How is External Wall Insulation installed? Step-by-step guide - Greenhus

How is External Wall Insulation installed? Step-by-step guide

External Wall Insulation is building work, not insulation work – it needs knowledge, skill and experience. At Greenhus, EWI is all we do, so we get it right first time – follow our guide to see how.

Greenhus installers will wrap and transform your property in a series of stages. This section gives a step-by-step guide, highlighting some details as well as common practices.

First, we need to assess whether scaffolding is needed. If so, we’ll sort it using one of our trusted scaffolding contractors.

Your installation will then feature 3 separate phases – enabling works, the installation, and re-enabling/clean-down.

Enabling works Step 1

01-ewi-enabling-works-property-perimeter-protection-woolaways-bungalow-sidmouth-devonProperty perimeter protection.

We lay down heavy-duty plastic sheeting around your property, so that any splashes/spills do not stain your paths or driveways.

Enabling works Step 2

02-ewi-enabling-works-preparation-of-walls-detached-house-tvistock-devonPreparation of walls.

The amount of preparation needed will depend on the condition of your existing wall coverings – in most cases, a simple rub-down will do, although sometimes we may need to hack-off your existing wall coating. The preparation needed is established at survey stage.

This images shows a house with synthetic sprayed-coating that had not proved durable, and which needed removing fully before installation could start.

Enabling works Step 3

03-ewi-enabling-works-temporary-downpipes-woolaways-bungalow-dulverton-somersetTemporary downpipes.

Because we need to access your whole wall area, we will remove your downpipes and fit temporary plastic tubes to keep your gutter water away from the walls during the installation.

Enabling works Step 4

04-ewi-enabling-works-moving-soil-pipe-detached-house-taunton-somersetExtending waste pipes, soil pipes and other pipework.

Adding insulation will make your walls thicker, any wall-mounted pipes will need to be extended out and away from the walls before we start. By doing this, your home or business will function as normal during the installation process.

This shows how the use of 2 “swan-neck” fittings have brought this soil pipe far enough away from the wall for the system to be installed behind it.

(Have a quick look here to see how these features can look when re-enabled.)

Enabling works Step 5

Using verge trim to overcome lack of roof overhang.

Many properties don’t have enough roof over-hang to accommodate the addition of External Wall Insulation. We use a dedicated “verge trim” to overcome this.


The insulation is fitted up under the verge trim, which is angled downwards to ensure water flows away from the system.

06b-ewi-enabling-works-verge-trim-bungalow-saltash-cornwallThis shows verge trim fitted to a gable with no roof overhang.

Enabling works Step 6

05-ewi-enabling-works-window-protection-film-detached-house-south-hams-devonFitting window protection film.

We will safeguard your glazing and window frames by fitting a protective layer for the duration of the installation.

Installing External Wall Insulation Step 1

07-installing-ewi-fitting-starter-track-terraced house-plymouth-devonFitting the starter-track.

External Wall Insulation does not extend to path level – instead, it starts at a level we discuss and agree, taking into account factors specific to each installation. When we agree the starting height of the system, we fit an aluminium carrier-tray (“starter-track”) to the wall to give the system a level starting point. The starter-track also allows the fitting of a bell-cast bead.

Walls should never be insulated to ground level. By keeping the starting point above ground level, we ensure no damp can be absorbed up into any part of the system

Installing External Wall Insulation Step 2

Application of insulation boards.


We apply a layer of adhesive to each board.


The boards are then stuck to the wall in a staggered pattern, like courses of bricks.


This shows how we account for window openings, i.e. a whole board is cut out rather than having joints at the corners (which could cause weakness and eventual cracking).

Installing External Wall Insulation Step 3


Unless your walls are absolutely flat, the insulation boards may stick out slightly in places. Any edges that stand proud are flattened off with a rasp, to ensure we have a completely flat surface for the next stage.

This is a vital step – if this stage is not done properly, the edges will show through as shadow-lines in the completed installation.

Installing External Wall Insulation Step 4

12-installing-ewi-hammer-fixings-end-terrace-house-teignmouth-devonMechanical fixing.

This shows panels secured by hammer fixings (in addition to the adhesive used between the panel and original wall). We insert 10 fixings per square metre. Greenhus installers take great care to ensure your system is fastened securely to your wall. The effect of wind blowing across the face of the system can create negative pressure or “wind-suck”, which could pull the insulation off of the wall. Some companies use adhesive-only, and some will use mechanical fixings only – Greenhus uses both to give you absolute peace of mind.

