Floating Deck Defined[+Answers to Your Questions]

The most economical and easiest deck to build is a floating deck. If you are looking for a platform to enjoy your backyard from. If you are an eager DIYer desiring to learn, building something at your place to enjoy a floating deck is an excellent choice.

Before going too far, I should define what a floating deck is.

A floating deck is a ground-level deck supported by free-floating footings. Often precast concrete deck blocks. The biggest distinction from other decks are the footings. Floating decks are not supported by frost footings but rather “float” on shallow footings.

Floating decks are attractive, being more economical and easier to build than other decks. Making them often the right solution for your backyard.

But you still have many questions. Questions about floating decks.

Where can you build a floating deck?

Are floating decks safe?

Can a floating deck include a pergola?

Which is why you are researching floating decks.

Having built many decks as a carpenter, including floating decks. I hope I can help you with your research by answering some of these questions. Let’s start with the most pressing floating deck question.

Are Floating Decks Safe?

Yes, feel free to enjoy your floating deck. It is safe. If built properly.

Sorry for making you nervous again.

But that is what it falls down to.

Sorry again for the image.

But floating decks safety has less to do with strength but more about seasonal changes. Floating decks are safe to use but potentially will move with seasonal changes. Of course, this will be more dramatic in regions with significant freeze and thaw cycles like Winnipeg, Manitoba, but much less in Miami, Florida, where practically speaking, all decks are floating with the frost level being so high, impacting the depth of footing little.

The most significant factor for a floating deck is if it is built correctly.

Are the correct size joists used? Spacing?

Are there sufficient footings?

The simplest solution is building your floating deck to code, even when you don’t have to. Since in most jurisdictions, permits are not required. I will get to that more later.

How Much Weight Can a Floating Deck Hold?

If the correct material is used and correctly constructed, floating decks are as safe as any other deck. Safe enough to support 50 lbs per square foot. To learn more, read how much weight can a floating deck hold.

Now for the elephant in the room.

Are Floating Decks Stable?

Don’t let the name trick you. Floating does not mean the deck is moving like a boat on the open seas or even a dock on the lake.

During the summer, when you use your deck the most, a floating deck is stable.

Spring is the most volatile time for a floating deck. When the ground under the deck thaws. The ground shifting and the deck supported by it. In extreme cases, the corner of a deck heaving or sinkhole swallowing the pier.

As I said, this is generally limited to the spring season.

When your morning commute gets a little rougher with potholes, it’s time to check under your deck. Are the footings still correctly supported? If not, gravel will need to be added or removed to level out your deck again.

Speaking of level.

Can You Build a Floating Deck on a Slope?

Now, this is a little trickier, Yes and No.

You can build a floating deck on a yard with a slight slope. A slope of less than 1″ per 1′ for example. This may not seem like much, but it adds up quickly.

The biggest limiting factor is the height of the deck.

A floating deck is limited to being a ground-level deck. Which in most states is a deck less than 30″ (760mm) from the ground. Not sure why I converted that to metric, does anyone in the States use millimetres?

In Canada, a ground-level deck is even lower a 24″ (600mm). No, in Canada, we still build in imperial, but code books are in metric, which can get a little confusing with all the converting.

But to our point. A 12′ (3.6m) floating deck resting on the ground at one end on a sloped yard may be too high on the other end. Going from 8″ (200mm) on the low side to 26″ (660mm) on the high side if the yard slopes 1 ½” over afoot. (38mm/300mm).

A greater sloped yard will make this even worse.

Another problem with a floating deck on a sloped yard is drift. The deck floating down the hill as time passes.

I am sweeping up dirt from my yard all summer because of the dirt drifting from the sloped yard onto the sidewalk.

Not like a sled down a sled hill but a slow drifting as the seasons’ pass. With the potential of the footings collapsing as some drift and others don’t.

Increasing the importance of anchoring or bracing. Something to fix the deck in place.

Now, what is something big that you could tie it to? How about the house?

Can a Floating Deck be Attached to House?

No.

A floating deck cannot be attached to the house. A floating deck can be built close to the house but not connected.

What is that saying?

“Unequally yoked.”

Paul was not talking about deckbuilding, or at least that I know about, but the principle still applies.

Your house and floating deck are not equalling in footings. The house is stable, and the deck is floating.

The strain between the house and deck can cause the deck to pull off or worse. Damage the house footings and wall with pressure on the foundation that the house was not designed for.

A deck supported with frost footings is fine for the house with equal vertical pressure. But a wild card of a floating deck can be too much for the deck and house.

Because of this, many floating decks are built in the yard, free from any concerns about the house.

How Close Can a Floating Deck be to the House?

