Desks and tables are framed with them. Benches in the garden are framed with them. Houses are framed with them.
On a construction site, the lumber you will see the most of will be 2 x 4s. Houses have been framed with them for more than 80 years. The switch to 2 x 4 framing occurred in the late 1940s when builders began using planed 2 x 4s that actually measured 1.5” x 3.5”, and that practice continues today in the US.
The customary practice in that framing is 16” on center for the vertical 2 x 4s. When upgraded to 2 x 6 framing, the practice is to set the verticals at 24” on center. By on center, we mean from the center of one 2 x 4 or 2 x 6 to the center of the next one as you move down the wall being framed. In some locales, 2 x 6 framing is actually code-required.
When calculating the load-bearing capacity of a 2 x 4, there is no standard answer, as many factors will determine the calculation. We’ll run through them all as we answer the main question of this article.
How Much Weight Can a 2 x 4 Hold?
A simple question, a complex answer. Is the 2 x 4 vertical, horizontal, or on its edge? Beyond that, there are other factors, including:
- Bending strength of the wood
- Distribution of the weight
- Where the weight is on the span
- Species of wood
- Grade of wood
- Load type
- Moisture content
So, for each of these factors and the positional aspect of the 2 x 4, the answer to how much weight a 2 x 4 can support will be different. It will also be influenced by what you mean by “support”: the maximum weight it can hold without bowing or the maximum weight it can hold without breaking.
How Much Weight Can a 2 x 4 Support Horizontally?
Generally speaking, a 2 x 4 can hold a horizontal load of between 20 – 40 lbs per linear foot if the weight is evenly distributed along the span. However, if the weight is centered on the span, it could be as low as 20 lbs or less, depending on the span.
How Much Weight Can a 2 x 4 Support on Edge?
What if the 2 x 4 were on its edge horizontally rather than on its side? It’s going to be stronger on its edge if for no other reason than it is thicker on its edge (3.5”) than it is on its side (1.5”). This becomes an important consideration when building rafters or shelves, for instance.
Assuming the load is evenly distributed along the span, a 2 x 4 can support up to 300 lbs on its edge, and sometimes more, depending on the other factors listed above. We’ll get to those factors later in this article.
How Much Weight Can a 2 x 4 Support Vertically?
The grain of the wood comes into play in this calculation. Wood is weakest with the grain, and horizontal position brings grain into play, whether flat or on edge. But, vertically, it will not bend against the grain. This means a much stronger support and a greater weight.
Additionally, the pressure from the load being supported will be distributed along the entire vertical length of the 2 x 4. In the case of framing a house, and where the vertical 2 x 4s will run every 16” on center along an exterior wall, the strength of the 2 x 4s will be substantial.
A single vertical 2 x 4 can support up to 1,000 lbs of load with little strain. A wall frame of multiple 2 x 4s, then 16” on center along the span, can support 10,000 to 20,000 lbs of load, if not more.
Factors Affecting the Carrying Strength of 2 x 4s
Species of Wood. With different densities and strengths, the species of the wood will affect the strength of lumber. Denser woods will bring more strength, and if the span to be constructed is long, a denser wood for your 2 x 4s would be a valid consideration.
The most common woods for 2 x 4s are pine, spruce, and fir, all softwoods. Of these species, Southern Yellow Pine is considered to be the strongest. While Douglas fir is also a common 2 x 4 species, it is not considered as strong as the others.
If you are working with a long span or a heavy load, you’d want to use Southern Yellow Pine since it is a denser wood than the other most common 2 x 4 materials.
Grade of Wood. Grade is determined by defects or their absence in the wood – knots, splits, warping, and others. The more defect- or blemish-free the wood, the higher the grade and the more stable and strong it will be.
The highest grade is structural lumber used for, you guessed it, structural support. It will be stronger and more durable, able to carry and support greater weight. No. 1 grade would customarily be used for siding and other construction projects; No. 3, for subflooring, a utility grade and stud grade; and No. 4 grade is an economy grade used for nothing more than very light framing.
Most home improvement stores and lumber yards will carry the select (structural) No. 1 and No. 2 grades of lumber. You can identify a lumber’s grade by the stamp on its side.
Load Type. What’s the 2 x 4 carrying? The type of load will have an impact on what the support capacity is for your lumber. Types of load include dead load and live load.
Dead load will include the permanent carrying weight, including framing, rafters, drywall, roof, and second floor – elements of construction that do not change and are applying their weight constantly without change.
Live load includes people, furniture, snow and ice, and even wind. Unlike dead weight, live weight is not putting constant pressure on the wood.
Weight capacity will be lbs per square foot times the square feet of a room. Load duration will also be a factor influencing the carrying capacity – the length of time the 2 x 4s will be able to support a load beyond normal without significant or even permanent damage. Wood will bend before it breaks, and when a load is no longer over capacity, wood will return to its original shape. When duration extends unduly, and the wood is no longer able to return to its original shape, danger results.
Moisture. We know that drier wood is stronger, more stable, and more durable than wood with a high moisture content. Wood with higher moisture content is referred to as “green” wood. Green wood can have a moisture content of between 24 and 29 percent.
Most lumber yards and home improvement stores will carry kiln-dried lumber. It is heated to about 125 degrees in large kilns to remove moisture and dry the wood down to between 6% – 16% moisture content. Kiln-dried is more stable than green wood and won’t twist or warp over time.
Some lumber companies will also air-dry lumber before it is sold. They’ll do so for between 2 – 6 weeks and bring the moisture content down to below 16%. It, too, will be much less likely to warp or twist over time once it is put in place.
However, if green wood is used in framing with 2 x 4s, it will become as much as 50% stronger after it dries.
Span. This one is pretty intuitive, actually. The longer the span, the less weight a 2 x 4 can carry. Span is the length that a 2 x 4 can cover without needing any support beneath it, like vertical studs, for instance. Obviously, also, the less spacing between studs offering that support, the greater the weight that can be supported over a longer span.
To give you an idea with numbers, follow this: A span of 11’5” with 16” spacing between studs will be reduced to 10’ 5” with 24” spacing between studs; while with 12” spacing between studs, that span can be increased to 13’ 2”.
In short, span can be increased by decreasing the spacing of support studs and thus carry and support greater weight over a longer span.
It’s always fun to watch things reach their limit before breaking, especially in slow motion. In answer to the question “How Strong is Lumber,” we give you the hydraulic press in this video.
It’s not exactly on point, but it does cover much of the conceptual information we have provided in this article. With the grain, against the grain, span, weight and pressure, support – all of these concepts are present in this video and provide visual data to illustrate the variety of factors that come into plan on how much weight a 2 x 4 can hold horizontally.
Building codes provide guidance on framing requirements, and visual inspection by building code enforcement officers will confirm the construction will be adequate to support the weight along the span that exerts pressure from what is above it. Now, you have a better idea of what goes into those building code requirements for framing using 2 x 4 studs.