2 hour fire wall between townhouses

[Jmeng1026]

I have been asked to design a townhouse unit that will be constructed on the rear side of an existing townhouse building.

I have designed townhouses before with a 2-hour firewall between units but that was all new construction.

Is there a way to get a 2-hour firewall without having to redo the existing rear wall of the existing unit?

Basically a one-sided firewall.

 

[dik]

Not likely, if it's a code requirement. This is a life safety issue. The firewall has to stand independent of either part of the two buildings.

 

[Greenalleycat]

Can you do it in masonry block? A 20 series block would easily provide that and could be built from one side while providing protection to both sides

 

[dik]

Can you do it in masonry block?

It requires lateral support in the event either half of the building burns down.

 

[Greenalleycat]

It requires lateral support in the event either half of the building burns down.

Just design it to cantilever? Super easy for single story. Two story would be a bit niggly as you'd need midfloor support on the existing building side - may be tricky to attach. The post fire load here is only 0.5kPa though so they're pretty small loads

 

[phamENG]

It requires lateral support in the event either half of the building burns down.

I don't think you would in this case, dik. The existing unit already has wall. The intent is to keep the adjacent unit from burning and prevent progressive collapse across units. The free standing masonry wall that has to stay up is a thing when it's the only wall between units. But if it comes down during the fire in this case, it's not necessarily going to endanger the existing unit. Not a great thing, having a block wall fall down, but if the building has burned to the ground anyway...

So I'd say building the back wall from masonry and tying it into the new unit for stability should be a winner. It's an atypical situation, though, so make sure you have buy-in from the architect and the building official before going too far down that road.