Termite attack on susceptible lumber above naturally durable support posts

IRG/WP 00-10370

J K Grace

A multi-year field study was designed to simulate the use of naturally durable sill plates (dodai) and floor support posts in Japanese housing construction and test whether Formosan subterranean termites (Coptotermes formosanus) would tunnel over or through these resistant timbers to attack susceptible Japanese red pine (Pinus densiflora) lumber placed above them. This test was intended to explicitly address the possibility that a durable timber placed upon a solid concrete footing might create a sufficient barrier to subterranean termites to protect the structure from attack, in the absence of any other termite control specifications such as soil insecticide treatment. Inspection after three years in the field revealed that termites had damaged a Kiso Hinoki (Japanese cypress, Chamaecyparis obtusa) sapwood (with heart center) post, and a Hiba Arbor-vitae (Thujopsis dolabrata) sapwood (with heart center) floor post, although they had not reached the red pine block above each post. However, termites had also fully penetrated a Kiso Hinoki (Japanese cypress, Chamaecyparis obtusa) heartwood post, and severally damaged the red pine block on top of it. None of the durable woods in this test were damaged to the point where they would pose any sort of structural hazard. However, they clearly do not represent a barrier to further termite foraging, and there is also variation in durability among different samples of these durable woods. Sole use of termite-resistant sill plates or floor posts (as commonly required in both Japanese and American construction), in the absence of any other termite control measures, cannot be relied upon to protect the structure from termite penetration and damage to the adjoining susceptible wood framing.


Conference: 00-05-14/19 Kona, Hawaii, USA

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