Notes from Windward: #62

Construction Phase Two - Setting the King Posts

     The first step in Phase Two involves faceing the gate section with 2x12 planks and installing the gate. Since that's "vertical work," it can go forward even with a foot of snow on the ground.

     The latter part of Phase Two involves constructing two 16' sections of the castle wall that extend forward at a 45 degree angle from the gate section. At the end of these two sections the wall has another 45 degree bend as the wall resumes its north-south run. Since angles are always weak points in a design such as this, tending to want to allow the wall to flex as a hinge would, the corner is re-enforced with a massive post that's set down into ground.

     Since that is work that would be made all the more difficult by a foot of snow, when a brief warm spell came through and melted the snow, we jumped at the chance to get the King posts in place.

The two King Posts in place

     Traditionally, the largest pole in a construction is called the "King Post." Back in the days before almost everything was shipped in large containers, ships had a set of king poles that were used to hoist cargo out of the hold and swing it over the side and lower it onto the dock.

     Since in our case, the location of the two King posts will define the next two sections of wall, standing them up and fitting them into position was a task that had to be attended to before we could start to lay out the side walls.

A view from the side

     The King posts will be connected to the gate with a series of horizontal 2x6's, but given the punishment that the wall has to be prepared to accept, we won't be actually attaching the horizontal supports to the King posts. Instead, we'll be using a mortise and tendon arrangement where pockets will be cut into the sides of the massive posts. The 2x6's will then just slide in for a purely mechanical fit that can expand and contract with the seasons.

     It's one thing to build a structure like this so that it will perform for one event; it's a good deal trickier to build in such a way that it will live and breathe with the seasons, and not tear itself apart as it responds to extremes of heat and cold, wet and dry.

     To tell a bit of a personal story, the first deck I built here served to create an entry way for Fern's trailer. I whipped it together in August and it proved very serviceable until about the next February when it collapsed in a grand pile of lumber. I was very embarassed.

     The post mortum showed that I'd made two key mistakes. The first was that I'd put the deck together using standard carpentry screws. They're good fasteners, and are way better than using nails for most applications, but they're brittle and just weren't able to handle the stress caused by my second mistake.

     When I put down the planks that formed the deck, I laid them snug one against the other; i.e. without a gap between them. That made for a very nice, solid floor, at least it did right up until the whole deck fell down.

     I built that deck in August, which is the tail end of our dry season. The lumber was correspondingly dry, and by not leaving enough of a gap between the planks to allow for expansion when the winter rain caused the wood to swell, I inadvertently set the stage for collapse.

     As the wood in each board swelled, it exerted pressure against the other boards, and ultimately against the carpentry screws that were holding the horizontal supports to the support poles. When the cumulative pressure got too much, the screws sheared off and down came the deck.

      We put the deck back together with the requisite gap between the planks, and haven't had a similar problem since.

Detail shot of a vetical plank showing the gap and the screw location

     For the horizontal castle decks, we're using a 1/4" gap, which will probably expand to about 1/2" when fully dry. For the vertical walls, we're going somewhat wider with an initial gap of 5/8". The other trick we've learned is to locate the screws which hold the plank to its support about one third of the way in from the edges. That also serves to minimize the stress on the screws as the wood goes through the annual moisture cycles.

Construction Phase Two - Facing the Gate Section --- Notes from Windward, Vol. 62