The Demising Wall Is the Cheap Part

What it actually takes to turn an industrial shell into functional small-bay space

By Jason Probert, Founder of SpanVor, and Quang Do, P.E., Principal Engineer at Pyra IXI

A 12,000-square-foot industrial shell can look like six future 2,000-square-foot bays.

Draw five lines on the plan. Add six storefronts. Multiply the smaller-suite rent by six. The deal can become more attractive before anyone has moved a wall.

Then somebody opens the electrical room.

There is one service. One meter. One panel. One rooftop unit. The restrooms are both on the same side of the proposed division. The sprinkler system was designed around a use nobody has verified. The building has utilities. The six suites do not.

The five lines were never just walls. They divided every shared system in the building.

Jason sees this in acquisitions and ownership—offering memoranda that describe a building's systems in language precise enough to sound verified and vague enough to mean almost nothing. Quang sees it when the panel cover comes off, the drawings stop matching the building, and a division that looked like carpentry becomes a utility project.

We came at the problem from different sides and reached the same conclusion:

The rent premium belongs to the finished bays. The construction budget belongs to the systems that make those bays work.

The finding, in four owner-level questions

Before a buyer treats one shell as six future leases, the building has to survive four questions:

Capacity: Can the shared infrastructure support the proposed tenants?
Distribution: Can power, air, water and life-safety systems reach every suite in a usable and billable way?
Compliance: Can the building legally support the activities the leases will allow?
Time: Which critical-path items belong to the owner—and which belong to a utility, reviewer or equipment supplier?

The walls matter. They simply are not where most of the uncertainty lives.

“The building has power” does not answer the question

“Power to the building” is one of the least useful phrases in an industrial offering memorandum.

It may mean the utility serves the property. It does not tell an owner whether the service has enough available capacity for six tenants, whether each suite can be separately metered, whether the existing switchgear can accept the proposed distribution, or whether three-phase power can reach the bays that need it.

The electrical budget is not one clean number per bay. It behaves as one lumpy shared cost plus a smaller repeating one.

The shared backbone is paid once for the building: service capacity, meter bank, current-transformer equipment, riser, service conductors, utility-side work and any required easement.
The per-suite increment repeats: panel, feeder, tenant disconnect, grounding, branch rough-in, engineering and permit work.

On recent Texas projects, the per-suite increment has landed around $30,000 to $50,000 when three-phase service and a panel must be delivered to an individual bay. That is an illustrative field range—not a bid, not a national average and not the total conversion cost.

The distinction is the useful part. If the existing service can carry the new tenant count, the repeating increment may be most of the work. If it cannot, the shared backbone can dominate the budget, and one backbone item can exceed the entire per-suite figure.

The meter is often the better clue

Six suites may require a new meter bank, current-transformer cabinet, revised riser, service conductors, trenching, transformer work and utility review. Those are not simply electrician decisions. They can require utility engineering, utility-furnished equipment and scheduling on somebody else's calendar.

Austin Energy's current meter-review guidance is a useful example because the triggers are broader than many owners expect. Review applies to projects involving three or more meters, larger services and modular metering; its published guidelines also address service upgrades, remodels and changes of use. Other utilities organize the process differently, but the lesson travels: metering is infrastructure, not an accounting preference.

One of Quang's recent projects makes the scheduling risk tangible. The design proposed increasing an existing 1,600-amp service to 2,000 amps. The existing transformer was already at capacity. The solution was not a better drawing or a larger breaker. It was a new independent service, a new utility pole and an easement across the parking lot.

That project had been underwritten as a service upgrade. It became a third-party infrastructure project.

We are deliberately not publishing a universal utility lead time. The mechanism is more useful than a number:

A panel is usually a subcontractor line item. A utility service is somebody else's queue. You may accelerate the first by spending more. You may only wait for the second.

The paper record is not the building

Every cost assumption above depends on knowing what is physically installed. That is often where the record fails.

On one field walk, Quang's team spent thirty-eight minutes hunting a panel. The drawing used one designation, the nearby equipment used another, and the correct label was eventually found reversed on the gear. Nothing about the circuiting was confirmed that day.

On another project, an earlier inspection record showed a 400-amp service while the currently submitted documents omitted it. The disagreement between the building and its paperwork contributed to a permit rejection.

On a third, a maintenance manager described a 1,200-amp main. But nameplate service size is not available capacity. The same manager's estimate of spare air-handler capacity moved from “maybe 60%” on the phone to “probably 20%” three days later while standing in front of the unit.

