PROPERTY ENERGY RETROFIT
External Wall Insulation
Transform your home with our expert External Wall Insulation. Enjoy a warmer, quieter space while enhancing your property's exterior appeal.
Quality Assurance
Our focus on precise specifications and skilled installation ensures lasting comfort and efficiency for your solid-walled home in Devon and Cornwall.
Expert Team
Our dedicated professionals bring years of experience to every project, guaranteeing top-notch service and results tailored to your needs.
Customer Focus
We prioritize your satisfaction, working closely with you to deliver exceptional outcomes that elevate your living environment and lifestyle.
External Wall Insulation
in Devon & Cornwall
External wall insulation (EWI) is one of the most effective ways to transform an older, solid-walled home — making it dramatically warmer, quieter and more comfortable, while giving the exterior a clean, refreshed finish. Done well, it's a once-in-a-generation upgrade that pays back in comfort every single day. Done badly, it can trap moisture and damage the very building it's meant to protect. The entire difference lies in the specification, the detailing and the quality of the installation — which is precisely where we come in.
We design and install external wall insulation across Devon and Cornwall, matching the right system to each individual property and finishing it to a standard you'll be glad to look at for decades.
What is external wall insulation?
External wall insulation is a layer of insulation fixed to the outside face of your walls, protected by a durable, weatherproof render or cladding finish. In effect, it wraps your home in a continuous thermal blanket.
Because the insulation sits on the outside, it keeps the mass of the wall warm, eliminates the cold spots and draughts associated with solid walls, and does so without losing a single inch of internal floor space or disrupting your rooms during the work. It also gives the building a fresh, uniform exterior and shelters the original masonry from the weather.
It's the natural solution for the many homes across the South West that were built with solid walls and have no cavity to fill.
Why EWI suits so many Devon & Cornwall homes
A large proportion of homes in Devon and Cornwall were built before 1920 with solid walls — solid brick, rendered masonry and solid stone — that have no cavity, lose heat quickly, and are expensive to keep warm. Add our exposed, wet and windy coastal and moorland climate, with plenty of wind-driven rain, and the result is homes that feel cold, suffer condensation, and cost a great deal to heat.
On the right wall, external wall insulation tackles all of that at the source: the wall stays warm, draughts and cold bridging are designed out, and the home becomes genuinely comfortable to live in year-round — while the new weatherproof finish protects the structure from the South West's demanding weather. It isn't right for every traditional wall, though — and earth-built cob, common across Devon, is a notable exception we explain below.
The benefits
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Warmth and comfort — even temperatures throughout, with the cold spots and draughts of a solid wall designed out
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Lower running costs — significantly reduced heat loss through the largest surface of your home
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No loss of internal space — unlike internal insulation, nothing changes inside
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No internal disruption — you keep using your rooms while the work happens outside
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Condensation and damp control — a correctly specified system keeps the wall warm and manages moisture properly
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A refreshed, protected exterior — a clean new finish that also shields the masonry from the weather
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Quieter rooms — a noticeable reduction in external noise
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A more valuable, future-ready home — improved energy performance and EPC rating
Breathable vs non-breathable — getting this right matters most
This is the single most important decision in any external wall insulation project, and the one cheap installers most often get wrong. Choosing the wrong system for your wall doesn't just underperform — it can cause real, lasting damage.
Why it matters
Many older buildings — solid stone, lime-mortared brick and other traditional construction — were built to manage moisture by breathing. They're vapour-open: moisture moves into the wall and evaporates back out again, keeping the structure healthy. This is fundamental to how a traditional building works.
Wrap a breathing wall in a sealed, non-breathable system and you trap that moisture inside the structure. Over time that can lead to penetrating damp, mould, frost damage, decay of embedded timbers (joist ends, lintels, bonding timbers) and a steadily deteriorating wall. The home looks fine for a season or two, then the problems begin — hidden inside the very fabric you've just paid to insulate.
Breathable (vapour-open) systems
For traditional, breathable buildings, we specify vapour-open systems: insulants such as wood fibre or mineral wool, finished with lime, mineral or silicone-silicate breathable renders. These let the wall continue to dry naturally, so moisture is never trapped. Wood fibre in particular also brings excellent summer comfort, slowing the passage of heat and keeping rooms cooler in warm weather.
Standard (non-breathable) systems
For modern or already non-breathable construction — cement-rendered walls, certain post-war solid masonry — a standard system using EPS (expanded polystyrene) or phenolic insulation with a polymer render is often the most cost-effective and entirely appropriate choice. These systems are excellent on the right building; the key word is right.
How we decide
We never guess. The correct system is determined by understanding how your wall is built and how it manages moisture — assessed as part of the whole-house survey and design carried out with our sister company, Dartmoor Energy. Where a wall's behaviour is borderline, we use condensation-risk (hygrothermal) analysis to model how the build-up will perform before a single board goes up.
Design considerations
External wall insulation is far more than sticking boards to a wall. Adding 90–150mm of insulation and render to the outside of a building changes its geometry, and every junction has to be detailed correctly. These are the considerations that separate a proper installation from a problematic one — and they're where our project management and trusted local contractors earn their place.
