DIY 60×32 Garage Foundation: Excavation, Footings, Waterproofing, French Drains & Concrete Slab

If you’ve been following our garage build series, you know this has been a dream project for me and my family. This first post covers our complete DIY garage foundation — and it ended up being a full project of its own.

Project Overview

• Garage Size: 60′ x 32′ with 3 independent bays
• Foundation Walls: 8-inch concrete
• Drainage: Perimeter French drain + dedicated gutter drain system
• Slab: Reinforced monolithic concrete slab
• Insulation: 1½-inch R-Tech rigid foam in shop and bathroom areas
• Special Features: Floor drains, bathroom plumbing rough-in, future vehicle lift reinforcement, decorative stamped concrete medallion
• Timeline: Two and a half months, excavation to finished slab

Site Preparation & Excavation

When I wrapped up in mid-spring, I started planning our dream garage — you can read all about how I planned and designed the detached 6-car garage in the first post of the series. The final garage foundation footprint came in at 60 feet by 32 feet, with 8-inch concrete walls, a full French drain system, and a monolithic slab.

I cleared the woods and vegetation with my little tractor, marked everything out with poles and spray-painted lines, and started digging.

My tractor just wasn’t powerful enough. Once I got through about 12 inches of topsoil, I was stuck — we’ve got clay and hard rock down there, and the machine was too small. I called in a guy with a Bobcat to clear and level the area, because the platform had to be laser flat (we were using lasers for everything).

Digging the Footings for Our Garage Foundation

Then I called the company doing my foundation walls and footing. They brought their own small excavator and dug out the trenches for the footing and walls.

Installing Rebar

A couple days later they came back to set the rebar. I helped — together we tied a lot of it around the perimeter. Every 24 inches from the footing up into the walls, the rebar had to stick out and tie in. All of that had to be done before the pour.

We had a lot of rain. I pumped water non-stop — I even had to buy a second pump, because the trenches turned into a pool. I called the inspector, pumped it out, and everything passed.

Pouring the Concrete Footings

On pour day, the equipment couldn’t get close because it was so wet — the concrete pump ended up 80 to 85 feet from the site.

Then that contractor failed on me. They didn’t show for about three weeks — rainy season, dirt everywhere — and they ran into problems with the forms. In the end they couldn’t finish the work they’d started, and they told me to go find another contractor. So I did, which cost a lot more, but the new crew jumped in right away and started setting walls on the footing we’d already poured.

Garage Foundation Wall Construction

They brought their forms — metal and some wood — and set them up over a couple days. It’s a critical job; everything has to be laid out by laser. They did good work.

We had a lot of blocks to deal with because of all the doors, including an overhead door in the back. Due to the sloped landscape and my desire to have 10-foot ceilings on the first level, we had to raise the side and rear walls higher than the front portal walls.

We ended up with eight-inch-thick walls and a lot of anchors. On the front and rear portal, I added extra metal ties beside the anchors. They’re Simpson portal ties, those metal plates that add holding force against high wind.

Waterproofing the Foundation

With the walls up, my job was waterproofing. All those months of excavation and wall work, we’d had a pool of water in there — water coming from every direction, me pumping non-stop. Since we hadn’t backfilled yet, I knew this DIY garage foundation needed serious waterproofing or we’d be dealing with moisture problems for years. I started with Drylok Extreme on the walls.

Then I went to Menard’s for their self-adhesive leak barrier foundation membrane. That stuff is beautiful — really good glue that sticks even to dirty concrete. I sealed the top areas with flashing and ran four- or five-inch flashing tape over all the seams. It’s so thick that gravel or rock won’t even penetrate it. Everything was sealed tight.

Installing French Drains Around the Foundation

With water that bad, I wasn’t going to let it just sit there, so I put in a French drain at the bottom of the garage foundation. I laid four-inch perforated corrugated pipe around the perimeter — sloped, so it drains away from the garage out to our storm ditch. A properly built French drain is one of the best investments you can make in any foundation.

Over the pipe I laid geotextile fabric, then packed clean half-inch to one-inch rock around it like a jacket, wrapping it all the way around the corners so dirt couldn’t get in. Then I backfilled just enough to cover it.

I added a second channel too — four-inch triple-wall pipe from Home Depot, smooth on the inside. I ran it around the perimeter and tied gutters and multiple drains to it, so everything drains out as one big system. It’s basically parallel to the French drain, just higher, and all sloped. Took a while, but I did it all myself.

Underground Plumbing

Now we could finally backfill and clean inside. The footing contractor had left a lot of dirt in there, and between the rain and the sticking-out rebar, we couldn’t get in to clean until the walls were up.

With walls, foundation, and drainage done, I started working inside. My main concern was the bathroom next to the office — the toilet drain, the vents, all of it had to go in now, because it’s all getting buried in concrete. I ran PVC for the toilet, drain, shower, everything, all sloped with vents, and tied it into the main, which runs up to the second floor.

