There are various steps and orders of events when it comes to house-building, but there are some fundamental points that are pretty universal. Structures are generally built so as to be plumb in the vertical direction and level in the horizontal direction. These are some of the oldest and most basic building principles known to man.
I won’t go into why this is so, as this is common knowledge to most folks out there. The more important question is how to ensure your structure is so! The construction process or order of construction, has been tested through trial and error, and streamlined over millennia, but many of the techniques and methods we use today have been around pretty much from the beginning.
In the Context of Wooden Structures
It’s pretty safe to say that the most efficient way to solidify or brace a structure, as well as check for plumb and level, is to do so after the main columns and beams are assembled. Why? Because the alternative is to do so before they’re assembled, which means you’d need to somehow secure the vertical position of each separate column in 2 dimensions — very inefficient.
So back to the original scenario. Being that no shear bracing has been fixed at this point, the structure still has the ability to move or sway considerably. This is of course, assuming that the beam-column joints have negligible moment resistance. It is therefore possible, given enough force, to push or pull the entire structure in a given direction. I will explain more further below.
Today, beams and columns are typically precut and assembled according to an accompanying diagram. However, even without the advent of modern precut woodworking technology, the principle is the same. Beams and columns have always been hewn, milled and dimensioned with varying tools to varying degrees of accuracy, and assembled so as to ensure gravitationally-favorable structures.
By ensuring the column-to-column span is the same both at the bottom and the top, one can assume that if one column is standing plumb, the other will be as well. This of course, only applies to the plane in which the columns are aligned. If you want to check for plumb in the perpendicular direction, you simply have to repeat the steps in that direction.
This principle is fundamental to structural design, and as basic as it is, is arguably one of the most important principles of wooden home construction. In today’s modern world of computers and software, we have the ability to design and tweak structures from the comfort of our homes and offices, crunching numbers and measurements that result in perfect dimensioning.
Once the lumber is precut and transported to the building site, it is assembled piece by piece. Dove-tail and other similar joint connections are toenailed from above with 75 or 90 millimeter nails — enough to hold the joint together in the vertical direction. These joints are later fastened with “hagoita“. Pin connections are another common joint system that utilizes hardware and pins to form strong joints that don’t eat into the cross-sectional geometry of either beam or column.
Pushing and/or Pulling the Boneframe into Plane
The first thing you’re probably thinking is “easier said than done”. It’s not like you can just single out a column and start pushing against it while eyeballing some spirit level you have tied around it. Well, there’s both good news and bad! Let’s start with the good.
The good news is that there are tools available that make this method extremely simple. The bad news is that they aren’t cheap, and don’t always result in the kind of accuracy you might be looking for. You should know that wood is never a perfect building material, and as such, is subject to shape-change and warping.
Also, the larger your structure is, the more apt it will be to veer from the intended dimensions — including at the foundation phase as well. What this means is that some columns may be plumb while others may not. The same thing applies to the beams as well. In other words, there is no such thing as an “ideal” specimen or scenario in real life. Live with it.
There are 2 tools needed for the job:
1.) “Yaokoshi” or “roof-lift”. This is the Japanese name for the particular tool I’m referring to. It’s basically a long steel jack of sorts, with a base that can be locked down onto a floor and an “L” shaped holder at the other end for locking onto a horizontal beam. By turning the center of the jack in the designated direction, it increases in length, essentially pushing at the beam it’s locked on to.
2.) “Sagefuri” or plumb-bob. There are the standard plumb bobs, which are little more than a weight fixed to string fixed to a coil that can be nailed into a column. And then there are those which are incased in aluminum housing manufactured to block the interference of wind. These versions typically come in lengths in the 2 meter neighborhood with an extendable component to allow greater accuracy.
We need to first devise a way in which to temporarily secure or hold the structure in the given position once we have pushed it into plane. Here in Japan we use what is called “karisuji” — temporary diagonal bracing. These will eventually be removed once the structural plywood (shear walls) is attached. They should be long enough to create a 45 degree angle with the floor and wall.
The karisuji should be placed in their relative positions with only their top ends nailed. This allows you to quickly nail the bottom end as soon as you confirm plumb. Karisuji should not protrude above the floor level above, out past the wall to the side, or below the floor level below. In other words, they should not be in a position to interfere with any of the subsequent steps of construction until they are ready to be removed.
There should be karisuji every 3.6 to 4 meters, in both dimensions (x and y), and adjacent karisuji should not be 45 degrees parallel to the other, but pointing in the other direction; ie, rotated horizontally 180 degrees. They should also be placed in locations where there are at least 3 main columns into which it can be nailed, preferrably top, middle, and bottom.
Now that we have our karisuji in place, we strap the sagefuri to a column of our choosing. Just make sure the sagefuri is strapped to the right side of the column. Determine in which direction the structure needs to be pushed to become plumb and set up your yaokoshi. Like the karisuji, yaokoshi is most effective at 45 degrees.
Make sure whatever it’s pushing on is solid and won’t move or break as the jack is turned. As you turn the jack, the structure should slowly begin moving. When you’ve confirmed the column is plumb, go ahead and nail the karisuji into the columns. This now concludes this section of the building. Repeat this step for all the karisuji and you’re ready to move to the second floor.