The performance of any form sheathing, whether made of plywood, metal, or fiberglass, is only as good as the performance of its support members. Form support is provided by various components. For wall panels, studs supported by cross members called walers provide direct support. For horizontal decking, joists give direct support. To hold support members in place, tension members are used. Because of their important function, support members must be carefully chosen to coordinate with sheathing selection.
Following are descriptions of various types of members available:
DIMENSIONAL LUMBER: The most commonly used support member, it is typically the least expensive material. However, reuse is limited because it can warp or split.
ENGINEERED WOOD: Because these components are factory-produced, their strengths are less variable than solid sawn lumber. These beams also tend to have longer life-spans and greater strengths than standard lumber.
ALUMINUM: These I-beams are light and durable. They cost more initially than wood but have a longer service life. Their low weight also makes them easy to handle, saving labor.
STEEL: Probably the strongest of the beam types, steel beams usually support greater spans or heavier loads than either wood of aluminum members. Their weight, however, makes them harder to transport and install.
ADJUSTABLE HORIZONTAL SHORES: Made of steel or aluminum, these beams used as joists under plywood sheathing offer flexibility and high load-carrying capacities.