DIY Hot Tub Case Study: Marc’s Build in an Awkward Space (UK)

Updated September 2026. I’ve tidied up Marc’s build story and added links to the guides that cover each stage in more detail. His videos and photos are all still here.

I love it when someone sends me a space that looks impossible and asks, “Can you fit a hot tub in there?” Marc from the UK did exactly that in May 2021. His space was an awkward wedge between the house and the garage, more of a pizza slice than a rectangle. Here’s how his DIY build went, stage by stage, in his own videos.

Background

Marc had been using an inflatable hot tub in this spot for quite a while. He’d been having problems with it for 16–18 months, and it had been repaired several times in the previous 12 months alone. He’d spent nearly £3,000 ($4,000) on repairs and still didn’t have a working hot tub. In the end it burst, and he’d had enough.

So he went looking for a better solution and found buildahottub.com. I was confident we could fit a tub in his space, even though it wasn’t a regular shape. First things first, Marc needed a design. (If you’re weighing up the same decision, I’ve written about it in Why build a hot tub when I can buy one?)

Initial contact and design

After finding the site, Marc and I talked through the design and drew up a scope of work. We went back and forth by email until he was happy with the layout. An odd-shaped space is exactly where a custom design pays off, because every seat, step and pipe route has to be worked out for that shape. I’ve explained how that works in Custom designed hot tub: the process explained.

Day Zero was ripping out the remains of the old inflatable tub and getting ready to dig. In the first video, Marc shows the space as it was.

Early May 2021: the dig

On day 5, a long bank holiday weekend, Marc started digging, aiming to get as much done as possible over the holiday. It was very hard going, because the ground was compacted stone. He brought in a digger, which took out a lot of it, but it still wasn’t as deep as he needed. So it was back to back-breaking digging by hand to get down to the level for the base.

That’s a very familiar story. I dug mine by hand too. For what’s under the water (sub-base, slab, insulation and so on) and how deep to go, see How to build a DIY in-ground hot tub: digging, base and blockwork.

Two weeks in: slab and first courses

Two weeks in, Marc had the slab in and was starting the corners of his blockwork. His plan was to go up two courses, pause, and fit the low-level pipework through the walls. With such a tight void around the tub, he knew that if he built the walls too high first, he’d struggle to reach down to the pipe level. That’s good thinking, and it’s worth copying if your tub is tight to walls or buildings.

The slab was a bit of a nightmare. It took him from 8am to 10:30pm, and it still wasn’t quite level. His next goal was to have the first two rows in and the seats ready by the weekend, so he could start the first part of the plumbing.

8 weeks in: control room and low-level plumbing

After 8 weeks, Marc was about halfway. It was time for the low-level plumbing. There wasn’t much room down the sides, so some of it couldn’t be finished until the structure was built. You can see the step, the skimmer and the plumbing heading off towards the garage.

By now, Marc’s main control room was done, in the garage. He’d mounted it on a board on wheels, so he can pull it out if he needs to work on it. I really like that idea. Access is one of the biggest things people get wrong with control rooms. I made mine too small and had to rebuild it. See Hot tub control room design considerations and The importance of control room position.

Marc was enjoying the build and was ready to get the electricity supply sorted. In the UK, that means a registered electrician. See A guide to hot tub electrics.

12 weeks in: plumbing and insulation

At 12 weeks, the blocks were in place and it was starting to look like a hot tub. Next was the plumbing, which was the part Marc most wanted help with. He found the plumbing designs we’d drawn up for him really easy to follow.

As the video shows, it wasn’t all straightforward. In a confined space, some of the fittings are very tight and very close together, which made some of the pipes and connections tricky. Marc did a fantastic job, and by this point the plumbing was almost done. If you’re at the same stage, How does hot tub plumbing work? and How to make the perfect PVC solvent weld joint are worth a read.

Then came the insulation. Marc dropped Celotex insulation boards down the sides, right next to the plumbing. That raises the insulation value of the tub and should make it much cheaper to run than a tub without insulation. More on that in DIY hot tub insulation.

Almost there

The next step for Marc was tiling. The weather was turning and he had a lot of work on, so we expected things to slow down for a while. It already looked fantastic. Great work, Marc. For tiling tips, see Hot tub tiles: everything you need to know.

At the time of our last update, the project was paused. I’ll share more here if Marc sends an update.

What Marc’s build teaches us

• An awkward space isn’t a deal-breaker. It just needs a proper design.
• Plan the pipework before the walls get high, especially in a tight void.
• Make the control room accessible. A wheeled board is a great trick.
• Insulate behind the walls while you still can.
• A DIY build takes months, not weekends. Here’s a real-world timeline: How long does a DIY hot tub build take?

Got an awkward space too?

If your space is an odd shape like Marc’s, try sketching it in the free Tub & Pool Designer Pro software. I can then turn it into architectural CAD and a 3D plumbing design made for your space. If a standard size fits, my DIY hot tub plans include the CAD drawings, plumbing layout, parts list and video course.

Building in a tricky space yourself? Tell me about it in the comments below. I read them all.

Cheers,
Andi

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Thanks - Andi

 

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