Here's How to Fix Your Sinking Deck

August 19, 2021

You step onto your deck to do a little barbecuing and notice something isn't quite right. Almost as if your deck is slanted to one side. After another look you realize what it is...

You have a sinking deck.

Images of emptying bank accounts and credit card charges spring up in your mind. How much does a sinking deck cost to fix? How do you fix a sinking deck? Is your summer trip fund about to be drained just to repair your deck?

Don't worry, a sinking deck doesn't have to mean a ruined summer! With a little DIY skill, you can repair your sinking deck with your own two hands (and some tools).

That Sinking Feeling

All decks are built on some kind of a foundation. Some foundations are better at resisting heaving or sinking than others. Deck blocks, for instance, don't resist movement very well. Screw piles, on the other hand, are excellent at defending against movement. If your deck is sinking, odds are it has something to do with the foundation.

(Soil also shoulders some of the blame when a deck sinks, but we'll get to that in a moment.)

Some symptoms of a deck foundation in need of repair are:

  • Areas of your deck that are noticeably lower
  • Decking or railings that are warped or splitting
  • Deck skirting that's pulling away from the deck
  • "Soft" areas of your deck where it wobbles or moves up and down

If you're seeing one or more of those problems on your deck, you're in need of foundation repairs. Ignoring a sinking deck will eventually lead to the structure failing completely. Tackle your sinking deck sooner rather than later - it's much easier to repair a deck in the early stages of failure!

Why Is My Deck Sinking?

Deck foundations are especially prone to sinking in Manitoba and Winnipeg because of our brutal winter weather conditions. Did you know our frost line extends to nearly 7 feet in some places? In fact, Winnipeg has the coldest weather of any major Canadian city. This intense weather does not play nice with foundations.

The soil in Manitoba, and especially Winnipeg, is also harsh on foundations. We have high amounts of clay in our soil, which creates a problem for deck foundations. Clay soils are what's known as expansive soils, which means they're prone to movement as the moisture content changes. When they get wet, they expand. As they dry out, they contract.

Manitoba Has Clay Soil, Which Can Be a Problem For Foundations

This constant expansion and contraction of the soil, plus the long cold winters, can wreak havoc on the foundation under your deck. So, let's talk about how you can fix it.

How Do I Fix My Sinking Deck?

There's a couple different ways you can go about repairing your sinking deck. You can either do-it-yourself or hire a professional.

Which is the right choice? Like most things, it depends. How bad your deck is sinking, what your level of skill is, and what kind of fix is going to be used all need to be taken into consideration.

There are three popular types of foundation, and your deck is likely built on one of them. These foundations are also your primary options when repairing a deck foundation:

  • Concrete piles
  • Concrete deck blocks
  • Screw piles

What option should you choose? Keep reading!

Do It Yourself Sinking Deck Fix

First, a warning. Nothing you read here is "guaranteed". Fixing a sinking deck can be a challenge, depending on the condition of the deck and your skill. If you try it yourself and end up with a deck that's worse than before, we aren't responsible. Practice good safety and use common sense. If it's a tough job or you aren't comfortable with it, hire a professional.

The goal is simple. You need to raise up the sinking area of the deck to make it level, then secure it with foundation support. Raising the deck shouldn't be too hard. Make sure you clear everything off the deck before working on it.

Unless your deck is built from solid oak (it isn't), you can probably lift it with a bottle jack or even a car jack. Again, be careful. If the deck slips, you could be injured or killed.

A Simple Jack Was Used to Lift This Sinking Deck

Once the deck is level, you need to shore it up with fresh foundation supports.

Choosing a foundation to secure your deck depends on your budget, DIY skill, time, and the location of your deck.

