Selecting suitable lumber for a project depends on many factors, including wood species, grade, moisture content, and dimensional size – all of which affect strength. 2x8s are a common dimensional lumber used for many structural purposes. If you’re wondering how much weight can a 2×8 hold, we’re here to help!
A 2×8 can carry between 859 and 1315 pounds vertically as a post depending on wood species, grade, and other factors. If used for a ramp, it can support up to 250 pounds per foot depending on span and other variables. On edge, it can support more than 200 PPL over 8 feet, or a center load of 370 pounds depending on all factors.
In this guide, we’ll identify how much weight a 2×8 can hold and the factors that affect its load-bearing capacity. We’ll discuss how much a 2×8 can support vertically, horizontally on flat, and also on edge. Plus, we explain how to use a load calculator and the effect of pressure treatment on 2×8 lumber strength. Our aim is to assist you with the selection of the best material for your project.
- How Much Weight Can a 2×8 Hold?
- What Does Affect 2×8 Load Bearing Capacity?
- How Much Weight Can a 2×8 Hold Vertically?
- How Much Weight Can a 2×8 Support Horizontally?
- How Much Weight Can a 2×8 Hold on Edge?
- 2×8 Load Capacity Calculator
- How Much Weight Can a Pressure-Treated 2×8 Hold?
How Much Weight Can a 2×8 Hold?
Determining how much a 2×8 can support depends on how it will be used and its orientation. A vertical 2×8 used as a post or stud differs in load capabilities from one used on edge as a beam or joist, or one flat-face up for a ramp or shelf. The amount also depends upon how and where forces are applied and for how long, the location of bracing or supports, plus the wood species, grade of lumber, span, and moisture content.
A dimensional 2×8 is actually 1-1/2” by 7-1/4” which gives it a cross-sectional area of 10.875 square inches (in²). The cross-sectional area helps determine the strength of lumber depending on the direction forces are applied.
A 2×8 positioned vertically to support a downward force will flex, twist, or buckle under too much load, as will one used as a ramp, but adding intermediate blocking or support improves the load ability. The same is true for a 2×8 on edge as a joist, rafter, or beam.
The direction of force and the orientation of the grain in the wood affect the load strength. A 2×8 used vertically as a post has the force applied longitudinally through its length. It won’t hold as much as one used in a stud wall since the stud is blocked and sheathed for lateral support and shares the load with other studs.
A single 8-foot 2×8 as a post will vertically support between 897 and 1,315 pounds before buckling, depending on wood species, grade, and other factors.
A 2×8 on edge as a rafter or joist has a cross-sectional dimension almost 25% larger than a 2×6 making it about 3.5 times stiffer than a comparable 2×6 joist. The load it can support depends on wood species, grade, span, and other factors.
A northern Douglas fir 2×8 under the best conditions can support a uniform load of 93 PPL (pounds per linear foot) when spanning 12 feet, 211 PPL over 8 feet, and 799 PPL if spanning 4 feet. So, the shorter the unsupported distance, the greater the load strength.
Laying a 2×8 down as a ramp is the weakest orientation as it is only 1.5” thick, the same as a 2×6 or a 2×4. However, the greater width does give it almost double the center load strength of a comparable 2×4 plank. A 4-foot Douglas-fir 2×8 can support a center load of about 30 pounds before the sag becomes excessive, a 3-foot plank a center load of 70 pounds, and a 2-foot length up to 250 pounds. Again, the shorter the span, the greater the load ability.
What Does Affect 2×8 Load Bearing Capacity?
The load-bearing capacity of wood depends on the wood species, grade, density, moisture content, and grain orientation along with other factors. The unsupported distance or span, along with how long the load will be applied, plus inertial or movement are also important factors to consider. Before starting any building that will shelter or carry people, always check with the local building department or a Structural Engineer.
Softwood or lumber from coniferous trees is commonly used for dimensional lumber in construction. Hardwood is usually from deciduous trees and has a greater density, so less shrinkage, and is typically used for flooring, furniture, and trim. However, both soft and hardwood can be used interchangeably depending on structural requirements, budget, and aesthetic appeal.
