Building a Shed: 2 Ways on How to Square a Shed Foundation

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By this time, you might have found the right location to build your DIY shed, accomplished all the building requirements, and now, you’re ready to get started. In building a shed, you always start with the base. 

The base is an important part of any structure. For your DIY shed, the base helps make the ground level, supports the weight of your shed, and allows air to circulate beneath. To achieve a stable and sturdier base, you have to keep your shed as perfect square as possible.

In this article, we’ll teach you how to square a foundation for a shed using two simple methods, but first, let’s talk about the three commonly used shed foundations:

1. Deck blocks

Deck blocks are the easy-to-install and inexpensive pre-formed mass of concrete used as support for any structures. Their top is formed with shape to hold beams or lumber for vertical posts. Using deck blocks as a foundation in building your DIY shed is helpful in ensuring you have an evenly spaced out area since it’s a material you can adjust easily. 

You have to note though that if you’re planning to store heavy equipment in your shed, using deck blocks as your shed foundation is highly discouraged. Deck blocks have the tendency to sink into the ground over time, and you wouldn’t want this to happen to your shed.

2. Concrete slab

A concrete slab is what’s commonly used as a structural element in modern buildings. It’s a flat, rectangular surface made of concrete. It is also considered as the most sturdy and most long-lasting foundation for sheds. 

Using concrete slab as your shed foundation will allow you to store heavy equipment, including vehicles. Although it is an ideal material to use for a DIY shed, it can also be time-consuming and expensive. Since concrete slabs are permanent materials, you have to ensure you’re doing it correctly.

3. Concrete blocks

Concrete blocks are similar to concrete slabs in terms of durability, but it is an easier alternative when it comes to installation. All you need to do is to follow the right leveling when you’re creating your layers. It is also a cheaper option compared to concrete slabs, but like deck blocks, they are not the best material to cater to your heavyweight shed equipment. 

Now that you are familiar with the basic shed foundation, let’s move on to how to square your shed foundation. 

Why is it important to square a shed foundation?

Having a near-perfect square shed foundation means having each corner close to a 90-degree angle. With a perfectly measured foundation, you only need one measurement for your walls and roof. This way, you wouldn’t need to do any unnecessary adjustments to your existing materials just to make them fit. 

There are two ways to do to get a square shed foundation:

1. Using a string and the 3-4-5 method

  • Post boards into the ground. Make sure they are placed in all the four corners of your shed. 
  • Using a string, run it around three boards to create a triangular shape. Make sure each side is straight and they are tightly and correctly placed in each corner.
  • Measure each side. The measurement for each should follow the 3-4-5 rule. Therefore the measurement of all sides of your triangle should fall between the multiples of the 3-4-5 rule. Correct measurements should be 6-8-10, 9-12-15, 15-20-25, and so on. All four corners should achieve this measurement to get a perfect 90 degrees. 
  • Adjust the placements of boards, if necessary.

2. Using a tape measure

This is a simpler method. You only need a tape measure and to use the diagonal measuring method.

  • Place your tape measure in one corner of the shed and stretch it out until you reach the exact opposite corner across your reference point. You should be measuring diagonally here.
  • Get the measurement.
  • Repeat the same method starting from the other corner. Make sure you get the exact same measurement. 
  • Adjust accordingly.


While it is possible to still build a shed without a perfectly square foundation, it can cause more troubles in the work process later on. It’s better to get ahead with the safest start to ensure a smooth working process. Don’t forget to check your measurements constantly as you go along your project. Double-checking if you’re still within the target angle and that nothing has moved would ensure a successful and perfectly squared shed.

For more tips, guides, and tutorials about shed building, regularly visit our site. We post useful and easy-to-follow content that can help you make your shed foundation plans come to life. Visit My Shed Plans for tips on how to make your dream shed.