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How Far Can a 2×6 Span Without Support? Joists, Rafter



V Susan
Hi! I'm Susan. I am passionate about woodworking, general DIY and home improvement. If you'd like to connect with me or talk about something you like at mellowpine, drop me a mail at susan@mellowpine.com


2x6 joist.

According to the International Residential Code 2021 (IRC), the maximum length a 2×6 can span as a floor joist is 12’-6”, as a ceiling joist is 20’-8”, as a rafter is 18’-0”, as a deck board is 24′, and as a deck joist is 9’-11”.

These values are only possible if the members are made with the SS grade (structural select) Duglous fir-larch wood type.

The selection of a span size is quite challenging and requires notable considerations.

The span length for a 2×6 or any type of wooden structural member relies on wood species, wood grade, the spacing between the members, total loads, and their location.

Thus, there is not a single maximum value for the spans a 2×6 can achieve when used as floor joists, ceiling joists, rafters, or in deck boards, etc.

This article is aimed at clarifying what a span is, how long a 2×6 can span as different structural members, without having any support, and what factors influence these spans.

What is Span in Construction?

Span is the measurement of the length in between supports.

It is usually measured center to center in between supports. A length measured as such is known as the effective span.

In addition to effective spans, there are also clear spans ranging from one face of the support to the other.

Spans vary depending on differing conditions. You will find different spans for the same-sized member in the case of a joist, a beam, or a diagonal rafter,

Loads also play a key factor in limiting span lengths. A same-grade and specie joist tends to have a smaller span as compared to a rafter under the same load.

How Far can 2×6 Floor Joists Span?

According to the IRC, a 2×6 floor joist can span anywhere between 6’-10” and 12’-6”. It is all based on the wood specie, grade, spacing, and loading.

A structural select (SS) grade 2×6 joist made from Douglas fir-larch has the greatest span length of 12’-6” for a 10psf dead load and 12” spacing, as indicated in the IRC 2021.

A grade#1 Douglas fir larch floor joist under 10psf dead load and 30psf residential live (sleeping areas) and 12” spacing spans a total length of 12’.

Similarly, for all of the above conditions, a Southern Pine wood 2×6 joist spans 11’-10”, whereas a Hem-fir spans 11’-7”.

As is evident, the span length increases as the spacing decreases.

Changing the spacing to 16” and keeping the rest of the conditions the same, a notable decrease in the span lengths is observed.

A Douglas fir-larch will now span 10’-11”, and a Hem-fir will span 10’-6”. Similarly, a Southern Pine joist will now span 10’-9”.

2x6 Floor Joists.
2×6 Floor Joists.

There are more spacing and loading conditions available in the code that give off different values for the span length of a 2×6 floor joist.

A 2×6 floor joist is often used in small cabins, sheds, or small two-story houses. It is advised to check into local codes as well before proceeding with construction.

Following is a table extracted from IRC 2021 that showcases the different span lengths of a 2×6 floor joist under a 10psf dead load and a 30psf live load.

Floor Joist Spacing(inches)SpeciesGrade2×6 Span(ft-in)
12Douglas fir-larchSS12-6
12Douglas fir-larch#1  12-0  
12Douglas fir-larch#211-10
12Southern pine#111-10
12Southern pine#211-3
24Douglas fir-larchSS9-11
24Douglas fir-larch#1  9-7  
24Douglas fir-larch#29-3
24Southern pine#19-4
24Southern pine#28-6

2×6 Floor Joist Span Lengths Under 10psf Dead Load and 30psf Live Load (IRC 2021)

For general floor joist span guidelines, read this: Floor Joist Sizing, Span, Spacing: IRC Requirements

How Far Can 2×6 Ceiling Joists Span?

Ceiling joists have to bear relatively lesser dead and live loads as compared to floor joists, and as such, have the tendency to span greater lengths.

The SS grade of the Douglas fir-larch is the maximum spanning member available in the IRC for a 2×6 ceiling joist, having a span length of 20’-8”.

The minimum possible span for 24” spacing provided in the IRC is 13’-1” for grade #2 Southern pine wood.

As evident from the code, all the spans for ceiling joists are relatively longer as compared to floor joists.

Ceiling joists are used to support the weights of attics and ceilings and roofs, but if the attic accommodates a sleeping space, then ceiling joists act as floor joists.

In this case, the joist span will have to be selected using floor joist tables.

2x6 Ceiling Joists.
2×6 Ceiling Joists.

Depending upon the ceiling finishing, the dead load is about 5psf for drywall and 10psf for a plastered wall.

Following is a table extracted from the IRC 2021 that showcases the different span lengths of 2×6 ceiling joists under a 5psf dead load and a 10psf live load.