Nothing had changed but the vantage point.

Nobody necessarily lied. Buildings change. Tenants leave. Circuits get reused. Contractors finish work that never reaches the record drawings. An as-built shows what somebody intended to document at a point in time. It does not prove what is energized today.

Before Quang relies on an existing-condition drawing, he wants five things checked:

Open the panel. Confirm bus rating, main breaker size, and available spaces versus usable spaces.
Find or create the one-line. A partial plan set is not an electrical map.
Pull the certificate of occupancy for the last permitted use. The flyer does not establish the lawful prior use.
Confirm which equipment serves which area at the equipment itself. Do not rely only on the drawing or somebody's memory.
Compare the ages of the architectural and MEP sets. Walls are often updated on paper while ducts, circuits and piping are not.

The cheapest investigation may be a few hours with the right people and the equipment open. The expensive version begins after the leases are signed.

One rooftop unit does not become six HVAC systems

A single-tenant shell may have one or two rooftop units serving open space. Divide the building and somebody has to determine which suite gets which unit, how ducts cross the new walls, how each tenant controls and pays for its system, and whether the equipment can support the actual use.

That last point matters because small-bay tenants do far more than store boxes.

An HVAC contractor, fitness studio, food producer, light manufacturer and e-commerce operator can occupy bays of identical size while creating completely different heat, ventilation, exhaust and electrical loads. A 2,000-square-foot rectangle tells the engineer almost nothing about what the air system must do.

The surprise is often makeup air

On one recent three-suite project, the plans called for warehouse exhaust at roughly thirty times the applicable minimum, but the intake did not follow. One suite showed a louver operating at about five times its rated face velocity. The other two showed no replacement-air path at all.

The likely result was not merely an unfavorable plan-review comment. It was a negatively pressurized space with doors that could become difficult to open.

The same project exposed another cost of divisibility: three suites created three parallel drawing packages, and a correction made in one package did not appear in its siblings. Smaller spaces multiply not only equipment; they multiply coordination.

Adding a rooftop unit can also become a structural question. Depending on the jurisdiction and the existing roof, new rooftop equipment or a hood may require sealed structural work or an engineer's letter confirming the roof can carry the load. In an adaptive-reuse project Quang reviewed, the roof could not carry a rooftop unit and the mechanical room shown on the original plan had become a data room. A seemingly ordinary HVAC solution became a different system with different power, access and humidity-control needs.

There is no universal “small-bay HVAC package.” The intended tenant use is part of the system design.

The wall is cheap. The rating is not.

The wall itself may be the most honest line in the budget. Studs, board and finish are ordinary construction and generally price the way an owner expects.

What the wall becomes is the problem.

Between tenancies, the required assembly may need to extend from floor to roof deck rather than stopping at the ceiling grid. On one project, the reviewer required a two-hour separation between suites and denied the set twice because the required wall was not shown.

Once a wall is rated, every duct, pipe, conduit and cable that crosses it becomes a coordination point: an approved penetration assembly, installation detail and inspection involving trades that had previously been working inside one open room.

This is where the shared-system problem meets the wall problem. Ductwork crossing into a second suite, conduit feeding a new panel and sanitary piping reaching a restroom all have to travel somewhere. The cheapest route on paper may disappear when the wall rating, an occupied neighboring suite or an owner-imposed no-penetration rule is considered.

The demising wall is the cheap part. The rating it carries—and everything that has to pass through it—is not.

“There are restrooms” is not a plumbing plan

The 12,000-square-foot building may already have two restrooms. That sounds helpful until both land inside Suite A.

Now the plan must answer a different set of questions. Does each tenant have lawful access? Can a common arrangement work? What occupant load follows from the proposed use? Can sanitary and water lines reach the right places without cutting across half the slab—or crossing another tenant's space?

In one recent example, a demised suite of roughly 1,800 square feet calculated to an occupant load of 41. It had one accessible single-user restroom. The applicable exception allowed one facility only for a tenant space with an occupant load of fifteen or fewer, so the suite required a second single-user restroom and a drinking fountain that the drawings had marked “not applicable.”

The important point is what created the cost: occupant load, not the wall. Dividing a building does not automatically add fixtures. The use placed into each resulting suite changes the occupant calculation, and the fixture requirement follows.

Plumbing review can also depend on another reviewer's work. In that example, the plumbing determination could not be closed until the plan analyst verified the occupant load. A sequence problem became a schedule problem.

