External Wall Insulation

What is EWI?

External wall insulation is installed by adding a weatherproof insulating layer to the outside of your wall. This could be in the form of a protective render. The thickness of the insulation is usually between 60 and 100mm thick. The materials used for external wall insulation are often referred to as a “system” because there are three components that must work together:

The insulation material

The fixing of framework

The finishing layer
(which is weatherproof and aesthetic)

Colours & Finishes

Canterbury Spa
On white receiver
Black & White
Flint on grey
Black & White
Flint on white
On yellow


Interested to know how the whole process works? Here’s how we get started, get working and get finished.

Our Liaison Officer will contact you to make an appointment to carry out a survey of your property at a time and date that is suitable to you.

They will also give you a rough guide as to the running order and timescales of the work. Rockwarm will then arrange with you a date for the work to begin, and for the scaffolding to be erected.

Your liaison officer will keep you informed of progress and any delays. All of our workers have identification badges and they should be visible to you; if you have any concerns please contact your Liaison Officer immediately.

The improvement work carried out to your property will inevitably involve a certain level of disruption, noise and mess during working hours of the day. However, every effort will be taken to keep this to a minimum.

The work schedule

  • Preparation

    Erection of Scaffolding

  • Plumbing

    Plumbing on external walls (e.g. Soil pipes from the bathroom & gas flues) will be extended to accommodate the insulation boards.

  • Fixtures

    External fixtures (e.g. alarm boxes, lighting, hanging baskets) will be removed. Wooden blocks will be fitted to your wall to make it easier to refit your fixtures so that they are put back in the same place once the insulation has been installed.

  • Boarding

    Installation of insulation board (Estimated at 1 to 2 days)

  • Rendering

    Render 1st, 2nd and 3rd coat. The second coat can look like the painted finish but it is a base layer. Please note: each layer of render requires a drying time. Hence the installers will not necessarily be at your property everyday, as they need to allow 4 drying times, plus this work must be done in dry frost free weather. Window sills will be temporarily fitted at this stage and protected with polythene film.

  • Windows

    Upstairs windows will be finished with an insulated UPVC strip above the top of the window.

  • Sills

    Window sills will be attached and sealed with silicone.

  • Fixtures

    External fixtures (e.g. alarm boxes, lighting, hanging baskets) will be refitted.

  • Snagging

    Snagging report. All work will be reviewed and minor alterations noted and completed. Please highlight any concerns to our Quality Inspector that you have at this stage.

  • Cleaning

    Cleaning of the windows, doors, down pipes and ground will be completed by the installer.

  • Sign off

    Rockwarm will sign off the work in accordance with the terms of the contract.

  • Finish

    Scaffolding will be taken down.

Your property will be regularly visited during the installation by one of our Quality Inspectors. Their role is to assess the quality of the installation at key stages and ensure that Rockwarm’s Health & Safety guidelines and procedures are being followed at all times.


Can I install items to my walls after the installation?

Yes but we would advise you to contact us for advice prior to any works being undertaken to ensure the system doesn’t become damaged or its structural integrity affected in anyway. Items should only be fixed into the newly installed walls with the correct fixings specific to that system (manufacturer supply and specification only). If you are planning any other refurbishment/maintenance works (new windows, extensions, etc) it may be better to undertake these works in advance of the external wall insulation, but our Rockwarm Surveyor will be able to advise you accordingly.

Is there a guarantee?

Rockwarm currently offer a standard company guarantee certificate for all its external wall insulation Systems, guaranteeing the materials for a period of 25 years. This guarantee is issued on each project at no extra cost.

Are the systems approved?

All EWI systems that Rockwarm install are accredited to BBA Standards. The systems are also Energy Savings Trust Recommended and Rockwarm are members of the National Insulation Association (NIA), and SWIGA (Solid Wall Insulation Guarantee Agency).

How durable is the system?

The EWI system is designed to withstand ‘normal’ wear and tear but should the system become damaged we can advise as to the best course of action to repair or replacement the effected area(s)/systems(s).

How much money will I save a year on fuel bills?

An average semi-detached home could typically save £450 – £500 per year on fuel costs (Source: Energy Saving Trust) but this can be higher if your home is made even more energy efficient through the incorporation of thicker insulation as part of the external wall insulation system.

Will I feel a difference once installed?

Yes – both in the winter and summer: improved insulation levels lead to a reduction in heat loss in the winter and reduces overheating in the summer.

What are the main benefits?

You’ll improve the thermal performance (energy efficiency) of your home, which will reduce your heating costs and also improve the visual appearance of the property.