Vapour Control Layers (VCL)

Vapour control lining forms part of a buildings external main walling. Vapour control lining, or VCL for short, is a plastic layer that restricts the movement of warm, moist air from inside a property into the external main walls. VCLs prevent excess moisture entering a wall’s cavity, behind the insulation. If a property does not have a VCL, the risk of interstitial condensation build-up in the external main walling increases, and this can lead to damp issues appearing both internally and externally.

This risk is only heightened if a property is built using unconventional construction materials, such as timber framing. In addition to the risks of dampness, the build-up of interstitial condensation in a timber frame construction can lead to rot/decay of the structure.

We recently carried out a HomeSurvey on a bungalow in West Dorset, which was originally built with a non-conventional structure of a timber frame (please refer to our other blog on Non-Conventional Construction for more information).

The external main walls of this 1960s bungalow were upgraded using Pavatherm and cedar cladding. Upon enquiries with the property owner and manufacturer of Pavatherm, it was disclosed that the external main walls did not include VCL as it was not required due to the constitution of the new external main walling. According to the manufacturer of this nature of walling, VCL layer is not required as the materials are vapour permeable, and allow condensation from internal walls to escape, reducing the risk of interstitial condensation in the main walling.

Whilst it was recommended that further investigations and enquiries should be made regarding the specification of this new nature of walling, it was noted that this is a modern, contemporary design and has not been able to be investigated through the test of time.

This should be considered prior to purchase of any property with external main walling of this nature as it could affect future saleability and value as some lenders are dubious about accepting this nature of construction for lending purposes.