Gravel Base Preparation

Then I moved to the shop. I want that area warm, so the shop floor gets insulated. First I brought in a big load of gravel and compacted it — four or five passes, water, more gravel, again and again until I had a really solid base.

Foam Insulation & Vapor Barrier

Then I laid 1½-inch R-Tech rigid foam boards (Home Depot) in the shop and bathroom areas and sealed every seam. This part matters: if you don’t seal it, water gets between the panels, and when you pour, the liquid concrete can float the foam up and wreck your pour. I sealed all sides, even the perimeter. To be safe, I also covered everything with big sheets of plastic, taped at the seams, so no water could get through.

Slab Rebar Installation for a DIY Garage Foundation

Then I set the slab rebar myself — half-inch, 12 inches apart, in a grid, all tied by hand. Took a while, but I did it right. I love those rebar chairs from Amazon; I used a bunch. I had a drain channel down the middle bay, so because of the channels I had to run rebar under it to connect all the rebar together. Following standard rebar spacing guidelines for concrete slabs is critical to prevent cracking under load.

Reinforcing for a Future Vehicle Lift

My son also asked me to plan for a future lift in the right side bay. We wanted to reinforce that area in case heavy equipment gets placed there, so I doubled up the rebar placement in that bay.

Pouring the Concrete Slab

With everything set, I called my flatwork crew — the concrete slab pour is not a one-man job. They brought a big crew, up to ten guys, and they were there all day.

We weren’t just pouring the 60×32 inside; we poured around it too. There’s space between the new garage and the old one, and the slab that connects the old driveway to the new slab — everything had to tie together. I wanted a monolithic pour, so it all went at once. I drilled into the old driveway and epoxied rebar in to connect old to new — I always do that, using Sika Anchoring Adhesive.

The multiple drain grids had to be sealed up properly so the concrete couldn’t get into them, and at the same time we had to be able to finish the concrete around them cleanly, with the right slope — so they took a bit of time on their own. Once we were ready, the guys started from the far left outside. We called twice for extra concrete and ended up with four full ready-mix trucks. The pump ran all day. A lot of concrete, a lot of guys — we were wiped out. It was a hard day.

Everything got done in one day — all the drains, a floor drain inside at the car wash and detail area, and the drains around the perimeter were sloped and finished correctly. We ended up with a nine-inch slab in some spots, a little more than I planned, but that’s fine. The bathroom was roughed in, fixtures in place. After all those muddy days, we finally had a solid concrete slab under our feet.

Stamped Concrete Details

But it came out beautiful. In the middle bay I rented a five-inch medallion stamp — I wanted something special there, since it’s the center of the garage, it’s exposed, and we walk through it a lot. I stamped a medallion in, and I did it myself with help from the guys.

For the little area connecting the old driveway to the new garage, I used a decorative stone-imitation stamp for better traction — just in case we get a little ice outside the garage, we’ll still have grip.

Driveway Expansion

I widened the driveway the next week — about 11 feet by almost 50 feet, adding another pass alongside the old driveway. Concrete took a lot of time and a lot of resources.

Lessons Learned

I didn’t plan on it, but our complete DIY garage foundation — from excavation to finished slab — took two and a half months. Plan for that kind of timeline if you’re tackling this yourself. Inspections stack on inspections, contractors can let you down, and the weather will make things harder than you expect.

If I were starting over, here’s what I’d do differently:

• Be careful with contractor selection. My foundation contractor didn’t show up for three weeks, left a bunch of dirt inside, and we had to redo some of the trenches later — and it cost me more for the foundation in the end.
• Have excavation and grading contractors lined up and ready. You want someone you can call to dig or backfill on short notice, the moment you need it.
• Be prepared for the unforeseen — especially drainage and waterproofing. Those problems are coming whether you plan for them or not, so budget the time and money up front.

But we ended up with a solid foundation, and the next job is framing — which I really love. Building this DIY garage foundation from scratch was one of the most challenging and rewarding things I’ve done. The next post is going to be all about framing.

In the meantime, good luck with your foundation or your garage build. You got this.

Shop This Build

• DRYLOK Extreme Masonry Waterproofer (Home Depot)
• Self-Adhering Foundation Membrane 200 sq ft (Menards)
• Henry 1½” R-Tech EPS Rigid Foam Board Insulation (Home Depot)
• HERCULES Rebar Chairs — 50 Count (Amazon)

Related Posts in This Series

• How I Planned and Designed My Detached 6-Car Garage From Scratch
• How I Built a Wall-Mounted Garage Car Wash & Detail Center — an IKEA Hack
• Framing (coming soon)
• Roof Trusses (coming soon)
• Garage Door (coming soon)