How do engineers/inspectors see or test what's behind the drywall/plaster?

Factual Questions
1

I’m thinking of one of these really old buildings. Eventually everything falls apart. So if I walk through a real old public building, I’m relying on the notion - hopefully correct - that these buildings are periodically inspected and have passed for safety. (Certainly every time you hear of some sort of collapse the media reports on when it was last inspected, which seems to suggest that these buildings are inspected periodically.) But the question is how exactly do inspectors tell if the structure is sound in light of the fact that some of the key structural elements are covered by plaster or whatever?

I fell to thinking about this about a year ago when I passed through one of these real old hotels. This was in a region of the country which was a popular vacation resort in the early 20th century, but whose glory days are long gone. So there’s not much new construction but there are a lot of very old hotels hanging on. In this hotel the staircases were visibly sagging and the floors seemed to have some give when you walked on them. So how do you know that they’re not about to cave in? I was relying on the notion that there must be some system of ensuring this, but I wonder how things of this sort lend themselves to inspection? For example, suppose some joint connecting the stairs to the floor is about to give way. How could anyone see this what with it being covered on both sides by carpeting and ceiling plaster? And so on.

2

We don’t know what is in the walls. It’s always a surprise. Now I’m not an inspector but have helped work on numerous old buildings and draw up prints for the submitals. You look at what you can see and make best guesses about the hidden stuff. Old buildings were not built to code. When you write the contract for the customer you always put wording in to the effect, “depending on actual conditions”.

If you really need to see in a wall space there are inspection cameras on flexible stalks. But that would only show what that space between two studs looks like. Most cases we would recommend removing the plaster to the bare studs, pull all the old wiring and plumbing out and start over.

I remember one client who wanted us to level out the living room floor. It sagged at least 2 inches in the middle. We installed beams and slowly starting jacking them up but before we even got half the sag out, none of the doors in the area worked anymore.

People yearn for the good old days when house were built by real carpenters. Don’t fool yourself. The average home builder simply did not understand, or know how to calculate the required beam strengths. Along with no beams over doorways and windows, inadequate rafter sizes and spacing, no lateral bracing, old houses and garages can be a mess.

New houses may be built cheaply, but they are to code and that will save your ass in the long run.

Dennis

3

I don’t know where you’d get an idea like that. Nobody’s going around inspecting old buildings for the hell of it.

Structural elements are inspected prior to finished walls going up. They will never be inspected again until and unless someone pulls a new building permit for renovations or additions. The only exception would be if someone calls in a complaint about something that looks structurally compromised; even then the only recourse for most jurisdictions is to tell the owner to fix it or condemn the building as a public safety hazard. If there are structural problems the onus is on the property owner to identify and repair them.

4

There are clues about …

The very first thing I check in any old building is how level the top floor’s top-plate is, where the wall meets the ceiling, this should be dead level through the whole of the building … any sag along the outside walls is Trouble (with a capital T) … if the first floor is wood framed, we can crawl underneath and inspect the beams and foundation … second floor can be checked by jumping up-and-down on it, should be sturdy … the attic should give us access to the roof framing (very important) … obvious stuff; walls bowed, floors crooked, doors and windows jamming, stairs one shouldn’t be jumping up-and-down on, cracks in the plaster/drywall etc etc etc …

If all the above is good then most likely the building is structurally sound … very little could go wrong without one (or more) of these things being apparent …

Buildings rarely just fall down, there’s always signs of impending tragedy … the few exceptions are usually someone not doing their job right, consider the St Louis hotel causeway that fell during the grand opening, the drawings were clear, but no one followed them … bunch of people not paying attention …

Plumbers with Saws-Alls … be very frightened …

5

In Providence RI they sent out city employees to look for cracking masonry and I don’t know what else. They will fine the owners if repairs are not made. I don’t know the details but I assume it’s a way to generate revenue through fines and support local construction companies. I would also assume other municipalities have or will grab onto this revenue scheme.

6

In NYC owners of buildings over a certain height are required to have their facade inspected for masonry problems every few years. But there’s no city employee running around doing inspections; the owner is required to hire an inspection company and submit a report to the Department of Buildings, or they get in trouble.

But while crumbling masonry is a hazard for pedestrians, it’s not a structural issue.

