduces room sizes.
We install EWI systems using EPS (expanded polystyrene), mineral wool, and phenolic insulation boards — each selected based on the property type, fire safety requirements, and thermal performance targets. The render finish is applied over reinforcing mesh, creating a durable, crack-resistant, weatherproof surface that protects the insulation and transforms the property's appearance.
At Judge Plastering Contractors, we've installed insulated rendering systems across London and the Home Counties for over a decade. We understand the building regulations, manufacturer specifications, and installation techniques required to deliver a system that performs as intended — for decades, not just years.
The Real Cost of Poor Insulation — and Botched EWI Installations
Solid-wall properties lose up to 45% of their heat through external walls. That's nearly half your heating bill disappearing through masonry that was built long before thermal performance was a consideration. In a typical London semi, that equates to £500–£800 per year in wasted energy — money that compounds year after year.
Poor EWI installation is worse than no insulation at all. Incorrectly fixed insulation boards leave gaps where cold air circulates behind the system — creating cold spots, condensation, and ultimately mould growth inside the wall cavity. Render applied without proper reinforcing mesh cracks within months, allowing water into the insulation and destroying its thermal performance.
We've removed and replaced dozens of botched EWI systems installed by inexperienced contractors across London. The common failures include: boards not mechanically fixed (relying on adhesive alone), mesh not overlapped at joints, base coat applied too thin, and inappropriate insulation type used for the exposure zone. Every one of these failures could have been prevented by following the manufacturer's installation specification — which many contractors don't read.
Choosing a cheap EWI installer is a false economy. A failed system costs more to remove and replace than a correct installation costs from the start. And during the years it's failing, you're paying full heating bills plus dealing with damp and mould — the exact problems the system was supposed to solve.
How We Install External Wall Insulation — Step by Step
Thermal Survey & System Design
We survey your property, assess the wall construction, check for damp or structural issues, and specify the correct insulation type, thickness, and render system to achieve your target U-value.
Preparation & Base Rail Installation
The external walls are cleaned and prepared. A metal starter rail is fixed at the base to support the first row of insulation boards and prevent pest access. Window reveals and sills are checked for adequate depth.
Insulation Board Installation
Insulation boards are fixed using adhesive and mechanical fixings (dual fixing for reliability). Boards are staggered at corners and around openings, with no gaps between joints. Every board is checked for flatness.
Reinforcing Mesh & Base Coat
A polymer-modified base coat is applied over the insulation. Alkali-resistant fibreglass mesh is embedded into the wet base coat with proper overlaps at all joints. Additional mesh reinforcement is applied diagonally at window and door corners to prevent cracking.
Render Finish & Completion
The chosen render finish — silicone, acrylic, or mineral — is applied to the specified texture and colour. All reveals, sills, and details are completed cleanly. The system is inspected, and you receive your written guarantee and product warranty documentation.
Benefits of Insulated Rendering for London Homeowners
Cut Heating Bills by Up to 45%
Solid-wall insulation eliminates the single largest source of heat loss in pre-1930s properties. The savings compound every year.
Eliminate Penetrating Damp
The render layer creates a weatherproof barrier while the insulation keeps internal wall surfaces above dew point — stopping condensation and damp at the source.
No Internal Space Lost
Unlike internal wall insulation, EWI adds thickness externally. Your rooms stay the same size, and you don't need to move radiators, sockets, or skirting boards.
Improve Your EPC Rating
EWI can move a property from EPC band D/E to band B/C — making it more attractive to buyers and potentially qualifying for green finance schemes.
Transform Property Appearance
A fresh render finish over insulation modernises any property. Choose from hundreds of colours and textures — no repainting needed for 20+ years.
System Guarantee Included
Manufacturer product warranties of up to 25 years, plus our own workmanship guarantee. Your investment is protected.
Our Insulated Rendering Work in Action
EWI Board Installation
Rigid insulation boards mechanically fixed to the external walls before rendering. Each board is precisely cut around windows and openings to create a continuous thermal envelope.
Spray-Applied Insulation Layer
A specialist spray-applied insulation coat being applied directly to blockwork. This method ensures full coverage and adhesion, creating a seamless thermal barrier.
EWI Systems, Materials & Technical Detail
EPS Insulation (Expanded Polystyrene)
EPS is the most widely used insulation board for domestic EWI systems. It offers excellent thermal performance (typical lambda value 0.032 W/mK), is lightweight, easy to cut, and cost-effective. We use white EPS for standard applications and graphite-enhanced grey EPS (lambda 0.031 W/mK) where greater thermal performance is needed with thinner boards. EPS is suitable for most residential applications up to 18 metres in height.
Mineral Wool Insulation
Mineral wool boards provide the same thermal insulation as EPS but with significantly better fire performance (Euroclass A1 — non-combustible). We use mineral wool on properties above 11 metres, buildings near boundary lines, and any application where enhanced fire safety is required. Mineral wool is also more breathable than EPS, making it the preferred choice for older solid-wall properties where moisture management is critical.
Phenolic Insulation Boards
Phenolic boards offer the highest thermal performance per unit thickness (lambda 0.020–0.022 W/mK). This means we can achieve the same U-value with a significantly thinner board — important where wall thickness is constrained by window reveals, boundaries, or planning requirements. Phenolic boards are more expensive but essential in specific situations.
Render Finish Options
Over the insulation and base coat, we apply a decorative render finish. Silicone render is our most popular choice — it's self-cleaning, breathable, crack-resistant, and available in hundreds of colours. Acrylic render offers excellent flexibility and colour range at a lower cost. Mineral (lime-cement) render is the most breathable option, ideal for heritage properties. Each finish comes in multiple textures: smooth, sponge-float, fine grain, and roughcast.
Building Regulations & Compliance
EWI installations must comply with Building Regulations Part L (conservation of energy) and Part B (fire safety). In many cases, a building notice or full plans application is required. We ensure every installation meets current regulations, including the updated fire safety requirements introduced after Grenfell. We use BBA-certified systems and can provide all documentation required for building control sign-off.
We install EWI systems across London, Brentford, Reading, and the Home Counties. See also our standard rendering and general building services.
Frequently Asked Questions
Warmer Home. Lower Bills. Guaranteed.
Get your free EWI survey and estimate. We'll specify the right system for your property and show you the projected energy savings.