Alternatives Tank Ideas for Seismic Area Highrise?

5/5/2026

I've got a high-rise project in a seismic zone higher than category C. We are required by IBC to have a secondary water supply other than the city supply (IBC 403.3.3). The structural team is pushing to not put the tank on the roof, and our site is extremely limited, so there is discussion about trying to bury the tank.

What pump/tank configurations are available for this situation?

I am aware of either a concrete or fiberglass tank with a vertical turbine pump, but can you tie in the city supply to a vertical turbine submerged in a tank?

Is there a way to appease this rule other than a secondary fire tank that I'm not thinking of?

Thank you in advance for any help.

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7 Comments

Ken Thackery

5/5/2026 08:20:51 am

We just did one of these. The 40k gal tank is buried under the building- under the FP room- with a plate the VT sits on. There is also a secondary Horizontal pump per the owners reqirements being a hospital. The VT is the primary and delivers 100psi to the roof 14 levels up. Send me your email and I can send you pictures and data. You have to bring the supply into the room so I'm not understanding the question.

anthony

5/5/2026 08:28:05 am

Other tank configurations:

Burry the tank and fire pump room. Have the pump room at the same ground level as base of the tank.

install a pressure tank. That will give you enough lift to get to your main pump. You'll need a room for the massive pressure vessels. Probably want a neutral pressure holding tank and a very high pressure air tank - this system would be comically large but technically you could do it.

Don't do any of these, they're just other ideas that 'could' work as an alternative to a vertical inline turbine.

I don't have the code reference but I could swear you're allowed to use an additional water main from an adjacent street

SShepherd

5/5/2026 08:58:37 am

All forms of tanks are available to you, but the key requirement is an "automatic" water supply. There will be questions on whether a suction tank with static volume or break tank. Tanks can be located within the building envelope at grade, above grade, or subgrade within the building footprint or beneath the building. All design options (pump and tank) are available, and all come with their own challenges. Highly recommend working with the water purveyor and the agency responsible for cross connection control as the water supply for the tank can come with its own challenges beyond the fire code or standard. Do not forget about the tank overflow if located within the building as the overflow needs to have a discharge point. I would highly recommend to not discharge the overflow within the building - try to discharge at grade. Coordination of a subgrade tank is very important and most likely will involve the structural engineer of the building. In my jurisdiction we have rarely seen alternatives to tank, as the water supply for the pumps must be reliable, and alternatives like the rooftop pool, or such just doesn't meet the reliability.

Jose R Figueroa

5/5/2026 09:56:20 am

I have observed the effects of minor E/Q on swimming pools. It's particularly concerning when they are located on the top floor. They can cause the building to sway. Disclaimer: I'm the FM or NFPA guy.

I oppose placing fire water tanks on the tops of buildings.

FM DS 3-2 Water Tanks for Fire Protection and DS 2-8 Earthquake Protection for Water-Based Fire Protection Systems strongly support the burial or grade-level placement of suction tanks combined with vertical turbine fire pumps, following specific seismic design and approval standards.

FM uses a global map with earthquake zones (50-year, 100-year, 250-year, 500-year, and >500-year) based on Data Sheet 1-2 Earthquakes, which differ from IBC/ASCE seismic categories. These zones estimate expected ground motion severity and frequency.

The best approach is to use a listed or approved tank buried underground. Consider soil pressures, lateral earth loads, buoyancy (anti-flotation anchoring is vital in areas with high groundwater), and seismic soil effects per geotechnical guidelines. Bottom plates are highly recommended, or full anchorage if no bottom plates are used, to prevent slipping, pipe damage, and liner deterioration.
Fully buried tanks are permissible if they satisfy these conditions and meet the AHJ requirements. Many manufacturers provide FM Approved tanks that are specifically tested and evaluated for seismic zones.ank following FM 4020 for structural integrity, including earthquake. Approved tanks are listed in the FM Approval Guide.
• Common FM Approved options suitable for burial/seismic high-rises. manufacturers like CST Industries — strong seismic track record when properly anchored. Alternatively Concrete (cast-in-place or precast) — designed per ACI 350/350.3/318 principles.
• Fiberglass (FRP) — lightweight, flexible, and excellent for seismic zones and burial (corrosion-resistant, good buoyancy resistance with proper design). Manufacturers like Xerxes offer underground FRP fire tanks that meet NFPA 22.. They exceed basic NFPA 22 in many cases for insurance purposes (e.g., larger volumes, redundant suctions, or enhanced coatings sometimes required by FM).
Your vertical turbine setup in a buried break/suction tank aligns well with FM, as long as the tank is FM Approved (or designed to equivalent principles) for the site’s zone, the pump/piping follows DS 3-7 or NFPA 20.
Practical Advice for Your Project
• Determine your site’s FM earthquake zone (via FM’s tools or Data Sheet 1-2) and share it with tank suppliers/structural engineers early. Buried FRP or concrete tanks are popular for tight urban seismic sites due to lower weight (less seismic force) and easier anti-flotation design. This approach satisfies both code (IBC) and FM insurance standards while keeping the tank off the roof. If you provide the city/location (for zone lookup) or approximate demand,

5/5/2026 10:41:21 am

If I understand correctly, you want to know how to eliminate a secondary tank and still satisfy the requirement of 2 separate water supplies, as required by IBC. I have successfully done this though involvement with the AHJ and their approval. In short, If the tank is sized to meet the demand and duration of the highest hazard, an auto refill, proven to refill at rate equal to the highest demand, it is the secondary supply.

Ron

5/6/2026 11:34:08 am

Another option we have used assuming it is large enough, is taking suction from a pool.

Anonymous AHJ

5/6/2026 12:04:19 pm

In our jurisdiction we have a situation similar to yours, a 10,000 gallon water tank was installed along with a water pump with a back up generator. The site is fully sprinkled and protected, the pump and associated piping is in an enclosed temperature controlled environment and what is exposed to the elements is insulated. No issues to date.

Alternatives Tank Ideas for Seismic Area Highrise?

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