Warmer rooms
A continuous insulation layer on the outside face keeps heat in the rooms you are paying to heat.
External Wall InsulationWith a Rendered FinishWarmer Rooms, Smarter Exterior
EWI wraps the outside of your house in insulation and finishes it in render: the same facelift a re-render gives you, plus walls that stop leaking heat into a South Wales winter.
Fixed-price quotes · 10-year workmanship guarantee · fully insured
15 years
in the trade, trading as MB Construction since 2019
10-year guarantee
workmanship guarantee on completed work
Fully insured
public liability & employer's liability
Fixed-price quotes
free, in writing, never a day rate
24/7 emergencies
emergency roof repairs, day or night
EWI Rendering, What's Involved
External wall insulation is an insulation board fixed to the outside face of the wall, reinforced with a basecoat and mesh, then finished with render. The house gains a continuous thermal layer with no internal disruption and no lost room space.
It suits solid-wall properties in particular, older Cardiff and Newport housing with no cavity to fill, where the walls themselves are the single biggest heat loss after the roof.
It is a detailing job above all. Boards have to be fixed and staggered correctly, reveals, sills, eaves, verges and the base of the wall all need working out, and every penetration has to be sealed. Done well it lasts; done carelessly it cracks at the joints and lets water behind the boards.
- Who it's for
- Owners of solid-wall or hard-to-treat properties with cold walls and high heating bills, and anyone planning a re-render who would rather gain insulation at the same time.
- When it's needed
- When the existing render or pebbledash needs replacing anyway, when rooms feel cold despite the heating running, or when condensation forms on internal wall surfaces in winter.
- Why a professional job matters
- EWI changes how the wall handles heat and moisture. Board fixing, mesh embedment, reveal detailing and the base of the system have to be correct, or you get cracking, cold bridges and water getting in behind the insulation where you cannot see it.
What Happens If It's Left
Nothing outside a house gets cheaper to fix by waiting. Here is how this one escalates.
Uninsulated solid walls waste heat continuously
Every degree of heating leaks straight through the masonry, and no amount of loft insulation compensates for it.
Cold walls make condensation and mould
Warm, moist indoor air condenses on cold internal surfaces, typically behind furniture and in corners, and mould follows.
Badly detailed EWI traps water
Water getting behind boards at a sill, reveal or the base of the wall has nowhere to go and works its way into the structure.
Cracking along board joints
Insufficient mesh embedment or poor fixing shows as straight cracks tracing the board layout across the finished render.
Common mistakes we're called in to undo
- Fitting EWI over a wall that is already wet from a roof, gutter or ground-level fault.
- Ignoring sill and reveal detailing, which is where most water gets behind the system.
- Bridging the damp-proof course at the base of the wall.
- Skimping on mesh reinforcement at corners and around openings.
- Taking a day-rate price on a system job where the specification is the whole point.
Our Process
The same five steps on every job, so you always know what happens next.
01
Survey
We check the wall construction, existing finish, damp, ground levels, gutters, roof overhang and every reveal, sill and penetration.
02
Fixed price in writing
A free, no-obligation quote covering scaffolding, board, fixings, basecoat and mesh, beads and the render finish.
03
Preparation
Scaffold up, old loose render removed, substrate made sound, base track set, and pipework, meter boxes and fittings taken off or extended.
04
Board, mesh and render
Insulation boards fixed and staggered, mechanically anchored, reveals and corners beaded, basecoat and reinforcing mesh applied, then the render finish coat.
05
Verification and completion
Details checked all round, fittings reinstated, scaffold struck, site cleared, 10-year workmanship guarantee handed over.
What You Get
Lower heating demand
Reducing heat loss through solid walls cuts how hard the heating has to work to hold a temperature.
No lost floor space
Unlike internal insulation, nothing is added inside the rooms and you do not lose depth off every wall.
No internal disruption
The work happens outside: no stripping skirtings, no redecorating room by room.
Fewer cold surfaces, less condensation
Warmer internal wall faces reduce the condensation that feeds mould in corners.
A new exterior at the same time
You get the rendered facelift and the insulation from one job, one team and one guarantee.
