In most cases, do-it-yourself projects do not go deep into specifics. Usually, you can assess just by how it looks and, if it is sturdy or not.
t the hardware store, someone will probably recommend what kind of wood you should get, based on your project. So how much weight can a 2x4 support, exactly? There is no one answer, as it depends on a few factors.
Type of lumber
A 2x4 wood can come in either softwood or hardwood. Softwood is more common and cheaper because the trees grow faster than hardwood trees. The 2x4’s are usually soft wood. Their common uses are in framing, but you can also use them for other things like furniture and decoratives.
There are 2x4 hardwoods as well. They take longer to reach maturity, which is why they can be expensive. The 2x4 hardwoods are commonly used in flooring, woodworking, furniture, and cabinetry.
When choosing the type of 2x4 lumber, you have to consider what you are going to use it for. What are you making? This helps you determine what hardness you might need.
There are so many kinds of trees, thus so many varieties in strength and quality of lumber. To help make things easier, you can determine the right kind of wood for the right purpose by following certain standards. For softwood, take note of National Softwood Lumber Standard provided by the US Department of Commerce. For hardwood, you can follow the grading system provided by the National Hardwood Lumber Association.
There are generally three classifications of softwood lumber. Furthermore, each classification has different grading systems.
The first classification is yard wood. It has two categories, which are common yard lumber and select yard lumber. Common yard lumber has three different grades while select yard lumber has two different grades.
As the name suggests, structural lumber is common in construction. It has seven different categories: light framing, structural light framing, studs, structural joints and planks, beams and stringer, posts and timber, and appearance framing.
Shop and Factory Lumber
Shop and factory lumber is lumber that is meant for remanufacturing and for non-structural purposes. Shop and factory lumber are commonly used for doors, boxes, and pencils.
Hardwood is generally simpler than softwood because there are just four different grades. These are FAS (First and Second), Select No. 1 Common, Select No. 2 Common, and Select No. 3 Common. In addition to that, it will also depend on the kind of hardwood. For more info, you can check out National Hardwood Association.
To know more about lumber grade, visit here.
To help you identify the perfect lumber, check the stamping on it. The stamp will indicate the lumber's characteristics. For instance, if it has a Stand and BTR stamp, it means it has a standard and better light framing. If it has an "S-dry stamp, it means the wood was surface dried. Everything I mentioned about the grading of the lumber should be shown on the stamping. To know the meaning of the abbreviations and stamping, click here.
Load duration refers to how long the lumber can stay loaded. You can determine using the material strength rating and the stiffness value. The stiffness value refers to the weight that can cause the wood to change shape or deform.
Your design greatly affects how much you can support on your 2x4. 2x4s come in different lengths and could be as long as 20 feet. The longer it is, the more tendency to sag towards the center, even with its own weight. If your design requires a long 2x4, make sure to add support as necessary to prevent it from bending, bowing, etc.
So how much weight can a 2x4 support exactly?
As I said, it depends. It depends on the kind of wood, the grade, the design of the project, and more. It also depends on the kind of load - if it is uniform or if it is a point load. In general, you can calculate it. Here is a wood column capacity calculator and a sag calculator.
It is difficult to provide an exact number but I hope this article helps you come to a close estimate. Use the references and the links to give you even more information. Good luck on your project!