Roofline and eaves extensions
When you thicken the walls, the existing roof overhang, verges and eaves may no longer project far enough to throw water clear of the new render. On many homes this means the roofline has to be extended — extending rafters or verges, fitting new bargeboards, and adapting soffits and fascias — so rainwater sheds away from the wall rather than running down the new finish. It's a significant part of the design and cost on many projects, and skipping it is a common cause of staining and water ingress. We plan for it from the outset.
Windows, doors and reveals
Thicker walls mean deeper window and door reveals. Left uninsulated, these reveals become cold bridges where condensation and mould form. We insulate the reveals, head and cill, fit new weathered cills with an adequate overhang and drip detail, and — where the design calls for it — discuss repositioning windows into the insulation line for the best thermal result.
Cold bridging and junctions
A wall is only as good as its weakest point. We design for continuity of insulation at every junction — eaves, verges, reveals, the ground-floor plinth, party walls and any projecting features — so there are no thermal weak spots left to undermine performance or cause localised condensation.
The plinth and damp-proof course
Where the system meets the ground, careful detailing is essential. We use a proper starter track and plinth detail, never bridge the damp-proof course, keep render clear of direct ground contact, and protect the base of the system from splashback — so ground moisture is never drawn up into the wall.
Rainwater goods, vents and fittings
Everything fixed to the wall has to be accounted for. Gutters and downpipes are removed and re-fixed on extended brackets to clear the new thickness; air bricks are sleeved through the insulation to maintain underfloor ventilation; and meter boxes, soil pipes, extract terminals, lights, flues and any heat-pump or boiler terminations are extended or relocated with the correct clearances.
Planning, conservation and boundaries
Because EWI changes a building's external appearance and footprint, it can require planning permission — particularly in conservation areas or on listed buildings — and you'll need to consider boundaries, the building line and any party-wall implications where walls thicken towards a neighbour. We advise on all of this as part of the design, and Dartmoor Energy can handle planning drawings and submissions where they're needed.
The finish
The render is the part you see every day, so it matters. We'll guide you through the options — silicone, silicone-silicate, mineral and lime renders, in a wide range of colours and textures, plus brick-effect and brick-slip finishes where appropriate — and detail the result to suit the character of your home, including period and conservation-sensitive properties.
Ventilation and the whole-house picture
Improving the airtightness of a previously leaky solid-walled home changes how it manages moisture and fresh air. Insulating in isolation, without considering ventilation, is how condensation problems start. As part of our whole-house approach we'll always flag where ventilation needs to keep pace — so your home is warm, dry and healthy.
Is external wall insulation right for your home?
EWI is outstanding on rendered, solid-brick and many solid-walled homes. But it isn't right for every property — and we'll always tell you so honestly.
On homes of real architectural character — exposed natural stone, granite or attractive period brickwork — wrapping the exterior would hide the very features that make the building special, and may not be appropriate or permitted. In those cases, internal wall insulation is often the better answer, preserving the external appearance while still improving comfort. Many homes also benefit from a combination of approaches across different elevations.
We do not apply EWI to cob
Cob — the traditional earth walling found right across Devon — is the clearest example of a wall that should never be externally insulated, and we won't do it. Cob survives on a simple principle: a good hat and good boots, and the freedom to breathe and dry. It is exceptionally sensitive to moisture, and covering its outer face changes how the wall weathers and dries, risking trapped moisture, decay and even structural slumping within the earth itself, as well as the rot of embedded timbers. Soft earth walls also won't reliably take the fixings an EWI system needs, and the cob is usually a character feature worth keeping.
For cob and other earth walls, the right approach is holistic: keep the wall breathing with lime renders and limewash, protect it with a sound roof overhang and a well-drained base, and put the insulation effort where it belongs — into the roof, the floors, draught-proofing, and carefully considered breathable internal measures — alongside efficient, low-temperature heating. That whole-house thinking is exactly how we approach every traditional building.
This honest, property-by-property judgement is exactly what a whole-house assessment is for.
Performance and U-values
A solid wall can lose heat several times faster than an insulated one. A well-designed EWI system typically brings the wall down to a U-value of around 0.30 W/m²K or better, in line with Building Regulations for upgraded walls — and lower still on deep-retrofit projects.
The insulation thickness needed to hit that target depends on the material's thermal conductivity (its λ, or lambda, value): higher-performance insulants such as phenolic achieve the same result in a thinner build-up than EPS, mineral wool or wood fibre. We specify the thickness and material to meet your performance target while respecting the design constraints of your home — overhangs, boundaries and appearance.
How we deliver your project
Every external wall insulation project we carry out runs on three principles:
Trusted local contractors. The quality of an EWI installation lives in the detailing, and detailing comes down to the people on site. We only use skilled local contractors we'd happily put on our own homes.
One point of contact. From the first survey to the final finish, you deal with one project manager who knows your home and your decisions — not a rotating cast of subcontractors.
A genuine whole-house approach. Working with our award-winning sister company Dartmoor Energy, your project begins with a proper assessment and design, so the insulation, ventilation and finish are planned together as one.