Can You Build a DIY Lap Pool? Size, Construction, Heating and Filtration

Last updated: September 2026

One of the most popular questions I get asked is whether you can build a DIY lap pool in your back garden or backyard. The short answer is yes, you can!

For anyone who isn’t sure what a lap pool is: it’s a regular pool, just longer and narrower, so you can swim real lengths without needing a swim jet. It’s built in much the same way as a plunge pool. The difference is the size, and a longer pool brings a few extra things to think about: a much bigger dig, a lot more water to heat and filter, and the pool safety rules. Here’s what to watch out for.

Lap pool or swim spa?

Before you commit, be honest about the space. A lap pool needs length. Here’s how the options compare:

	Lap pool	Swim spa / exercise pool
Typical size	30–50ft x ~10ft (9–15m x 3m)	14–20ft x 8–10ft (4.3–6m x 2.4–3m)
How you swim	Real lengths and tumble turns	On the spot, against a counter current jet
Water to heat	Around 30,000–60,000 litres	Around 12,000–25,000 litres
Best for	Long, narrow gardens, a side return, a boundary	Most back gardens

Dimensions.com puts typical residential lap pools at 30–50ft (9.1–15.2m) long and about 10ft (3m) wide. If you haven’t got that sort of length, don’t force it. A short lap pool means turning every few strokes, and a swim spa will serve you better. See How to build a DIY exercise pool and Can I build a DIY swim spa?

Size and depth

• Length: as long as the garden sensibly allows. Measure your stroke. Most people want at least several full strokes before they turn.
• Width: around 2m (6–7ft) is enough for one swimmer. Two side by side want 3m (10ft) or more.
• Depth: Dimensions.com gives 0.9–1.2m (3–4ft) at the shallow end and 1.6–1.8m (5–6ft) at the deep end. For a DIY build I like a single, even depth of about 1.2m (4ft). It’s simpler to build and plenty for lap swimming. A lap pool isn’t a diving pool, so don’t design it or use it as one.
• Steps: keep them out of the swim lane, in a corner or recessed into the end wall.

Construction

Building a lap pool is very similar to building a plunge pool. The biggest difference is the dimensions. You have the same construction options, and it can go in-ground or above ground, though I’d go in-ground every time. The ground supports the walls, and it looks far better.

• Concrete block (CMU): simple and cheap. Lay the blocks, tie in vertical rebar from the slab, then core-fill them with concrete.
• ICF (insulated concrete form): polystyrene blocks that act like Lego for adults. Stack them, add rebar, fill with concrete, and you get a strong, insulated wall in one go. On a pool this size that you want to heat, the insulation really matters. It’s what I’d choose. See the best ICF blocks.
• Poured concrete with formwork: possible, but on a long pool the formwork gets expensive and awkward. I wouldn’t recommend it for a DIY lap pool.

There’s a full comparison in Hot tub wall construction: what are the options? The same applies to pools.

The dig and the base

A lap pool is a big hole. A 12m x 2.5m pool dug to around 1.6m, with room for the walls and to work, is well over 50m³ of soil, and it bulks up by around a third once it’s dug. Hire a digger and book the muck-away before day one. Check for buried services first (LinesearchbeforeUdig in the UK, 811 in the USA).

Then it’s the same build-up as any in-ground pool or tub: compacted sub-base, a membrane, insulation, a reinforced slab with the main drains, a hydrostatic relief valve and pipe sleeves in place before you pour. I’ve written the whole process up in How to build a DIY in-ground hot tub: digging, base and blockwork. On a long pool, get your setting out spot on. Check the diagonals and use string lines, because a small error at one end is a big one at the other.

Finishing

You have three main options: paint, tiles or a liner. Each has its pros and cons.

Finish	Pros	Cons
Epoxy pool paint	Cost-effective, sturdy, easy to apply on a long pool	Needs repainting every few years. Doesn’t look as good as tile.
Tiles	Always a safe bet. Versatile, long-lasting, and you can tile lane lines and targets on the end walls.	The most labour and cost. Needs a proper waterproof membrane underneath.
Liner	Waterproof in one go, smooth underfoot	Very technical to measure, cut and fit, so best left to the pros. Can be punctured.

For tiles, use pool-rated tiles with a pool-grade adhesive and grout, over a pool-rated waterproofing membrane, and flood test before you tile. See waterproofing, grout and tile adhesive and hot tub tiles. For liners, see Can I use a liner on my DIY hot tub?

Heating

While it isn’t essential, I highly recommend some form of heating. Direct electric heaters are far too expensive to run on this much water. They suit small bodies of water like hot tubs. For a lap pool, go for an air source heat pump or gas.

Here’s why. It takes about 1.16kWh to heat 1,000 litres of water by 1°C. A 12m x 2.5m pool with 1.2m of water holds about 36,000 litres, so every degree needs about 42kWh of heat. At the Ofgem price cap rate of 26.32p/kWh (October to December 2026):

36,000 litre lap pool	Direct electric heater	Heat pump (COP of 4)
Raise it by 1°C	about £11	about £2.75
First heat-up from 12°C to 28°C	about £176	about £44

These are my own figures and ignore heat losses, so real costs are higher, but the gap between the two columns is the point. The US Department of Energy puts pool heat pumps at a COP of 3–7, working best when the air is above 50°F (10°C). You can find heat pumps for pools on parts4tubs.co.uk, and there’s help choosing one in How to choose the right air source heat pump for your hot tub or pool. For sizing a heater to your volume, try my heater size calculator.

