Sawn Treated

The preferred timbers for outdoor use are pressure treated spruce. The degree of treatment is dictated by the potential exposure to moisture during the stages of building. However, if the building is planned for a more rural location, then sawn, ungraded timber (but pressure treated) would be an excellent alternative.

Treated sawn timber grade C16 and C24, can be used outdoors providing it has been pressure treated. UC1, UC2 and UC3 timbers should withstand occasional wetting during construction but their main use is intended for use in a covered construction such as stables, timber frame extensions and standalone buildings. These are considered protected timber structures and typically include roofing felt, moisture resistant ply and timber cladding.

Tanalith timber and pressure treated timber are often confused with one another. Tanalith refers to one family of timber treatment types that includes Tanalith E; Tanalith MF and Tanalith Lifestyle. In practice most timber coming out of a treatment plant has been treated with Tanalith E! Pressure treated timbers have excess moisture removed and then been treated with timber preservatives – they might have been pressure-treated with Tanalith but the phrase “pressure treated” is not brand specific.

The lifespan of sawn treated timber is largely determined by the suitability of the timber for the desired application. A sawn 25mm thick timber should last 10-15 years if used for hit & miss fencing. However, if used incorrectly – say used as a post - the cladding timbers would probably last 2-3 years. They should be out of ground contact and supported with UC4 posts.