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6 Steps to Prevent Weathering in EWI


Thermal performance and comfort are gaining increasing interest in the construction and housing industries. External wall insulation is known to reduce heat loss and improve the thermal performance and comfort of a property. It is a method that has gained significant traction in the UK in recent decades.

Yet, a key consideration when attempting to improve and optimise the thermal comfort of an EWI property is to minimise weathering and water ingress. This involves ensuring no water penetration from the external environment can occur and that the insulation layer remains dry.

This article is intended as a guide for EWI practitioners – including architects, retrofit designers and installers. We will outline the concept of weathering, how it happens, and set out a series of best practices to effectively protect your property from weathering.

How to prevent weathering (6 steps)

Protecting against weathering is an effective way to ensure your insulation system lasts. This can be achieved by considering the EWI system details, identifying possible risks, and providing potential solutions.

The guidance we suggest in this article considers a range of typical construction elements which may be found on most retrofit installation projects and identifies the potential risks as far as weathering. In this article, we will lay out a set of best practices that you should consider in the early stages of installation. Adopting these at a later stage may result in higher costs and problems arising later.

Step 1 – Conduct a pre-installation survey

In the first instance, you should conduct a detailed survey before installation. This should be carried out by a professional surveyor and should consider things such as location, ventilation, heritage, and risk assessment.

All weathering control details should be provided to installation teams. No installation work should be undertaken until specified information has been obtained, confirmed and a plan of action pulled together.

Step 2 – Qualified installers

EWI installers should have undergone professional training to ensure the installation is completed to a high standard. Installers should be able to read and understand the thermal bridging control details so the system can be installed correctly.

EWI Pro Training Academy provides installers with the highest quality installer training courses, delivered by render specialists with years of experience. Find out more here.

Step 3 – Install the system

Installers should be aware that they are responsible for ensuring the system has been installed correctly to minimise weathering potential. Installers are responsible for ensuring the system has been adequately sealed and is weather-tight.

EWI installers should also seek to identify faults that could harm the occupants’ installation or their health and safety.

Step 4 – Sealants

The project should be adequately sealed. However, sealants should not be the main mode of weatherproofing and sealing gaps. You should also make use of appropriate backing material e.g., hydrophobic tape or proprietary backing rod.

Where sealants are employed to provide a barrier to penetration, you should ensure that the correct sealant is used. Installers should follow the guidance that accompanies the render system.

Step 5 – Sealing Tapes

Sealing tapes are recommended as a means of further weatherproofing the installation. Some sealing tapes are hydrophobic (closed-cell foam), these add further water sealing capabilities to your installation as well as a continuous seal to join adjacent lengths.

Step 6 – Beads, Trims, Flashings

The resistance to weathering of beading is dependent on the level of exposure to UV light and temperature changes. You should consider these factors in the installation process as they can impact the materials. E.g., thicker PVC components are prone to bowing upon temperature changes.


In this guide, we have discussed the necessary steps that should be taken in order to avoid weathering and water ingress in an EWI system. Ensuring each of these steps has been accounted for is the most effective way to prevent these issues – causing you complications further down the line.