Structural Integrity and You: a quick, dirty and woefully incomplete guide to making educated guesses about building stability.

OK. First, a disclaimer. One that holds for everything here at HtBS,
but holds especially true for this post. I am not an engineer, I am not an
architect. I am an undergraduate student of two social sciences that
are particularly removed from reality: Philosophy and Government Theory. The information below has come to
my personal aid in my personal misadventures (that's me in the pic), but it is not to be taken as authoritative in any fashion. If you have qualms about the structural integrity of a building, stay out of
it!!! There are people who know a lot more about this than me. This is not meant to encourage any of you to enter potentially dangerous structures. That said, some of you will anyway. Hell, some of you probably already do. And if that's the case, here are a few things about structure that you ought to keep in mind. (Oh, and remember that, on a long enough time line, in the words of Summer at Shatter Creek,
"Structure falls apart, and there's nothing you can do about it." Keep your wits about you.)

So. You want to know about buildings.
All of my experience comes from work in New Orleans, where foundations are just pilings because of the high water table. most of these houses are single story, and the structures are all relatively small. the task at had was to assess whether the houses could be safely gutted, and so it was taken for granted that we could peel off drywall in order to examine the wall studs or ceiling beams. So, as always, Extrapolate at your own risk.

You should equip yourself with (at least): a powerful flashlight, a decent-sized crowbar, and a hardhat.

Before you enter the Building in Question (B in Q for short), walk around it.
First, examine it from a distance. You'll need good eyes for this, and
a fair intuitive sense of geometry. Are it's lines straight? is the
line where the roof beginsparallel to the ground? If the structure has
siding or, for some other reason has lines on it that ought to be
parallel to the ground, are they? If not, or if these lines warp or
curve, this could indicate that the frame of the house is sagging in
particular areas--that for one reason or another the frame or
foundation in a particular section is no longer bearing the weight it's
supposed to. The same is true of cracks in a brick or plaster exterior.
Now some sagging is normal for old houses, and some sagging is purely
superficial (e.g. a brick face that's separated from the frame), but it's a good sign that you'll have to look deeper.

Get closer. Look for obvious problems. Look in the windows. Are there
ceiling beams hanging down? If so, you have a large problem on your
hands. Does the floor look intact? solid enough to walk on? Get up
close to a corner and follow the foundation or the line of pilings with
your eye. Does it warp at any point? If the B in Q is on pilings, are
theyperpendicular to the ground, or do they lean under the weight of
the B in Q? In the case of pilings, get on your knees and look under
the house with that flashlight of yours (told you to bring something
bright). Check to see that the pilings are under major floor beams. If
a few pilings tilt or lean, that's OK. Like I said, any old house is
going to shift and twist a little. But houses where the beams are no
longer on the pilings, or where the piling tilt or foundation warp is
extreme are not safe. If you are not sure, assume the worst. Be smart. These pilings have to bear the weight of the entire structure and distribute it safely to the ground on which they stand. If they don't
look up to the task, stay out! If everything looks acceptable to you, you may decide to enter.

If that hardhat wasn't already on, it's time to put it on. And realize that it's far from comprehensive protection. Now before we proceed, its time for a little informal theory. Now a building, minimalistically speaking, is four walls and a ceiling. Due to the ductile nature of wood, among other things, it doesn't make sense for the ceilings of most good sized houses to be comprised of singular beams running from
the top of one side wall to the top of it's opposite: the wood would sag in the center, and the overall structure would be flimsier. Enter the load-bearing wall, stage right. If one builds a third wall,in between the two side walls, the center of the ceiling beams can rest on this third wall, eliminating the sag and beefing up the structure. Indeed, the ceiling beams can now be made of two shorter pieces of wood (easier to acquire), one running from each side, jointed together with this joint supported by the third, center wall. This wall is known as the load-bearing wall. It is very important that you identify the load bearing wall, for it's integrity is crucial to the integrity of the overall structure. If you are standing on the threshold of the front door of the B in Q, then ceiling beams usually run perpendicular to your line of sight. The load-bearing wall, by its definition, runs perpendicular to the ceiling beams, in order to support them. Locate the direction of the ceiling beams and you can locate the load-bearing wall.

First, though, have a look around. Is the floor solid? If you can walk on it without it creaking or shifting, stomp on it a bit, and see if it still feels solid. Better yet, if that crowbar of yours is of good heft, whack the floor in front of you with a blunt end--better it go through a weak spot than your foot. Once you're sure of your footing, take note of the lines inside
the house. Are the doorframe angles all close to 90*, or do they seem to have shifted? if they've shifted, is there a pattern to the shift (i.e. are they all leaning in similar directions to similar extents) or are there shifts in all directions? The first indicates that the house is leaning, which can be dangerous. The second could indicate that different parts of the structure are leaning in different directions--that is, the structure is coming apart.

If all looks acceptable to you, it's time to have a look at the studs and beams themselves. You can do this by taking a crowbar to the plaster or drywall of the wall/ceiling, and having a little look. Of course, this part is destructive. When I was in New Orleans, we were assessing mold-affected houses to be gutted, and so the drywall/plaster already needed to come down. You may not have this luxury. If you don't, take your best guess at the load-bearing wall (in addition to what was said
before, it usually runs the length of the structure), locate a stud within it by tapping or using some fancy stud-finding device, and give the stud a good kick. If it's solid, and nothing else that you've seen so far makes you worry, chances are the structure is in decent condition. Rest easier, keep the hardhat on for good measure. If you can start tearing at the walls, however, then by all means, do so. Once you've identified the load-bearing wall, tap the ceiling joints with your crowbar. Are they solidly atop the load-bearing wall? Or is the wall misaligned underneath it, no longer supporting the beams at the joint where they meet? such misalignment can be the result of the warping we looked for
earlier. If the joints are not firmly atop the load-bearing wall, that wall is not doing its job, namely bearing the load. Be wary of the B in Q's structural integrity. If the joints are atop the LBW, give a few of its studs a solid tap or a firm kick to see that they're still connected at both ends, top and bottom. Be sure to check more than one spot on the load-bearing wall, as warping and shifting can be localized.

If all checks out up to this point, you can very cautiously say, to your self and in a quiet, non-authoritative voice, that the structure is in halfway decent shape. This, of course, says nothing of its long term durability or scientific soundness. In fact, this doesn't say much of anything at all. But should you find yourself in a building of dubious merit, this should help you know what to keep an eye out for.