What Size Beam Do I Need to Span 20 Feet? | Detailed Guide

What size beam do I need to span 20 feet – The beam is a load-bearing structure as well as a flexural member of the roofing system in the building.

The vertical transfers all incoming live load, deal load, and even the self-load of RCC slab in the column through column beam joints.

These increase the development length of the structural element. The size of the beam depends on the span between 2 support in the buildings. The Beam is a structural member especially subjected to flexural stresses as well as shear forces.

Placing the right-sized beam is quite important for ensuring the accurate management of the stress and forces. The main reason is that size of the beam is especially governed by the various shear forces and stresses.

One of the biggest questions that everyone needs to have is “what size beam do I need to span 20 feet”.

How Sizes Of Beams Are Decided?

The beam is subjected to loading all kinds of the bending moment that are mainly developed from the column. Normally, the moment carrying capacity of the beam depends on the depth of the beam.

The width of the wall is also mainly calculated under this process so that it is more efficient for calculating them accordingly. The width of the beam needs to be sufficient to provide rebars along with the other side cover as well as spacing between the bars.

With assuming width and effective depth of beam are calculated based on the bending moment along with the overall depth of the beam.

These are mainly determined by easily adding the cover to depth calculated. Normally, there are different types of beams that include the

  • Cantilever Beam
  • Simply Supported Beam
  • Continuous Beam
  • Lintel Beam
  • Fixed Beam
  • Overhanging Beam
  • Primary Beam
  • Secondary Beam

Are you adding space to a room or making structural changes, then it is quite important to have the proper support in the beam. It is quite an efficient option for adding the beam that provides more structural support.

Getting accurate beam size is important. When you are considering a 20-foot span, then it is also quite important to know about the appropriate size of the beam accordingly. When you consider the wooden beam, it has to be at least 18 inches in depth for 20-foot spans.

Determining the size beams required for specific spans is quite important for assuring the perfect attributes. Cantilever Beams are rigid structural element extends horizontally. Simply supported beams have supported at least two ends.

These have one end free while the other end with the support. The continuous beam is mainly supported by 2 support end.

  • Flange Thickness
  • Web Thickness
  • Fillet Radius
  • Flange Width
  • Beam Depth

What Size Beam Do I Need For A 20 Foot Span?

The size of the beam is mainly important calculated during the construction of the roofs. Beam plays an important role in the strong holding of the column and another system in the building.

This also plays an important role in reducing the effect of natural calamities such as the storm or winds. The beam will be provided on the top bar as they would mainly experience better compression.

The bottom bar mainly has tension that gives better support for the building. Tension bar especially enables with the bending moment as well as stirrup more activities provided to encounter shear forces.

For RCC Concrete Beam:

When you are taking the standard size of RCC concrete beam size with Width and Depth of beam is 230mm (9″) or 230mm x 230mm. Depth of beam increases or decreases with a span that are mainly applied with a load on the beam.

Normally, there are many numbers of aspects that decide the beam size with the depth and width of the beam.

IS 456:2000:

The IS 456:2000 is a suitable option for designing the 2- 3 storey building, and the minimum size of the RCC column is recommended at

  • Cantilever Beam Span to Depth Ratio is 7 (Span/Effective Depth=7)
  • Supported Beam Span to Depth Ratio is 20 (Span/Effective Depth=20)
  • Continuous Beam Span to Depth Ratio is 26 (Span/Effective Depth=26)

Thumb Rule Method for Size of Beam Need for Span 20 Feet:

When calculating the beam size for a 20-foot span based on the Simply Supported beam size, then it is known for

  • Simply Supported Beam Span for the depth ratio is 20 (Span/Effective Depth=20)
  • Effective Depth = 20 ×12″/20 = 12″
  • Diameter Of Bar = 16mm, clear cover of 1″
  • Overall depth = effective depth + clear cover + 1/2dia of bar
  • Overall depth = 12″+1″+0.3″=13.3″
  • Taking round figure beam depth = 15″
  • Width of beam = D/1.5=15″/1.5
  • Width of beam = 10″
  • Result is 12″ inch

For Continuous Beam Span:

When calculating the continuous beam span then it is mainly enabled with other aspects and gives more stability. Continuous Beam Size for 20 foot span is mainly based on the effective depth ratio, and they are calculated with