Installing External Wall Insulation Step 5


We will fit corner beads to all window and door openings, together with stop beads against window and door frames.

  • Corner beads allow us to form square openings with neat, sharp edges
  • Stop beads prevent the EWI-system from touching another material with different properties. (Different properties, e.g. expansion rates, can cause cracks.)

Installing External Wall Insulation Steps 6, 7 & 8

Application of meshcoat.

The meshcoat gives the system its strength – 2 layers of strengthening render are applied (steps 6 and 8), with a fibreglass mesh trowelled in between the first and second layers (step 7).

  • This means the system will be strong enough to withstand knocks and bumps. You can also lean ladders against it when (e.g.) you need to clean your windows.

14-installing-ewi-applying-meshcoat-cottage-wellington-somersetThis photo shows the mesh “trowelled-in” to the first render coat. A second coat is then applied.

15-installing-ewi-meshcoat-detail-end-terraced-house-plymouth-devonHere you can see the two coats sandwiching the reinforcing mesh.

Installing External Wall Insulation Step 10

Application of primer.

16a-installing-ewi-priming-terraced-house-plymouth-devonA primer is painted on to the meshcoat. The primer contains fine quartz granules, which provide a “key” for the final render. It’s also colour-matched to the final render, so that there is no risk of the primer “showing through”.

16b-installing-ewi-colour-matching-primer-terraced-house-plymouth-devonThese customers wanted a green finish for their home, so you can see why it’s important to colour-match the primer.

Installing External Wall Insulation Steps 11 & 12

Application of textured render.

17-installing-ewi-applying-topcoat-end-terraced-house-plymouth-devonThe final render is now applied (step 11). Although applied using traditional tools, specialist skills are needed to get the best finish. Greenhus installers have these skills, acquired through training and many, many years of experience.

18-installing-ewi-floating-topcoat-end-terraced-house-plymouth-devonThe render is then “floated-up” to bring out the texture (step 12).

Installing External Wall Insulation Step 13

Window sills of your choice.

Adding insulation to your walls will create deeper window reveals. Your window sills will also need to be deeper to take account of this. Greenhus has various solutions and styles to choose from:

Option 1 – uPVC window sill extensions.

20a-installing-ewi-window-sills-upvc-bungalow-tavistock-devonThese complement existing uPVC windows, with clean lines and a neat appearance.

Option 2 – Slate sills – Type 1

20b-installing-ewi-window-sills-slate-type-1-tiverton-devonThese sill extensions are popular when creating a traditional look. You may be limited to this type of “undersill” depending on the way your windows drain. This will be established and discussed at survey stage.

Option 3 – Slate sills – Type 2

20c-installing-ewi-window-sills-slate-type-2-taunton-somersetThese are used when you demand a particular appearance. (Please note that these can only be laid in lengths up to 1.2m – for wide window openings, there will be a joint between the 2 lengths.)

Option 4 – Concrete-effect window sills.

20d-installing-ewi-window-sills-concrete-effect-semi-detached-house-saltash-cornwallUsed where a particular appearance needs to be maintained, we simply replicate the original cast-concrete sills using insulation and render. Often finished in a contrasting colour to highlight the detail.

Option 5 – aluminium sills

20e-installing-ewi-window-sills-aluminium-semi-detached-house-plymouth-devonThe great advantage of these sills is that they can be ordered in any RAL colour, so they can feature as part of a colour-coordinated makeover where traditional white uPVC or grey natural slate wouldn’t be suitable.

Re-enabling works.

19a-installing-ewi-re-enabling-terraced-house-plymouth-devonAll pipework, fixtures and fittings are now secured permanently to your walls, using specially-developed fixings. We also seal around all openings and where pipework extends out from the render.

19b-installing-ewi-re-enabling-downpipe-and-verge-trim-detached-house-taunton-somersetThis detail illustrates how we cope with the challenges presented where a property requires verge trim.

Finishing and tidying-up

As well as sealing all openings, we clean and sweep your paths, and bag and remove all rubbish.

From this…


Via this…


To this…


Don’t forget our FAQ section!

Discover how External Wall Insulation from Greenhus can transform your home or business premises - complete our Contact Form and we’ll call you back, or speak to us on 01822 819 911

expand Click Pictures To Expand

To find out how Greenhus can help you plan a great improvement to your home or business,
complete our Contact Form or call us on 01822 819 911