One of the most difficult aspects of building my deck was figuring out the right sized dimensional lumber for a joist or a beam. I chose 2x10s for their strength even though they were bulkier. I ended up doubling them for beams, but I began to wonder how far one 2×10 can span without support?

The length of one 2×10 joist span depends on the wood species and how far apart it is from the next 2×10. A 2×10 southern yellow pine joist can span 16 feet and 1 inch without support. A doubled 2×10 beam can span 11’ without support for a deck that is 4’ wide.

Lengths of 2×10 joists and beams vary depending on the application you are using them for as well. For instance, deck joists and beams have different load requirements than a balcony or living room floor.

In this article, we will look at all the possible scenarios in which you would use a 2×10 to support a span. We’ll explain the maximum spans allowable for 2×10 joists and beams and all the variables that go into calculating a 2×10 span, including species, spacing, location, and more.

How Far Can a 2×10 Span Without Support?

An SYP (Southern Yellow Pine) 2×10 lumber span can reach up to 14’ when used as a joist with 16” spacing. If using SPF or Redwood lumber, then the span maximum for the same distances will be half to a full foot less.

For a beam, a 2×10 will either be doubled or tripled depending on the desired span. There are no instances when you would use a single 2×10 as a support beam as a single cannot bear the load required for a structure such as a deck or a home.

When we say that a beam or joist can span a certain distance, this implies that both ends are supported with no supports in between. Span tables assume you are not cantilevering your joist or beam. If you are, then a different size lumber may be required – usually larger to support the cantilevered end.

Below we’ll go over specifically beams vs. joists and how far a 2×10 can span in each application, but it is critical to understand that not all 2x10s are created equal.

First, there are different species of dimensional lumber. You’ll usually only choose one type, and what you can buy depends on where you live. If you live in the Southern US, then you’ll get SYP. Live out west? Then you’ll probably have some type of Redwood or SPF. SYP is much stronger than Redwood.

Second, each species of lumber is graded. Span tables usually default to a no. 2 grade. However, if you were to purchase “select” grade dimensional lumber – fewer knots and imperfections – it would likely be stronger.

How Far Can a 2×10 Beam or Header Span?

A 2×10 beam – made up of two 2x10s nailed together – can span up to 11’ without support beneath a deck that is 4’ wide. For a more normal-sized deck, the same beam can span 8’, supporting a deck that is 8’ wide.

You can also triple a 2×10 beam. In that case, you could span up to 15’ for decks that are 4’ wide and up to 10’ for decks that are 8’ wide.

For the abovementioned calculations, we are using SYP or Douglas fir as the species. Spruce-pine-fir lumber would result in spans exactly 1’ less than above. Tripling these species would result in spans that are 2’ less than the tripled SYP beam.

And finally, if using Ponderosa pine or Redwood lumber, expect spans to be 2’ less whether doubled or tripled compared to SYP lumber.

If you are building a deck, then you will have room to include a double or tripled beam as you see fit.

However, if you are building a header to support a door or window, then you are constrained to the width of your framing lumber. If you are using standard 2×4 studs, then you’ll only be able to have a double header. Make sure to factor the header spans into your building plans.

How Far Can a 2×10 Rafter Span?

A 2×10 rafter that is spaced at 12” intervals can span up to 26’ 2”. This is for a roof that has a slope of 4:12 or greater. If you have a low slope roof and the same interval of rafters, then your 2×10 can span 22’ 8”.

Know that nearly all roofs are spaced further than 12” apart – either 16” or 24” o.c. So if your rafters are 24” apart, a 2×10 will span 19’ 5” for steeper pitched roofs and 18’ 2” for roofs that are not steep, or below a 4:12 slope.

How Far Can 2×10 Floor Joist Span?

2×10 floor joists can span up to 20’. However, this is for 12” o.c. spacing for live loads that are 30 psf. This is unrealistic because any living space or deck requires a joist that can support a 40 psf live load. Otherwise, the joists are not to code.

It would be more practical to use a 2×12 in the above situation, which would likely support 40 psf – building code requirement for living space – and you could space them further apart.

With 16” spacing, a floor joist can span up to 14’ as long as it is not cantilevered and terminates with support on either end. If the joists are 24” apart, then one 2×10 joist can span up to 11’ 5”. These lengths are for SYP lumber.

