Floor Joist – Types, Spacings, Standard Sizes, Advantages

Floor joists are horizontal structural elements that extend into an open space, usually between beams, which then transfer loads to vertical structural elements.

These beams, part of the floor system, carry weight with everything in the room, including walls, furniture, appliances, and even people.

Floor Joist
Source: mycarpentry.com

Types Of Floor Joists

There are 3 main types of floor joists:

  1. I Joist
  2. Solid Lumber
  3. Open Web Truss Joist

1. I Joist

I-shaped floor joists are robust, lightweight “I” -shaped wooden components that meet the required performance standards. I-joists consist of upper and lower flanges that resist bending, are joined to the ribs, and provide exceptional shear resistance.

The flange material is usually laminated veneer (LVL) or fine lumber and the strip is made of plywood or OSB. The robust combination of structural elements results in a versatile, economical frame element that is easy to install in residential and light commercial projects.

Advantages Of I-Joists 

 I-joists have a longer span than solid lumber joists.

 The installation process of I-joists is easy.

Disadvantages of I-Joists 

 I-joists can not stand fire for a longer time.

 I-joists are expensive when compared to other types of joists.

2. Solid Lumber Joists

Solid lumber floor Joists are closed planks, usually made of old wood. Their range is affected by various factors such as types, board size, distance, and deviation.

Solid Lumber Joists in the work area are still common, but wood supplies are depleted, and using young wood on a beam can damage the wood.

Advantages Of Solid Lumber Joists

 Solid Lumber Joists can resist fire for a longer duration.

 These are less expensive than engineered trusses.

Disadvantages Of Solid Lumber Joists

 These are not environmentally friendly.

The span distance of Solid Lumber Joists is very limited.

3. Open-Web Truss Joist

These joists offer more advantages than other types of joists, such as range of depth, longer span, and load-carrying capacity. Open-Web Floor Truss Joist has low moisture capacity and shrinks less.

Advantages of Open Web Floor Truss

 Open-web trusses joist is best suited for a longer span.

 These trusses can bear greater concentrated loads to carry bearing walls and roof loads from above.

Disadvantages of Open Web Floor Truss

 Open web truss is costlier than I-Joists.

These joists are difficult to customize accordingly.

Advantages and Disadvantages Of Floor Joist


  • The floor joist can bear the live load, Dead load, and Impact load.
  • The installation process is more affordable.
  • These are very efficient in supporting the structure.
  • They are verticle members and act as beams to transfer the load to the ground.


  • Floor joists have limited options in terms of design and model.
  • They are relatively heavy when compared to other trusses.
  • They require support from walls, columns, and beams.
  • These are not preferred for large areas.

Standard Size and Spacing Of Floor Joists

Floor Joist Span (Feet) Floor Joist Standard Size Spacing (Inch)
6, 7 & 8 2×4 16
10′ 2×6 16
12′ 2×6 12
15′ 2×8 16
16′ 2×8 12
18′ 2×10 16
20′ 2×10 12
24′ 2×12 16
25′ 2×12 12
Standard Size And Spacing Of Floor Joists


Q. How many types of Floor Joists are there, and what are those?

Ans – There are 3 types of floor joists present.

  • I Joist
  • Solid Lumber
  • Open Web Truss Joist

Q. What are the standard sizes of floor joists?

Ans – The standard sizes of floor joists depend on the span of the joists, ranging from 2×4 to 2×12.

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