In the ground
If you need your shed anchored against wind or up off the ground, then you will need a foundation that goes into the ground.
This would typically be pressure treated wood or a concrete footing or pier. But if you live in an area with frost, you will need to dig your footers below the frost line to prevent frost heave.
Another example would be a concrete slab. This would serve the dual purpose of a floor also.
An on grade foundation sits on the ground and is the least complicated to build. A skid foundation is the easiest. Place 2 pressure treated 4×4 or 4×6 skids on the ground, parallel to each other.
You can add some concrete blocks underneath for additional height or termite protection, or as spacers to level them. Then just build your shed on top of these skids.
You can also nail two 2×4′s or 2×6′s together to make your skids. The advantage of this is additional strength in the event you can’t find a single skid long enough for your shed.
A concrete slab is probably too complicated for the average weekend shed builder. It is also the most expensive of the floor options. But it has your several advantages. It will never rot or be eaten by termites.
Also a concrete slab will have no space underneath for little animals to live. Plus a concrete slab will hold a lot of weight, be easy to clean, and keep your shed firmly anchored to the ground.
But a wood floor is the typical option for most wood sheds. 2×4′s or 2×6′s 16 inch on center covered with 3/4 inch plywood will hold a lot of weight and is uncomplicated to build. As long as your skid and block foundation is on firm ground, you can store thousands of pounds on a basic wood floor.
The skids will keep your wood shed off the ground and away from termites. Being off the ground, air can circulate below the floor and dry out moisture between rains.
I would typically build the floor its self from un pressure treated wood for this reason. However if you live in an unusually wet environment you might want to build the entire floor, both frame and sheeting out of pressure treated lumber.
This table shows the cost to build each shed in terms of it’s size and cost efficiency. Including
- The area of the shed in square feet (Sq.Ft.)
- Cost to build next larger length (Cost/2 ft)
- And the dollar cost per square foot (Cost/Sq.Ft.)
You will notice that the larger sheds are much cheaper to build in terms of the cost per square foot.
And in cases of going from 6 to 8 ft, 10 to 12 ft, 14 to 16 ft, and 18 to 20 ft in length it costs very little to build the next longer size.
This is because certain sizes have a lot of waste and the next length up has very little or no waste. And you are paying for the lumber whether you use it in the shed or cut it off and throw it away.