7

Some cities do this in the Cleveland area. I think the money angle is about right. But while the work they recommend does improve the structure, what they really want is for the front of the house to look good. Location, location, etc, you know.

Front steps, sidewalks, porch railings were prime targets because they can be quickly identified by driving by. My step son made a nice living repairing porches and straightening garages. Front porches are the worst designs of all. The main beams run the whole width of the house, 20 feet or more. Maybe they are 20" apart. Never 16" They only span that distance because there is a cross beam under the middle running from a column in front back to the house. It rots after 50 years and everything sags after that. When we take it apart I have heard homeowners proudly exclaim, “Wow, look at that lumber! It’s 2 1/2” wide! It’s 9" deep! It’s solid oak!" Yeah, and that isn’t anywhere near large enough, there aren’t enough of them, they are not pressure treated. You are going to fall through soon.

Very few porches have their columns supported by adequate footers. Just 2 foot square brick columns sunk down 3 feet. They start tilting outward, exacerbated by rotten wood that no longer adds lateral support. This opens up the flooring for water and it rots and collapses under each column. Those nice Doric columns you admire so much are just sitting on the floor boards*.* There is no continuous blocking from bottom to top. They aren’t nailed down. That allows the top floor to sag, etc. Sometimes I just had to shake my head and say “We can’t save it by any economical means”. Some of those porches weigh several tons. Two floors with a roof over the top and everything starting to pull away. We can’t even tear it off safely with our equipment, you need big excavators with grasping jaws.

Back to the OP. I now have a lifetime of living by safety codes at least some of it spent on building design and things like fire safety. When I look through historic buildings this all pops into my mind. Fire trap! Where is the second exit from an upper floor? Where is the lighted Exit sign? How many steps is it from this inner room to an exit? Can I find it in the dark?

I was once in a neat antique store on the West Side. The building was an old bank, 5 floors up and a large basement. Most of the upper rooms were crowded with architectural salvage, including blocking the hallways. The basement was a labyrinth of connected rooms with no windows, wooden shelves with narrow aisles in every room. I stopped at one point and just thought, "What in the HELL would I do if the lights go out?

** Most people don’t realize there is absolutely nothing holding front porch columns in place except weight and friction. When we raise an upper porch slightly, they just fall over. I have never seen one even toe nailed down. If they topple they hit the ground and explode. They are made of many pieces of wood and all the glue is so brittle they cannot take any shock. There are no fasteners, no dowels, no splines. Just old glue joints.

Dennis

8

The drawings were indeed clear, but showed something that was quite impracticable to construct. To get over this, an apparently trivial change was made that greatly increased the stresses in the supports. The design change was not thought through and never reviewed.

https://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse

9

As others have said, the actual structure (as well as the plumbing, electrical etc) are inspected before the drywall goes up. Generally ‘inspections’ are just a walk through. My business has a building inspection (that includes plumbing), electrical inspection and fire inspection every year. They essentially just take a walk through the building, note anything that needs to be changed or brought up to code and see if they find anything new that needs to be address.

None of those people (even though one of them would be the same inspector) is looking to see if the building is about to fall down. I assume if something caught their eye they’d point it out, but they’re typically checking for things that will start fires, shock someone, let sewer gas into the building or let dirty water in to the public water system.
While my store isn’t that big, most of them are only here for a few minutes.

Now the health inspections, those are much more in depth.

10

Usually.

In my youth I worked as a plumber’s sidekick doing new home plumbing. I was just supposed to fetch stuff from the truck, in reality I was putting in copper water lines, abs waste lines, and freaking gas lines as well.

One of the housing plans was horribly behind schedule. Another crew had put all the copper in a home, but some of the lines were never soldered (the kid cut, fluxed, etc, but the Master Plumber never soldered the one section). In the rush that was going on, the plasterers finished the walls.

I was there for some reason when the final inspection was going down. They turned on the water and gradually the one wall began changing colors as water permeated through.

Oh my.

11

Yeah, I mean they’re supposed to. Once in a while you’ll hear about an inspector making someone pull (some? all?) of the drywall down to see whatever it is they’re looking at and I believe many (all?) jurisdictions will add a penalty to your fee if you don’t get a final inspection before closing up the walls.