Why Protecting Gable End Insulation from Water Ingress is Essential

Why Protecting Gable End Insulation from Water Ingress is Essential

The insulation terminates at plate level when cavity walls are constructed by incorporating partial fill insulation. It is common practice to terminate insulation at plate level across the gable ends rather than extend it up to the roofline. The question arises of whether the top of the insulation, where it horizontally crosses each gable end, should be protected against gable end water ingress given the expanse of unfilled cavity wall rising above it. Could penetrating water use the top of the gable end insulation as a bridge towards the inner skin?

Understanding Gable End Water Ingress Risks

In theory, rainwater penetrating the exterior skin of a correctly constructed cavity wall should not get anywhere near the insulation. But in practice, this is not the case.

Challenges with Gable Wall Insulation Placement

Within the triangle of masonry forming the gable are many wall ties. Water will track along a perfectly positioned wall tie until the twist or feature of the tie directs the water to drip off it and fall into the cavity below. A conventional tie can discharge water halfway across the cavity within a 100mm cavity incorporating 50mm partial fill insulation. So, where that partial fill insulation terminates horizontally across a gable, the top of it is exposed. Water falling onto an exposed insulation top edge will either pool on it or gravitate into it. In both instances, with the insulation secured against the inner skin, capillary permeation results. This can occur where tie and insulation placement is perfect – the problem where ties are not perfectly centred, or insulation placement is uneven is more extreme.

Mitigating Gable End Water Ingress with Best Practices

The best practice is to protect the top of the gable end insulation to prevent this possibility from happening.

Choosing the Right Solution: Gable End Insulation Protection

Using a preformed cavity tray will ensure any water dripping from higher-level ties cannot fall onto or into the top of the insulation. Cavity Trays Ltd manufactures several trays suitable for this purpose. A popular choice of contractors is the Type CD Cavity Dropcloak. This preformed tray conveniently does not require building into the exterior skin but protects the insulation top and inner skin.

Expert Insights on Gable End Insulation Protection

‘There might be a temptation not to protect the top of gable end insulation in such an application’, commented a Company spokesman, ‘but it is essential as it takes only a couple of ties to cause a damp nuisance and rectification high on a gable wall once the building has been completed is costly.

The Type CD Cavity Dropcloak is listed within the new Technical Manual ‘Protecting the Building Envelope’, which was released this month (May 2011) by Cavity Trays Ltd.

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