This guideline describes a test method for wood to be exposed to the weather out of ground contact. The main objective of the method is to evaluate the durability of wood in above ground exposure as shifted overlaid stakes, which form the so called double layer. The method is applicable to the testing of untreated, treated and modified wood. Initially it was developed and found to be most useful for testing of natural durability. As a simple and effective test method, it spread quite fast. Up to now more than 30 double layer tests are running in different countries of the world. The inventors of the double layer test were asked to come up with a full and precise guideline for this test methodology to enable interested scientist making use of this test method. Therefore this IRG- document was written as an instruction for those who would like to perform this test.

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