Snow load is a critical consideration in the design of any structure, particularly in regions that experience heavy snowfall.1 For decks, snow load can significantly impact the required beam size and span.2 This article will guide you on how to adjust beam spans to accommodate snow loads.
Understanding Snow Load
Snow load is the weight of accumulated snow on a horizontal surface. Its magnitude depends on several factors, including:
- Snowfall Intensity and Duration: The amount and duration of snowfall significantly impact the accumulated snow load.
- Snow Density: The density of snow varies depending on factors like temperature, moisture content, and wind.3
- Roof Slope: Steeper roofs shed snow more easily, reducing the potential snow load.4
- Local Climate: Regional climate patterns, including average snowfall and historical snow depths, are crucial for determining design snow loads.5
Impact of Snow Load on Deck Beams
Snow load can significantly increase the stress on deck beam span chart, particularly for covered decks or those located in areas with heavy snowfall. This increased load can lead to:
- Deflection: Excessive bending of the beams, resulting in sagging and potential structural failure.
- Overstress: The beams may be subjected to stresses beyond their design limits, leading to cracking or breaking.
Adjusting Beam Span for Snow Load
- Determine the Design Snow Load:
- Consult Local Building Codes: Building codes provide guidance on determining design snow loads based on your location and climate.6
- Consider Local Snowfall History: Review historical snowfall data for your region to assess potential snow loads.
- Calculate the Total Load:
- Dead Load: The weight of the deck itself (beams, joists, decking, railings).
- Live Load: The anticipated weight of people, furniture, and other items on the deck.7
- Snow Load: The calculated design snow load.
- Use Span Charts:
- Consult Span Charts: Use span charts specifically designed for snow load conditions. These charts will provide guidance on allowable spans for different beam sizes and materials under various snow load scenarios.
- Adjust Span or Beam Size: If the initial span calculation based on dead and live loads alone exceeds the allowable span for the anticipated snow load, you may need to:
- Reduce the Span: Decrease the distance between the support points for the beams.
- Increase Beam Size: Select larger beams with greater load-bearing capacity.
- Increase Beam Spacing: Reduce the spacing between the beams to distribute the load more effectively.
Example
Let’s say you are designing a covered deck in a region with a significant snow load. You estimate the total load (dead load + live load) to be 40 pounds per square foot. The design snow load for your location is 20 pounds per square foot. Using a span chart for treated lumber that accounts for snow load, you might find that a 2×12 beam can safely support this combined load over a 12-foot span, whereas a 2×10 beam might not be adequate.
Additional Considerations
- Roof Design: If your deck has a roof, ensure that the roof structure is designed to withstand the weight of snow.
- Snow Removal: Regularly remove snow from the deck to minimize the load on the structure.8
- Consult with a Professional: For complex deck designs or if you have any doubts, consult with a qualified engineer or structural designer. They can perform detailed calculations and ensure the safety of your deck under various loading conditions, including snow load.9
Disclaimer
This article provides general guidance on adjusting beam spans for snow load. It is not intended as a substitute for professional engineering advice. Always consult with a qualified engineer or structural designer to ensure the safe and proper design and construction of your deck, especially in regions with significant snowfall.
By carefully considering snow load and making appropriate adjustments to beam spans, you can ensure the safety and longevity of your deck, even in challenging winter conditions.