What temperature? For lap swimming, cooler is better. U.S. Masters Swimming recommends 77–82°F (25–28°C) for competition pools, and warns that hard exercise in hot water can be dangerous.

Plumbing and filtration

A lap pool is very similar to a plunge pool in terms of plumbing, just bigger. The basics:

• Main drains: fit two, teed together, with certified anti-entrapment covers. The US Pool Safely rules for public pools require multiple drains to have their cover centres at least 3ft apart, so one person can’t block both. I’d follow that on a home pool too. See Installing a main drain.
• Skimmers and returns: on a long pool, use more than one skimmer and spread the returns so the water circulates end to end, with no dead spots. See How to install a skimmer.
• The pump: use a pool filtration pump, ideally variable speed, sized to turn the water over through the filter each day. If the control room sits below the waterline, the pump is flooded by gravity. If it’s above, you need a self-priming pump. Don’t use a hot tub jet pump for filtration on a pool this size. It’s built for the wrong job and it’ll cost you in electricity. See How to choose a new pool pump and the shocking truth about pool pump running costs.
• The filter: a sand filter is the best choice here. It’s cost-effective and suits a pool of this size. Yes, larger cartridge filters exist, but in general a sand filter is the way to go. See Sand filters explained.
• Top-up: a long pool loses a fair bit to evaporation, so consider an auto top-up.

Sanitation

You have plenty of options for keeping a lap pool clean and safe:

• Chlorine or bromine: the traditional choices. The CDC recommends at least 1ppm free chlorine in pools (2ppm if you use stabiliser), with pH between 7.0 and 7.8.
• Salt: a popular choice at the moment. A salt chlorinator makes chlorine from salt in the water. It’s not quite “throw some salt in and forget it”, but there’s less day-to-day work than dosing chlorine or bromine yourself. See saltwater pros and cons.
• UV, ozone or active oxygen: these help, but treat them as extras. UV and ozone only treat the water passing through the plant room, so you still need a residual sanitiser in the pool. I wouldn’t recommend ozone in most cases, although it has its place depending on the circumstances. See Do you need ozone?

Covering

If you heat your lap pool, cover it. Evaporation is by far the biggest source of heat loss from a pool, and the US Department of Energy says a cover can save 50–70% of heating costs and cut the top-up water by 30–50%. A solar (bubble) cover on a roller is the simple option. An automatic or slatted cover is easier to use on a long pool, costs more and can double as a safety cover.

If you don’t heat it, a cover still keeps the leaves and debris out, which means less work for the filter and for you. You could leave it uncovered, but you’ll be skimming a lot more.

Permissions and safety

• UK: the Planning Portal says outdoor domestic swimming pools often don’t need planning permission because they can be installed under permitted development. Check with your council if you’re in a conservation area, national park, green belt or near a listed building. The electrics are special: BS 7671 Section 702 applies, with zones around the pool, only 12V AC SELV equipment in the water, 30mA RCD protection and supplementary bonding. Use a registered electrician.
• USA: expect a building permit and an inspection of the NEC 680 bonding. Most areas also require a barrier. The International Swimming Pool and Spa Code sets the top at not less than 48in (1,219mm) above grade. See Do I need a permit? and A guide to hot tub electrics.

Common mistakes

• Too short to swim in. If you can’t get a decent length, build a swim spa instead.
• Setting out a long pool badly. Check the diagonals and use string lines.
• Underestimating the dig and where the spoil goes.
• Heating it with a direct electric heater.
• No cover on a heated pool.
• A single main drain, or a single skimmer at one end of a long pool.
• Treating UV or ozone as the only sanitiser.

Planning your own lap pool?

A lap pool is a custom job, because it’s shaped around your garden. Draw it in the free Tub & Pool Designer Pro software, and I can turn your design into architectural CAD and a 3D plumbing design that you can build from or use for permits.

If you don’t have the length, my swim spa plans (14ft x 8ft to 20ft x 10ft) pair with a counter current swim jet, and my 20ft x 10ft plunge pool plans are a good starting point for a bigger pool.

FAQs

How long does a lap pool need to be?

Typical residential lap pools are 30–50ft (9–15m) long. Shorter than that and you’re turning every few strokes, so a swim spa with a counter current jet may suit you better.

How deep should a lap pool be?

About 1.2m (4ft) of even depth is plenty for lap swimming and simpler to build. Some lap pools are deeper at one end, but a lap pool isn’t for diving.

Can I build a lap pool myself?

Yes. It’s built like a plunge pool, just longer: a reinforced slab, block or ICF walls, a waterproof membrane and a finish. Leave the electrics to a registered electrician, and a liner to the pros if you choose one.

What’s the cheapest way to heat a lap pool?

An air source heat pump plus a good cover. Direct electric heating on this much water is very expensive.

Do I need planning permission for a lap pool in the UK?

Often not, as outdoor domestic pools can fall under permitted development. Check with your council if you’re in a conservation area or other designated land, or near a listed building.

Thinking about a lap pool? Tell me the size of your garden in the comments below. I read them all.

Cheers,
Andi

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Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi