THE USES OF WOOD 



479 



the ordinary house, and there is no better material than 

 wood for these. When a little more strength is wanted, 

 without the addition of much weight, kingposts give the 

 desired result. As the size of the structure increases still 

 further, and a larger, heavier roof is required, trusses are 

 introduced. The truss is a sort of bridge which reaches 



GOOD AFTER TWENTY-SEVEN YEARS OF SERVICE 



These shingles of western red cedar show little signs of decay though they 

 have been on the roof 27 years. A few are loose, but that is the fault 

 of poor nails and not of bad shingles. This affords an excellent example 

 of the necessity of using none but the best nails in putting on a shingle 

 roof. Photograph by the West Coast Lumbermens' Association. 



from wall to wall, and its function is not only to support 

 the roof, but also to tie the walls together and prevent 

 them from spreading apart by the push of the weight 

 above. The wooden roof truss has been a favorite study 

 with architects, and they have improved old forms and 

 invented new, until roofs of great size are practicable 

 without posts intermediate be- 

 tween the walls to sustain the 

 load. Walls more than one hun- 

 dred feet apart may be spanned 

 with safety by trusses, and that 

 style of roof is considered eco- 

 nomical under certain conditions. 

 The designers of roof trusses 

 have borrowed ideas from bridge 

 builders, and they have also fur- 

 nished ideas to bridge builders. 

 A single wooden bridge span, 

 without supporting arches, has 

 been found practicable up to a 

 length of 360 feet or more, and 

 if it were necessary to do so, 

 roofs could be built from wall 

 to wall that far apart by a similar 

 use of wood; but that is not 

 necessary, for it is more econom- 

 ical to have midway posts or 

 columns as supports. But such 

 supports or piers are not always 

 practicable in bridge building, 

 and that accounts for bridge spans 

 being longer than roof trusses. 

 Steel competes with wood as 

 roof truss material, and this 



metal can be used wherever wood answers, provided it is 

 not barred by cost, and if excessive weight is not objec- 

 tionable. Wood is much lighter than steel, and for trusses 

 of moderate length is cheaper, even when the cost of 

 steel is normal ; and at this time, when steel is up in price 

 because of the war, the expense of building wooden 

 trusses, unless they are very large, is far below the cost 

 of steel. But, since the strength of material must be in- 

 creased in proportion to the length of the truss, a limit in 

 size is finally reached beyond which wood cannot compete 

 with steel, even at the present high cost of the metal. 



The building of wood roof trusses for large buildings 

 has greatly increased in this country since the beginning 

 of the European war, when the price of steel rose rapidly. 

 It has surprised many people that wood is so well adapted 

 for that high class of architecture ; and the stimulus thus 

 given the use of wood may be expected to have results in 

 years to come. 



Investigations of the strength of American woods have 

 given valuable assistance in their use in roof supports 

 as well as in other large structures. It is fortunate that 

 some of the strongest and most abundant woods are mod- 

 erately light, thus affording maximum strength with 

 minimum weight, making wood an ideal material for 

 large roofs and their supports. Old churches and halls in 

 England have enormous beams as roof supports. Some 

 are larger than the situations called for, but the strong 

 woods of England are quite heavy and the builders want- 

 ed to be on the safe side and used large timbers. In 

 America, equal strength is secured by using lighter woods 

 in smaller beams and braces, arranged in a more scien- 

 tific manner. Among the excellent structural timbers of 



PROCESS OF MANUFACTURING RED CEDAR SHINGLES 



The shingles are sawed automatically by the machine on the left of the picture 

 trues the edges and cuts out the defects on the clipper saw in the center of the pii 

 them ready to be bunched. Photograph by the Clear Lake Lumber Company, Cle 



