Planning a lap pool

Decide what a lap means in your house

Lap pool covers two different things. One is real training: three or four swims a week, 800 m to 2 km at a time, stroke and pace that matter to you. The other is exercise swimming: twenty steady minutes, a few times a month, mostly in summer. Both are good reasons to build, and they lead to different pools.

The training pool is worth optimising ruthlessly — length before everything, calm water, nothing in the lane, a heated season. The exercise pool can be a family pool that happens to have a clear 10 m run down one side, which is a cheaper and far more sociable object. Decide which one you are building first: everything below trades garden, budget and running cost against each other.

Length: what each number feels like

Stroke rhythm starts at about 10 m. Below that you turn before you have settled, and the swim becomes interval training whether you wanted it or not. At 12–15 m it feels continuous: a moderate swimmer covers 12 m in roughly fifteen seconds, so turns arrive often but stop interrupting. At 20 m and up the pool is no longer the limiting factor, and 25 m is competition length.

Put it in lengths rather than metres and the choice gets concrete. A 1 km swim is 83 lengths of a 12 m pool, 67 of a 15 m pool, 40 of a 25 m pool. If that number horrifies you, build the longest pool the garden allows. If you genuinely do not mind turning, a 12 m pool will serve you for decades and costs far less to build, heat and cover. The 12 × 4, 15 × 4 and 18 × 4 rectangles in our plan library are the classic lap formats — open one in the designer and stretch it to your site.

Measure the length that matters: inside face to inside face at the waterline. A cover roller housed inside the pool takes 40–60 cm out of the swim, and a projecting coping a few centimetres more. If the swim has to be 12 m, say exactly that to the builder.

Width, and what extra width costs

2.5 m is enough for one swimmer. It leaves roughly a metre of clear water either side of a normal stroke, which keeps your hands off the walls and your wash from returning immediately. Below 2.2 m the turbulence is noticeable within a couple of lengths — you can feel the pool pushing back.

Two people side by side want 3.5–4 m. Before you write that down, look at what it does to the rest of the project. A 15 m pool at 2.5 m wide holds about 50 m³; the same pool at 4 m holds 81 m³. That is 60% more water to heat, more surface to lose heat from, a bigger heat pump and a bigger cover — forever, not just at build time.

Most households find the second lane gets used a handful of times a year. If that sounds like yours, put the width budget into length instead: an 18 × 3 m pool holds about the same water as a 14 × 4 m one and is a much better swim.

Every metre of length you add makes the swim better; every metre of width you add makes the pool more expensive for the rest of its life.

One depth, everywhere

1.35–1.4 m from end to end. That is deep enough that your hand does not brush the floor on the catch and your feet clear it on the kick, and shallow enough to stand up and talk without hunting for a shallow end. A lap pool does not want a deep end: it only adds water to heat and a slope to swim over.

Go to 1.4–1.5 m if anyone in the house tumble-turns, because a tumble needs room above the floor and a wall you can plant both feet on. Diving needs 3.5 m or more and has no place in a private lap pool — decide that once, out loud, and design accordingly.

Uniform depth also simplifies everything else. The shell is straightforward, the cover lies evenly, the robot has no slope to climb, and the water is the same temperature at both ends, which you notice after two lengths.

Calm water is designed, not lucky

In a narrow pool your own wash is the opponent. Every stroke sends waves to the wall, the wall sends them back, and in 2.5 m of width they cross and meet you again within seconds. Over 40 lengths that is the difference between swimming and fighting.

Two decisions settle it. The first is the edge: a deck-level overflow edge absorbs waves into the perimeter channel instead of reflecting them, which on a lap pool is a training benefit rather than an aesthetic one. A skimmer pool, with its 15 cm of freeboard, bounces the wave off a hard wall — workable, but you feel it. The second is the inlets: floor inlets, or wall inlets set low and aimed along the pool rather than across it, so circulation does not nudge you sideways on one side of every length.

The third, cheaper decision is where the cover lives. A roller sitting in the water at one end is both an obstacle and a wave-maker. Put it in a pit or a bench, cast with the shell.

Nothing in the lane

A lap pool should be an empty box of water. Steps belong in a corner, or on the end wall you enter from and never turn on; a ladder looks less generous but keeps the lane completely clear and costs almost nothing. A tanning ledge belongs in a different pool, or in a widened bay at one end — never along the lane.

Lights go in the long walls, not the end walls. An end-wall light sits exactly where your eyes go on every breath and every push-off, and it dazzles for half of every length. Handrails, if you want them, go at the entry rather than at the turning wall: a hand meeting a rail at speed is the one genuinely dangerous thing in an otherwise safe pool.

Walls, turns and the line on the floor

Your feet meet the turning wall thousands of times a season, so the finish matters more here than anywhere else. Tile or a smooth, well-floated render is kind to skin; a rough or sandy finish takes the top off a toe within weeks. Keep both end walls genuinely vertical — a sloped wall gives nothing to push against — and the coping flush or set back, because a stone lip over the water is a thing to hit with a hand.

A dark tile stripe, 20–25 cm wide, down the centre of the floor is the cheapest upgrade in the whole project. You swim straight without lifting your head, and you know where the wall is before you reach it. Add a short cross bar near each end and you have a proper target line for the price of a few tiles.

When the length isn't there: counter-current

If the garden will not give you 10 m, a counter-current unit in a 5–7 m pool gives endless swimming in place. A strong unit moves something like 50–75 m³ of water an hour through a wide nozzle and draws 2–3 kW while it runs. Cheap jets produce a narrow, fast stream you fight rather than swim in; this is one purchase where the good version is a different product, not a better one.

Test one before you design a pool around it. Some swimmers settle into the current within ten minutes and never miss a real lane; others cannot get past the fixed position, the noise, or the way the flow punishes an asymmetric stroke. Twenty minutes in a showroom answers a question no specification sheet can.

The running maths is friendly. A 6 × 3 m pool at 1.35 m is about 24 m³ — less than half a 15 m lane — so it heats quickly, holds its heat under a cover and stays at swimming temperature for a long season. If the goal is a swim four mornings a week, that can be worth more than the 12 m pool you could not quite fit.

What goes wrong in practice

1. Measuring the length on the outside

   The drawing says 12 m, the shell is 12 m, and the swim turns out to be 11.3 m once the cover pit and the coping have taken their share. Agree the clear water length in writing before anyone digs.

2. A step at the turning end

   It removes half a metre of swim on every single length and puts a hard edge exactly where your feet arrive. Steps go in a corner, or at the end you enter from and never turn on.

3. Going narrow to go long

   At 2 m wide your own wash meets you mid-pool and the stroke never settles. 2.5 m is the floor; find the extra length somewhere other than the width.

4. A light in the end wall

   It is the one light you look straight into, every length, every breath. Long walls only, set low enough that the beam passes under the swimmer.

5. Heating a long pool with no cover

   A lap pool is mostly surface, and surface is how heat leaves. Uncovered, the heat pump spends the whole season replacing what last night took away.