Ceiling Joist Spacing(inches)SpeciesGrade2×6 Span(ft-in)
12Douglas fir-larchSS20-8
12Douglas fir-larch#1  19-11
12Douglas fir-larch#219-6
12Southern pine#119-6
12Southern pine#218-8
24Douglas fir-larchSS16-4
24Douglas fir-larch#1  15-9  
24Douglas fir-larch#215-0
24Southern pine#115-6
24Southern pine#213-11

2×6 Ceiling Joist Span Lengths Under 5psf Dead Load and 10psf Live Load (IRC 2021)

How Far Can 2×6 Rafters Span?

Rafters are used to support sloping roofs of houses.

Similar to joists, rafter spans are also influenced by wood species, wood grades, spacing, and loads acting on them.

The dead load on rafters incorporates loading caused by wind, snow type of ceiling finishing, and weight of the ceiling material (metal, tile, etc.).

Rafters are capable of spanning longer than joists because they have to carry less loads.

2x6 Rafters.
2×6 Rafters.

The IRC provides details about 2×6 rafter spans under various spacings and loading conditions.

The SS-graded, Douglas fir-larch 2×6 rafter spans about 18’-0” under a dead load of 10psf and a live load of 20psf, having no ceiling and a 12” spacing.

The span decreases to 16’-4” if there is an attached ceiling under the same parameters.

Moving to a different species, such as the SS-graded Hem fir, and keeping the rest of the parameters the same, it is seen that the span length reduces to 11’-10”.

The minimum span length available for a 2×6 rafter in the code is about 8’-4” for grade #3 Southern pine, having 24” spacing and the same loading conditions.

The following tables have been extracted from the IRC that indicates the required and possible spans for 2×6 rafters.

The tables are for dead loads of 10psf and live loads of 20psf, firstly having unattached ceilings and then with attached ceilings.

RaftersSpeciesGrade2×6 Span
(inches)   (ft-in)
12Douglas fir-larchSS18-0
12Douglas fir-larch#1  17-4  
12Douglas fir-larch#216-10
12Southern pine#117-0
12Southern pine#215-7
24Douglas fir-larchSS14-4
24Douglas fir-larch#1  12-6  
24Douglas fir-larch#211-11
24Southern pine#112-9
24Southern pine#211-0

Rafter Span Lengths Under 10psf Dead Load and 20psf Live Load (Unattached Ceiling). (IRC 2021)
(inches)  Spans (ft-in)
12Douglas fir-larchSS16-4
12Douglas fir-larch#1  15-9
12Douglas fir-larch#215-6

Rafter Span Lengths Under 10psf Dead Load and 20psf Live Load (Attached Ceiling). (IRC 2021)

How Far Can 2×6 Decks Span?

Decking refers to the platform that is placed on top of joists enabling one to walk over it and place furniture on it.

Interior deck joists are made of plywood or oriented strand board (OSB), whereas exterior decks are often made from 2×6 lumber or 5/4×6 lumber members.

The 2×6 joists offer more strength having a greater thickness as compared to the 5/4×6 ones.

The IRC code has detailed guidelines on decking and has provisions regarding it.

Following is a table extracted from the IRC that provides decking span details for 2×6 joists under a 40psf live load and a 10psf dead load.

SpeciesSpacing (inches)121624
Size (inches)Span (ft-inch)Span (ft-inch)Span (ft-inch)
Southern pine2×69-119-07-7
Douglas fir-larch ,Hem-fir ,Spruce-pine-fir2×69-68-46-10
Redwood, Western Cedars, Ponderosa Pine, Red Pine2x 6 8-108-06-10

Deck Joist Span Lengths Under 10psf Dead Load and 40psf Live Load. (IRC 2021)

The common wood species used for decking include Southern pine, Douglas fir-larch, Red pine, etc.

For a 2×6 joist, Southern pine spans the longest at 9’-11”. The spans for interior decking are, on average larger than the ones for exterior decking.

For the same loading and spacing conditions, a grade #2 Southern pine spans a length of 10’-3”.

Details about the maximum cantilever length a specific member can span are also mentioned in the code.

For a 2×6 Southern pine, the maximum allowed cantilever span is about 1’-3” for 12” spacing, 1’-4” for 16” spacing, and 1’-6” for 24” spacing.

2x6 Lumber Decking.
2×6 Lumber Decking.

How far can a 2×6 Deck Beam Span?

Deck beams are rested on posts and similar structures, and they carry the loads from joists.

In addition to wood species, grade, loads, and spacing, beam spans also depend on the joist spans.

A 2×6 beam carries the same typical dead and live load variables.

For a 40psf live load and a 10psf dead load, a grade#2 Southern pine beam having a 2×6 size and joist spans of 6’ will span about 4’-11”.

Under the same conditions, a double beam can span about 6’-11, while a triple beam can span the longest at 8’-2”.

An increase in the Joist spans leads to a decrease in the beam span.

