How to DIY Concrete Deck Footings

There is one major project left on the Main House Fixer Upper here at One Hundred Acres Home, and that is the replacement front and back decks. We’ll we’re finally ready to get the new decks in, in full DIY fashion. This post will show you how to DIY your own concrete deck footings for large redwood decks.

Below is a before photo of the back deck during demo. You can see how decayed the old joists were. The deck basically crumbled under a crowbar, and the ledger was fully rotten through.

Once we got the decks demo’d, I built some quick temporary stairs to appear our home insurance and to give access to the house while I completed all the other projects on the Main House before finally getting to the real replacement decks. Below is a photo of the temporary stairs and landing at the back door.

You can see how rotten the siding is from the old deck ledger. It was rotten fully through in some spots so rats were getting into the crawlspace and burring holes in the floor insulation. Lol. So yeah, I replaced the siding, doors and windows, and even replaced all the rat-laden floor insulation before finally coming back to the deck project.

Deck Drawings and Permit Submittal:

Before you just start digging holes, you’ll likely need proper plans or drawings of the deck. Most building departments require a permit for decks serving exit doors, so make sure to check your local requirements.

While I was working away on other projects, I got the permit drawings and submittal documents together for the replacement decks. I submitted the documents to the building department and had to wait about a month for their review. With that done, I had the OK to start building! And because this is a total DIY deck build, I also needed to sign an Owner-Builder form and acknowledge a ton of risks that I’d be taking on. But don’t worry, it’s fine.

If you want some proper guidelines on how to build or design a deck, check out this prescriptive guide for residential decks.

Depending on how complicated your deck project is, you may need to hire a licensed engineer and/or an architect for the permit drawings. Best of luck to you. I hope you get approved to build quickly!

Dig Footing Holes:

Alright, let’s get digging! The ground does not freeze where I’m at, so the footings only need to be 12 inches below natural grade to meet code here. However, we are required to design for a heavy 60 psf live load due to some decks and balconies collapsing recently. So the size and spacing of these footings may seem a bit excessive.

Below is a photo of my progress digging for the back deck. Because I’m doing this myself, and I wanted to save the headache of building square concrete forms, I’m using concrete pier tubes for the formwork. More on that in the next section.

Outside of the rock areas, I dug the holes with a simple shovel and moved the dirt in a wheelbarrow to an area that could use it.

The pink yard flags dimension the footing spacing along the house. Since I’m using formwork, I dug oversized holes and will very carefully measure once I set the forms.

This area has a lot of large granite rocks, so I occasionally used a jack hammer to chisel away an area for a footing.

One last important point, see the two rows of footings with one row very close to the house? That is because the replacement decks will be built as stand-alone decks. Aka, there will be no ledger connection to the house. I really don’t want to create the rot conditions like we saw with the old siding. I replaced the old siding with T1-11 plywood siding. Since it’s a wood product, it’s still susceptible to rot. But now there will be a 1/2 inch gap between the siding and the deck and, woohoo, no rot!

I’m replacing both the front and back decks. Below is a progress photo of my footing holes along the front. Here you can see the replaced siding with board and batten trim and somewhat janky but functional temporary stairs.

Formwork for Concrete Deck Footings:

To avoid the headache of constructing square formwork for the footings, I opted for 16 inch diameter concrete tube forms. Below are the two 12 foot long tubes that I picked up from a local building supply store. The truck lumber rack came in really handy here. However, these tubes were not cheap. If I remember correctly, they were about $60 each. I figure I’m saving a ton by DIYing this project, so I’ll splurge a bit here to save time.

Next, I cut tubes into sections for each footing of about 14 to 16 inch lengths. That allowed for at least 12 inches below grade and a few inches above. The tubes are made of basically really stiff cardboard, so I was able to cut them with the Japanese hand saw in the photo below. I also tried using a powered oscillating saw to speed up the process, but it was too messy.

Place Concrete for Deck Footings:

With the holes dug, the formwork in place, and the footing rebar on hand, I called the building department for a footing inspection. Thankfully, this is a relatively simple job, and I got the “OK” to place the concrete footings.

Below is my concrete progress on the front deck footings. These were placed in colder weather, so I mixed in warm water from the house using that red pot. This will help the concrete cure properly since our well water is very cold and it was about 45 degrees F. outside during the day. Basically, I don’t want the concrete to start off too cold or it wont cure properly. And I definitely don’t want it to freeze! If you’re interested in how to cure concrete in cold conditions, check out this post here.

Yes, you can buy a concrete fixer, but that’s just another tool to rust in the yard. So I mixed concrete in a large wheelbarrow you can see in the photo below. Each footing took about three 80 pound bags of concrete. I mixed each footing batch in a wheelbarrow and then simply placed the concrete for each footing with a shovel. The concrete should have some slump, but it should NOT be soupy! Follow the directions on the concrete bags.

Below shows you the rebar I placed in each footing. The rebar is a bit overkill, but I’d rather build something sturdier than it needs. I placed about 3 inches of concrete base and then set the rebar in the concrete.

With the concrete still wet, I very carefully set the post bases for the deck posts per the photo below. These are Simpson PBS post bases with a 1 inch standoff base to help reduce rot in the wood posts.

I used a string to make sure the post bases were all in-line. And I measured everything excessively before placing. Use a small hand-held level to help place the post bases level in the concrete.

Curing Concrete Footings in Cold Weather:

So, the chemical process of curing concrete actually releases some heat. That’s a good thing in cold weather because you do NOT want the concrete to freeze while it cures. If it freezes, the water in the concrete mix will crystalize and the concrete won’t cure properly. More on curing concrete in cold weather here.

It was forecasted to drop into the mid-20’s Fahrenheit overnight while I was working on these footings. That’ right on the boarder of when concrete will start to freeze but, like I mentioned, it does heat up a bit so it won’t freeze right at 32 degrees F.

To keep my new footings warm and cozy, I covered them in towels and small electric blankets that usually keep my cats warm at night. The cats had to rough it for a few days while I warmed each footing at least one night before moving on to the next.

Below you can see my gumdrop footings being kept warm and cozy. Ha! Silly. But it worked!

Below is more progress on the front deck footings. I kept the temporary stairs in place as long as I could because we’re living in the house I do this work! Once I move those stairs away, we’ll be using a ladder for in and out of the house. Our cats will not be happy about that.

Completed Replacement Deck Footings:

Here are the finished footings for the back deck! Remember, they are beefy because of the design 60 psf live load. Also, the footing line along the house allows the deck to be separated from the house. That way we have a 1/2 inch air gap and no rot!

The footings along the back deck do have some elevation change. The wood posts in the post bases will vary in height so that the deck beams are level. I triple-checked that the high footings allow for all the framing we need. More on that in the next deck framing post. Stay tuned.