Granary construction A
s Trevor mentions, he and I have cor- responded regarding his model of an early grain storage building. I pointed
out the prototype for his model was con- structed with cribbed or finger joint con- struction, so he asked me to write a side piece detailing how these wood grain build- ings were constructed. Crib or finger joint construction (not to be confused with mod- ern finger joints, which are machine cut glue joints used to connect short pieces of wood) essentially means that the walls are built up by laying the boards flat, wide edge down on top of each other, and long nails or spikes are driven down through each row. On a tall elevator 2″×12″’s or 2″×10″’s
were at the bottom, then progressively 2″×8″’s, 2″×6″’s and 2″×4″’s were used as the height of the wall increased. The result- ing wall was incredibly strong, able for the most part to withstand the pressure of mil- lions of bushels of grain. The wider the board, the less chance of the wall bowing out, but it also consumed large amounts of lumber. Millions of board feet went into a large grain elevator. To this, Trevor cleverly responded, “If
Crib joint construction
Stud walls, however, cannot withstand tremendous horizontal pressure without ad- ditional support. Grain is like water: it flows down and out. Rectangular buildings can’t handle such pressure; they are strongest in the corners and weak in the middle of the wall, which is one reason round structures became popular for storing water and grain. The use of long metal rods through the
building, with large plates on the outside of the building, is one way to combat the forces of grain pushing outwards on the walls. Many older grain buildings have hor- izontal timbers on the exterior walls with the nut, bolt and washers of these tie rods clear- ly visible. The lower to the ground, the clos- er these tie rods are, just like the support bands on a water tank. At the same time, cribbed construction is
weakest at the corners, where water and rot will introduce cracks and weakness in the boards, causing them to fail. Factor in the destructive nature of rodents gnawing away for a chance at the mother lode of a free meal and you can see the importance of keeping the wood construction protected from weather with siding in good condition. A few years ago I photographed a “blow
out” of a wood grain elevator in Villisca, Iowa. The grain had gotten wet, began to swell, and blew out the lower corner of the building, splitting apart the fingers. A grain elevator built of cribbed construc-
tion will have angled corner braces posi- tioned inside the bins. These are typically horizontal 2″×6″’s set into the wall at a 45- degree angle, tying the two walls together across the corner. Crib style construction goes back to the
e f
that’s the case, why don’t we see this type of construction more often?” Then he an- swered his own question, “We do. We just don’t realize it. That’s because this con- struction has one big weakness, which is that if the boards are exposed to weather, moisture in the joints can severely weaken the walls and cause the wood to rot. Many, many traditional ‘prairie skyscrapers’ are built using finger joint construction, then clad in clapboard or sheet metal siding to protect them from rain and snow.” He is correct. The construction is hidden
behind protective siding, just like buildings today have their structure covered by sid- ing. Most of us are more familiar with stud construction, where vertical studs form the skeleton of the wall and are covered with siding on the exterior and sometimes plas- ter or drywall on the interior. A look into an old garage or shed will reveal this type of construction.
RAILROAD MODEL CRAFTSMAN
days of log cabin construction, where logs were laid on top of each other with the ends interlocking via notches. The advent of di- mensional lumber, made available because of powered sawmills, enabled construction that was quicker and consumed less lum- ber, but the design stayed the same, boards laid on top of each other interlocking at the corners. Instead of notches to hold things together, long nails were used, driven down through several layers of lumber. Remem- ber, in the days when these prairie sky- scrapers were built, wood and labor was cheap, and this type of construction did not required skilled labor. If you could lift a board or pound a nail, you could get a job. One interesting note for modelers: The combined weight of the vast amount of lum- ber, along with the grain in the bins, tended to compress the wood at the bottom of the wall, causing a 100-foot tall elevator to “shrink” several inches in height in the first years after its construction. The lower hori- zontal clapboards on the exterior were only nailed along the top to prevent their splitting or popping loose as the horizontal planks compressed and settled. Also, note there are no vertical corner trim boards on wooden grain elevators, as this compression action would pop the trim off the building. The clap- boards have angled cuts to fit at each corner, a tedious chore. In later years, once the building had shrunk to its settled height, cor- rugated metal siding could be applied with- out danger of coming off.—DOUGLAS HARDING
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