If you have Spruce-pine-fir lumber, then your span changes to 13’ 7” for 16” joist spacing. Redwood can support a 2×10 joist up to 13’ – one entire foot less than Southern yellow pine.

As you can see, the species of your wood matter. Having SYP lumber available could mean the difference between using 2x10s versus a larger – and more expensive – dimension of lumber such as a doubled 2×12.

2×10 Floor Joist Capacity

2×10 floor joists are designed to hold a 40 pound per square foot (psf) live load, plus a 10 psf dead load. Span tables indicate distance maximums for floor joists, with distances indicating the maximum length a 2×10 can span while still able to hold a 40 psf live load.

A live load is classified as any load that is variable in the deck or room, such as furniture, people, or other items. The dead load is simply the part of the structure supported by the joist or beam.

Span tables are intended to give builders information about the appropriate size of dimensional lumber to use when constructing in certain places.

A span table will, therefore, tell you the appropriate length of 2×10 to use to ensure your size of the deck, beam, or joist will support a 40 psf live load on a deck.

Bedrooms and attics are the only areas of a house that require less capacity than a 40 psf live load – they only require 30 psf or less. In these instances, you span your 2×10 joists further as they are expected to withstand a lighter load than, say, a deck, living room, or balcony.

Balconies require floor joists to hold up to 60 psf. The primary reason for this high load capacity requirement is safety. Since balconies could be quite high, the integrity of the floor framing is critical. Thus the 2x10s you would use on a balcony would not be able to span as far as a deck.

Finally, as you increase the width of your dimensional lumber, you’ll drastically increase the strength of your joists. Even increasing the spacing of the larger joists will still create a stronger joist structure than smaller lumber that is closer together.

How Much Weight Can a 2×10 Beam Hold?

A 2×10 beam is meant to hold up to 40 psf of live load and 10 psf of dead load, just like a joist. An SYP 2×10 single-ply beam can hold 144 pounds per lineal foot (plf). A double-ply beam of the same species can hold 288 plf and a triple-ply can hold 488 plf. These are for 10’ spans.

Understanding the plf of your beam is important, but span tables already take the plf of a beam into account and tell you the allowable span of your 2×10 beam depending on the width of the structure above it and other factors.

So while it is informative to know the raw weight your beam can hold, all you need to know is the information from your beam span table. If you need to span a 10’ gap with your deck beam made of 2 2×10’s, then the span tables tell me that my deck cannot be wider than 5’ unless I add another beam or increase the size of my lumber.

If you want to know how much your beam can hold but can’t find out the information online, then you can calculate it based on the minimum load requirement required by the building code.

Thus, if you have a tripled 2×10 beam and a span of 8’, with a deck that is 8’ wide, then that means you have an 8×8 deck. Multiply to find the square footage, which is 64 square feet. Multiply 64 by 50 (live load plus dead load) and you get 3200 pounds per square foot. Your beam can hold 3200 pounds.

Beam Span Calculator

One of the handiest tools you can use when calculating a new deck or renovation project is a beam span calculator. This tool will allow you to choose the species of lumber you have and the type of member you want to calculate, such as a beam, rafter, or joist.

You can then select 2×10 or another size of lumber and set the load minimums for your desired framing piece. Thus if you want to calculate joist size for a bedroom, you can change the live load from 40 to 30 psf.

Finally, a calculator can tell you how big or small a joist or beam you’ll need. But it can’t account for things like the type of footings you have, post size, or snow load. There are other calculators for those factors, and they should be considered when planning your next project.

Snow load is a big variable in some locations, and you would be remiss if you planned a deck or other structure and didn’t consider the added weight brought on by snow that would be brought to bear on your rafter or beam. In many cases, you will have to shorten your span.

Conclusion

A 2×10 beam, joist, or rafter is merely a part of a larger picture. While we can use span tables and calculators to determine the distance a piece of lumber can bridge before it needs more support, we also need to account for all factors that might affect that piece of wood.

No 2×10 is structurally sound unless it has a decent foundation. When planning your next build, ensure your posts and footings are built up to support your desired 2×10 framing. Be sure to also account for environmental factors like snow and excessive moisture, which could alter your span distances.

I wish you good luck planning and constructing your next project with 2×10 lumber. Plan your project thoroughly to ensure your 2×10’s have the proper support to hold up your investment for years to come.