Article - Issues with EWI materials

ewi failure
EWI Shrinkage
ewi failure
EWI Failure, Glasgow
What are the issues with External Wall Insulation (EWI), and why are they happening?

An EWI system is made up of several different layers of render bonded to the insulation board. The insulation and render work together to form an external envelope around a building which protects it from the weather and prevents any water ingress.

The integrity of the EWI system becomes quickly compromised if the boards used to bond the whole system together are even slightly wet upon installation. Many cases of system failures have moisture sodden insulation boards at the heart of the problem with Mineral Fibre and Phenolic insulation boards being most susceptible as they have high water absorption rates.

High levels of moisture in the insulation boards during installation can result in a weaker bond between the boards and render which overtime can cause cracks in the render and ultimately system failure. Moisture can also cause shrinkage of the insulation boards as they dry out, resulting in a visible (and unsightly) pillowing effect on building facades.

Here at SPI we would strongly recommend the specification of Stylite Plustherm Expanded Polystyrene for your EWI project due to it's benefits over other types of insulation:

  • Hydrophobic - EPS repels water and vapour, it physically can't hold any water, its chemical properties wont allow it.

  • Vapour permeiable - EPS is ever so slightly permeable, meaning that a small amount of water vapour can pass through, EPS can breath.

  • Does not lose any performance over time - EPS is one of very few insulation materials that does not lose any properties over time.

  • Cost to performance ratio - Due to its simplicity EPS can offer the best values for the best price in comparison to all other materials.

EWI system designer BBA certificates state that all insulation should be kept dry on site, but practically we all know this isn't possible when installing materials outside.

As such EPS is the perfect insulation type and will minimise the risk of an EWI system failure.