Floating decks are a great way to reduce cost and construction work. One of the drawbacks of a floating deck is movement.
By very definition, a floating deck will move. Sitting on the surface of the ground, it is as stable as the ground beneath it. A floating deck’s movement is often connected to seasonal freezing and thawing by can also be caused by other factors.
The ground’s stability under the deck is the most significant contributor of a floating deck’s movement. Followed by water management under the deck’s base, which compounds the movement caused by the freeze-thaw cycle.
If a floating deck has good support, it will move very little. Two things are required minimize a floating deck, drainage and stability properly. If the deck’s base drains away moisture from under the deck block, it will reduce water opportunities to freeze and move the deck.
Equally important is the stability of the base under the deck, not sinking under the deck’s weight or absorbing water. This is probably the single largest floating deck failure source when the ground below the deck gives way, the deck sinking into the ground.
I have witnessed this first hand. A number of years ago, I was building a deck in a new community. A few houses over, someone had recently finished their deck. Unfortunately, they had installed deck blocks on uncompacted ground. Once a level deck to watch their kids
play in the yard was now a slide into the yard. The corner of the deck sinking and the steps tearing off the deck under the stress.
But this does not need to happen. With the right base material, a floating deck will only be floating in name only.
Good construction practises will minimize a deck’s movement.
But before answering how to minimize movement, there are limitations in application.
Can a floating deck be attached to House?
Both by code and good construction practises, a floating deck cannot be attached to a house. It does not matter how well you build the deck. It does not matter if there is zero deck movement. A floating deck cannot be connected to the house. You can construct a floating deck beside the house, but a floating deck cannot be connected to the house.
Now with that out of the way, let’s get to the best floating deck construction practices. What can be done to minimize deck movement?
Stable Deck Base to Limit Deck Movement
All decks, regardless of size or height, must be built on stable ground. Without a stable base under the deck, it will move. The material under the deck block makes all the difference.
Compacted Base Material Limits Deck Movement
This is a requirement even with poured frost deck footings. In fact, compacted ground is a requirement of all foundations, from decks to houses to skyscrapers. The base must be compacted enough to support the weight of the deck and the people on it.
First, make sure that the ground under the deck block has settled. Like my story of sinking dirt and deck. If there has been a recent evacuation, extra care must be taken to compact the soil. Or give your yard and ground a few years of freezing and thawing to compress the ground.
One of the most unstable bases to build on is organic material. Loam, commonly called topsoil, is excellent for plants is its ability to hold moisture. But this isn’t good for decks, and it causes movement.
Like those little pet sponges that you soak in water to grow. Material with organic matter soaks up water, swelling and increasing in size, raising the deck above it. When the water drains and the material dries, the deck drops. This constant up and down pressure pushes the soil out from under the deck footings, increasing the deck’s movement.
It is good practise to replace this unstable topsoil with material that can be compacted.
Both gravel and sand have a higher bearing capacity than clay and definitely better than loam, topsoil, which practically has none. Compacting gravel or sand under a deck block will do wonders for minimizing movement.
Gravel also has another benefit.
Drainage Minimizing Deck Movement
Water is the disturber of decks. It can wash out the support under a deck. Water can freeze, shifting the deck above it. Water can swell the wood or the dirt, pushing the deck up before dropping it down. What you do with the water under your deck makes all the difference. In particular, drainage. If the water under the deck blocks can drain, it will move the deck very little.
Two common base materials with providing excellent drainage are gravel or sand. Both allow the water to drain away from the under the deck block but can be compacted. 2″ (50mm) of compacted gravel or sand under each deck block will minimizing the deck’s movement.
Installing Floating Deck Footings to Minimize Movement
The key to reducing movement in a floating deck is how you install the deck blocks. To help you build a floating deck with less movement.
Since deck blocks are cheaper and easier to install than poured footings, you can increase the number of blocks and reduce the beam’s size and joists if you want. Personally, I like to build it the same as a deck with frost footings.
Material Needed
- Deck Pier blocks, according to deck design
- Bag of gravel, one per Deck Block
Tools Needed
- Spade
- Compactor
- Small hand shovel
- Tape measure
- Spirit or a Laser level
Pier Block Installation
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!
Conclusion to Floating Deck Movement
By very definition, a floating deck will move with the ground. But with the proper care taken during construction and the correct base material under the deck blocks, this can be minimized. Creating a stable deck that can be enjoyed for years to come.
