Rack Storage Tenant Improvement in an Existing Warehouse
A 240,000 sq ft speculative warehouse in Polk County has an existing wet-pipe system designed for Class III commodity stored 12 ft high at 0.20 gpm/sq ft over 2,000 sq ft. A new tenant proposes four-level rack storage of packaged Group A plastics to 22 ft, with 8 ft main aisles and 6 in flue spaces. The tenant's contractor proposes to keep the ceiling sprinklers and add in-rack sprinklers only at the rack faces along the main aisles, arguing that the 8 ft aisles provide separation and that the plastic is 'cartoned.' The owner wants permit drawings in ten days because the lease starts in six weeks. The local AHJ has not reviewed the storage arrangement. The contractor's design technician has not performed a commodity classification or asked for the rack layout, and the existing hydraulic placard shows 0.20/2,000 with a 750 gpm supply.
1. What is the central design error in the contractor's proposal, and what information must be developed before any permit drawings are produced?
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The central error is treating a storage design problem as a simple head-layout problem. Under NFPA 13, storage protection is driven by commodity classification, storage height, rack arrangement, aisle width, flue spaces, and ceiling height -- not by the existing light-hazard placard.
Packaged Group A plastics are a higher-hazard commodity than Class III. Calling the product 'cartoned' does not automatically make it Class III; the packaging, product, and storage arrangement must be evaluated. An 8 ft aisle does not eliminate the need for in-rack protection, and in-rack sprinklers at the rack faces only are not a recognized substitute for a complete storage design.
Before drawings, the contractor must obtain rack elevations, commodity and packaging data, storage height, ceiling height, aisle widths, flue dimensions, and the existing sprinkler layout. A qualified designer must select a compliant design option -- for example, an ESFR design if the ceiling and aisle conditions permit, or a CMDA design with the required in-rack sprinklers -- and then perform the hydraulic calculation. The existing 750 gpm supply may also be inadequate once the real demand is calculated. Submitting the proposed drawings would put a noncompliant design into the permit process and shift the risk to the contractor.
2. The owner demands that you submit the drawings as proposed to meet the lease date. As the contractor of record, what should you do and what should you tell the owner?
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Do not submit drawings that you know do not reflect a compliant design. A permit drawing is a representation that the system meets the applicable code; submitting the face-only in-rack layout after identifying the defect creates liability for the contractor and can expose the company to disciplinary action.
Instead, send the owner a short written design advisory: the proposed storage is a higher-hazard rack storage arrangement, the existing ceiling-only system was not designed for it, and face-only in-rack sprinklers are not a code-compliant solution. State that a storage design must be completed before permit drawings can be sealed and submitted.
Offer a schedule path: immediate data collection, a design selection meeting with the owner and rack supplier, a hydraulic calculation, and an AHJ pre-submittal meeting. If the owner wants to preserve the lease date, propose interim options such as limiting storage height or commodity until the permanent design is permitted. Put the schedule and cost impact in writing. If the owner insists on the noncompliant submittal, decline in writing and escalate to management; do not let the lease date override the code requirement.