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Is There A Requirement To Fill Inaccessible Cavities With Insulation?

arwat23

arwat23

SAWHORSE
Joined
Sep 19, 2023
Messages
448
Location
California
I'm working on a project where we're converting an existing garage to an ADU. Due to the existing structure and client wishes, we have a rather large inaccessible cavity. I've been told on multiple occasions by my supervisor that we need to fill these types of spaces with insulation, so I have. Plans approved, permit issued, no problem.

Except now the contractor is coming to me saying they're trying to save money (understandable) and think that filling this space with insulation is overkill. Below is an image showing part of the floor plan. The walls on the north and west side are exterior walls. All interior walls (shown grey) are new and have insulation in them.

I've been digging through codes for a while now and can't find a section that directly addresses this. This isn't my area of expertise, so I could be overlooking something obvious. Does anyone here know where I should look for this requirement?

Using 2019 California Codes - Residential Code (based on IRC but heavily amended), Fire Code (based on IFC), Building Code (based on IBC), etc.

1718911705217.png
 
For a CRC project I'm going to say no. I've run across this a few times on commercial spaces when the fire marshal will require it. I think it comes out of the NFPA 13 standards, but I've never looked it up. CRC projects can use the 13-D standards, and those are far simpler requirements. Seeing as it's an ADU they probably don't even need sprinklers if they qualify for the exemptions in R313.2
 
steveray said:
If you use IRC energy or IECC, most likely..Assuming the garage was not previously conditioned:
N1110.2 (R502.2) Change in Space Conditioning
Any unconditioned or low energy space that is altered to become conditioned space shall be required to be brought into full compliance with this chapter.

And the windows and the air sealing and.......
Click to expand...
Ch11 of the IRC is not adopted by CA. One of the many things we do to make things extra complicated... I believe our energy codes are unique to us and not based off IECC or IRC.

Energy Code wise, I'm not concerned. Both the exterior and interior walls are insulated and meet what's required by the California Energy Code. I've been told that this filling in a cavity thing is a fire issue.
 
Joe.B said:
For a CRC project I'm going to say no. I've run across this a few times on commercial spaces when the fire marshal will require it. I think it comes out of the NFPA 13 standards, but I've never looked it up. CRC projects can use the 13-D standards, and those are far simpler requirements. Seeing as it's an ADU they probably don't even need sprinklers if they qualify for the exemptions in R313.2
Click to expand...
No sprinklers are needed luckily.

I know next to nothing about sprinkler requirements. If sprinklers were required for this project, would this cavity need to be filled with something or have sprinklers in it?
 
arwat23 said:
I know next to nothing about sprinkler requirements. If sprinklers were required for this project, would this cavity need to be filled with something or have sprinklers in it?
Click to expand...
NFPA 13 is a referenced standard. The building (or residential) code will tell you what is required. There are three (at least) different options for the systems, 13, 13-R, or 13-D. NFPA-13 systems are the most complex, and expensive. CRC 313.2.1 says "... installed in accordance with R313.3 or NFPA 13D." R313.3 is a prescriptive design because the residential code is intended to be a prescriptive code. It is a limited code though, you can only build one- and two-family dwellings or town houses.

The building code covers everything else and relies more heavily on referenced standards. Chapter 9 tells the user what kind of sprinkler system is required, and the standard it must be designed to. I believe that NFPA-13 requires sprinkler heads in concealed spaces, unless they are completely full of insulation.
 
Look at CBC 718 concealed spaces. It can be achieved other ways. OOOPs I see your in the residential code. CA Fire code section 707.

2019 CFC 708.4.2 perhaps
 
Last edited:

2022 CA Res. Code
R302.11 Fireblocking​

In combustible construction, fireblocking shall be provided to cut off both vertical and horizontal concealed draft openings and to form an effective fire barrier between stories, and between a top story and the roof space.

Fireblocking shall be provided in wood-framed construction in the following locations:
  1. In concealed spaces of stud walls and partitions, including furred spaces and parallel rows of studs or staggered studs, as follows:
    1. Vertically at the ceiling and floor levels.
    2. Horizontally at intervals not exceeding 10 feet (3048 mm).
  2. At interconnections between concealed vertical and horizontal spaces such as occur at soffits, drop ceilings and cove ceilings.
  3. In concealed spaces between stair stringers at the top and bottom of the run. Enclosed spaces under stairs shall comply with Section R302.7.
  4. At openings around vents, pipes, ducts, cables and wires at ceiling and floor level, with an approved material to resist the free passage of flame and products of combustion. The material filling this annular space shall not be required to meet the ASTM E136 requirements.
  5. For the fireblocking of chimneys and fireplaces, see Section R1003.19.
  6. Fireblocking of cornices of a two-family dwelling is required at the line of dwelling unit separation.
 
There is a section in NFPA 13 that says concealed spaces featuring open-web joists must be fire-blocked to create compartments that are pretty small. Doesn't look like that's the case here, though.
 
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