The Roof. A sought-after element on many buildings by the, ahem... "curious" in nature. Yes, they offer a lot in the way of point-of-view and spiritual oneness. However, walking a roof is one of the many avenues in life where things can go horribly wrong for you for absolutely no reason. In this thread, I'm going to offer what I know in hopes to keeping my fellow explorers safe. It's mostly common sense but roof systems can appear to be sound and not actually be safe at all. Before we go through wit this I will say that there's really no such thing as a roof you can trust.
BE ADVISED: ANY ROOF CAN BE A HELL-HOLE UNDER THE RIGHT CONDITIONS.
Let's start with the DIFFERENCE BETWEEN A ROOF AND A ROOF DECK. A roof deck is the laid down on a flat roof, with the roof system installed on top of that. A deck can be wood, metal or concrete as listed from weakest to strong. Of course, a deck can be observed from the top floor. You may have to peek your head inside a drop-tile ceiling or wade through insulation but you'll find one of the three said materials.
What I determine to be the "safest": CONCRETE DECKS. These can be found in locations such as large hospitals or malls, where buildings were made of complete concrete all the way up to the roof deck and the roof being applied on top of that; a built-up roof. Note, I did claim that these are the safest but that does not mean they are "safe" in meaning by the word. That just means that the event of a concrete deck system failing from under your feet is unheard of but that's not saying it can't happen. A badly damaged infrastructure can have an unsound concrete deck and those can fail as well. HOW TO DETERMINE: Concrete decks are the easiest to inspect. You just want to make sure the deck doesn't have any ridiculous cracks in it. If a building with a concrete deck is in the process of demolition then it's unsafe to travel. If the deck is riddled with deep, wide cracks then it's unsafe to travel.
GALVANIZED METAL DECKS would have deep 4-inch corrugations and are the most common, typically used for smaller buildings like strips malls and schools. Metal decks are little more trustworthy than wood because metal won't sponge up the way wood will. Water will usually run downhill on a metal deck and always find it's way inside through a hole. Thus, granting a longer time before rust sets in vs. rot in wood. However insulation is typically applied on top of this decking if a leak is bad enough, the insulation will soak it up and that will give way to oxidation and then rust soon after. HOW TO DETERMINE: Metal decking that has significant rust damage will likely be oxidized on the underside, visible from inside the top floor. A large spot of rust on the deck panel is all you need to know that you're not going on the roof that day.
WOOD DECKS are the least trust-worthy and all around very questionable. A 2x10 deck is laid with insulation and/or roof applied on top of that. Wood decks are usually found in houses, apartments or much older buildings. Wood decks are harder to come by but they do exist and pose enough of a threat to need information handy on them. A compromised wood deck can be determined from underneath the decking, but just because the underside of a decking doesn't have visible rot, doesn't mean that the side touching the insulation isn't. HOW TO DETERMINE: Look for rot. That's it. A compromise wood deck can show sagging but otherwise, it's still a gamble that what can appear to be a good wood deck is actually compromised from the roof-side. A large enough area in that manner can introduce a hell-hole.
Next, you must know that there a DIFFERENCE BETWEEN A ROOF AND A BUILT-UP ROOF, which are often applied on top of any of the three above mentioned decking types. These roof systems are often gravel or one of two roll types: 2-ply or bitumen. 2-ply materials are either TPO or PVC and are typically white upon installation. These materials are basically super thick pool liners and are VERY slippery when dirty. Black Death isn't a plague, here, it's the accumulation of algae on the roof. Bitumen is either rubber roofing of granulated roofing sheets, which are fairly common. These are identified by either a black or silver or white-coated surface, or an often white colored granule much like the surface of a shingle. A built-up roof on a concrete decking is usually a pretty safe bet, but a built-up roof on a wood or metal deck should be navigated carefully. Rock roof systems are common, as well. HOW TO DETERMINE: There's only one good way to navigate a built-up roof, and that is to just heed caution. You want to be very weary of soft spots on the roof. A strong built-up system should be firm and easy to walk on. If a spot on this system feels notably spongier, it may be compromised and should be avoided. If you notice the roof rippling in front of you, like a waterbed, it's widely compromised and you should just turn back. The soft spots will likely be what you'll encounter on a compromised built-up roof system. Just baby step it, and you'll find the weak spots. Avoid algae on single play roof systems. On residential buildings such as apartments, bitumen and rock roofs can be applied over a wood deck system. When navigating these roof systems, be weary of the roof's stability. If the decking seems springy, it's compromised. The same applies with built-up roof systems on metal decks. Really generally applies with all roofs, but these decking types should especially due to the nature in which weight is transferred. They're also very easy to underestimate in comparison other roof systems.
Next, I'll talk about METAL ROOF SYSTEMS. These roof systems are easy to spot problem areas because they'll be rusted out, plain and simple. Metal roof panels are installed directly to the metal I-beam beneath. Assuming the general stability of the building is trustworthy, there shouldn't be any reason not to trust the I-beam. This I-beam will be your friend. You can locate it by following the screw line on the roof. Use that screw line to navigate the roof. Another hazard on the metal roof system can be algae, identified by green or black spots. Algae spots are very common on metal roof systems and can often lead to you eating major fuck if you're not careful. HOW TO DETERMINE: You want to pay attention the the screw line. If the immediate area surrounding the screw heads is badly rusted, it's a good bet the entire panel is a danger zone.
And lastly, I'll talk about PITCHED ROOFS. I'll generally never get on one. Pitched roof system generally include shingle, Spanish terracotta tile, slate and even metal. The dumbest ways to get hurt are on these roof systems. They're usually on residential homes, smaller apartments or sometimes use as a garnishment on more expensive buildings. I would advise you avoid pitched roofs as a whole. HOW TO DETERMINE: A quick check from the attic side for dark spots and saggy joicing will tell you if can trust these roof types. While traversing this roof type, be weary of springy decking and soft spots. Shingles can look innocent but not be bitten down all the way, and can result in them sliding out from their position while you're on top of them. Spanish terracotta tile must be inspected from underneath before exploring. These won't show any indication from the top side, of a compromise deck system. I'd like to add that while I deem pitched roof types to be more risky, anything Spanish terracotta or slate is pretty dangerous.
While you're on a roof, it's a good habit to keep your eyes out for SKYLIGHTS. These can be curbed into built-up roof and flat on metal roofs. Metal roof sky panels are a real danger on metal roofs because they won't be easily seen unless you're looking at the roof. These are very easy to fall through. EVERY SKYLIGHT IS A POTENTIAL HELLHOLE.
Every roof should be treated extremely seriously. We are talking about abandoned buildings. I know everybody has their own way, but the roof is no playground. It's the barrier between you and a nasty free fall that will change your life. Especially if you fly solo. I hope I helped someone understand a few things that might keep them safe. I have 5 years experience in many different applications of roofing so ask me a question and i'll see if I can answer it.