Timber cladding in Scotland

Richard Gibson

Overlooking the north side of Lerwick harbour, the project at Gremista on Shetland is the largest development undertaken by Hjaltland Housing Association. It consists of 66 flats and houses as well as two buildings providing residential accommodation for people with special needs, and has proved very popular with residents, with nearly 50% of the houses occupied through a shared-ownership scheme.

The rainfall at Lerwick is not excessive (c.1171mm per annum), but high wind speeds make the risk of wind-driven water penetration into the wall fabric of buildings a serious problem. This is compounded by the unsuitability of the stone available on Shetland for the manufacture of high-quality concrete blocks. The combination of these factors gives harled blockwork cladding a tendency to leak, leading to moisture problems in the wall fabric and a consequent increase in maintenance costs. Because of these problems, Hjaltland Housing Association analysed the ongoing performance and costs of conventional blockwork cladding against timber cladding and found the latter to be the more cost-effective alternative in the long term.

Richard Gibson

Hjaltland Housing Association already owns 100 timber-clad houses which it purchased from Scottish Homes. Constructed 25 years ago by the Scottish Special Housing Association, they still perform well and are similar to earlier timber-clad kit houses on Shetland which were imported from Norway and Sweden in the 1940's and which also still give dependable performance. These precedents afforded the Association confidence in the durability of timber-clad housing in the local exposed conditions, and vertical board-on-board cladding was selected since it appeared to offer the most resistance to wind-driven rain penetration. The preservative-treated softwood cladding was carefully detailed for drainage and ventilation and was given an opaque water-repellent coating.