What size beam do I need for a 18 foot span? determining the appropriate beam size for an 18-foot span depends on various factors, including the load it will support and local building codes.

The size of the beam you need for an 18-foot span will depend on several factors, including the type of wood, the load it needs to support, and local building codes. However, as a general guideline for a residential application, you might consider a laminated veneer lumber (LVL) or glulam beam. For an 18-foot span, a common size might be a 3 1/2 inches x 9-1/2 inches LVL or glulam beam, but this can vary based on the specific requirements of your project and local building codes.

Beam is generally made of reinforced concrete providing with reinforcement Steel. or made of timber, wooden structure or Laminated veneer lumber (LVL) or Glulam is one of the most widely used engineered wood products for constructional applications.

It is load bearing structure and flexural member of concrete that vertically transfer all the incoming dead load, live load and self load of rcc slab to the column via column beam joint through development length of structure element.

Size of beam generally depending on span between two support and all the load acting on it. Beam is structural member subjected to flexural stresses and shear forces. The size of the beam (width and depth of beam) are governed by the different type of shear forces and stresses.

When the beam is subjected to loading the bending moment is developed and the moment carrying capacity of the beam depends mainly on the depth of the beam.

How the size of beam could be decided?, in case of RCC beams an appropriate width of the beam is assumed on the basis of experience, the magnitude of maximum bending moment and in some cases on the basis of the width of the wall present below the beam. This width of the should be sufficient to provide rebars with sufficient side cover and spacing between the bars. After assuming the width the effective depth of the beam is calculated based on the bending moment and then the overall depth of the beam is determined by adding effective cover to the effective depth calculated.

Beam is different types like cantilever beam, continuous beam, simply supported beam, fixed beam, overhanging beam, lintel beam, primary beam and secondary beam. A cantilever beam is a rigid structural element that extends horizontally,one end is free and is supported at only one end. Simply supported beam is supported at two end and continuous beam is supported by more than two support end.

Beam is provided with the top bar which experience compression and bottom bar which experiences tension. Mainly tension bar encounter the bending moment and stirrup of which are provided to incounter the shear forces.

There is various method to deciding beam size its width and depth of beam. 1) IS 456:2000, 2) Thumb rule method.

**1) According to IS 456:2000** for designing of minimum size of RCC column for 2- 3 storey building its recommendation is:- a) for cantilever beam span to effective depth ratio is 7 (span/effective depth=7), b) for simply supported beam span to effective depth ratio is 20 (span/effective depth=20) and c) for continuous beam span to effective depth ratio is 26 ((span/effective depth=26).

**2) Thumb rule method**:

You can also calculate the size and depth of the beam according to thumb rule method mention below:- 1 foot (span of the beam) = 1Inch (depth of beam), If the span of the beam is 18 feet, then the depth of the beam will be 18 inches, beam depth taken as 18″ and beam width 18/1.5= 12″, taking as 12″.

The size of the beam needed to span 18 feet depends on various factors. Typically for a rough estimate, you could consider using a 12″×15″ RCC beam, 9-10″ GLULAM or LVL (laminated veneer lumber), a triple 2×12 wood beam or a double 2×14 wood beam for 2-3 storey residential building applications.

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**What size beam do i need for a 18 foot span**

Typically for a 18 foot span as a rough estimate, you could consider using a 12″×15″ RCC beam, 9-10″ GLULAM or LVL (laminated veneer lumber), a triple 2×12 wood beam or a double 2×14 wood beam, or ISMB-300, or W12 steel beam for 2-3 storey residential building applications.

**RCC beam size for 18 feet span**

The rcc beam size required for a 18 foot span should be at least 12″×15″ (or 300× 380 mm) in which beam width is 12″ and beam depth is 15″, providing with minimum of 4 nos of 12mm bar at top, 4nos of 16mm bar at bottom of Fe500 with Stirrups T8@6″C/C and M20 grade of concrete ratio (1:1.5:3) with clear cover 25mm.

**Steel beam or rsj size for 18 feet span**

As per general thumb rule, for 18 feet span size of steel beam or universal beam or w beam or I beam or UB’s or hot rolled section or Rolled steel joist (RSJ) should be ISMB 300 or UB 300×140 or W12 used for residential building or projects or construction in which depth of section of beam is 300mm (12″) and width of flange or width of beam is 140mm (5.5″). This is ideal, standard and most suitable size of steel beam or RSJ beam used for 18 feet span under normal load condition.

**Wood beam size for a 18 foot span**

As per general thumb rule, for a 18 foot span, size of wood beam should be 3-2×12 dimensional lumber used for residential building or projects or construction in which depth of section of beam is 300mm (12″) and width of beam is 6″. So, a 3-2×12 wood beam needed to span 18 feet.

**LVL beam size for a 25 foot span**

Typically for a 18 foot span, size of LVL beam or GLULAM should be 3-1/2″×9-1/2″ (or 9 to 10 inches deep and 4 inches wide). So you need something like a 9-10″ GLULAM or LVL to span upto 18 feet used for residential building or projects.

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**Conclusion**:-

Typically for a 18 foot span, you would need at least either 12″×15″ RCC beam or 9 to 10″ GLULAM or LVL beam, 3-2×12 wood beam, ISMB 300 or UB 300×140 RSJ, or W12 steel beam.