Building a Hot Tub with ICF Blocks: A Tennessee DIY Project

Last updated: September 2026

In this case study, I’d like to introduce you to Jeffrey and Dave, a DIY duo from Tennessee, USA, who are tackling a hot tub build with a difference.

This project uses insulated concrete form (ICF) blocks, which I thought would make a great video and article for fellow DIYers. So let’s get right into it!

Meet Jeffrey and Dave

Jeffrey and Dave had a clear vision for their hot tub and got in touch for help designing the plumbing and supplying the parts. Their chosen spot, tucked away down a set of steps, was perfect for a hot tub. They had some initial plans, and my job was to help turn that vision into something actionable. To do that, they hired me for custom design consultancy.

Building with ICF blocks

One of the most notable things about this build is the insulated concrete form (ICF) blocks. ICF blocks are hollow expanded polystyrene forms with the insulation built in and slots for rebar. Think of them as Lego for adults: you stack them up, fill them with concrete, and you’ve got a strong, insulated structure. It’s what I’d use if I built my own tub again.

Benefits of using ICF

• Insulation: it keeps the heat in, which is perfect for a hot tub.
• Quick assembly: the blocks stack easily, which cuts the build time.
• Durability: once filled, you get a solid reinforced concrete wall with little risk of cracking.

For more, see the best ICF blocks for building a hot tub, TubBlox and ICF hot tub walls and block, ICF or poured concrete?

Step 1: laying the foundation

Jeffrey and Dave started with a solid foundation, taking care to get the curved front of the tub in place, as you can see below. The foundation is the base for the hot tub walls and steps. My guide to building a concrete slab for a hot tub covers this stage.

Step 2: building the ICF structure

With the foundation done, the next step was assembling the ICF blocks. Once the main blocks were in place, they fitted the basic plumbing, including 2.5in pipes running through the walls and a return pipe. There’s more on pipe sizes in DIY hot tub plumbing.

Step 3: setting up the control room

The control room is cleverly tucked under the steps, and insulated to keep the equipment enclosed and protected from the weather. It houses the hot tub’s equipment and controls, making the most of the space while keeping it out of sight. See hot tub control room design considerations.

Step 4: the concrete pour

After months of preparation, it was time for the concrete pour. They had the concrete delivered, which made things simpler. Consolidating the concrete during the pour was crucial to get rid of air pockets and make sure the structure was solid.

Tips for a successful ICF pour

• Consolidate the concrete, gently. In an ICF wall that means a small internal “pencil” vibrator, not a plate compactor (a whacker plate is for compacting the sub-base, not wet concrete). Fox Blocks recommends a pencil vibrator, “quickly in and slowly out”, and Polarwall suggests a 25–32mm (1–1.25in) poker, or tapping the outside of the forms. Don’t overdo it, as too much vibration makes the aggregate settle to the bottom.
• Separate pours can be easier. A mono pour (one continuous pour for the floor and walls) has its advantages, but Jeffrey and Dave found that pouring the base slightly raised inside the ICF blocks was more manageable. I’d only recommend a mono pour if you have someone on hand who has done several before.

Curing and next steps

With the concrete poured and set, the structure was left to cure. Once it had cured, the next jobs were finishing the plumbing, waterproofing the interior and applying the final surface finish. See hot tub waterproofing, tile adhesive and grout.

Latest update

More ICF builds to follow: ICF block hot tub? Absolutely!, Adam’s ICF hot tub and out with the cedar, in with an ICF in-ground hot tub.

Planning your own ICF hot tub?

My DIY hot tub plans give you the CAD drawings, plumbing layout, parts list and video course for a range of standard sizes. If your site is awkward, like a spot down a set of steps, I can design around it with architectural CAD and a 3D plumbing design or plumbing consultancy.

What do you think of Jeffrey and Dave’s ICF build? Let me know 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