UL 10A-2009 pdf download – Tin-Clad Fire Doors.
3.6 The actual thickness of the boards shall be not less than 3/4 in (1 9.1 mm). 3.7 The boards shall not be less than 4 in (89 mm) nor more than 8 in (1 78 mm) in nominal width. 3.8 The nominal width (or stock width) is greater than the actual width over the tongue and groove. 3.9 The boards shall be free from wane (bark), decay, knot or other holes, loose knots, unsound knots, or knots exceeding 2-1 /2 in (64 mm) in any dimension. 3.1 0 Lumber of a No. 2 Common or Construction grade or better will meet these requirements. However, because some pieces of No. 2 grade are unacceptable, the kind of lumber used and its condition shall be judged from characteristic properties of the wood as commonly known. These characteristics include: a) DECAY – Destruction of the wood substance due to the action of wood-destroying fungi; Note: ″Dote″ and ″rot″ are synonymous with ″decay″ and are any form of decay which is evident either as a dark red discoloration, not found in the sound wood, or the presence of white or red rotten spots. b) ADVANCED (Typical) DECAY – The older stage of decay in which the destruction is readily recognized because the wood has become punky, soft and spongy, stringy, ring shaped, pitted, or crumbly; c) INCIPIENT DECAY – The early stage of decay which has not proceeded far enough to soften or otherwise perceptibly impair the hardness of the wood; d) KNOT – That portion of a branch which has become incorporated in the body of a tree; e) LOOSE KNOT – A knot which is not firmly held in place by growth or position; f) TIGHT KNOT – A knot so fixed by growth or position that it firmly retains its place in the wood piece; g) HOLLOW KNOT – A hollow knot is an apparently sound knot except it contains a hole over 1 /4 in (6.4 mm) in diameter or a void area behind the knot; h) CHECK – A separation along the grain, the greater part of which occurs across the rings of annual growth; i) WANE – The lack of wood from any cause, or bark on the surface of lumber.