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Treatments – moisture measurement

The moisture content of timber is an important factor influencing in-service performance.

For example buildings should not have interior linings installed until the preservative treated timber framing has a moisture content below 20%.

The most accurate procedure for determining wood moisture content is the “oven drying method”, but this is impractical for timber already in-service.

Hand held moisture meters are used, the two most common being resistance or capacitance meters. Both measure the effect that moisture has on the passage of electric currents through materials, but neither type is particularly reliable outside a wood moisture content range of 5 to 28%.

The accuracy of the meter reading is also affected by preservative type, its concentration and other factors such as wood density. It is important that any meter is regularly calibrated and an appropriate correction factor is applied to the meter reading to determine the timber moisture content.

Both BRANZ and Scion have undertaken assessments of various types of moisture meters. More information on their use can be located on their websites.