Moderately heavy to heavy constructional timbers ranging in density from about 720 to 880 kg/m3 air dry (or at 15% moisture content). Some timbers under this classification are actually heavy and strong enough to be classified as Heavy Hardwoods, but they lack sufficient natural durability when exposed to the weather or in contact with the ground and treatment with preservatives is necessary before use. Most of them, however, are naturally durable in temperate countries where wood destroying agents are less active.
