Direct answer
An attached spa is a second vessel with its own hydraulics, heat profile, and safety fittings, not a decorative corner of the pool. The layout choice — raised, flush, or spillover — decides how it is plumbed, how it interacts with an automatic cover, and how much equipment the pad must carry, so it belongs in the earliest drawings.
Key takeaways
- Raised, flush-deck, and spillover spas are structurally and hydraulically different projects, not styling options.
- A spa that heats fast needs its own hydraulic thinking and drives heater sizing for the whole system.
- A flush spa inside the pool's rectangle can live under one automatic cover; a raised spa cannot.
- Spa suction and jet fittings are safety-critical items governed by code — specify compliant, listed fittings from the first drawing.
An attached spa is the most common upgrade in custom pool design, and it is often underplanned. It is a second vessel with its own temperature, hydraulics, and code obligations. It looks small in a rendering and large on the drawings.
Three layouts, three different projects
- Raised spa. The spa sits above deck level, often spilling into the pool. It reads as architecture, gives bathers a wall to lean on, and keeps spa heat somewhat separate. It also breaks the deck plane and any pool cover line.
- Flush spa. The spa rim sits at deck level, inside or beside the pool’s footprint. It is quieter visually, safer to step into, and when placed inside the pool’s rectangle it can sit under the same automatic cover as the pool.
- Spillover detail. Raised or flush, a spillover keeps the spa hydraulically connected to the pool in pool mode. It is a valve-and-elevation design detail that must be drawn, not improvised.
Choose the layout together with the cover intent from automatic pool cover planning. A flush spa under one cover is simple. A raised spa means two covers and a track that terminates cleanly.
What a spa does to the equipment plan
The usual design shares pump, filter, and heater between the vessels, with actuated valves switching modes, plus dedicated jet pumps or a blower for the spa side. That adds rows to the equipment schedule. It also sizes the heater, because a spa needs to heat quickly on demand to be useful.
All of it lands on the pad, so the valve cluster, extra pumps, and controls need the space reserved in the pad layout from the start.
The safety line item
Spa suction is where hydraulics meet code most directly. Suction outlets, their covers, and their arrangement are regulated safety items. Specify listed, compliant fittings and let your builder and inspector verify the hydraulic design against local requirements. Specify this on the first drawing, not as a punch-list check.
Getting it built in the right order
Spa walls, benches, plumbing loops, and any spillover elevations are set at the steel-and-plumbing stage of the construction sequence. Record the layout choice, shared-equipment decisions, and fitting specifications in the new pool project checklist so the spa is designed as a vessel before it is built.
What this page does not decide
Jet counts, seat ergonomics, and finish choices are taste. Hydraulic sizing and fitting compliance are engineering and code. This page is narrower: make the layout decision early, because the rest of the project inherits it.
Frequently asked questions
Does a spa share equipment with the pool?
Usually the pump, filter, and heater are shared, with actuated valves switching between pool and spa modes, plus a dedicated jet or blower system for the spa. Fully separate equipment sets exist but cost more; the shared design is why spa decisions reshape the whole equipment schedule.
Which spa layout works with an automatic cover?
A flush spa placed inside the pool's rectangle can sit under the same automatic cover as the pool. A raised spa breaks the cover plane, so it needs its own cover and the pool cover tracks must end cleanly before the raised wall. Decide spa layout and cover intent together.
Why do spas heat fast but cost more to run?
A spa is a small volume heated to a high setpoint, often on demand. That drives heater sizing — the heater must lift the spa quickly to be worth having — and it rewards insulation, a spa cover for standby, and honest expectations about energy use.
Sources
- Pool Safely campaign resources — U.S. Consumer Product Safety Commission Accessed August 27, 2026.
- Standards and codes — Pool & Hot Tub Alliance Accessed August 27, 2026.