Most commercial space in Frisco is new, and that sounds like good news when you sign a lease. New roof, new slab, a rooftop unit with the warranty paperwork still in the folder. Then July arrives, the dining room sits at 79°F right through dinner service, and somebody tells you the air conditioning is broken.
Usually it is not broken. Shell building HVAC is a sizing problem, and it was decided before you ever walked the space.
What a shell building actually is
Developers build most retail and mixed-use space in Frisco as a grey shell or vanilla shell: four walls, a roof, a slab, utilities stubbed in, and a packaged rooftop unit sitting on a curb. The shell has to be leasable to anybody — a nail salon, an insurance office, a boutique, a taco shop — so the landlord’s engineer sizes that rooftop unit against a generic retail load and leaves the rest to the tenant at buildout.
That is a sensible way to build a building. It is a poor way to cool a restaurant.
The two numbers that explain the whole problem
Load rules of thumb vary by engineer, but the trade press states the gap plainly. Contracting Business publishes cooling rules of thumb of roughly 321 square feet per ton for a retail sales floor and about 132 square feet per ton for a restaurant dining room.
Put those side by side. A dining room needs roughly two and a half times the cooling per square foot that a retail floor does — and that is before you add a kitchen, a hood, or the make-up air unit that feeds it.
Run it on a real space. Three thousand square feet sized as retail lands somewhere near ten tons. The same three thousand square feet, if it were all dining room, wants something closer to twenty-two. Nobody builds a restaurant that is all dining room, so the real answer sits in between — but it is never close to the shell number. If you put a restaurant into a retail shell, you did not inherit a marginal system. You inherited well under half the machine you needed.
Three shell building HVAC shortcuts that turn up over and over
The unit was sized for the shell, not for you
This is the root of it. Every other symptom downstream — long run times, a dining room that climbs during service, humidity you cannot get rid of, a thermostat that never satisfies after 6 p.m. — traces back to equipment chosen for a tenant who never moved in.
The curb locks you into the original tonnage
Going from ten tons to twenty is not a like-for-like swap. The roof curb was built for the original unit’s footprint and duct openings. A larger unit needs a curb adapter or a new curb, a structural look at the added weight, larger electrical service, and often a different duct layout on the inside. That is why the quote is never what the tenant expects, and why “just put a bigger one up there” stalls for a season.
The ductwork stopped where the shell stopped
Shell duct is typically a trunk with a few stubs. Buildout then adds walls the original layout never anticipated. Air goes where nobody needs it, and the diffusers at the far end of the run — usually the ones over the window tables — deliver almost nothing. Sometimes the tonnage is defensible and the distribution is what failed.
How to tell undersized from broken, in ten minutes
A broken system and an undersized system fail in visibly different patterns, and you can separate them without a gauge set.
A system that is broken cannot hold temperature at any load. At 10 a.m. with nobody in the building, the room still drifts.
A system that is undersized works fine until it does not. Empty at 10 a.m.: fine. Half full at 2 p.m.: fine. Full dining room at 7 p.m. on a 100°F day with the line running: the temperature climbs and does not come back down until the rush ends.
- Note the room temperature at 10 a.m., empty, with the thermostat set where you normally keep it.
- Note it again at the peak of your busiest service.
- During that peak, put a hand in the supply air at a diffuser. If it is still blowing cold while the room stays warm, the equipment is working — there is simply not enough of it.
- Watch the unit itself. Running continuously and never satisfying the thermostat at peak, but cycling normally in the morning, is a capacity pattern, not a failure pattern.
Cold air plus a warm room equals a capacity problem. Warm air at the diffuser equals a repair.
What to do about it, cheapest first
Replacing the rooftop unit is the last option on this list, not the first. A shell building HVAC complaint is worth working through in this order:
- Confirm the existing unit is making full capacity. Fouled coils, a low charge, a stuck economizer, or one dead compressor on a two-stage unit all imitate undersizing exactly. A unit running on half its compressors is not undersized, it is broken — and that is a far cheaper day.
