Energy efficiency remains a hot topic for the construction industry. Insulated Render Systems, otherwise known as ‘External Walling Insulation systems (EWI)’, are often seen as a way of improving the energy performance of older properties. However, new developments in EWI has seen the popularity of these systems rise in new build projects. 

EWI systems are made up of a decorative external render finish applied onto an insulant. The system is fixed to the substrate construction either by mechanical fixings, adhesive render coat or a combination of the two. Reinforcement mesh is usually incorporated into base layers of the render.

We take a look at different types of renders and what to consider when installing EWI systems.

The renders typically fall into 3 main types:

1.  Traditional renders and finishes

2. Thin coat renders and synthetic finishes

3. Pre-formed cladding materials

Top 10 things to consider when installing EWI systems:

1.  The render must not be applied onto saturated substrates as this may affect the bond strength and adhesion.

2.  Protection must be provided when applying either the insulation boards or the finish render in rain or other inclement weather, to avoid trapping moisture in the system.

3.  Render coats must not be applied in temperatures below 5°C.

4.  Vented cavities or ‘weep holes’ should not be blocked.

5.  Timber supports and blocks within the insulated render system should not be used.

6. Ensure all fixtures and fittings which penetrate the insulation system are appropriately sleeved and fully sealed in accordance with the system manufacturer’s recommendations.

7. The installation of EWI’s at window/door reveals often fail due to poor detailing or support, often by wooden boards. The manufacturer’s details must be followed and appropriate trims should be provided at openings, corners, angles and interfaces etc.

8. The insulation board may require to be keyed to receive the desire base coat and reinforcement, depending on the manufacturer’s specifications.

9.   Reinforcement mesh should be accommodated throughout the base coat application with additional reinforcement to vulnerable areas and corners of openings etc.

10. Movement joints in the backing substrate should be mirrored through the insulated render system and formed in accordance with the manufacturer’s recommendations.

Fixing of EWI systems:

  • Dot and dab method of fixing using adhesives is not acceptable on masonry substrates. A full coat of approved adhesive must be applied across the full face of the substrate with a tooted finish according to the manufacturer’s specifications.
  • An approved proprietary mechanical fixing should be used in accordance with the design requirements when needed. This generally consists of a minimum of 5 fixings per full insulation board/8/m² elsewhere with additional fixings to corners and reveals.
  • Additional mechanical fixings may be required at the edge of zones to satisfy the wind load conditions.
  • The insulation boards must be installed in a staggered ‘brick bond’ and overlapped at corners.

External Fixtures:

All fixings, cables, fence, posts, light fitting, satellite dishes and other ancillary fittings and fixtures should be installed carefully after the insulate render system has been completed.

If the EWI is installed as part of a refurbishment project, the following should be observed:

  • Remove existing and provide temporary downpipes and avoid allowing the temporary downpipes to spill water over the render system.
  • If required reset all drainage gulley’s to accommodate the insulation system thickness.
  • If required ensure that any gap around the window and door frames is correctly sealed against rain penetration before application of the insulated render system.
  • Mechanical fixings for these external features must be taken through the substrate construction and not solely fixed to the EWI.

For more information on working with Render see our previous articles on ‘Using the right render to protect against the elements’ and ‘Weep holes in rendered walls’.


Please Note: Every care was taken to ensure the information in this article was correct at the time of publication. Any written guidance provided does not replace the reader’s professional judgement and any construction project should comply with the relevant Building Regulations or applicable technical standards. However, for the most up to date LABC Warranty technical guidance please refer to your Risk Management Surveyor and the latest version of the LABC Warranty technical manual.


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