Touching but not connected. You can build a floating deck right beside your house as long as they are not attached.

Often a small gap like a ½” (12mm) between the house and deck will allow unhindered movement.

A design element to be aware of is movement at the door. If the deck heaves or drops in the spring, making your nice step from the house awkward.

What was once a nice step down to the deck now is a significant drop.

Because of this, I often favour attaching a deck besides house.

And the fact that most new houses come with a deck ledger for the back door making attaching so tempting. A couple of hours of digging and mixing concrete and a night to let it set up, and I don’t have to worry about it for years to come.

Can You Build a Pergola on a Floating Deck?

A pergola on a floating deck is a beautiful touch, especially on a floating garden deck. Adding comforting shade while you enjoy a book on the deck or a moment to listen to the birds and bees enjoy all your hard work.

But…

Yes, a word of caution adding a pergola to a floating deck. Everything is amplified with distance and height. A small change on the deck can make a huge change to the pergola.

Pergola often being 8′ (2.4m) tall. One corner of the deck heaving a ¼” (6mm), so tiny you won’t even notice it. But that small change can put the post out of plumb over 2″ (50mm). Now that you will notice, and can put a strain on the pergola and deck frame.

Small changes on a floating deck are big changes to a pergola.

Movement can be minimized by compacting gravel under the footings before building the deck. Which I would advise at all times but super important if adding a pergola to the deck.  

Can You Build a Floating Deck Over a Septic Tank?

Only if you have an access door or the floating deck is small enough to lift off.

Bio-sol recommends that a septic tank be cleaned out every 2 years but sometimes can wait as long as 5 years depending on where you live.

That may seem like a lot of time, but summers and winters move quickly.

You don’t want to be hiring a crane every time you need to pump out your septic tank. The deck may look small, but even at 10 lbs a square foot, a 10×10 deck is 1 000 lbs. That’s a lot of muscles to move. I am not sure I have that many buddies who want to put their backs out of place.    

Afloating deck is a great way to cover that ugly lid and create a usable place in your backyard, but design wisely. Don’t create a bigger problem.  

Do Floating Decks Rot?

No more than other ground-level decks. But decks close to the ground will rot quicker than decks with sufficient ground clearance and ventilation.

Deck ventilation is one of the often overlooked parts of a deck design. Wood needs to breathe. That includes the wood joists under the decking. They will absorb moisture from the ground and need to expel it into the air to prevent rotting. Decks without sufficient ventilation will rot quicker.

Compounded with the moisture issue of ground-level decks is proximity to the ground. Dirt is made up of millions of helpful fungi making the soil rich and helping plants to grow. By breaking down material. Including your deck. A deck floating on the ground will increase the amount of fungi on the wood, increasing rot.

This doesn’t mean you cannot build a deck close to the ground or even slightly buried. You just need to take steps to prevent deck joists from rotting. The best way for decks in contact with the ground is using wood treated for ground contact.

Where to Build a Floating Deck?

Floating decks are sometimes the best decks to build. Beyond savings in time and money.

For example, around a tree. A tree with all its roots is both hard to dig frost footings and can damage or, worse kill the tree. Often a better solution is a floating deck. With minimal ground disturbance, you can enjoy the shade of the tree on your deck without damaging the tree’s roots.

Floating decks are also a great option to act as a cover over an unsightly spot in your yard.

Like a septic tank lid or a bald spot on the lawn that just won’t grow grass.

A floating deck is an economical solution requiring minimal work. And when you are ready for something different. A floating deck can be moved to another location or just removed.

Do You Need a Permit for a Floating Deck?

One of the advantages often touted about floating deck is that they don’t require a permit.

But here are a few cities with their deck permit requirements.

In Calgary, a deck less than 24″ (0.6m) doesn’t require a permit.

In Austin, Texas a building permit is not required for a deck less than 30″ but a zoning permit is.

In Los Angles, California a deck under 30″ from grade a permit is not required.

In Miami, a permit is not required if the deck is less than 18″ from the ground.

In Chicago, if the deck is less than 30″ from the ground a permit is not required.

In Helena, Montana, a deck is exempt from a building permit if it meets a list of requirements, less than 30″ being one of them, along with not being attached to a house.

Just scanning over this list of cities, and when a deck permit is required, it is much more a question of height than footings. Decks that are low enough do not require a permit. Higher decks with increase risks if they fail. Thus require a permit. If floating footings or frost footings support the deck is irrelevant.

This is surprising because often, people claim floating decks don’t require permits. More accurately, ground-level decks often don’t require permits.     

Check with your jurisdiction before building your deck. Regardless if it is floating or not.