Douglas-fir, hemlock-fir, Southern yellow pine (SYP), and SPF (spruce-pine-fir) are softwoods frequently used for house construction and framing. Douglas-fir and SYP are often considered the strongest, but hemlock isn’t far behind depending on orientation. SPF is often the weakest dimensional lumber option and the least expensive.
Hardwoods such as oak, maple, cherry, hickory, and black walnut are commonly used for furniture and cabinetry. They are also used for building purposes, including flooring, decorative accents, trim, wall panels, banisters, spindles, railings and stairs. Due to its strength and straightness, oak was often used for structural beams too before the advent of readily available steel beams.
Span often refers to the distance a wood member can traverse without support. The unsupported distance a 2×8 can span depends on numerous factors. Wood species, grade, load variables, moisture content, location, bracing, blocking, and spacing between parallel members all affect span. Some wood species and lumber grades can span further than others, so check the International Residential Building Code (IRC-2021) span tables for current information.
If used for headers or girders on exterior bearing walls, the number of stories, building width, and live and dead load variables affect span. Similar factors affect interior girders and headers too. The greater the loads, the shorter the distance. However, headers and girders are often doubled, tripled, or quadrupled so they can span further.
A 2×8 has a maximum span between 9’-5” and 16’-6” as a joist depending on all variables. If used as a rafter, the span ranges from 8’-3” and 23’-9” based on all factors. A 2×8 ceiling joist for an uninhabited attic can span 13’-3” to more than 26’ under various conditions. So, it is paramount to check all variables when selecting materials and before beginning to build.
There are two main ways lumber is graded in North America. Based on specific characteristics like grain angle, knots, splits, checks, and wane, it is numerically graded for strength. Select Structural (SS) has the strongest graded characteristics and is the most expensive.
It is commonly used for visible structural purposes where its appearance and strength are needed. No.1 is also referred to as construction grade, No.2 as standard grade, No.3 as utility, and No.4 as economy grade.
SS, No.1, and No.2 are commonly used structurally in the construction industry while No.3 and No.4 are used for non-structural purposes. No.1 and No.2 grades of the same species often have similar strengths, although No.2 may have more visible defects, so structural drawings may list required materials as ‘No.2 or Better’.
The other way of grading is by appearance depending on how clear of defects or how pretty the plank looks. The lumber may be graded alphabetically from A to E, as well as using terms like ‘Select’, ‘Prime’, ‘Common’, ‘Superior’, ‘Choice’, ‘Quality’, and other catchy words. It should be noted that lumber graded A could be structurally grade SS, No.1, No.2, or even No.3. The appearance grade is often determined by the retailer or by some mills.
The moisture content (MC) of different wood species affects load-bearing strength. The higher the MC, the weaker its load-bearing strength. Dry lumber can be as much as 50% stronger than fresh-cut greenwood. Air-dried lumber usually has an MC of around 12 or 13%, while kiln-dried has an average MC of 15%. Trim and other millwork, though, often have an MC between 6% and 8%.
It should be noted, that most lumber arrives at a build site and its moisture content is affected by humidity and exposure to precipitation. However, by the time the lumber has been used for structural framing and the house is buttoned up, the MC is down to 12 to 13%. As the moisture content decreases, the lumber can twist, bow, or even crack, so it is often left strapped in its bundle until needed.
Type of Load
Lumber can be exposed to vertical, horizontal, and longitudinal loads depending on the orientation and use of the 2×8. The lumber may be placed to withstand one primary force direction, but it may also experience force loads in other directions too. Much depends on design, location, and environmental factors.
The weight of the building materials, including those attached or resting on structural components, is referred to as the dead load. It is usually inert and non-moving and often ranges from 5psf to 20psf. It is a calculated value based on structural dimensions, volume, and unit weight values. The dead load includes floors, walls, sheathing, interior and exterior finishes, beams, roof, cabinetry, fixtures, and even permanent furniture.
