**************** Disclosure to Promote the Right To Information Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public. Mazdoor Kisan Shakti Sangathan "The Right to Information, The Right to Live'' IS 4891 (1988) : preferred cut sizes of structural timber - Specification [CED 13: Building Construction Practices including Painting, Varnishing and Allied Finishing] Jawaharlal Nehru 'Step Out From the Old to the New" aj^&vi iJii^s:y%K^ isb^^ni^seg :<>5&i| mT'5K^5?::5:^>^i»l K^^^iXSVCd^ Satyanarayan Gangaram Pitroda Invent a New India Using Knowledge Bhartrhari — Nitisatakam ''Knowledge is such a treasure which cannot be stolen" ^'^^^r k BLANK PAGE ^*-^^^ PROTECTED BY COPYRIGHT IS: 4891 - 1988 ( Reaffirmed 2005 ) Indian Standard SPECIFICATION FOR PREFERRED CUT SIZES OF STRUCTURAL TIMBER { First Revision ) UDG 674-4: 691-11 : 389-171 ® Copyright 1989 BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NEW DELHI 110002 Gr 2 April 1989 IS : 4091 - 1988 Indian Standard SPECIFICATION FOR PREFERRED CUT SIZES OF STRUCTURAL TIMBER ( First Revision ) 0. FOREWORD 0.1 This Indian Standard ( First Revision ) was adopted by the Bureau of Indian Standards on 19 September 1988, after the draft finalized by the Building Construction Practices Sectional Com- mittee had been approved by the Civil Engineer- ing Division Council. 0.2 Timber finds its use in several items of cons- truction worksj particularly in roof trusses, purlins, rafterSj doors, windows, partitions, etc. Due to extreme shortage of timber, there is need for its rational use and this is an essential aspect of tim- ber design, 0.2,1, As a step in this direction, Forest Rese- arch Institute, Dehra Dun has developed stock designs for a number of standard roof trusses and purlins making it feasible to use the small dimen- sioned stocks of timber. Based thereon is a need for formulating a set of cut sizes for structural timber. Such a set of preferred cut sizes will facilitate large scale procurement, seasoning, chemical treatment, marketing and prefabrication of various building components as also the dimensional coordination between door frames, partitions, etc. 0.2.2 This standard was first published in 1968 and present revision has been undertaken to incorporate the sizes based on experience gained in design and use of timber structural parts as well as from Indian Standards published on the subject. This revision, therefore, contains up- dated data on sizes adopted in standard designs, door/ window components and deviations in sectional dimensions during conversion for effective shrinkage due to the effect of change in moisture content. 0.2.3 This standard is necessary adjunct to IS : 1331-1971* on cut sizes of timber which cover sizes for all uses. 0.3 For the purpose of deciding whether a parti- cular requirement of this standard is complied with, the final value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with IS : 2-1960t. The number of significant places retained in the round- ed off value should be the same as that of the specified value in this standard. *Specification for cut sizes of timber ( second revision ). fRules for rounding off numerical values ( revised ). 1. SCOPE 1,1 This standard covers preferred cut sizes of timber for use in the following units: a) Roof trusses; b) Roof purlins, rafters, floor beams, etc; c) Partitions framing, covering; d) Centering; and e) Door/window/ventilators, 2. PREFERRED SIZES 2,1 Preferred cut sizes shall be as covered in Tables I to 4. These sizes are sawn sizes obtained from air dried timbers. The seasoning and preser- vation of timber is carried out in accordance with IS : 1141-1973* and IS : 401-1982t. 2.2 For centering the preferred sizes shall be the same as for partition framing covered in Table 3, 2*3 Tolerances 2.3.1 a) 1) For measurement up to 100 mm: to +3 mm 2) Measurement above 100 mm: — 3 to +6 mm b) Length for all sizes: to +10 mm ♦Code of practice for seasoning of timber. tCode of practice for preservation of timber ( third revision ). 1 IS : 4891 - 1988 TABLE 1 PREFERRED CUT SIZES OF STRUCTURAL TIMBERS FOR ROOF TRUSSES ( SPAN FROM 3 TO 20 METRES ) Thickness in mm 20 25 30 35 40 50 60 80 Note 1 — For truss spaas marginally above 20 m, preferred cut sizes of structural timber may be allowed. Note 2 — Preferred lenghts of timber : 1, I'S, 2, 2'5 and 3 m. {Clause 2 A ) Width in mm 40 50 60 80 100 — — 40 50 60 80 100 120 140 160 40 50 60 m 100 120 140 160 — — 60 80 100 120 140 160 — — 60 80 100 120 140 160 — — 60 80 100 120 140 160 _ — — 80 100 120 140 160 — — — — 100 120 140 160 TABLE 2 PREFERRED CUT SIZES OF STRUCTURAL TIMBER FOR ROOF PURLINS, RAFTERS, FLOOR BEAMS, ETC Thickness in mm 50 60 80 100 [ Clause 2A ) Width in mm A. 80 100 120 140 __ — 80 100 120 140 160 — — 100 120 140 160 — — 140 160 180 200 Note — Preferred lengths of timber: I'S, 2, 2'5 and 3 m. TABLE 3 PREFERRED CUT SIZES OF STRUCTURAL TIMBERS FOR PARTITION FRAMING AND COVERING ( Clauses 2 A and 2,2) Thickness in mm 10 15 20 25 30 40 50 60 80 Width in A. mm 40 50 60 80 — — „ 40 50 60 80 100 _ — — — 40 50 60 80 100 120 160 200 — 40 50 60 80 100 120 160 200 240 40 50 60 80 100 120 160 200 240 40 — 60 80 100 120 160 200 240 — 50 — 80 100 120 160 200 240 — — 60 80 100 120 160 200 240 — 80 100 120 160 200 240 Note ^~ Preferred lenghts of timber : 0'5, 1, 1*5, 2, 2'5 and 3 m. IS : 4891 - 1988 TABLE 4 PREFERRED CUT SIZES OF TIMBER FOR DOOR/WINDOW/VENTILATOR COMPONENTS ( Clause 2 A ) Thickness in mm Width in mm 15 20 25 30 35 40 50 60 — — — — 50 60 25 — — — 50 60 — 30 — — 50 60 -- _ 35 =. 