  • Continuous Beam Span to Depth Ratio is 26
  • Span/Effective Depth=26
  • Effective Depth = 20 ×12″/26 = 9.23″
  • Dia Of Bar=16mm
  • Clear cover of 1″
  • Depth = effective depth + clear cover + 1/2dia of bar =
  • Depth = 9.23″+1″+0.3″ = 10.53″
  • Taking round figure beam depth =12″
  • Width of beam = D/1.5=12″/1.5
  • Width of beam = 8″
  • Width of beam is taking as 9 inch

When the size of the continuous beam based on a 2 to 3 storey residential building, then the 20 foot span would be calculated with the thumb rule.

These are mainly enabled with 9″×12″ and beamwidth is 9″. The beam depth is 12″ so that it is easier to place the 12mm bar at the top in 2 numbers, 12mm crank bar of Fe500 and 16mm bar at the bottom with 2 numbers.

Understanding Loads On Beams:

Before analyzing the size of the beam, it is quite important to understand different loads. Normally, there are 2 types of load such as the

  • Interior Load
  • Exterior Load

Determining whether the beam is going to be on an outside wall or inside is quite important for analyzing the size.

Outside Wall – When the outside wall is placed along with the clear span trusses, they are precisely enabled on load in the walls.

For the building-sized 24’ x 24’ having trusses, half the load is mainly enabled on walls like 30lbs. Load on the wall is twice as much as the load would for buildings in the center wall.

Interior Beams- The interior beams include roof load, and it is important to make sure that they are arranged in exact sizes. Loads are structural support for the building, so that it is important to calculate accurately.

Simplified Sizing And Wood Strength:

No matter what kind of material is used in the process, they are mainly enabled with adequate stiffness, shear resistance and strength. Normally, there are various attributes that provide a suitable option for determining the span and size of the beam.

These are mainly enabled with the structural ability of engineered along the sawn-wood beams. Formulas are dependent on a wide array of variables.

These are also mainly enabled with other attributes like species of wood, grade, size, type of load, deflection limit and many more.

Bearing – Based on International Residential Codes, the beam or header does not contain the bearing of less than 1-1/2”. According to the code, anything above 5’ is required to be treated as a double process.

There may be a requirement for bearing space, and it is a more convenient option for enabling better attributes.

Fastening – The Beams with the feature of higher than the one-ply requires to be fastened using nails or bolts. International Residential Codes especially dictates the minimum of 32” O.C. staggered pattern.

These are mainly enabled with the minimum of 3” x .120” nail. When the 3-1/4” x .131” groove shank nail is enabled with 4 feet across laminate, then it would provide good results.

For Beam Needed To Span 12 Feet:

For estimating the Beam span, there are various methods available. When it is mainly supported with the span of 12 feet without overhang, then it is quite efficient for a double-ply beam that spans equivalent of depth in inches.

When it is enabled with a 2×12 beam, and it goes 12 feet, then 2×10 beam can go even upto 10 feet. Choosing the experts for analyzing the process is quite important so that this could automatically ensure the complete attributes with extensively saving more time in the process.

It is important to determine the total load per foot that beams will hold.

Lumber Size Of The Beam To Span For 20 Feet:

Max. Live Load 60 lbs/ft2 (2873 N/m2)

Maximum Span (ft – in)
Nominal Size (inches)Joist Spacing Center to Center (inches)Lumber Grade
2 x 122413′ – 2″
2 x 141220′ – 10″
1618′ – 0″

The formula for the section modulus is beam based on the width times beam depth squared divided by 6. Normally, two 2-by-6 standard beams is enabled with the actual dimensions of 1.5-by-5.5 inches. A double 2×12 beam would span for 12 feet, and (2) 2×10 could span 10 feet.


When you are calculating the RCC beams, then it is important to know about the appropriate width of the beam that are assumed based on the calculation along with the magnitude of the maximum bending.

Home Base Project Team
Home Base Project Team
At The Home Base Project, we offer practical, real-life tips and inspiration about DIY, decorating and gardening. The Home Base Project provide the best information about home renovation and design, connecting home design enthusiasts and home professionals across the world.


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