What is a Footer (or Caisson) in Deck Construction?

There’s obviously more to building a deck than just laying down some timber and hoping for the best. But when you look up what equipment you need, there’s a lot of construction jargon that might not make sense to you. One of the most important words you’ll see when wanting to know more about building a deck is ‘footer’ or ‘caisson’. 

Footers provide support for your deck. They are essentially a hole dug into the ground filled back in with concrete to create a strong base for your deck. You can use the word footer, footing, caisson, and pier when referring to deck footers as they all serve the same purpose. To support your deck and the weight transferred on the deck between people and furniture. 

Naturally, as progression goes, there are numerous types of footers that you can use depending on the size and style of your deck. There will be footers specifically recommended for certain types of construction and it’s always best to speak to a professional if you’re unsure. Carry on reading below for further information on footers, how they work and why you need their support. 

How Does a Footer Work?

The footings carry and evenly spread the weight of the deck and any weight on top of the deck such as people and/or furniture as well as any other constructed patio or pergola features. Decks will usually have a maximum weight load that they can handle depending on how they’ve been designed, and which materials have been used in the construction process, including your footers.

The find out the exact specifications of the size of footers for your deck project, you will have to consult your local building permit office. They can tell things like exactly how deep and how big in diameter the holes will have to be to pass inspection.

Here is a simplified step-by-step guide on how to install a commonly used footer and how a footer works:

Dig a hole

Once you’ve checked with your local utilities and building department that it’s safe to dig in your yard, dig a hole that goes a few inches below your frost line. If this is a permitted deck then you will have exact dimensions of how big the hole will be.

You don’t want to incur any extra fees or damage costs for hitting and breaking plumbing pipes so it’s imperative to find out where it’s not dangerous to dig. 

Compact loose dirt.

Compact the loose dirt in the hole so that the bottom is flat. Then check each hole’s measurements to ensure they are the same so each caisson works efficiently. 

Put a hollow cardboard tube in the hole (if necessary). 

Some deck projects may require the use of cardboard tubes to extend the caisson up out of the ground a certain number of inches. 

The concrete footers can be poured directly into the hole without using a cardboard tube for most projects but for some yards, the grade or other circumstance might dictate the use of these tubes to ensure the measurements are correct and the supports are the same across each footer. 

Get an Inspection Signoff.

At this point, you should have a set number of hollow holes in the yard and if this is a permitted deck project (as a very large number are) then it’s time to call in an inspection to get your permit signed off on caissons. 

Add wet cement and fill the hole completely. 

You can now start adding the cement to your caisson holes until they are completely full of cement. Smooth out the top layer and let the cement fully dry ensuring the posts are completely set within their footings before building your deck on top.

Add anchors if necessary. 

This is also the point in which you want to add any type of anchor system for making a caisson to post connection. For instance, you may choose to add ‘J’ anchors to the wet cement. You can then come back after the cement dries and install 4×4 post bases to the threads of the ‘J’ anchor sticking out of the completed caisson.

So how does it work?

The footing ensures a sturdy and strong deck even in harsher weather. They make sure ‘live’ and ‘dead’ weight is evenly distributed across the deck’s surface. Footings are an extremely important part of your decking especially if you have a larger and elevated deck. 

What is a Concrete Footer?

The above process is one of the most common footing installments for decks and is what’s called a concrete footer. 

The digging and the time-consuming process might take a few days and a lot of effort, but by using concrete footers you will thank yourself in the long run for the durability and longevity of this type of footer. 

Here are a few advantages of using concrete footers for your deck:

  • Can support larger items and more weight. 
  • Can be used for larger decks by area size. 
  • Sturdy and durable for longer-lasting deck support. 
  • Permanent, strong, and weather-resistant. 

What Size Footings do I Need for a Deck?

The size, shape, and number of footings you need for your deck will depend on the size and shape of your finished structure. 

Typically, most deck footers will not be spaced more than 8 feet apart. Larger footers for bigger decks can cope with more space between them. To ensure safety and sturdy decks, many builders will place the footers approximately every 4 feet apart, but it will really depend on the size and shape of your planned deck.

Here are a few options for deck footers that you might consider depending on the type of deck you’re keen to build:

  • Poured concrete footers. 
  • Pre-cast cement blocks. 
  • Buried post footings/footing pads.
  • Stackable cement piles. 
  • Screw piles.

You can find everything you need to know about deck footings and spacing here in the International Residential Code, Significant Changes to Deck Provisions.

What is the Frost Line?

When we refer to the ‘frost line’, we’re talking about the point at which the depth of the inground soil can freeze. The frost line can freeze and thaw depending on climatic changes and that’s why it’s important to ensure your footing is below the front line. 

To avoid your deck moving or ‘heaving’ as we call it from thawing and freezing soils, we dig and place the deck footers below the frost line. 

The frost line in Colorado is approximately 36 inches below ground level although some colder areas in Colorado can be as deep as 48 inches. 

To confirm the depth of the frost line in your area you should call your local building department to check. If your deck requires a permit, you’ll need this information handy on your application form too. 

What is Sonotube used for?

We mentioned hollow cardboard tubes earlier. For construction purposes, these are called Sonotubes. They are large, hardened, hollow, cardboard cylinders or tubes that are specifically designed for pouring concrete into them once placed in pre-dug holes. 

At TNT Home Improvements we use Sonotube for caissons that need to extend further out of the ground for permit reasons. They ensure a cleaner finish to the deck footing and are an easy way of keeping the post and cement directly where it’s meant to be to ensure weight coverage for the decking. 

Sonotube comes in a variety of sizes and lengths making it easy to buy or cut to measure with little waste. 

Because they’re made from reinforced cardboard, Sonotube is lightweight, cost-effective, easy to work with and they provide a perfect column-shaped footer for a more attractive design to the bottom of your deck. 

They also help to make measuring the pre-dug hole easier as well as keeping the cement and post in place, to the desired measurements.  


Ensure your deck is safe, stable, and secure by installing the right footings for your dream deck. If you want to ensure the safety and stability of your deck by having the footings installed accurately, you might consider hiring a professional company to build the perfect deck for your home. Here at TNT home improvements, we’ve dug thousands and thousands of caissons and have the expert equipment to make this part of the job a breeze.  

If you are located in the Northern Colorado/ Southern Wyoming area, then give us a call today at 970-663-2868 or fill out the contact form to make an appointment to discuss your next deck or home improvement project.