There are two common footings options for a backyard deck, deck blocks or frost footings, including concrete piles, screw jacks, and many more. The biggest difference between each is from where the deck is supported, below the frost or floating on the ground. Which type of footings should your deck have?
Deck blocks are a good idea for low decks, decks around trees, areas with low frost levels and economical decks. It is a bad idea to use deck blocks when attaching the deck to the house, on stable ground or supporting elevated decks, pergolas or a roof. The use of deck blocks is rarely a good idea for decks requiring permits.
Well, that settles it. Deck blocks are good for some decks, but not all. How can you determine which is best for your deck? Let me explain more when deck blocks are a good idea, and when they are not.
First is your level of comfort. Deck blocks can only be used for floating decks. If you are not comfortable with the idea of your deck rising and falling with the ground. Then deck blocks are not for you. Frost level footings are more stable and can support more weight, and last much longer than deck blocks.
But if you are okay with a little up and down and are not building a deck to be enjoyed by your grandchildren, then maybe deck blocks are a good idea.
When Deck Blocks Are a Good Idea
Deck Blocks Are Better for Decks Around Tree Roots
Trees are the classic iceberg situation. There is more to the tree under the ground than above. A deck around a tree is an excellent way to enjoy the tree’s shades. But a deck around a tree has some complications, especially with roots. I have an entire article about deck construction requirements over tree roots.
But using deck blocks instead of footings simplifies all this. Deck blocks can be installed without disturbing the tree roots. Removing the concern about cutting critical tree roots killing the tree. With the deck block resting on the ground, away from the tree roots.
Care must still be used in adequately installing the deck blocks. You still want a good deck, not just an easy deck. But I will get to that at the end after we discuss when deck blocks are a good idea and when not.
Deck Blocks are a Good for Ground Level Decks
Deck blocks are never good for elevated decks, but for a ground-level deck, they may work. A general rule is any deck that is less than 24″ (600mm) in Canada or 30″ (760mm) in the States. But check your local building code. Frost levels and permits play into the answer.
But with many low-level decks, deck blocks are a good idea.
Deck Blocks are a Good for Areas with Low Frost Levels
If your frost level is less than 6″ (150mm) like in southern California or Florida, burying deck blocks a few inches down might be all you need to support your deck. As the frost barely penetrating the ground. Making deck blocks a good idea, still supported from below the frost line without all the mess of concrete.
Deck Blocks are a Good Idea for Temporary Decks
No, I am not talking disposable decks. Here today, gone tomorrow. But deck blocks would be good for that too.
I am talking about RV campground situations, out at the cabin or planning to move in a few years anyway. Places where a deck would be enjoyable for five to seven years but not an heirloom deck.
I love Mike Holmes and his call to build things better, but. Not everything we build needs to last forever. Sometimes it is better to spend less money and time on for the moment but not forever.
I have sometimes wondered about people paying for composite decking that will last 25 years or more when they plan to move in less than five. But I digress, back to deck blocks.
Deck blocks are a good idea in places like RV campground and Trailer parks, where you are not permitted to build something permanent. Deck blocks provide a good base for the deck without violating bylaws for temporary construction only. With deck blocks just like the mobile home beside it, you can jack it up on a trailer and move it to its new home without worrying about footings when the time comes. Hey, you can even reuse the deck blocks on the next site.
Deck Blocks Require Less Work
One of my shop teachers use to say, “A good carpenter is lazy and cheap.” A little for shock value, but really. If you want to build a deck for the backyard in a weekend, precast deck blocks may be a good idea. Digging and pouring footings will take a day or more of your weekend. Really eating up your deck building time.
Even when properly installed, deck blocks should take no more than 30 minutes each. Poured concrete footings will often take a couple of hours or more to dig and pour. Then it would be best if you waited at least a day for the concrete to set. Concrete blocks are ready to use out of the truck. A little base work on the ground, and they’re ready.
As an added bonus, if placed incorrectly. It is a lot less work to move a deck block than a footing. Just saying.
Deck Blocks Save Money
Like the say goes, “cheap”. If deck blocks will provide sufficient strength, they are cheaper than poured footings and require less work. How much cheaper depends on your frost level and deck footing requirements.
In Calgary, deck footings are required to be 10″ (250mm) diameter, 4′ (1.2m) deep will cost $60 in material. For the concrete, forms and post saddle. A deck block will only cost $15 for the deck block and base material like gravel under the deck block. Saving you $45 per footing. A floating deck saves you a minimum of $200 compared to a fixed deck in material alone.
