744 



IOWA DEPARTMENT OF AGRICULTURE. 



PUATE 



d-j 



30'-0" 



HElGttT OF OPEniMGS 



In order to preserve the silo in good condi- 

 tion it is absolutely necessary that the half-inch 

 lumber with which the silo is ceiled, be pro- 

 tected from dampness. To this end the plaster 

 must be of good quality and kept perfectly water- 

 tight by cementing up any cracks that may 

 appear, so that the wood shall receive no mois- 

 ture from the silage. The wall must also be ven- 

 tilated, for by allowing a free circulation of air 

 betvv^een the sheeting and the lining, the lumber 

 will be kept dry. In this silo a two-inch space 

 was left at the top above the plaster and below 

 the plate. In this way the air was allowed free 

 access to enter from the bottom, between the out- 

 side covering and the inside lining, and pass into 

 the silo through the openings at the top. These 

 spaces were covered with heavy wire netting of 

 one-third inch mesh to keep out rats and mice. 

 (Cut 20.) 



Theoretically the outside covering should be 

 put on horizontally so that the strength of the 

 material which forms the cover might add to 

 the strength of the silo. There are, however, 

 several practical difficulties in putting sheeting 

 on in this manner. The lumber cannot be more 

 than a half-inch thick and spring to a circle 

 twenty feet or less in diameter, and any siding 

 as thin as this, which is carried in stock, is prac- 

 tically clear lumber and necessarily high priced. 

 Another difficulty is that the only half-inch stuff 

 that can fce purchased at the lumber yard, which 

 will make a water-tight cover, is common house 

 siding. This, in order to be sprung to a circle, 

 must be rabbeted on the back side of the thick 

 edge so as to fit over the thin edge of the board 

 below and allow the siding to lie flat against the 

 studs, 'xlabbeted siding cannot usuaUy be ob- 

 tained at a lumber yard and it is extra trouble 

 and expense to have this work done at a mill. 

 Another serious difficulty in putting the siding 

 en horizontally is that at the end of each board 

 there is a strong outward pull against the nails 

 and as soon as the boards become slightly de- 

 cayed at the ends they are likely to pull off over 

 the nails. 



Owing to these objections and to the fact that 

 it was our aim to use, as nearly as possible, lum- 



(Cut 19.) 



ber that is carried in stock by all lumber yards, it was decided to put 

 hoops on the outside and build them up of the same half-inch material 



