Save Money \(ith Common Sense Lumber And

Timber Design Specifiications

By Charles F. Crais, Sales Engineer Pope & Talbot, Inc., Portland, Oregon

During this period of high construction costs and cotrstruction material shortages, it behooves the engineer to tailor his design and timber specifications to fit the available material.

With the present stepped-up demand for construction grade lumber, it is only natural for the mills to be somewhat selective in their cutting schedules. For this reason, many schedules for stress grade lumber and timber which require odd sizes, non-standard surfacing, free-of-boxedheart stringers or extremely long lengths are practically unobtainable. Frequently the design specifications call for hard-to-get high stress grades when a lower stress grade, r,vhich is obtainable, tvill suffice.

Slight changes in design or modification of specifications to use the available material constitute savings'in time ai{ money for both buyer.and supplier. To realize these savings. the designer of timber structures should limit his design to standard sizes and mill lengths where possible. Odd sizes reflect the additional costs of special setups in the mill for sawing and surfacing, while using mill lengths eliminates the waste from cutting. Keep in mind that the basic price is based on the mill length furnished regardless of the net length required.

If surfacing is required, specify S4S (surfaced four sides), which is standard for mills equipped for surfacing. The SIS1E (surface one side, one edge) which is quite often found in bridge decking specifications gives the designer the same net section as the S4S but leaves the mill man with the problem of how to dispose of the over-run (extra cutting) or fall-down (material which does not meet the grade requirements).

Permit dapping large size timbers at bearing surfaces as an alternate to the usual specified surfacing of SlE to required depth. This rvill allow a large number of mills not equipped for surfacing to submit competitive prices and a structurally stronger piece will be supplied. Standard surfacing of %" off on large stringers rreedlessly reduces the section modulus where the bending stress is highest.

Irlan to splice such items as laminated decking, as multiple or random lengths are much easier to obtain than a large number of pieces of a specified length. Never specify a. single long length rvhen tl,e end product is to be cut irrto sevcral short lengths such as bridging or blocking and rvhenever practicable, permit the use of built-up or spliced members for such itcms as wheel guards, caps and sills. \Vatch carefully the grade requirement and specify the lowest stress which will dc the job. All too frequently, specifications call for high stress grades select structural timl>er for non-load-bearing members such as filler blocks, bridging and wheel guards when a lower, more obtainable, less expensive grade w'ill suffice. Keep in mind the use of the lorver grades rvhen designing for both economy and availability.

As a precautionary measure, permit alternate bids. This will allow suppliers tc offer the available material and even though different than specified, it will often be acceptable and save needless time and cost of re-advertising.

A final caution is specify preservative pressure treatment for all lumber and timber products exposed to decay or attack by wood-destroying organisms. The small additional cost of preservative treatment is cheap insurance against structural failure from decay or termite damage. High replacement and maintenance costs, both labor and materials, are practically eliminated rvhen the material is properly pressure-trelted according to American WoodPreserver's Association specifications.

Attempts are often made to realize a small initial construction saving by irot specifying preservative treatment.

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