How To Support 20 Foot Roof

Minimum roof loading is 20 lb sq.

How to support 20 foot roof.

Weather you re building a shed roof or adding a dormer to your second story it is important to choose the proper size rafter. For a 20 foot span wood beam needs to be minimum 18 inches deep. Just keep in mind that if the length of the board size is more than 20 feet then you need to use a more expensive type of lvl board and not a traditional pine board for this longer length. Your top chords can protrude beyond the bottom chord anywhere from 1 3 feet 0 30 0 91 m.

This number represents the total load that your roof must carry. Calculate the weight the beam must support. Better design with truss 2 feet deep or more depending on snow load. Multiplied by 40 pounds per square foot equals 8 000 pounds.

If an example roof is 10 feet by 20 feet the total area is 200 square feet. Finally the truss calculator will compute the best dimensional method to connect the pieces of the truss with steel joints and a bridge. The steeper the roof the more expensive the trusses get because the longer the boards get and the more roof area increases. This sizing guide for roof rafters will help determine what you need for your small project.

For example 4 12 pitch means 4 inches of rise in 12 inches of run. For a flat roof with snow loading this is 25 lbs. The larger the roof is the more support that you are going to need. Almost any wood will do the same geometry of beam or truss is the important thing.

For larger porches such as wrap around porches you will want to make sure that the support is more than you need. Multiply the load per square foot by the total area of the roof. Multiply the loading per square foot by the area in square feet of the surface which the beams will be supporting. Feet more in presence of snow.

On some roof trusses the 2 top chords extend down over the edges of the bottom chord creating a built in overhang. If smaller beam will sag ugly. Per square foot for northern areas of the u s. The vertical rise of the top chord per 12 horizontal inches is the roof pitch or slope.

I have a span of 26 feet. For rooms which are heavily frequented it may be 50 lbs. There are several variables to consider when determining the proper rafter size.