The fixture itself is not always the largest cost. Routing may require slab cutting, work inside another tenant's space, after-hours access, a longer vent path or a different location entirely. An HVAC contractor's plumbing needs may be modest; a gym, church, commercial kitchen, pet-care operation, food producer or vehicle user can change occupant counts, drainage, grease, backflow, wash-down and hot-water requirements. The rent roll may call all of them “small-bay.” The building systems do not.

Code families and local amendments also vary. Houston and Austin, for example, have adopted Uniform mechanical and plumbing codes alongside their building-code frameworks. Owners should price the requirements that govern the actual address and intended use—not a fixture table found for a different jurisdiction.

“Fully sprinklered” does not describe what the system can protect

Fire protection depends on what the tenant is doing and storing. Commodity, storage height, rack configuration, aisle layout, hazardous materials, occupancy and fire separations can all matter.

A system acceptable for one tenant may not support the next tenant's operation without modification. The change can involve more than relocating sprinkler heads around new walls. It may require a hydraulic review, alarm changes, different separations, egress work or a separate approval path.

Quang's owner-level question is better than the usual checkbox:

What commodity, at what height, on what rack, was this system designed to protect—and does that match the tenant you are about to sign?

The exact thresholds depend on the adopted code and local rules. In Houston, for example, published high-piled-storage requirements vary with commodity and storage height, and fire-alarm and sprinkler work can travel on permit tracks separate from the building permit. The practical diligence can start with a tape measure and an inventory conversation before it becomes a redesign.

The equipment inside the bay may matter more than the bay's square footage.

A city permit may not be the only approval track

Owners often build the schedule around the municipal building permit. The actual critical path may also include utility, fire, accessibility, health, environmental or special-district review.

Texas accessibility is a useful example. TDLR says projects with total estimated costs of $50,000 or more must be registered and submitted for review under the state's architectural-barriers process. A project below the threshold may still have to comply with the Texas Accessibility Standards, and a local jurisdiction may still require registration.

Federal accessibility obligations can extend beyond the area receiving new finishes. Under the U.S. Department of Justice's ADA guidance, an alteration affecting a primary-function area can require an accessible path of travel—including serving restrooms and drinking fountains—up to the point at which that additional work becomes disproportionate. The federal rule uses 20% of the primary-function alteration cost as that limit.

The number matters, but the larger lesson is that “below $50,000” and “the city approved it” are not universal safe harbors.

Quang sees four parallel approvals discovered late more often than owners expect:

Accessibility registration and review.
Health-department review for food users, where an incomplete food-service package may not enter substantive review at all.
Fire review when nobody measured storage height or confirmed the commodity.
Utility- or special-district rules that differ from the city assumption.

On one project, the city allowed one type of grease interceptor while the governing district required an underground concrete unit and sampling well. Quang estimated the change at roughly $12,000 to $20,000, driven less by the tank than by excavation, weight and installation.

That does not mean every shell needs every approval. It means the approval map belongs at the start of the plan.

Same rectangle, different building

Square footage is a poor proxy for tenant-improvement scope. Consider two identical 2,000-square-foot bays.

| | Suite A: contractor storage and a desk | Suite B: food producer | |---|---|---| | People and use | Small crew; limited customer presence | Employees, production and possibly customers | | Plumbing | One modest restroom arrangement | Fixture count, hot water and drainage tied to use | | Air | Ordinary ventilation | Exhaust and replacement air may be required | | Power | Modest equipment load | Production equipment can require materially more service | | Specialty scope | Limited | Hood, gas, grease, wash-down or health review may apply |

Same rectangle. Same asking rent per square foot on the flyer. The system scope is not in the same order of magnitude.

This is why tenant mix cannot be an afterthought. A landlord can build a flexible shell, but flexibility comes from preserving pathways and capacity—not pretending every future use is the same.

The acquisition version of the problem

The cleanest-looking small-bay deal can be the easiest one to underwrite too lightly.

New paint, attractive storefronts and a tidy shell encourage the buyer to focus on unit count and rent. Older product creates the opposite temptation: a lower basis or lower in-place rent can look like the opportunity.

Both can hide deferred functionality.

An older 3,000-square-foot bay may be less expensive because the market has mispriced it. It may also sit on shared electrical service, aging rooftop equipment, one water line, uncertain fire-protection capacity and plans that no longer describe the building. Part of the rent discount may be somebody else's deferred capital.

That does not make the property a bad investment. It changes the price of the plan.

