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New multi tenant structure attaching to existing single family

tws2106

Registered User
Joined
Jun 11, 2021
Messages
4
Location
San Diego
Hi There - First time post here but hope its an easy one. Working on a project where our client wants to add a multi family dwelling to an existing single family (400 SF). Below are my understandings of our options. We have to add sprinklers to the project since the code (CBC) requires all new residential to have sprinklers.

  1. My understanding is attaching to the existing would change the occupancy of the structure from R3 to R2 as we would have more the 2 dwelling units in one structure. This would mean making the single family comply with R2 requirements. This would add construction cost as we think we would have to add sprinklers to the existing single family.
  2. Our other option is to add a fire wall between the two structures. The existing structure is 1 story and the new is 3 stories. Would our openings not be be limited on the second and third floor since it no longer shares the wall with the existing structure?
 

khsmith55

Bronze Member
Joined
Oct 23, 2010
Messages
216
Location
Glenwood Springs, CO
It appears you are correct. However, I question the cost of a firewall as opposed to retrofitting the existing Residence with a NFPA 13R sprinkler (assumed).
 

tws2106

Registered User
Joined
Jun 11, 2021
Messages
4
Location
San Diego
If we place an imaginary lot line right up against the existing structure - would we have to upgrade the existing building to comply with separation distance? IE open the walls and change to rated assemblies?
 

cda

Sawhorse 123
Joined
Oct 19, 2009
Messages
20,358
Location
Basement
""We have to add sprinklers to the project since the code (CBC) requires all new residential to have sprinklers"""

Missed that or read it wrong,,,

Just sprinkle the Existing off the new system you are putting in, Not that many more sprinklers,,,

Might be able to get away with a 13 D system, does not help much, but a possible option, and solves your other problems.
 

Robert

Registered User
Joined
Jan 29, 2016
Messages
284
Location
Pinole, CA
Hi There - First time post here but hope its an easy one. Working on a project where our client wants to add a multi family dwelling to an existing single family (400 SF). Below are my understandings of our options. We have to add sprinklers to the project since the code (CBC) requires all new residential to have sprinklers.

  1. My understanding is attaching to the existing would change the occupancy of the structure from R3 to R2 as we would have more the 2 dwelling units in one structure. This would mean making the single family comply with R2 requirements. This would add construction cost as we think we would have to add sprinklers to the existing single family.
  2. Our other option is to add a fire wall between the two structures. The existing structure is 1 story and the new is 3 stories. Would our openings not be be limited on the second and third floor since it no longer shares the wall with the existing structure?
This is an interesting topic. Since CA has allowed junior ADU's, one can now have 3 separate dwelling units in a building which kicks it into R2 classification as you noted. That said, do the existing stairs (inside or outside) of the R3 need to conform to R2? Egress requirements too. Could you use the existing building code to allow the existing R3 to remain unsprinklered and just sprinkle the new? I used an AMMR once to only sprinkle the new addition instead of the entire home. To your question about openings above the existing structure, there is a code provision about vertical separation of openings either by distance or by rated horizontal projections.
 
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