2018 IRC Deck Beam Span Chart: A Comprehensive Guide
The 2018 International Residential Code (IRC) provides crucial guidelines for residential construction, including the design of decks and their supporting structures. One of the most essential aspects of deck construction is determining the appropriate beam span based on the load and span requirements. This article will delve into the 2018 IRC deck beam span chart, providing a clear and concise guide to help you understand and apply these critical regulations.
Understanding Deck Load Requirements
Before diving into the beam span chart, it's essential to understand the load requirements for decks. According to the 2018 IRC, decks must be designed to support a live load of 40 pounds per square foot (psf), along with the dead load of the deck itself. This live load accounts for the weight of people and furniture typically found on decks.
Dead Loads
Dead loads, or permanent loads, are the weights of the deck structure itself, including the joists, beams, and any attached structures like railings or benches. These loads are constant and must be considered in the design process.
Live Loads
Live loads, on the other hand, are temporary and can vary significantly. For decks, the live load is typically the weight of people and furniture. The 2018 IRC requires decks to be designed to support a live load of 40 psf, with a concentrated live load of at least 200 pounds applied over an area of 4 square feet.
2018 IRC Deck Beam Span Chart
The 2018 IRC provides a table outlining the maximum allowable beam spans for various deck materials and depths. This chart is based on the assumption that the beams are supporting uniformly distributed loads (UDLs) and are made of either No. 1 or No. 2 grade lumber.
| Material | Depth (inches) | Maximum Span (feet) |
|---|---|---|
| Douglas Fir-Larch | 2x8 | 8 |
| Douglas Fir-Larch | 2x10 | 10 |
| Douglas Fir-Larch | 2x12 | 12 |
| Spruce-Pine-Fir | 2x8 | 7 |
| Spruce-Pine-Fir | 2x10 | 9 |
| Spruce-Pine-Fir | 2x12 | 11 |
It's crucial to note that these spans are based on the assumption that the beams are supported at both ends and are not cantilevered. If the beam is cantilevered, the maximum allowable span must be reduced by one-third.
Factors Affecting Beam Span
Several factors can affect the maximum allowable beam span outlined in the 2018 IRC deck beam span chart. These factors include:
- Load Combination: The chart assumes that the beam is supporting only UDLs. If the beam is supporting a combination of UDLs and concentrated loads, the maximum allowable span may need to be reduced.
- Beam Spacing: The chart assumes that the beams are spaced at 16 inches on center. If the beams are spaced further apart, the maximum allowable span may need to be reduced.
- Beam Slope: The chart assumes that the beam is level. If the beam is sloped, the maximum allowable span may need to be reduced.
Engineered Design
While the 2018 IRC deck beam span chart provides a useful starting point for designing deck beams, it's essential to remember that it is not a substitute for a proper engineered design. For complex or unique deck designs, it's crucial to consult with a licensed structural engineer to ensure that the deck is safe and compliant with all relevant building codes.
In conclusion, understanding the 2018 IRC deck beam span chart is a critical step in designing safe and durable decks. By considering the load requirements, consulting the chart, and accounting for any additional factors, you can ensure that your deck's supporting structure is up to code and capable of withstanding the loads it will encounter.
