According to the International Residential Code 2018 (IRC), the maximum length a 2x6 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 2x6 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 2x6 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 2x6 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 2x6 Floor Joists Span?
According to the IRC, a 2x6 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 2x6 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 2018.
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 2x6 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”.
There are more spacing and loading conditions available in the code that give off different values for the span length of a 2x6 floor joist.
A 2x6 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 the IRC 218 that showcases the different span lengths of a 2x6 floor joist under a 10psf dead load and a 30psf live load.
|Floor Joist Spacing||Species||Grade||2x6 Span|
2x6 Floor Joist Span Lengths Under 10psf Dead Load and 30psf Live Load (IRC 2018)
For general floor joist span guidelines read this: Floor Joist Sizing, Span, Spacing: IRC Requirements
How Far can 2x6 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 2x6 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.
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 218 that showcases the different span lengths of 2x6 ceiling joists under a 5psf dead load and a 10psf live load.
|Ceiling Joist Spacing||Species||Grade||2x6 Span|
2x6 Ceiling Joist Span Lengths Under 5psf Dead Load and 10psf Live Load (IRC 2018)
How Far can 2x6 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.
The IRC provides details about 2x6 rafter spans under various spacings and loading conditions.
The SS-graded, Douglas fir-larch 2x6 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 same, it is seen that the span length reduces to 11’-10”.
The minimum span length available for a 2x6 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 2x6 rafters.
The tables are for dead loads of 10psf and live loads of 20psf, firstly having unattached ceilings and then with attached ceilings.
Rafter Span Lengths Under 10psf Dead Load and 20psf Live Load (Unattached Ceiling). (IRC 2018)
Rafter Span Lengths Under 10psf Dead Load and 20psf Live Load (Attached Ceiling). (IRC 2018)
How Far Can 2x6 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 2x6 lumber or 5/4x6 lumber members.
The 2x6 joists offer more strength having a greater thickness as compared to the 5/4x6 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 2x6 joists under a 40psf live load and a 10psf dead load.
|Size (inches)||Span (ft-inch)||Span (ft-inch)||Span (ft-inch)|
|Douglas fir-larch Hem-fir Spruce-pine-fir||2x6||9-6||8-8||7-2|
|Redwood Red Pine||2x6||8-10||8-0||7-0|
Deck Joist Span Lengths Under 10psf Dead Load and 40psf Live Load. (IRC 2018)
The common wood species used for decking include Southern pine, Douglas fir-larch, Red pine, etc.
For a 2x6 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 2x6 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.
How far can a 2x6 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 2x6 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 2x6 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 tripe 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 2x6 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 2x6 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 2x6 member Span?
A 2x6 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 2018.
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 2x6 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 2x6 Can Span?
The span distance for a 2x6, in reality, is controlled by various factors. Such as the species of wood, its grade, location of the member, loads, and the provided spacing.
The span lengths of 2x6 members change with the specie of wood used.
The IRC 2018 includes various species of wood against which the span lengths for a 2x6 member are listed.
Members made from Douglas fir-larch span the longest. While members made from Southern pine and Spruce-pine-fir have relatively shorter spans.
Wood grades also influence span lengths of 2x6 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 2x6 member can bear.
The IRC 2018 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 2x6 members decrease with an increase in the total loads acting on them.
A grade #2 Douglas fir-larch 2x6 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 2x6 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 2x6 members. It greatly influences the span lengths of these members.
A grade#1 Hem-fir 2x6 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 2x6 members reduces their achievable span lengths.
How Much Weight Can a 2x6 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 2x6 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 2x6 can carry up to 7000 pounds without buckling.
A horizontal 2x6 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 2x6 having a 10’ span will then carry about 500 (10x50) pounds of load along the span length.
The code has dictations on other configurations of 2x6 members and the consequent total loads each configuration can bare.
2x6 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 2x6 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 a good option.
Frequently Asked Questions (FAQ)
Can a 2x6 span 20ft?
A 2x6 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 2x12 size is required to allow spans of 20ft for floor joists.
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