For most other 2×6 wood species having the same conditions as above, the average double beam span is about 5’-5”.

While It is 7’-4” for triple beams of most species having the same conditions.

How far can a 2×6 Header Beam Span?

Header beams are special categories of beams used over windows and door openings in a wall frame used to carry and transfer the load above them.

A header beam span is determined mainly by the location of the beam and the load it has to bear.

The span requirements vary for header beams in interior and exterior walls.

The header span is also dependent on the building width, total stories, floor conditions, and superimposed dead load (such as snow load).

As the width of the building and the number of floors rise, the header span will decrease.

How Far Can a 2×6 Member Span?

A 2×6 joist has various applications, as it can be used on floors, roofs, ceilings, walls, and construction of other frames. Each member has its own span length.

As such, the different span lengths for each member are defined in local and international codes like the IRC 2021.  

In addition to international codes, it is always beneficial to investigate local codes because available structures are commonly localized.

As a general thumb rule, a trial joist length can be taken as 1-1/2 times the depth of a board (in feet).

The range provided by the codes for 2×6 lies between 2’-1” to 20’-8”. Ceiling joists, however can span farther due to the absence of live loads.

What Factors Impact How Far a 2×6 Can Span?

The span distance for a 2×6, in reality, is controlled by various factors. Such as the species of wood, its grade, the location of the member, loads, and the provided spacing.

Wood Species

The span lengths of 2×6 members change with the specie of wood used.

The IRC 2021 includes various species of wood against which the span lengths for a 2×6 member are listed.

Members made from Douglas fir-larch span the longest. While members made from Southern pine and Spruce-pine-fir has relatively shorter spans.

Different Wood Species.
Different Wood Species.

Wood Grade

Wood grades also influence the span lengths of 2×6 members. A grade refers to the degree of defects present in the wood being used for a structural member.

They provide information about the strength of a member and also determine the deflection, capacity, and loadings a 2×6 member can bear.

The IRC 2021 code includes four categories of grades which include, structural select (SS), #1, #2, and #3.

SS-grade lumber is the best quality lumber and can span the longest.

#1 and #2 grades have relatively more defects in them but are used more commonly.

Out of the four grades, #2 grade is the most widely used grade of wood.


The spans of 2×6 members decrease with an increase in the total loads acting on them.

A grade #2 Douglas fir-larch 2×6 floor joist spans 11′-10″ under a 10psf dead load and 30psf live load.

While it only spans 11′-8″ under a 20psf dead load and a 30psf live load.


The span lengths of 2×6 members change according to their location in the frame.

The spans for a bedroom can be larger than those of the living room because there are fewer people in a bedroom at a particular time.

A bedroom may only have two to three people at a time, while a living room can have up to 8 or 10 people causing more loads.


Spacing is the distance provided between two adjacent 2×6 members. It greatly influences the span lengths of these members.

A grade#1 Hem-fir 2×6 floor joist spans 11′-7″ with 12″ spacing under a total load of 30psf.

The same member spans only 10′-6″ if the spacing is increased to 16″.

Thus an increase in spacing between 2×6 members reduces their achievable span lengths.

How Much Weight Can a 2×6 Carry?

The total load-bearing capacity is dependent on the orientation of the member, its location, the distribution of loading, and the duration of loading.

Orientation refers to whether or not the 2×6 member lies on the end or vertically, horizontally, or in a diagonal manner, or has a flat surface up or the edge.

The location of the point of application of load and the distribution of load must also be factored in.

Additionally, the duration of load also plays an important part in determining the final span length.

A vertical 2×6 can carry up to 7000 pounds without buckling.

A horizontal 2×6 on edge is said to carry about 50psf, comprising of 10psf dead load and 40psf live load.

As such, It can be estimated that a 2×6 having a 10’ span will then carry about 500 (10×50) pounds of load along the span length.

The code has dictations on other configurations of 2×6 members and the consequent total loads each configuration can bare.


2×6 lumber has a wide range of applications, such as floor joists, ceiling joists, rafters, deck joists, deck beams, etc.

The maximum span allowed for a 2×6 is important to understand from a safety standpoint.

To do this, one must also understand the factors upon which the span lengths are dependent.

The span is affected greatly by the wood species, the wood grade, the spacing, and the loads the member has to carry.

If you need larger spans in your project, trusses and I-joists are good options.

Frequently Asked Questions (FAQ)

Can a 2×6 span 20ft?

A 2×6 can span up to 20ft as a ceiling joist having 12” spacing, but not as a floor joist.

What lumber size can span 20 feet?

A 2×12 size is required to allow spans of 20ft for floor joists.

V Susan
Hi! I'm Susan. I am passionate about woodworking, general DIY and home improvement. If you'd like to connect with me or talk about something you like at mellowpine, drop me a mail at susan@mellowpine.com