Your beams will need to bear the load of not only your decking materials but additional components of the frame itself.
Formula for determining deck load with a roof over.
7 feet the distance between the ledger and the beam divided by 2 half of the load multiplied by 12 the length of the deck multiplied by 50 psf the load which equals 2 100 pounds.
Multiply the load per square foot by the total area of the roof.
If an example roof is 10 feet by 20 feet the total area is 200 square feet.
To do this i use conservative too heavy dead loads and full snow loads regardless of pitch.
Default is 50 psf which you can change.
To determine the maximum load capacity of your deck start by calculating its total area and multiply by 50 psf.
Determine the transient load of the roof.
Don t get confused with what weight you might think or want to load the deck with.
It then determines the total load from each tributary area based on the design load of your deck.
This is the amount of weight that must be supported by the pier.
While joists provide a horizontal support system for deck boards beams provide support for the joists.
This number represents the total load that your roof must carry.
For dead loads you are correct.
This number is then multiplied by 50 which is the 40 psf live load 10 psf dead load mentioned earlier.
The exterior wall and the headers within will carry all loads from the mid point of the house between the supporting walls to the outside of the house including the roof overhang.
Multiplied by 40 pounds per square foot equals 8 000 pounds.
Technically you should use the actual rafter length when adding up the weight of roofing materials.
This is highly regional as weights of snow for example range from 10 to 300 pounds per square foot based on moisture and volume of the snow.
However in my practice i typically use the horizontal run of the roof for both types of load.
If you drove a dump truck over it yes this would throw all our calculations out the window.
So a 100 sqft deck would be designed to support 5000 lbs.
Remember these loads are distributed uniformly over the entire surface of the roof.
Total number of boards dsa sbc x 1 1 calculate how much deck material you need for your new deck.
To determine the load of a deck pier you must take half the length of the joist span multiplied he length of the beam span measured from pier to pier.
Deck beams and joists go hand in hand as the framing materials for your deck.
The total load for each tributary area is then divided by the area of each footing in order to determine the load psf imposed on the soil.
This is all of the natural stresses imposed upon a roof such as snow loads rain loads and wind loads.
