When building a shed, or any structure like it, the foundation is the most important aspect. A solid foundation means the shed has a better chance of remaining structurally sound for as long as possible.
There are various types of foundations but all should be strong enough to support a shed, no matter the size. One method that many would-be shed builders try is to use deck blocks for the foundation.
Deck blocks are a mass of concrete that have already been formed. They are made to hold lumber for vertical posts or wooden beams to support various structures.
While these tend to look similar, deck blocks can vary in size and shape. Some are wider at the base than their top or completely square. The question remains, is it safe to build a shed on these deck blocks?
In today’s article, we are going to answer just that. Read on to find out what you can expect when building a shed foundation out of deck blocks.
When to use deck blocks
Deck blocks are generally used as a more temporary form of foundation. These are usually simpler to use for free-standing or floating structures. When the construction is below grade (the top of the soil) and concrete piers are not required, deck blocks are typically used.
Most of the time, deck blocks are used for freestanding structures that are low to the ground. They are also quite common when mixing concrete becomes difficult to transport or use. Their simpler portability makes them a more popular choice, especially on sites where concrete mixing is not possible.
When not to use deck blocks
There are some times when deck blocks should not be used. One example is when you need to attach your project to a permanent structure that has frost requirements and/or protection. They should also be avoided in high wind conditions or high uplift situations.
These blocks are very rarely used for residential structures and are usually prohibited if you have to comply with frost heave regulations.
We highly recommend consulting with your local building code office to check whether deck blocks are allowed for your type of project. Different areas have different regulations and requirements. It is sometimes necessary to use auger-type tie-downs (metal screw-like items). These go into the ground to fasten and secure the structural framing members.
Other kinds of ground anchors are also used for Mobile Homes as these can provide lateral support and prevent any uplift during high wind or stormy situations.
How to build a shed on deck blocks
As your shed will be sitting on the blocks, you must level them off first. If you use posts on the blocks, the grade level will not be as important as the beams that sit on the blocks. If the beams are on the blocks, this will need a lot more attention when leveling.
To complete this task properly, you will need:
- A tape measure
- A level
- A mason line
- Safety glasses
- A laser level
- Knee pads
- Write out a plan for where the blocks will be situated. When you have a plan, ensure no steps are skipped or missed.
- Make a decision on whether excavation, compaction, or gravel needs to be placed to reach the shed’s height. Gravel isn’t always required but some people prefer to use it.
- Depending on the steepness of the ground where you want to build the shed, you may need to place your blocks in more unusual positions.
- Calculate where the blocks will go. Prepare this area using level string lines, or another level method/device.
- You should compact the ground to make it as level as possible.
- Once you have placed the blocks down continually, ensure that the structure is level with the longest level you have and then, square it up. Do not use a 2” level on 16” lumber as this will not show the proper level.
You can measure diagonals or use a 3-4-5 multiples technique. This is where you mark from one corner to 3” on one leg while the other side should be 4”. When measuring between the marks, it should be 5”. Such multiples can be used for larger sheds or structures.
Steel deck supports
Despite being stable bases, deck blocks can be hard to level if the ground settles. This is especially true once the shed has been built. If the ground becomes disturbed while you try to level the deck blocks, there will be a higher risk that they will become less level as time goes on. Fortunately, you can combat this and make the deck blocks adjustable.
By utilizing adjustable 4×4 steel deck supports, you can reduce the movements and create a level base for the deck blocks. These steel supports fit into the center hole of the blocks and are easily adjustable to make your shed as level as possible without much ground disturbance.
For this task, you will require:
- Deck blocks
- 4×4 adjustable steel deck supports for each deck block
- A concrete mix
Here’s how to do this method:
- Remove any loose material on the blocks with a wire brush.
- Using dish soap, remove any oil or grease from the steel supports.
- Separate the bracket and bolt from the sleeve at its base.
- Dry fit the base cylinder into the deck block hole. Ensure the corners are supported by the block so it sits firmly in the concrete.
- Fully embed the cylinders in the concrete.
- Place tape over the top of the cylinder to keep the concrete out.
- Wet the block to create a better bond between it and the concrete. Use a trowel and fill the hole and slots of the deck block with concrete.
- Tape end first, push the 4×4 cylinder into the concrete in the deck block’s center.
- Get the steel base plate and angle it so it rests on the deck block.
- Smooth the concrete out and remove any excess mess. Allow the concrete to harden and dry.
The foundation should now be ready for you to build your shed on top.