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Exception for minimum flow requirement inquiry

RonKirk59

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Joined
Dec 6, 2024
Messages
5
Location
Seattle
Is it possible to calculate a flow rate that is lower than the 1000 GPM prescriptive minimum for Type V-B construction that can be used to submit under a residential building permit review?

Situation: Current City code from per Fire Marshal requires 1000 GPM. Current Flow Rate is 550-800 GPM with a water cert of 650 GPM.

The property owner is installing a mobile home 28 x 38 = 1,064 SF and is under permit application. Fire review occurred late in the permit process, holding up the permit and throwing the owner a financial curve ball. I am attempting to see if there is a legitimate way to present an argument to the City / Fire Marshall that would be a reasonable justification for a lower than prescriptive water flow.

Based upon my (ignorant) knowledge of the IFC, it seems that water flow is based upon the structure size, and there is a calculation for that. Since this is a small footprint, not attached or ancillary structures, and no structures within 50 ft, 1000 GPM seems excessive for that structure. If I could argue that 650 GPM was adequate for that structure based upon IFC measures, and that alternatives would cause financial hardship, the City is actually very accommodating, understanding and willing to consider an alternative if justified.

Otherwise the options are main and hydrant upgrade ($30-50k) or fire sprinklers ($25-30k) plus plan review though DLI...

Any thoughts or suggestions would be greatly appreciated!!!
 
Most codes allow for alternate means of compliance in lieu of the prescriptive requirements. It takes a bit more engineering.
Could you offer to sprinkler the home per NFPA 13D? The "D" means it is using you domestic water line instead of a dedicated water line.
Flow rates are typically about 0.05 GPM/SF, so 1064 Sf would require 53.2 GPM for an entire house. The 13D standard only requires up to a maximum of 40 GPM.

None of this is a slam dunk, and these are just rough numbers and a crude explanation. It just helps to show that the practical amount of flow to extinguish a fire on a mobile home that size is much less than 1000 GPM.
 
1,000 GPM seems impossible. The OP states that the flow rate is certified at 650 GPM and that’s not good enough for a mobile home? That’s damned near enough for a rocket launch pad. What am I missing?
 
Most codes allow for alternate means of compliance in lieu of the prescriptive requirements. It takes a bit more engineering.
Could you offer to sprinkler the home per NFPA 13D? The "D" means it is using you domestic water line instead of a dedicated water line.
Flow rates are typically about 0.05 GPM/SF, so 1064 Sf would require 53.2 GPM for an entire house. The 13D standard only requires up to a maximum of 40 GPM.

None of this is a slam dunk, and these are just rough numbers and a crude explanation. It just helps to show that the practical amount of flow to extinguish a fire on a mobile home that size is much less than 1000 GPM.
I apologize for the later response. I didn't refresh this screen until today, really appreciate your input, we are on the same thought path. I've been a GC for years, and in structural/zoning have successfully found alt means of compliance, in this case, I don't have the source calcs within the IFC.

Domestic sprinklers are an option based upon existing flow rate. Requires a 1" water line, installed cost of $12-18k + +/- $5k 1" meter upgrade. And you're right that if domestic sprinklers are OK with 40 GPM (albeit early attack) 1000 gpm (fully involved) still seems excessive gpm.

My thinking is that I understand the need for prescriptive minimums because they have to consider a baseline for size of the avg house, margins etc. And, I am thinking that there is some formula or calculation for a 1,000 sf mobile home that (in my opinion) 650 GPM would satisfy a rational and safe argument for this dwelling.

I have not been able to find that calculation or methodology within the IFC or ICC yet... and still looking. This is a young family, working hard, and dealing with a financial curve ball that I am sure that can be solved to meet safety concerns.

Really appreciate your input, and any resource information that you might have. Definitely not specialized area of knowledge.
 
1,000 GPM seems impossible. The OP states that the flow rate is certified at 650 GPM and that’s not good enough for a mobile home? That’s damned near enough for a rocket launch pad. What am I missing?
Sorry for the late reply, getting used to the site! We do site infiltration testing, 650 GPM will wash the structure off the property. And, neither fire marshal or Building Official can deviate from minimum prescriptive code without a site specific calculation for that structure and size.

I have seen hints in the IFC to that formula but have not found the code section or formula, yet. I am pretty sure that with that calculation that the FM or BO would consider a reasonable request for and exception.

I appreciate your input, if you have any thoughts on how to access that formula or code section would be eternally grateful.
 
There used to be a fire marshal Bill here at the forum. Perhaps there are others that might weigh in.
 
I have reason to believe that you have a FM reaching out in your DM.
 
Hello ICE.... I saw and responded to the DM's! Thank you for the heads up. I did not see the message menu, feeling rather foolish about that. Getting to know the site. Great information and super helpful.
 
2018 IFC
SECTION B103
MODIFICATIONS

B103.1 Decreases.
The fire code official is authorized to reduce the fire-flow requirements for isolated buildings or a group of buildings in rural areas or small communities where the development of full fire-flow requirements is impractical.

B103.3 Areas without water supply systems.
For information regarding water supplies for fire-fighting purposes in rural and suburban areas in which adequate and reliable water supply systems do not exist, the fire code official is authorized to utilize NFPA 1142 or the International Wildland-Urban Interface Code.

Click on the XL spread sheet after you open the link

 
2018 IFC
SECTION B103
MODIFICATIONS

B103.1 Decreases.
The fire code official is authorized to reduce the fire-flow requirements for isolated buildings or a group of buildings in rural areas or small communities where the development of full fire-flow requirements is impractical.

B103.3 Areas without water supply systems.
For information regarding water supplies for fire-fighting purposes in rural and suburban areas in which adequate and reliable water supply systems do not exist, the fire code official is authorized to utilize NFPA 1142 or the International Wildland-Urban Interface Code.

Click on the XL spread sheet after you open the link


Super helpful, thank you. Ran the calcs, Total GPM for NFPA 1142 is 250 GPM for this building size (1064 sf). From my practical perspective, this seems reasonable given the type and size of the structure. Appears that B103 is possibly where I could find a potential to propose an exception. Per the worksheet, it would appear that the GPM calc for this structure is 38% of available water flow (650 gpm). Financial hardship could be considered, maybe. Since there are other mobile homes within the 650 ft radius, perhaps some share financial burden could absorbed by the water district. Appreciate your help and resources and other thoughts. This is a difficult one to navigate!!!
 
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