What sort of "fire resistant" exterior materials could work with a relatively inexpensive 3 story house that's 6 feet apart from another (yeah, the separation can be that small; and in my somewhat crowded 1-2 story house neighborhood far away from Somerville, with 0.14 acre lots, my house is ... 3 feet or less from the property line, then there's a driveway, then not many feet to a 2 story house; our garages have 1 foot of separation)?
Even if you were to build a Somerville today, you'd be hard pressed to achieve such a thing, instead, more separation is required (which does comport with your specification point).
(Although that's not part of the code. Which does say if you've got townhouses, or two family houses (for this level of the code I've purchased/you can find online: http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_201...) they've got to have a firewall between them that's rated for 1 hour.)
A triple decker that has its stud bays dense packed with cellulose, 3 inches of continuous exterior rock wool insulation, and fiber cement siding is pretty damn fire resistant, even with <6 foot separation. Getting rid of exterior-facing wood and empty stud bays, which are fantastic heat pipes and chimneys, the flammability goes way down.
Having lived in Somerville, there's another reason to eliminate empty stud bays: holy crap it's cold. We spent something like $200/month heating under 1000 sq. ft. to 62 degrees F in the winter for four hours a day. Take a wildly inefficient boiler, uninsulated steam pipes, crappy radiators next to exterior walls, and no insulation, and you get a hot basement, a freezing apartment, and insane natural gas use.
I would love to see a law that requires landlords to get a basic energy audit and advertise the estimated heating cost. Then they'd have an incentive to fix it, which, quite frankly, is cheap: just blow dense-filled cellulose into the stud bays, insulate the pipes in the basement, and upgrade the boiler. At, say, $15k per unit, it'll pay for itself in a few years of tenants who want to heat to 68F for more than four hours per day.
(Amusingly, my place had new double-paned windows. They were invariably warmer than the plaster walls in the winter.)
Landlords already have an incentive to make their units more energy efficient--they can capture the revenue stream that currently goes to the gas, electric, and oil companies. I'm not sure why more landlords don't do this though. Probably because methods that don't disturb tenants (e.g. exterior rock wool or foam insulation) run afoul of zoning/setback/property tax assessment rules, and those that do comply (e.g double stud wall retrofits) disturb the tenants and/or reduce marketable space.
Especially since stud bays in those days were often continuous, they used available back then very long pieces of wood to frame the entire building, instead of stacking floors on top of each other: https://en.wikipedia.org/wiki/Framing_(construction)#Balloon...
Yeah, I can see that, most likely long enough to give the fire department plenty of time to save the adjacent buildings, as I witnessed once (but didn't know their construction details). I worry about flat roofs, though, how fire resistant do they tend to be? Original formula asphalt shingle with an organic base aren't super fire resistant from what I've just read and basic principles (when I re-roof, which will require taking off 3 layers (!) plus the original wood shingles, I'll be sure to get the more fire resistant fiberglass base ones).
If you're taking shingles, chances are you don't have a true flat roof (or just a terribly built one), since those are supposed to continuous roofing in order to withstand water puddles. Back in the day the only material available was asphalt tar, which obviously isn't very fireproof. Modern alternatives such as EPDM and TPO though are plenty fireproof, especially if placed on top of polyisocyanurate insulation (which doesn't burn, only char) instead of directly on the wood deck.
Sorry for my lack of clarity, I was talking about both types of roofs, since the classic Somerville triple decker has a flat roof, and the classic Philadelphia a pitched roof with shingles. I was wondering about the former since I've never seen one as such, aside from some one story commercial ones when I lived in a higher adjacent apartment.
And thanks for the comments, you've saved me some research when it comes time to replace my roof.
Florida normally has concrete block. Newer construction has that covered in insulation and then stucco, which is more concrete.
Note that Florida houses are inexpensive. They are insulated pretty well, obviously for the opposite reason.
The nicer houses in Florida are solid poured concrete. Considering the expense of property in Massachusetts, the extra expense of poured concrete would be a smaller portion of the total cost. You might as well do it. You're already paying quite a bit for the land; why build a shack?
This apartment was constructed elsewhere, assembled on site. You could see whole units (I remember seeing the kitchen microwave) dangling from construction cranes.
This seems like yet another issue of baking the solution in to the specification instead of just asking for what you actually need/want.