Notes from Windward: #62

Contruction Phase One - Pouring the Pads

     The first phase of the construction involves the center section of the castle; the wall with the gate, and the attached platform.

Overview of the gate
and platform section
righthand side is north

     One way to look at the construction of most any sort of building is that you're working to create a roof, and need some way to hold that roof up there. In the city, the most common way to do that is to use 2x4 lumber to build a perimeter wall that sits on a perimeter foundation and holds the roof up.

     In the country, the most common structure type is called a "pole barn." That's a building in which the roof is held up by poles, although instead of actual round poles, the most commonly used "poles" are treated six by six beams. In our case, the poles at each corner of the platform are 6x6 beams, with 4x6 beams used as additional supports along the north and south side.

     The twelve foot deep and sixteen foot wide platform is supported by two rows of poles ten feet apart. It's a cantilevered design in that the platform extends beyond the support poles by 30 inches on each side. One reason for going with that design is that it looks really neat and castle like.

     Another reason is that this design will allow us to create a "tunnel of death" behind the gate. When the attackers force their way through the gate, they find themselves in a twelve foot long tunnel running under the platform. In order to take the castle, they not only have to get through the gate, but then they have to fight their way through the bottleneck behind the gate.

     In a pole barn, the weight of the roof is supported by this perimeter of poles, and in turn, that weight has to be transfered to the earth. If the poles were just stuck into the ground, the weight of the roof would tend to force the poles into the ground the way you could push the blunt end of a pencil into an apple. While it's easy enough to push a pencil into an apple, it's not so easy to push your finger into the apple. The reason is that the end of your finger covers about four times as much area as does the blunt end of a pencil, and therefore your finger applys only one fourth the pressure.

     That's why the first step in building any pole barn structure is to dig a series of holes some eighteen inches in diameter and some thirty inches deep. The second step is to mix up some concrete and pour six inch pads into the bottom of those holes.

     The math is fairly straight forward. The actual surface area of the butt of a 6x6 pole is about thirty square inches, whereas the surface area of that concrete pad is more than 250 square inches, an eightfold increase in the load that pole can bear without sinking into the ground.

     There are two reasons for going down at least thirty inches deep. When the water in the soil freezes, it expands and creates an effect called "frost heave." This truly is one of the elemental forces in nature; it can easily crack a boulder or a foundation, no problem. By digging down below the level which is subject to winter freezing we insure that our foundation pads won't be distrubed, and we also get down to a more compacted (i.e. able to bear a greater load) level since frost heave is one of the key forces that stirs up and loosens the top soil. It's the force that makes it seem as though a cleared field will grow a new crop of rocks each winter, and it's why the surface of especially wet areas are almost paved with rocks. Here at Windward you can generally follow the underground movement of water by following the trail of surface rocks thrown up by frost heave.

Roy and Walt mixing a batch of concrete

     The true frost depth here is somewhere between twelve and eighteen inches. We did down even further to give the poles an increased lateral stability. For example, the holes for the poles on our hay barn go down more than 40 inches, but going that deep in this case would be overkill, especially given the stability provided by the gate and wing sections of the castle wall. After the poles are hoisted vertical, inched around into their exact locations, and a web of bracing in applied, the dirt will be packed back into the holes to support and secure them. Here too, water will be used to settle and compact the earth as the holes are filled in some six inches at a time over a few days.

Pouring the pads

     For projects such as this, we mix our own cement by hand in a wheelbarrow. The mix we use is five gallons of rock, three gallons of sand and a gallon and a half of portland cement with water to suit. When we're pouring concrete in contact with the ground, we tend to go a bit on the wet side. Once there's enough concrete in the hole, a few jiggles with the mixing hoe to level the concrete, and we're done.

     Now that the pads for phase one are done, it's time to start raising the poles and setting them in place, something which is a bit tricky when you're talking about twenty foot long 6x6 beams.

Construction Phase One - Raising the Poles --- Notes from Windward, Vol. 62