Before underwriting a conversion or acquisition, we would want answers to at least these questions:

What electrical equipment is physically installed, and what does a current load review show?
How many meters exist, who owns them, and what would the proposed suite plan require?
Do panel schedules and one-lines match the equipment in the field?
Which rooftop units serve which areas, and what condition and remaining life do they have?
Can the roof support added equipment, and is every mechanical space still being used as one?
Where are water, sanitary, gas and condensate routes relative to proposed suite lines?
What is the required wall assembly, and what must penetrate it?
What commodity and storage height was the fire-protection system designed to support?
Which certificates of occupancy, permits, violations and inspection records describe prior uses?
Can entrances, restrooms, parking and routes support the intended uses and accessibility obligations?
Which tenants require fire, health, environmental or specialty review?
Which utility, approval or equipment item controls the earliest realistic rent commencement?

That is not a demand for a perfect building. It is a demand for an honest budget.

What should “tenant-ready” mean?

The phrase often means “clean and empty.” Quang's definition is narrower and more useful:

Tenant-ready means the suite has capacity that can reach and serve it, a code path for the use the lease permits, and every required approval identified—not merely the city's building permit.

That definition also shows where pre-tenant capital can create flexibility.

On one shell, Quang's team ran a second capped sanitary line beside the main and preserved open ground near the sewer for a future grease interceptor. They did not install the interceptor; its size would depend on a tenant's future fixture count. The relatively inexpensive decision preserved a pathway and avoided the prospect of later cutting finished concrete simply to reach the system.

The same logic can apply to spare conduit, structural allowances, meter locations and planned penetrations: preserve the path where it is economical; defer tenant-specific equipment until the use is known.

Frequently asked questions

Is the demising wall really the least expensive part?

Not on every project. The phrase captures the larger underwriting point: the wall is visible and easy to price, while capacity, distribution, compliance and utility timing can be harder to discover and materially more expensive.

Does every small-bay conversion require new three-phase power?

No. The requirement depends on existing service, available capacity and the intended tenants. The diligence task is to verify what exists and compare it with the uses the owner plans to allow.

Can an owner design one standard bay for every tenant?

An owner can create a flexible base condition, but no single package economically fits every use. Food production, fitness, vehicle work, light manufacturing and storage can impose very different requirements on identical floor areas.

What is the first thing a buyer should verify?

Start with the shared backbone: electrical service and metering, water and sewer routes, HVAC allocation, fire-protection basis and the certificates of occupancy. Then test the proposed tenant plan against those physical facts.

Key takeaways

A small-bay conversion divides every shared system, not merely the floor plan.
Separate the electrical backbone from the repeating per-suite cost; they behave differently in both budget and schedule.
Existing drawings are evidence, not proof of what is installed or available today.
Tenant use—not square footage alone—drives HVAC, plumbing, fire-protection and approval scope.
“Tenant-ready” should mean capacity, distribution and a lawful approval path, not simply clean floors and fresh paint.
The goal is not a perfect building. It is an honest budget before the price and opening date are committed.

The practical starting point is simple: underwrite the bay, not the rectangle. SpanVor helps owners and investors identify the properties worth investigating; Pyra IXI helps determine whether the systems inside those properties can support the plan.

For the wider diligence framework, use the Small-Bay Asset Passport. Read why small-bay is not miniature big-box industrial, examine the construction argument in Metal Is Not a Four-Letter Word, and explore the broader investment thesis in the Small-Bay Industrial Investor Primer.

You can explore industrial and small-bay properties across the United States with 14 days of SpanVor All-Access—no credit card required—at spanvor.com/trial. Learn more about Pyra IXI's commercial MEP engineering work at pyraixi.com.

One last thing, since you read this far: the code SpanvorBlog takes 25% off a SpanVor Pro subscription—where the property-level intelligence behind posts like this one lives.

About the authors

Jason Probert is the founder of SpanVor, an industrial real estate data platform built around the properties, tenants, projects and operating details that broad market statistics often miss.

Quang Do, P.E. is Principal Engineer at Pyra IXI, an MBE/HUB-certified commercial MEP engineering firm serving Texas, Florida and Wisconsin. He works on mechanical, electrical and plumbing design from concept through permit and helps owners, architects, contractors and developers identify fit-out and plan-review problems before they become field problems.

Project examples in this article are drawn from real work and have been anonymized. Actual project scope depends on existing conditions, intended use, the serving utility and locally adopted codes. This article is an underwriting and diligence framework, not project-specific engineering, legal or code advice.