EWI Rendering in Detail
Materials, methods and the variations we cover across Cardiff, Newport and the wider South Wales area.
Where EWI makes most sense
Solid-wall houses, non-traditional construction and properties where the existing render is failing anyway. If the render needs replacing regardless, the extra step of adding insulation first is the efficient moment to do it.
Board and fixing
Insulation boards are bonded and mechanically fixed with the correct anchor pattern, joints staggered and tight, with a base track or bell detail setting the bottom of the system clear of ground level.
Reinforcement layer
A basecoat with alkali-resistant mesh fully embedded, plus extra diagonal reinforcement at window and door corners where stress cracking starts.
Detailing at openings and the roofline
Reveals and soffits insulated to limit cold bridging, sills extended or replaced to throw water clear, verges and eaves extended where the added thickness needs it, and every vent, flue and pipe sealed back into the system.
Finishes
Through-coloured render finishes in a range of textures and colours, chosen with you against the rest of the street so the house does not end up the odd one out.
Moisture and ventilation
Making a house warmer and more airtight on the outside makes ventilation more important on the inside. Existing vents are kept clear and extended through the system, never covered over.
Where we carry out this work
We work from Crumlin Drive in St Mellons across Cardiff, Newport, St Mellons, Vale of Glamorgan, Caerphilly, Penarth and the surrounding South Wales area. See the areas we cover, browse all of our services or head back to the MB Construction homepage.
EWI Rendering, Common Questions
How much does EWI rendering cost?
It depends on the wall area, insulation thickness, scaffolding, the amount of detailing at openings and the finish chosen. We survey the property and give you a free fixed written price.
How much will it save on heating?
Savings depend on your walls, heating system and how you use the house, so we will not quote you a figure we cannot stand behind. What we can say is that solid walls are typically the largest remaining heat loss once the loft is insulated.
How long does the work take?
A full house runs over a number of weeks including scaffolding and curing between stages. Your quote sets out the expected programme.
Will it change how the house looks?
Yes, the walls become slightly thicker and the finish changes completely. We work through reveals, sills and the roofline at survey stage so the proportions still look right.
Do I need planning permission?
Many properties do not, but listed buildings, conservation areas and some flats and non-standard properties do. We will flag anything we see at survey, and you should confirm with the local authority before work is booked.
Can EWI be fitted to a damp wall?
Not until the cause of the damp is fixed. Where that is a roof, gutter or ground-level problem, we can deal with it first, we cover roofing and groundworks too.
Is the work guaranteed?
Our workmanship carries a 10-year guarantee, and we hold public liability and employer's liability insurance.
Are your quotes really free?
Yes. We come out, look at the job properly and put a fixed price in writing. There is no charge for the visit and no obligation to go ahead.
Do you charge a day rate?
No. Every job is quoted as a fixed price. The figure you agree is the figure you pay, whether the work runs quicker or slower than we expected.
Is the work guaranteed and are you insured?
All of our work carries a 10-year workmanship guarantee, and we hold both public liability and employer's liability insurance. Ask to see the documents before work starts and you will get them.
Which areas do you cover?
We are based on Crumlin Drive in St Mellons and work across Cardiff, Newport, the Vale of Glamorgan, Caerphilly, Penarth and the surrounding South Wales area.
Related Services
Rendering
Render is weather protection first and a facelift second. We prepare the substrate properly, detail the beads and stops crisply, and price the whole elevation as one fixed figure.
View Rendering →Painting & Decorating
Most paint and paper jobs fail at the preparation, not the finish. We fill, sand, treat, prime and size before a brush or a roll goes near the wall, so the room still looks right in five years.
View Painting & Decorating →New Roofs
A full strip and re-roof that ends the patch-and-hope cycle: one fixed price agreed before we start, one small team on site from first tile to last, and a roof that keeps South Wales weather out for decades.
View New Roofs →Get a fixed price for external wall insulation
Book a free survey. We will check the walls, the detailing and the damp risk, then put a fixed price in writing.
- Free, no-obligation site visit and fixed price in writing
- 10-year workmanship guarantee on completed work
- Public liability & employer's liability insured