4X0 



AMERICAN FORESTRY 



American softwoods are longleaf pine, Douglas fir, west- 

 ern larch, hemlock, and spruce. These possess great 

 strength in proportion to their weight, and there are sev- 

 eral others which are little, if any, inferior. 



Shingle roofs are lighter than those of most other 

 materials which can properly be regarded as competi- 



FIGHTING FIRE BEFORE IT STARTS 



Shingles may be rendered partly fireproof by treating them with certain 

 chemicals. Two shingles are shown in the cut. That on the left is 

 untreated, the other is treated, and both were given an equal chance 

 to burn. The photograph is from the U. S. Forest Products Laboratory 

 at Madison, Wisconsin. 



tors. The weight per square foot of tile roof is from 

 12 to 25 pounds; of slate 10 pounds; and of shingles 

 from one to three pounds. If a roof is large, the dif- 

 ference in total weight between a covering of shingles 

 and one of slate or tile is so great that the architect must 

 determine the factors of safety with the utmost caution. 

 Engineers work out the strength of woods by test- 

 ing them, and construct tables whereby one wood may 

 be compared with another, all being measured on the 

 same basis. The figures usually given show the "modulus 

 of rupture," which means "measure of the breaking 

 strength." Modulus of rupture is a technical term. The 

 table which follows gives the strength of twelve well 

 known woods, but instead of using the term "modulus of 

 rupture," to express strength, the figures are worked out 

 to show what load in pounds would be required to break 

 a stick approximately two and five-eighth inches square 

 and resting on supports one foot apart. Expressed in 

 that manner, the meaning is clearer to the untechnical 



person than it would be if the somewhat cryptic term 

 "modulus of rupture" were employed, and yet precisely 

 the same figures are used. 



Wood Load in pounds 



White pine 9,600 



Eastern hemlock 9,700 



Douglas fir 10,300 



Red spruce 10,800 



Sitka spruce 11,200 



Southern cypress 1 1,300 



Yellow poplar 11,800 



Western larch I3.S00 



Shortleaf pine 13,900 



White oak 15,200 



Pignut hickory 22,500 



The foregoing figures represent seasoned wood. The 

 strength is much less if the woods are tested green. As 

 wood dries, its strength increases. 



If the strength were figured out on the basis of or in 

 proportion to the weights of the different woods, the 

 surprising showing would be made that white oak is the 

 weakest wood in the foregoing list, and Sitka spruce 

 the strongest. Weight for weight, that far western wood 

 is stronger than pignut hickory, and that explains why it 

 is preferred for airplanes where the greatest strength 

 and the least weight are demanded. In a lesser degree, 

 the same requirement must be met in roof timbers, and 

 it is apparent that if heavy woods, like oak, were employed 

 in excessive amounts, a point might be reached where the 

 roof would collapse under its own weight. 



The nail which fastens the shingle on is often not given 

 due consideration, yet it is as important as the shingle 



SAWING SHINGLES OF CHESTNUT TIMBER 



Shingles of this wood are durable and its use opens the way for utilizing 

 timber of small size killed or likely to be killed by blight, thus saving 

 what otherwise might be wasted. The mill here shown is in Frederick 

 County, Maryland. Photograph by courtesy of the Maryland Board of 

 Forestry. 



itself. When the nail rusts through, the shingle is loose 

 and is liable to blow off. There is no economy in buying 

 and laying high grade shingles and fastening them on 

 with low grade nails. First class roofs cannot be made 

 if second class nails are used to fasten the shingles on. 

 The ordinary wire nail may be destroyed by rust in a 

 few years. The zinc-coated nail is recommended, and if 



