Sprinklers Required with Combustible Insulation?

8/11/2026

Are sprinklers required in a noncombustible concealed space that contains combustible insulation?

I have a contractor who is trying to use polyurethane spray foam insulation in a noncombustible concealed space above a ceiling. It is an NFPA 13 system and they do not want to sprinkler it.

To my knowledge, this spray foam insulation is combustible, and by filling a noncombustible space with it, it will need sprinklers. They are trying to propose intumescent paint, but I don't believe that changes anything for them.

Do you all know of any applicable exceptions in this situation or if they don't need sprinklers?

I think 9.2.1.13 is the only relevant section from 13, but I am having trouble finding whether this foam exceeds the 1,000BTU per square foot. Thank you.

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9 Comments

Jesse

8/11/2026 08:30:09 am

In order to omit AS protection in the atic, the void needs to be filled with non-combustible or limited combustible insulation. There are many spray foam insulation products that are cocmbustible, and that would negate the reasoning for omitting protection there.

anthony

8/11/2026 09:02:57 am

Jesse has it here. Add combustible construction to an otherwise non combustible space it becomes a combustible space. This isn't a trick question here.

8/11/2026 10:54:20 am

This was my thinking. Just wanted to make sure I wasn't being ignorant because the customer does not agree with me and I like to check myself before putting my foot down.

Todd Wyatt

8/11/2026 08:34:11 am

The scoping Code (e.g. IBC-2024) requires WHERE an automatic sprinkler system (ASPS) is required to be installed per Occupancy Classifications, Specific Building Areas and Hazards, and/or during Construction.

The referenced Standard (e.g. NFPA 13-2025) includes omissions to ASPS installation.

If the Contractor is attempting to utilize the NFPA 13 9.2 Allowable Sprinkler Omission Locations of “filling an unsprinklered combustible concealed space with noncombustible insulation”, the insulation is required to be “noncombustible.”

Concealed spaces over isolated small compartments not exceeding 55 SF in area shall not require sprinkler protection.

Concealed spaces over horizontal chases and soffits not exceeding 160 CSF in volume shall not require sprinkler protection.

Todd Wyatt

8/11/2026 08:34:55 am

REFERENCES

IBC-2025
Chapter 9 Fire Protection and Life Safety Systems
Section 903 Automatic Sprinkler Systems
903.2 Where Required
903.2.1 Group A
903.2.2 Group B
903.2.3 Group E
903.2.4 Group F-1
903.2.5 Group H
903.2.6 Group I
903.2.7 Group M
903.2.8 Group R
903.2.9 Group S-1
903.2.10 Group S-2 Parking Garages
903.2.11 Specific Building Areas and Hazards
903.2.12 During Construction

NFPA 13-2025
Chapter 9 Sprinkler Location Requirements
9.2 Allowable Sprinkler Omission Locations.
9.2.1.7
Concealed spaces filled with NONCOMBUSTIBLE INSULATION shall not require sprinkler protection.
9.2.1.7.1
A maximum 2 in. (50 mm) air gap at the top of the space shall be permitted.
INSIGHTS : In some cases, filling an unsprinklered combustible concealed space with noncombustible insulation might be more economically advantageous than installing sprinklers. It is frequently a practical problem to completely fill concealed spaces with insulation. In the 2013 edition, language was added to permit a 2 in. (50 mm) air gap between the top of the insulation and the roof or ceiling above. Exhibit 9.4 provides an example of this requirement.
9.2.1.8
Concealed spaces within wood joist construction having noncombustible insulation filling the space from the ceiling up to the bottom edge of the joist of the roof or floor deck shall not require sprinkler protection.
9.2.1.9
Concealed spaces within composite wood joist construction having noncombustible insulation filling the space from the ceiling up to the bottom edge of the composite wood joist of the roof or floor deck and with the joist channels separated into volumes each not exceeding 160 ft3 (4.5 m3) to the full depth of the composite wood joist, with material equivalent to the web construction, shall not require sprinkler protection.
9.2.1.10
Concealed spaces over isolated small compartments not exceeding 55 ft2 (5.1 m2) in area shall not require sprinkler protection.
9.2.1.11*
Concealed spaces created by soffits of combustible construction below noncombustible or limited combustible ceilings separated into volumes each not exceeding 160 ft3 (4.5 m3) by noncombustible or limited combustible materials shall not require sprinkler protection.
A.9.2.1.11
Sprinklers are allowed to be omitted from horizontal chases and soffits that have noncombustible or limited combustible finishes that can contain mechanical and or plumbing equipment, ductwork, or electrical components. The 160 ft3 (4.5 m3) limitation is intended to limit the movement of fire within the chase or soffit. It is not the intent of this volume limitation to require dampers or other mechanical separations within ductwork, or other equipment that are not otherwise required.
INSIGHTS : The types of concealed spaces addressed by 9.2.1.11 and A.9.2.1.11 create spaces similar to other concealed space areas already addressed by the standard. This language makes it clear that these types of spaces, regardless of what mechanical and or plumbing equipment, ductwork, or electrical components are present in the space, are not required to be sprinklered provided they meet the conditions outlined in 9.2.1.11. The 160 ft³ (4.5 m³) limitation is consistent with other permissions for the omissions of sprinklers in concealed spaces throughout Section 9.2, such as those found in 9.2.1.6 and 9.2.1.9.

Erik

8/11/2026 09:07:43 am

9.2.1.1 NFPA 13 (2019) - Concealed spaces of noncombustible and limited combustible construction with MINIMAL combustible loading having no access shall not require sprinkler protection.

Seems to me, you have a lot more than minimal amount of combustible material up there and it would require sprinkler protection.

In regard to intumescent paint, I highly doubt there is a listing that would allow it to be used on combustible insulation. Typically intumescent paint is planned for because it has very specific listing / requirements, I don't know if I have ever seen it used as an after thought to make up for a missed mistake.

8/11/2026 10:56:34 am

Thank you for clarifying. I also believe this is above the threshold of minimal combustible loading but I also understand that is an engineering judgement and was looking for second opinions.

Jack G

8/11/2026 09:41:35 am

Erik has it correct.
The space is non combustible.
You are adding combustible insulation and it’s not filled to the top.
It must be protected with sprinklers as the space becomes combustible.
I’m the 70 s energy crunch builders of commercial and residential construction used foam to conserve energy.
I watched a fire in a sprinklered building completely envelop the building from a fire in the vestibule. Foam board on the exterior beneath the siding. Housesame in less than 2 minute.

zackery geddies

8/11/2026 01:22:09 pm

take a look at Mineral wool such as Rock wool. It is non combustible and it has a thermal value.

Sprinklers Required with Combustible Insulation?

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