Spa Construction: Built-In Spas and Hot Tubs for Pools and Backyards

Spa Construction Options and What Each Costs

The biggest cost decision is timing. A spa planned with the pool shares excavation, equipment and finish work; a spa added later reopens all three.

Fixr prices a spa added to an existing pool at $13,000 to $19,000, against $6,000 to $10,000 during a new build, because the contractor has to cut into the pool structure, run new plumbing and electrical, and usually replaster the pool so the finishes match. If a spa is even a maybe, ask your inground pool builder to stub out the plumbing during the original build.

Portable hot tubs are the low-cost alternative: Fixr lists $1,000 to $15,000 installed. They need a level pad and a dedicated circuit; Stout Design Build budgets $500 to $2,000 for both. Built-in spas cost more but sit flush with the deck, match the pool finish and can share the pool’s equipment.

What 2025 Building Permits Say About Pool-and-Spa Projects

Cost guides survey contractors. Permit records show what homeowners and builders actually declared when they applied, city by city.

In Nashville the median pool-and-spa permit declared $188,204 in 2025 against $100,000 for a pool alone. In Los Angeles the gap was $2,000, and in Fort Worth pool-and-spa permits declared less than pool-only permits. One plausible reading is scope: in Los Angeles 80.1% of classifiable pool permits included a spa, so a spa is part of an ordinary project there, while in Nashville the 18.0% that include one tend to be larger custom builds.

Local market pages: Phoenix (Mesa is in the table), Dallas (Fort Worth), and Florida’s Tampa, Orlando and Miami; Houston covers the rest of Texas.

How a Built-In Spa Is Built, Step by Step

1. Design and placementRaised beside the pool with a spillover, flush with the deck, or standalone. Decide seat depths, jet count and whether the spa shares the pool’s pump and heater.
2. Permits and plan reviewMost jurisdictions want plans showing the spa, its barrier and the electrical layout; see our pool permit guide.
3. Layout and excavationThe spa is dug with the pool, or cut into the deck beside an existing pool.
4. PlumbingSeparate suction lines and jet manifolds, plus valves that switch between pool and spa modes when equipment is shared.
5. Steel and shotcreteA reinforced concrete shell, with the spillover edge set level so water sheets evenly into the pool.
6. Electrical and bondingGFCI-protected circuits, equipotential bonding of metal parts and, where the code applies, an emergency shutoff switch within sight of the spa.
7. Tile, coping and interior finishUsually matched to the pool, which is why adding a spa later often means refinishing the pool too.
8. Start-upBalance the water, set the heater and thermostat limit, and walk through controls with the builder.

For the wider sequence a spa fits into, see the pool construction process. Surface material choices are compared in gunite vs fiberglass vs vinyl.

Heating a Spa and Monthly Running Costs

HomeGuide estimates that an inground hot tub costs $100 to $300 a month to run (HomeGuide). Heat is most of it. At U.S. average prices in July 2026, a heat pump at COP 5.0 delivered heat for $10.73 per million Btu and an 82% efficient gas heater for $31.14 (PC&S calculation from EIA and EIA gas prices).

Spas complicate that comparison. A spa is small and is often heated on demand for an evening, which favors a gas heater’s fast recovery even at a higher cost per Btu. A heat pump for the pool and gas for the spa is one way to split the difference; ask your builder to model both. A tight cover matters more than the fuel: DOE says covering a pool when it is not in use can save 50% to 70% of heating costs (DOE Energy Saver).

Spa Water and Safety Rules Builders Must Design For

CDC lists hot tub jets that create droplets or mists, along with sweat and dirt from bathers, among the things that reduce chlorine levels. The numbers below are why spa construction details, such as controller placement and drain covers, deserve more attention than they get.

Of 560 treated recreational water outbreaks reported to CDC with onset from 2009 to 2023, 176 were at hot tubs or spas, and 147 of those involved Legionella. Hot tub outbreaks caused 20 of the 22 deaths in that period (CDC NORS, analysed in our pool illness outbreak report). The same chemistry applies to a backyard spa, just with fewer users.

Inspection records show the same pressure. In Louisville Metro, Kentucky, 53.6% of spa free chlorine readings from October 2021 to April 2024 were below the 3.0 ppm minimum, against 14.5% of pool readings (PC&S analysis of Louisville Metro data).

Drain covers matter in a spa because the suction is concentrated in a small vessel. Spas, hot tubs and spa components account for 11 of 83 U.S. pool and spa recalls since 2001, and a 2026 recall pulled 340 spa drain covers for entrapment risk (CPSC; PC&S recall registry).

Electrical, Shutoff and Barrier Rules for Spas

• GFCI protection. The National Electrical Code added spas and hot tubs to its GFCI requirements in 1981 (IAEI Magazine).
• Emergency shutoff. The International Swimming Pool and Spa Code section 313.7, as adopted in Decatur, Texas, requires an emergency shutoff switch for spa pumps and blowers within sight of the spa and at least 5 feet horizontally from its inside walls (City of Decatur). Some cities exempt one- and two-family homes, so check your local adoption.
• Switch and light clearances. Farmington, Minnesota’s residential hot tub handout requires lighting switches at least 5 feet from the water’s edge and GFCI protection for lights and switches 5 to 10 feet away (City of Farmington).
• Barriers and covers. Under the 2024 ISPSC, a spa with a lockable ASTM F1346 safety cover is exempt from the code’s barrier sections 305.2 to 305.7 (ICC via UpCodes). Many states and cities amend this; our pool fence laws by state report tracks who does.

Choosing a Spa Builder

In states with a dedicated pool license, spas usually sit inside it. California’s C-53 Swimming Pool Contractor class covers contractors who construct swimming pools, spas or hot tubs. Arizona has a separate B-10 class for spas and hot tubs with 18 active licenses in July 2026, Alabama’s swimming pool classification includes a Hot Tubs & Spas sub-class, and Nevada has an A-10b Residential Spas class (PC&S license review).

• License for the right class Pool or spa class where the state has one; a licensed electrician for the wiring everywhere.
• Ask how the spa heats Shared heater or its own, gas or heat pump, and expected time to heat from cold.
• Ask about suction outlets Number of outlets, listed covers and their rated service life.
• Ask about controls Where the emergency shutoff and controls will sit relative to the water.
• Get the spa itemized Shell, plumbing, equipment, electrical and finish as separate lines so bids are comparable.

More on comparing bids: how to choose a pool builder and inground pool cost.

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