From the questions my insurance company are asking, I gather a firewall must be an externally visible wall between units (protruding above the roof line as described by denimnyc), and is of particular concern to insurance companies where old buildings are wood framed, with no masonry dividing walls.

It seems that many historic Jersey City row houses are wood framed with no firewalls.

Robin.

Last year I did some firewall improvement work on a 2 family home that shared a common wall with an adjoining building. You could crawl from one building to the other through the attic.

My guys installed 5/8 inch type X drywall to the roof line and sealed every opening with fire rated urethane foam. We then filled the attic with cellulose (fire retardant insulation).

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This is all true, but in the old buildings, this is what you've got.

Up to current code or not, it is the existing, "grandfathered" condition. The trigger for upgrading is usually dependent on a renovation and how intensive it is.

Unfortunately the party walls between the historic rowhouses do not qualify as firewalls for insurance purposes...nor do they meet today's building code requirements. True firewalls between dwellings must extend beyond the construction of the roof... by 3 feet. Fire can still spread from one rowhouse to another from the adjacent roof if the firewall separating two rowhouses do not extended beyond the roof construction.

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For a rowhouse, the firewalls are typically the masonry "party walls" that separate the individual rowhouses. For a single family, that is the only answer.

For a multi-unit building, in addition to the party walls serving as the firewalls, the walls that separate the dwelling units from the common corridors and stairways are also required to be firewalls.

A "firewall" is a wall assembly that is constructed so as to resist the passage of smoke and fire for a given time period. Typically, the walls noted above are required to have a fire-rating of 2 hours (masonry party walls) and 1 hour (dwelling unit/corridor walls) in a non-sprinklered building. There are variations also depending on number of units, height, area and # of floors, etc.

The ratings of various wall, floor, roof and building element assemblies are compiled by various testing agencies, the biggest in the US being Underwrites Laboratories (UL).

For insurance on an old historic rowhouse, the insurance company is aksing me where the firewalls are (i.e. How many units between firewalls).

How would I determine this? Does the JC zoning department have this information?

Robin.