Concrete Piles

Concrete Piles Might Not Be The Best Foundation for a Deck

If you're looking to use a concrete pile, your process should look something like this:

  1. Excavate where the pile needs to go (remember, a foundation needs to extend below the frost line, which can be more than 6 feet)
  2. Place a cardboard concrete tube in the hole, backfill to stabilize it, and insert rebar
  3. Mix concrete and pour in tube
  4. Insert saddles (metal pieces that transition from the pile to your deck)
  5. Repeat for the number of piles you need

Concrete piles can be a good foundation under heavy, heated structures - but under light and unheated structures like decks they might not be the best choice. You need to excavate a very deep hole in order to get below the frost line, and that's difficult work. Plus, you need to deal with piles of dirt. Pouring concrete is also a challenge, as any moisture left in the concrete after curing will be a point of failure when winter comes.

If the dirt keeps collapsing into the hole you're digging, the soil could be too loose for a concrete pile. In that case, you might need to use an alternative such as a screw pile.

Concrete Deck Blocks

A concrete deck block install goes like this:

  1. Figure out where the blocks need to go, and excavate a 12" deep by 24" square area
  2. Fill the excavated area with ¾ gravel
  3. Put the block on top, and make sure it's level with your other blocks (remove or add gravel underneath as needed)
  4. Use a 4×4 to secure your deck to the block

Deck Blocks Are Cheap and Easy, But Don't Resist Shifting Well

Concrete deck blocks are the most affordable option here, less than $10 a piece in most cases. However, they're my least-favorite option. You may need to use a lot of them to ensure the deck doesn't sink again, and they're extremely prone to shifting with the soil. But, they're the easiest to install and the most affordable.

Screw Piles

If you've ever looked at deck foundations, you may have seen ground screw anchors at local building centers. Honestly, my advice would be to not even bother with this foundation type. While I personally believe that a professionally-installed screw pile foundation is the best option for fixing a sinking deck, DIY screw anchors have a huge downside.

How not to install a Reliable Screw Pile

The screw anchors you can pick up at a building center are usually only 50" long. That's not even close to being long enough to anchor below our deep frost line. A DIY screw anchor will experience major shifting over winter seasons, because it isn't deep enough to resist frost. So, while I do recommend a screw pile foundation, I do not recommend that homeowners use ground screw anchors from a building store.

What's the Best Do It Yourself Deck Fix?

As you can see, each DIY option has its pros and cons with no clear 'winner'. Concrete piles are less prone to shifting when compared to deck blocks, but they're expensive and hard to install. Deck blocks are cheap and easy to install, but highly prone to shifting. And while DIY screw anchors are easy to install and cheaper than concrete, they don't anchor deep enough to be useful.

My honest advice? When it comes to a sinking deck, sometimes it's best to let a professional deal with it. Making your deck level and ensuring that it won't just sink again can be a tricky project, especially depending on the location of your deck and the state of the foundation.

Professional Deck Repair

The alternative to a DIY deck repair is hiring a professional to put your deck back on level ground.

But, what should you look for if you're hiring a pro to do the work?

  1. Make sure whoever you're looking at hiring is trustworthy. Look up Facebook and Google reviews, and check out their website if they have one. Do they present themselves professionally? Are their reviews positive?
  2. Ask questions. Do they do this kind of work often? What about examples of their work? A good contractor will be happy to showcase the work they've done.
  3. Find out what method they use to secure a deck. Concrete and screw piles are the two most common methods for professionals. Of the two, screw piles are becoming a popular alternative to concrete, especially among Winnipeg deck builders. Check out WinDeck's comparison of concrete and screw pile deck foundations by clicking here.

Take some time to find a quality contractor to level your deck. There are too many hacks who are happy to take your money and give you poor quality work.


When it comes to fixing your sinking deck, there's no 'one answer'. In some cases, a DIY fix can be a great option. For others, you may find that a DIY option will be too difficult or time consuming. The best option is to assess your situation and be honest about whether or not it's something you can (or want) to tackle yourself.

If you want a free estimate on a professional repair for your sinking deck, contact your VersaPile professional by clicking here.


View More