Building a deck requires careful planning and proper load calculations to ensure its structural integrity. Using a deck beam span chart is an essential part of this process, as it provides guidelines for selecting the right beam size and spacing based on the expected loads. Understanding how to use the chart involves more than just picking a beam size; you need to calculate the load that the deck will carry and make sure the chosen beam can safely handle it.
Here is a step-by-step guide for calculating loads with a deck beam span chart:
1. Understand the Types of Loads
Before you start using the deck beam span chart you need to understand the different types of loads your deck will support. These loads are critical because they influence the beam size, span, and spacing.
- Dead Load: This is the weight of the deck’s permanent structure, including the decking, beams, posts, and other components.
- Live Load: This refers to the weight of temporary loads such as people, furniture, and outdoor items.
- Environmental Load: Environmental factors like snow, wind, and rain can add to the load that the deck needs to support.
Typically, for residential decks, the live load is assumed to be 40 pounds per square foot (psf), and the dead load is 10-15 psf. However, you might need to adjust these values depending on the specific requirements of your project.
2. Calculate the Deck Area
To calculate the load on each beam, you first need to determine the total area of the deck that each beam will support.
- Measure the length and width of the deck.
- Multiply these dimensions to calculate the total area of the deck.
For example, if your deck is 12 feet wide and 20 feet long, the total area is:
Deck Area=Length×Width=12′×20′=240 sq ft\text{Deck Area} = \text{Length} \times \text{Width} = 12' \times 20' = 240 \, \text{sq ft}Deck Area=Length×Width=12′×20′=240sq ft3. Calculate the Dead Load
The dead load is the weight of the deck structure itself, including beams, decking, and other materials. You need to calculate how much weight will be placed on each beam based on the deck's material and design.
For example, a typical dead load might range between 10-15 psf for wood decks. Let's assume a dead load of 12 psf for this example.
To calculate the total dead load for the deck, multiply the deck area by the dead load value:
Dead Load=Deck Area×Dead Load Value=240 sq ft×12 psf=2880 lbs\text{Dead Load} = \text{Deck Area} \times \text{Dead Load Value} = 240 \, \text{sq ft} \times 12 \, \text{psf} = 2880 \, \text{lbs}Dead Load=Deck Area×Dead Load Value=240sq ft×12psf=2880lbsSo, the total dead load on the deck is 2,880 lbs.
4. Calculate the Live Load
The live load is the weight that will be applied to the deck, such as people and furniture. For residential decks, the live load is generally assumed to be 40 psf.
Multiply the deck area by the live load value to calculate the total live load on the deck:
Live Load=Deck Area×Live Load Value=240 sq ft×40 psf=9600 lbs\text{Live Load} = \text{Deck Area} \times \text{Live Load Value} = 240 \, \text{sq ft} \times 40 \, \text{psf} = 9600 \, \text{lbs}Live Load=Deck Area×Live Load Value=240sq ft×40psf=9600lbsSo, the total live load on the deck is 9,600 lbs.
5. Account for Environmental Loads
Depending on your location, environmental factors like snow load or wind load may need to be considered. The snow load is particularly important in colder climates.
If you're building in an area with snow, check your local building code or snow load chart to determine the appropriate snow load. For example, snow load could range from 10 psf to 50 psf, depending on your region.
For example, if you're in a snow-prone area with a snow load of 30 psf, you would calculate the snow load as follows:
Snow Load=Deck Area×Snow Load Value=240 sq ft×30 psf=7200 lbs\text{Snow Load} = \text{Deck Area} \times \text{Snow Load Value} = 240 \, \text{sq ft} \times 30 \, \text{psf} = 7200 \, \text{lbs}Snow Load=Deck Area×Snow Load Value=240sq ft×30psf=7200lbsSo, the snow load on the deck is 7,200 lbs.
6. Total Load on the Deck
Now that you have the dead load, live load, and any environmental load, you can calculate the total load on the deck. Add the values from each category:
Total Load=Dead Load+Live Load+Environmental Load\text{Total Load} = \text{Dead Load} + \text{Live Load} + \text{Environmental Load}Total Load=Dead Load+Live Load+Environmental LoadUsing the example numbers:
Total Load=2880 lbs (Dead Load)+9600 lbs (Live Load)+7200 lbs (Snow Load)=24,680 lbs\text{Total Load} = 2880 \, \text{lbs (Dead Load)} + 9600 \, \text{lbs (Live Load)} + 7200 \, \text{lbs (Snow Load)} = 24,680 \, \text{lbs}Total Load=2880lbs (Dead Load)+9600lbs (Live Load)+7200lbs (Snow Load)=24,680lbsSo, the total load the deck needs to support is 24,680 lbs.
7. Calculate the Load per Beam
Next, you need to determine how many beams will be required and how much load each beam will carry. To do this, you need to determine the beam spacing (the distance between each beam). The span chart will help you identify the maximum beam spacing based on the beam size and material.
For instance, if your span chart allows for a beam spacing of 8 feet, and your deck is 12 feet wide, this would mean you need 2 beams across the width of the deck.
To calculate the load per beam divide the total load by the number of beams:
Load per Beam=Total LoadNumber of Beams=24,680 lbs2=12,340 lbs\text{Load per Beam} = \frac{\text{Total Load}}{\text{Number of Beams}} = \frac{24,680 \, \text{lbs}}{2} = 12,340 \, \text{lbs}Load per Beam=Number of BeamsTotal Load=224,680lbs=12,340lbsSo, each beam must support 12,340 lbs of load.
8. Use the Deck Beam Span Chart
Now that you have calculated the load per beam, you can refer to the deck beam span chart to determine the appropriate beam size. The chart will provide information on how much load each beam size can support for a given span and material type.
For example, if you're using a 2x10 wood beam, the chart might show that a beam of this size can support a maximum load of 12,000 lbs at a span of 10 feet. Since your calculated load per beam is 12,340 lbs, you may need to use a larger beam, such as a 2x12, or reduce the span.
If you're using steel beams, the span chart will give you similar information, but steel beams can typically support much larger loads, allowing for greater spans.
9. Finalize Your Beam Size and Spacing
After checking the deck beam span chart and ensuring the selected beam size can support the load, confirm the beam spacing as well. The chart will also provide maximum spacing distances for the selected beam size to ensure safety.
If the calculated load exceeds the span chart’s maximum load capacity for a given beam, you will need to adjust your design by either increasing the beam size or decreasing the span.
Conclusion
By following these steps, you can accurately calculate the loads your deck will need to support and select the right beam size and spacing using the deck beam span chart. The key steps involve:
- Understanding the types of loads (dead, live, environmental).
- Calculating the deck area and the loads.
- Determining the number of beams and the load per beam.
- Referring to the span chart to select the right beam size and spacing.
Always ensure you follow the guidelines and consult with professionals if needed to ensure that your deck is safe, stable, and compliant with local building codes.
