SUBS #2:
Sheer Wall vs. Shear Wall [Meets Code vs. Earthquake PROOF!]

Site and factory built structures are both commonly "stick built".

The walls are generally 2x4 or 2x6 studs, covered with siding on one face and drywall on the other. I refer to this as "sheer wall" because it is so weak.  You can put your fist through drywall, and some siding materials are not much stronger.  This "sheer wall" has strength in only one direction.  Even if steel studs are used, it is still "stick built".   If you look at a stick house being built on site, you will see many temporary diagonal braces keeping the framed walls from collapsing during construction, because they have almost no strength on their own.  The studs will only support weight that is perfectly balanced straight down from above.  Without the temporary bracing, the whole house would collapse into a heap of sticks similar to a child's "pick up sticks" game.

Even after the inner and outer walls are installed, the whole thing will still collapse into a heap of sticks during an earthquake, so building codes require some walls to be shear walls to withstand lateral stresses.  These shear walls are often 3/8" plywood diaphrams nailed to the studs to make large continuous strong walls [though other materials and methods are used].  These shear walls brace and reinforce the sheer walls that make up the rest of the building.

Often, these shear walls are a very small part of the structure, and you can see buildings under construction with little pieces of isolated shear wall in corners and other places, and all of the rest of the building just a pile of sticks.

Modular [panelized] construction makes it very easy to put up a building in which EVERY PLANE is a monstrously strong shear plane.  A 3/4" plywood deck that meets code for flooring is twice as thick and many times as rigid as a a typical 3/8" shear wall.  If that same floor panel is also used for wall and roof panels, then EVERY PLANE OF THE BUILDING IS A SHEAR PLANE that vastly exceeds building code requirements.

If each one of those shear planes [walls, ceilings, floors] is rigidly attached to every other plane it intersects along the entire length of intersection, you create a building that probably approaches an order of magnitude stronger than conventional construction.

Constructed in this way, the entire building becomes essentially an incredibly strong and rigid box beam in which every room is a sub-cell.   A small to medium size building would be strong enough to pick up one edge with a fork lift and tip over on it's side [lowering gently with another fork lift] and it wouldn't much care.  You could probably move it around by rolling it slowly in this manner and do only cosmetic damage.

[Caution! Children: DO NOT attempt this at home!]

You could construct a building so earthquake proof that you would die from being bounced around inside before it would collapse on you.

Since the Northridge and Kobe earthquakes killed a lot of people in "approved" housing, many people have realized that "meets code" might not nearly be good enough, and "earthquake proof" can easily mean the difference between life and death.

I think your house should be strong enough that if a telephone pole falls on your child's bedroom, IT should either bounce or break.  Your building should be substantially intact, and you should go back to sleep and tell the phone company in the morning.

Modular [panelized] construction makes it easy to achieve these design goals in a building which is extremely simple to assemble.

Bill Dur <billdur@net-prophet.net>

modular.systems * Simple Universal Building System * "Superior By Design"