Live load is added to the dead load for a total load factor, which affects span and other building concerns. The live load is moving or moveable but may stay stationary for extended periods and often includes imposed loads. However, it isn’t considered to have an acceleration or impact force. It usually includes moveable furniture, people, pets, and machinery.
Three other important variables are snow, wind, and seismic loads. Snow is usually temporary but often considered a live load. It can also be an impact force or load when it falls off one part of a structure onto another part.
The wind generates a horizontal force or load in its prevailing direction. Its force and velocity produce a wind load depending on the size, shape, and location of the structure. Seismic activity depends on location, and many structures are designed to withstand horizontal and vertical forces ground movement can create.
How Much Weight Can a 2×8 Hold Vertically?
A single vertical 2×8 used as a post can hold between 897 and 1,315 pounds depending on grade, wood species, moisture content, and density. A dry-use SS Douglas fir can support 1,315 pounds but only 1,181 for wet use, and a No.2 only 1,108 and 992 pounds respectively in similar conditions.
If using an SS SPF instead, it will similarly support 896 or 805 pounds, and a No.2 SPF only 762 or 685 pounds respectively. So, the different factors affect load capability.
How Much Weight Can a 2×8 Support Horizontally?
The distance a 2×8 spans horizontally as a ramp or shelf, along with wood species, grade, and other factors, affect the amount of weight it can support. A center load on a horizontal Douglas fir 2×8 will support 30 pounds if 48” long, 70 pounds if 36” long, and 250 pounds if only 24” long.
An SPF 2×8 will hold 25 pounds, 61 pounds, and 206 pounds under similar distances. The shorter the unsupported span, the greater the load the 2×8 can support.
How Much Weight Can a 2×8 Hold on Edge?
A 2×8 is commonly used on edge as a joist, rafter, header, or beam. The amount of weight it can support depends on wood species, grade, moisture content, deflection limit, span, and duration. 2x8s used for structural purposes are typically restricted to spans based on load variables, spacing between parallel members, and distance between supports.
The current IRC or local building code is the best place to get information about acceptable loads for spans and spacing based on wood species and grade.
Under the best conditions, a 2×8 spanning 4 feet can support 799 pounds per linear foot (PPL), 211 PPL if supported at 8 feet, and 93 PPL if supported at 12 feet. If using a 2×8 to support a center load weight, a Douglas fir plank on edge and supported at 4 feet could hold approximately 2900 pounds, but only about 370 pounds if supported at 8 feet. The shorter the unsupported span, the greater the weight a 2×8 can carry.
2×8 Load Capacity Calculator
There are numerous online calculators to assist with determining span distances, but fewer if you’re looking for load capacity. Most calculators use engineering formulas to perform the calculations so you don’t have to. However, they are often done in isolation from other factors, so use them as a rough guide and always check with a professional for actual values.
Jonathan Ochshorn, an archetect, provides a good online wood column load calculator that identifies load capacity for different column sizes. All you have to do is select the species, grade, lumber dimensions, load duration, and wet service or not. You do have to input unbraced height based on axis orientation, though. Another helpful calculator for determining loads for planks on flat or edge is The Sagulator. Both are easier to use than working through the formulas.
How Much Weight Can a Pressure-Treated 2×8 Hold?
Pressure-treated lumber refers to wood that has undergone a pressurized treatment that helps protect it from insects and rot, or moisture, or in some cases from fire. Green or brown pressure-treated lumber is typically for exterior use, blue for moisture, and red/pink for fire. However, its load-bearing capacity is the same as dry use if it is so used.
The load capacity or strength of green or brown-treated lumber is limited to the same factors as untreated lumber but with the addition of a ‘wet service factor’ when used outdoors. The wet service factor decreases the comparable dry load capacity by about 10%.
The IRC and local building codes, though, do not identify any difference in load strength based on treatment. So, a pressure-treated 2×8 will support as much as an untreated 2×8 when used for structural purposes.