It is important for any building to be level, and the type of structure, whether it is a shed, a garage, a backyard office or some other use, there are several factors that will determine what type of foundation will be required. No matter what the foundation, the building will not function properly unless it is level. The doors and windows rely on a level building to work properly, and the roofing system is designed to direct water off of a level building.
Take a good look at where your new shed or garage should go. If the building is a small building with a pressure treated floor system, chances are that it can use dry stack cinder blocks to provide a level foundation for the building or shed.
The next thing you need to take into consideration are the local building codes. Many people are under the mistaken impression that a portable building does not require a building or zoning permit. In almost every case a zoning permit is required, and depending on the size of the building a building permit may also be required. There may be some exceptions, for example if you are a working farm and the building is going to be used for the farm operations. In Virginia for example, all buildings require a zoning permit and buildings larger than 200 sq ft require a building permit and buildings over 256 square feet also require approved footers.
Types of Foundations
There are four main types of foundations, dry stack cinder block, dug and poured footers columns, crushed gravel, or poured concrete slab. The type of footer you need to use is primarily dependent on the type and usage application for the building, shed or garage that you are getting.
1. Dry Stack Cinder Block
This is generally the choice when a shed or building has a pressure treated flooring system and is small enough that it doesn’t require footers. Dry stack cinder block requires the least amount of preparation to the site. Generally as long as the site has been cleared and the ground is solid, and the slope is less than 18” from the highest point to the lowest point, the site is ready for the building or shed to be delivered and then blocked with cinder block.
2. Crushed Gravel Foundation
A crushed gravel foundation is generally used when a site may encounter moisture problems, as the crushed gravel can aid with drainage. When preparing a crushed gravel foundation, as a general rule of thumb, the pad should be at least two feet wider and two feet longer than the building or shed that is being placed upon it. The building or shed will probably still have to have some cinder blocks to level the building as even the most level crushed gravel foundations tend not to maintain a perfectly level surface. A lot of times when a crushed gravel foundation is put in, people put a frame around it to hold the gravel in place, if you do put a frame in, you need to make sure that it doesn’t impede delivery of your building. Any building going on a crushed gravel foundation needs to have a pressure treated flooring system.
3. Dug Footer Pillars
Dug footer pillars are generally used when a building is large enough for the government to require an inspected foundation for a building that has a wood flooring system. The depth of the footers is determined by your location and the local government with the frost line for your location playing a major role, i.e. the footers have to extend below the frost line. There are two types of categories for dug footers, the first is flush footers, where the site is level and the footers come flush with the top of the ground, the other is pillars for the instance where the finished site is not going to be level so the footers have to extend above the ground in order to provide a level foundation for the shed or building.
4. Poured Concrete Slab
A poured concrete slab is the most expensive option and is generally required for a building that is the size of a two car garage or larger and is going to be used to store cars or other gasoline powered equipment. Some municipalities will require a slab only when a garage door is in the building. Generally when a building is to be put on a poured concrete slab, the building is ordered without a flooring system and the concrete slab functions as the floor.
The choice is partly up to you, and partly depends on what your local government requires. It is also best to get all applicable permits approved before the building is put into place, that way you can be sure that you don’t have to do any remedial work to comply with the permit requirements.
Your comments or questions are welcome.