Beneath the floor you walk on, portable sheds sit on 4×4 or 4×6 skids, which themselves sit on the ground or on blocks. On top of the skids is a series of boards (called “floor joists,” usually 2×4’s) that are the support system of the floor. Pretty much every builder uses treated skids, but not everyone uses treated floor joists. Some will only used treated wood for the outside band (or outer joists). The building will last longer (and the floor will actually be stronger) if the entire floor structure–skids and joists–is made of treated lumber.
As with the floor, the walls have a structure of boards that support the siding and keep the building from blowing over in a storm. These are called studs. Look for three things.
- The size of the studs. For years, 2×4’s (which, strangely, are actually 1.5″ x 3.5″) were standard. Now, to cut costs, some sheds are made with 2×3’s. Those are simply not as strong, and will not hold up as well.
- The distance between the studs. Standard is 16″ OC (“on center,” which simply refers to the distance between studs). Some sheds are built 24″ OC, but because the studs are too far apart, eventually the siding will start to cup and bow.
- The top plate–the horizontal member on top of the stud wall. Standard construction is to have a double 2×4 plate. Cheaper construction uses only a single 2×4 plate.
The rafters make up roof structure, and are what give the roof it’s basic form. Like the studs, the rafters should be 16″ OC. Just as your roof has two sides, so the rafters that hold up the roof are made up of at least two 2×4’s. Some rafters are held together by stamped steel “gussets,” and some by glued wood gussets. The wood gussets are probably actually stronger because of the way the steel plates are designed, but either work fine–as long as the rest of the structure is solid.
Just remember that when you’re buying a shed, you’re not just buying a shed–you’re starting a relationship. You are deciding who designs the shed to fit your particular needs, who will move it for you in the future (or even whether or not they will move it), and who you will call when you need repairs. For more on how to discover a great shed company, see 5 Questions to Ask Before You Buy.