50 60 — — — 40 50 60 80 100 80 iOO 80 100 80 100 80 100 80 100 — 100 160 180 200 220 240 __ 160 — — — 240 — — 160 — — — 240 120 — — — — - — 120 140 — — — — — Note I — Preferred timber lengths ( wall opening module of 100 mm ) for frames: 590, 790, 890, 990, 1 190, 1 290, 1 990 and 2 090 mm. Preferred timber lengths for shuttersi 460, 500, 560, 700, 800, 900, 1 100, 1 200, 1 905 and 2 005 mm. Note 2 — For beading of 15 mm thickness, 25 and 40 mm width, and for 20 mm thickness, 25, 30 and 40 mm width may be allowed. Note 3 — For lock and bottom rail of 30, 35 and 40 mm thickness, 150 and 200 mm width and for 50 mm thickness, 150, 200 and 240 mm width may be allowed. 2,3.2 Tolerances in door/window/ventilators components shall be permissible as under: a) b) Frames Shutters 1) Doors ±3 mm i) Width ±3 mm ii) Thickness ±^1 mm No tolerance for panels 2) Window/ventilators, etc Width 40 mm and less ±1 nii^ Above 40 mm ±3 mm 2.3.3 Cut sizes of timber as stocked and speci- fied in tables are normaiiy at moisture content of 20 percent. But at the time of fabrication and erection, the timber members are required to possess 12 to 20 percent of moisture content of the oven-dry v^eight according to IS : 287-1973*. Thus a lateral shrinkage effect in the stocked sizes of timber will take place and, therefore, the ulti- mate shrinkage to v/hich the tim.ber v/ill be subjected to has got to be compensated in the very first instance at the time of converting the timber at 20 percent moisture content for stock- ing purposes. 2.3.4 A method for adjustment of dimensions at different moisture content is given in Appendix A along with an illustrative example, 2.3.5 Other sizes may be produced or stocked to meet specific demands or to ensure full utiliza- tion of the logs or their off-cuts. ♦Recommendations for maximum permissible moisture content for timber used for different purposes ( second revision ). APPEND IX A ( Clause 2.3.4 ) ADJUSTMENT OF DIMENSIONS AT DIFFERENT MOISTURE CONTENTS A-1. All the tabulated sizes shall be taken as standard at 20 percent moisture content/ A-2. For dimensions along the grain, no allowa- nces shall be made for moisture content differing from 20 percent moisture contents. A-3. For cross-sectional dimensioris, the following allowances shall be made irrespective of radial or tangential directions. A-3.1 For timbers of specific gravity below 0'6 ( or dimensional stability 60 percent of teak and IS : 4891 - 1988 above ), the change in the dimensions shall be calculated on the basis of 0*2 percent per unit moisture content differing from standard 20 per- cent moisture content. A-3.2 For species of specific gravity 0*6 and above ( or dimensional stability below 60 percent of teak ), the change in the dimensions shall be calculated on the basis of 0-3 percent per unit moisture content differing from standard 20 per- cent moisture content. A*3.3 Example: Data 1) 2) Exact dimension required for actual fabrication later according to the engineering drawing Moisture content at the time of fabrication later 3) Moisture content in the first instance at the time of sawing and storing 4) Specific gravity of the timber species used SOLUTION a) Let the dimension in the first instance at the time of sawing/storing be = 100 mm — 12 percent = 20 percent — below 0-6 = X mm b) Difference in moisture cont- ent between time of storing and the time of use later c) Now for 1 percent difference in moisture content, per- centage deviation in corres- ponding dimension d) For 8 percent difference in moisture content, percent- age deviation e) For 8 percent difference in moisture content, the physi- cal deviation from corres- ponding dimension at the time of sawing and storing Therefore, x — 0*016 x will have to be f) OY X = = 20-12 = 8 percent = 0-2 per- cent ( for, timber spe- cies with specific gra- vity below 0-6) := 0-2 X 8 percent = 1*6 percent = 1 6 percent of a: = 0016 xmvci 100 mm 101-63 mm Similarly, the corresponding dimensions ( that is, 1 '63 mm oversize ) in the first instance at the time of sawing/ storing for all the four zones into which India is divided according to moisture content vide IS : 287-1973* can be worked out. *Recommendations for maximum permissible moisture content for timber used for different purposes ( second revision ). 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