Understanding the Concept of Span in Construction: A Guide to Rafter Ties and Table Spans

When it comes to construction, understanding the concept of span is crucial for designing and building structures that are safe, efficient, and cost-effective. In this article, we will delve into the world of spans, exploring what they are, how they vary depending on different conditions, and what factors influence their length.

Defining Span

A span refers to the measurement of the distance between two supports or points in a structure. It is usually measured center-to-center, between the supporting members. In other words, it is the length between two points where a load-bearing member, such as a joist or rafter, rests without having any support.

Types of Spans

There are different types of spans, including effective spans and clear spans. Effective spans refer to the actual distance between supports, while clear spans range from one face of the support to the other. Effective span is an important concept in construction, as it determines the maximum length a member can span without having any support.

Factors Influencing Span Length

Several factors influence the length of a span, including wood species, wood grade, spacing between members, total loads, and their location. For example, the selection of a suitable span size requires consideration of the type of wood used, its quality, and the distance between supports. Additionally, the weight and distribution of loads on the structure also play a significant role in determining the maximum length a member can span.

IRC Guidelines for Span Lengths

The International Residential Code (IRC) 2021 provides guidelines for the maximum length a 2×6 or any type of wooden structural member can span. According to the code, the maximum lengths are:

* Floor joists: 12’-6”

* Ceiling joists: 20’-8”

* Rafters: 18’-0”

* Deck boards: 24’

* Deck joists: 9’-11”

In conclusion, understanding the concept of span is essential for designing and building structures that are safe, efficient, and cost-effective. By considering factors such as wood species, spacing between members, total loads, and their location, builders can select suitable span sizes to ensure the integrity and stability of their structures. Whether you are a builder, architect, or homeowner, this guide provides valuable insights into the world of spans and how they impact construction projects.

Rafter tie span table