How Safe Are Townhouses and Duplexes?

TL;DR Townhouses and duplexes are probably not much more or less dangerous than single family homes, and on balance are probably a little safer from structure fire risks.

A friend on Facebook, in reaction to the meme above, expressed concern that townhouses and duplexes might be more vulnerable to threats like fire and insect infestations (relative to single family homes) or unlawful entry via the attic, and that even if current building codes address these concerns, that codes are not widely complied with to alleviate this risk. My own home which is half of a duplex, does not have a firewall that extends to the attic and has a shared open attic space (it was built in 1925, long before current fire and building codes were in place).

While this is a facially plausible possibility, I am skeptical of all of these points.

Structure fires were way down in the U.S. from 1977 to 2021, which suggests that more stringent building and fire codes are having the desired effect of reducing the risk of home structure fires:

Structure fire statistics are lumped by 1-2 unit homes v. "apartments" which seem to include everything from structures with three or more townhouses to high rise apartments, so the distinction between single family homes and duplexes is hard to evaluate:

Another fire statistic publication provides raw data in chart form, and reveals that there are slightly fewer deaths per fire in duplexes than there are in single family homes, despite the fact that duplexes have more residents, on average, than single family homes:

The structure fire statistics aren't provided as rates relative to the percentage of housing stock of each time in residential units, although another source sheds some insight into the existing mix. If the chart below is right, there are about 1/3rd as many townhouses and duplexes as there are single family homes (or less), but the number of fires in duplexes is about 11th of the number of single family homes (with considerable uncertainty because the distinction between single family homes and duplexes isn't made in about half of the data).

There are about 32% as many apartment fires as there are single family home fires, but it is unclear from the illustration above where the percentage of housing stock that counts as apartments rather than 1-2 unit residences fits between 10%/62% (for 20+ unit apartments) and 32%/62% (for all attached residences except single family homes), so somewhere between 1/6th and 1/2. The 5% of the housing stock that is not elsewhere classified probably fits into the other categories of residential structure fires in the fire statistics. The statistics aren't inconsistent with the likelihood of a fire being roughly the same for apartments as for 1-2 unit residences, but don't definitively establish this point either and could err in either direction.

Apartment fires are much less deadly per fire than single family home and duplex fires, despite having far more residents per fire, on average, in a distinction that has arisen since 1980, probably due to more strict building codes for apartments built since then:

The statistics above don't completely and finally resolve the issue, although they do seem to suggest that duplexes and townhouses at a minimum, aren't materially less safe than single family detached homes. The homeowner's insurance bill for my duplex is not very much different than for a comparable single family home, which suggests that there isn't much of a difference in risk.

Also, modern townhouses and duplexes do require a firewall between each unit, in a building and fire code requirement that I suspect is followed in a very high share of all new builds, although though my friend is more skeptical about code compliance (and I would agree that code compliance is patchy in smaller scale renovation work).

Note also that these trends exist despite the fact that apartment dwellers tend to be younger and less affluent than duplex and townhouse dwellers, who in turn tend to be younger and less affluent than single family home dwellers, on average, and one would generally expect, a priori, that younger and less affluent residents would be more likely to do things that would cause fires (although younger people are less likely to smoke and are probably more likely to live in more recently built housing).

Shared walls (and ceiling/floors in apartments) also have benefits. Most notably, they increase HVAC efficiency.