- Check the kitchen exhaust and make-up air side. A hood pulling more air out of the building than the make-up air unit puts back drags hot outside air in through every door and gap. That looks like a cooling shortfall and is not one.
- Rebalance and extend the ductwork. Often the fastest real improvement in a space that was built out around shell duct.
- Add a dedicated unit for the worst zone rather than replacing the whole system to satisfy one room.
- Replace and upsize — with the curb adapter, structural review, and electrical service scoped honestly in the quote rather than discovered on installation day.
We work through that list in order on commercial HVAC repair in Frisco calls, because the first two items resolve a meaningful share of “we need a bigger unit” complaints. If the equipment genuinely is at the end of its life, our repair or replace decision guide walks through that call, and we have broken down what a rooftop failure actually costs in North Texas separately.
If you are still shopping for space in Frisco
Three questions before you sign, whether the space is on Preston Road, in the Rail District, out at Fields, or in one of the newer pads along Eldorado Parkway:
- What is the rooftop unit’s tonnage, and what load was it sized against?
- Who owns the rooftop unit under the lease — and who pays for replacement, not just repair?
- Is there a make-up air unit, and is it interlocked with the hood?
- Is the equipment inside a screen wall, and how much clearance does it actually have? (That one matters even more for your refrigeration.)
A load calculation before the lease is signed costs a fraction of finding out the answer in July — and it turns shell building HVAC from a surprise into a line item you planned for.
Frequently asked questions
What is a shell building?
A shell building is commercial space delivered with the structure, roof, slab and utilities in place but no tenant buildout. A grey shell has bare walls and an unfinished interior; a vanilla shell adds basics like drywall, a ceiling grid, lighting and restrooms. In both cases the rooftop HVAC unit is usually sized against a generic retail load, not against the business that eventually moves in.
How do I know if my rooftop unit is undersized or just broken?
Compare an empty morning to a full service. A broken system cannot hold temperature even with nobody in the building. An undersized system holds fine at low load and loses the room at peak occupancy. During your busiest hour, put a hand in the supply air: cold air coming out of the diffusers while the room stays warm points to a capacity shortfall, not a failure.
Can I just put a bigger rooftop unit on the existing curb?
Rarely as a straight swap. The roof curb was built for the original unit’s footprint and duct openings, so a larger unit usually needs a curb adapter or a new curb, a structural review for the added weight, larger electrical service, and duct changes inside. It is doable, but it should be scoped and priced before the old unit comes off the roof.
How much more cooling does a restaurant need than a retail store?
Roughly two and a half times as much per square foot for the dining room alone. Contracting Business publishes rules of thumb of about 321 square feet per ton for a retail sales floor against about 132 square feet per ton for a restaurant dining room. Kitchen equipment, hood exhaust and make-up air add load on top of that.
Who pays for the rooftop unit in a commercial lease, the landlord or the tenant?
It depends entirely on the lease, which is why it is worth reading before you sign. Many retail leases make the tenant responsible for routine maintenance and repair while the landlord keeps responsibility for replacement, but plenty of leases push replacement to the tenant as well, and some cap the landlord’s exposure at a dollar figure. We are not attorneys and this is not legal advice — have your own attorney read the HVAC clause.
Get a straight answer on your rooftop unit
We are commercial-only, licensed and regulated by the TDLR under #TACLA109085C, and we work across Frisco, Collin County and Denton County 24 hours a day, 365 days a year. If your dining room is losing the fight at 7 p.m., we will tell you whether you have a repair, a distribution problem, or a genuine capacity shortfall — and we will tell you which one before we quote anything.
Call (972) 412-8300 or request service online. More on what we cover: commercial HVAC repair in Frisco, commercial HVAC repair in Plano, our North Texas commercial HVAC services, and what preventive maintenance actually covers.