But before we say that deck blocks are a good idea, there are some situations when deck blocks are not. There is a little weighing the pros and cons, but if you answer yes to one, deck blocks are a bad idea.
When Deck Blocks Are a Bad Idea
Don’t Use Deck Blocks on Soft or Unsettled ground
Building code and common sense says don’t build on ground that will sink. If the soil is soft or hasn’t had time to settle, deck blocks are a bad idea.
A few years ago I was building a deck in a new neighbourhood. And saw a guy climbing and frustratingly working under his deck. In the excitement of a new home, he had built a deck in the backyard before the ground had time to settle. Now his deck was sinking into the ground. I am not talking a fraction of an inch, but a sinkhole was forming below his deck block. With the deck tilting so much that a chair could slide on it. Not a good situation.
If the ground is soft or has been recently excavated. Digging footings down to undisturbed soil is a good idea. The dirt may look stable, but if over a soft pocket that hasn’t had a chance to freeze, thaw and settle. You may find out differently. Only use deck blocks where the ground can support them.
Don’t Use Deck Blocks for Decks Attached to a House
Deck blocks are only for floating decks, but if you attach the deck to the house, one side is floating. The other is not. Putting strain on the house’s foundation and potential for the deck to pull away from the house. If the house has footings below the frost line, so should the deck connected to the house.
You can build a deck beside a house without attaching it to the house. A freestanding deck not connected to the house is an option; click here to read more.
Deck Blocks are Bad for Elevated Decks
A deck higher than two feet (0.6m) from the ground needs stable footings. Deck blocks may work well for a ground-level deck were shifting a half or an inch or so will not affect the deck’s structure. But with height comes increase risk and potential for failure.
A one-foot deck post out of level, even a quarter-inch, is not a danger, but a post-eight-foot-tall will have much greater effect with the same degree out. That ¼” over a foot now becomes two inches at the top. The post tilting so much that only the edge of the post is supporting the beam. Not a good situation and this is why deck blocks are a bad idea for elevated decks. If a low deck sinks a 1/8″ it’s no big deal. If a deck block supporting an eight-foot-tall post is a much different story.
Related to height are pergolas or deck roofs
Don’t Use Deck Blocks to Support a Deck Pergola or Roof
For all the same reason not to block a high deck. A deck pergola or roof with its tall posts increases the impact of sinking or heaving along with the risk of failure.
If a few hundred pounds of timbers could fall on you and your guest, you want something that is stable. Deck blocks are good for supporting a low deck, but not something overhead. Overhead structures should be supported by permanent footings designed to support the load.
Deck Blocks and Permits
In most cities, if a deck permit is required, deck blocks are a bad idea. There are some exceptions, but most jurisdictions require frost footings for all permitted decks.
Often this has to do with attachment to a house or height. As we already mentioned, it’s a bad idea to use deck blocks for elevated decks and ones attached to the house. If its bad construction practice it will not be permitted. That’s a good thing.
So, if it still seems like a good idea to use deck blocks, here are a few pointers for installation. Deck blocks are as good as they are installed. Installed correctly, they are great. Wrong, well, you get the point.
Good Deck Blocks Installation
Most deck blocks have a 12″ (300mm) base and are 8″ (200mm) high. Some have a cavity on the top to hold a 4×4 or 6×6 post. Others also have notches allowing you to run a single-ply beam material over the deck block.
Plan out your deck and its required support to determine how many deck blocks you will need. Sketching out a simple plan on a scrap piece of paper helps to make it clear where to place each block and how many you will need.
It’s the base under the deck blocks that makes all the difference. Good base, good support.
- Dig out the topsoil and level the ground where the deck block will sit. It is essential to remove all organic material as this will make the block unstable.
- Place about 2″ (50mm) of non-organic drain material in the hole and compact. This is to provide drainage under the deck block to minimizing heaving. The water draining away and space between the rocks provided room for the ice to form without moving the block.
- Place the deck block and level with a two-foot or torpedo level. Add or remove base material to level the block as required. Make sure to compact before setting block to minimizing shifting later.
- Now that was easy!
Now you’re ready to build your deck. Enjoy your extra outdoor living space in your backyard, besides your RV or where ever a floating deck with deck blocks works for you.
For a complete guide to building a floating deck, click the link. I go step by step what I all did to build a floating deck. Pictures and all.