Loading conditions are detailed below.
2 x 4 roof beam.
L stands for the span of the beam in feet.
The total load is 4 000 pounds.
A 2 2x10 can span 10 feet and so on.
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Two 2 by 4 beams together would not be enough.
For light load roofs 24 o c.
A 2 by 8 beam would be sufficient.
Refer to sfpa s publication southern pine headers beams download in publications that includes all size selection and allowable load tables.
6 8 10 12 14 16 18 southern pine.
Here we have a wood framed gable roof.
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The numbers in gray indicate the distance between the support posts.
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This type of beam keeps the building from spreading.
A two 2 by 6 standard beam has actual dimensions of 1 5 by 5 5 inches which would give a section modulus of 1 5 x 5 5 x 5 5 6 7 6 which is not enough for this example.
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Let s consider a basic gable wood roof framing design.
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For the initial calculation f can be estimated at 1 000.
For each application a pdf download is available.
Numbers in blue are joist spans beam to beam or house to beam joist spans.
In the example the beam spans the 10 foot width of the roof.
A double 2x12 beam can span 12 feet.
Spacing your 2 4 shed rafters at 24 on center limits the width of your roof.
2 4 rafters can span up to 7.
The formula for the section modulus is beam width times beam depth squared divided by 6.
A collar tie or beam figure 7 7 is a piece of stock usually 1 x 4 1 x 6 l x 8 or 2 x 4 fastened in a horizontal position to a pair of rafters between the plate and the ridge of the roof.
An essential part of planning a patio roof or gazebo project is determining the number size and spacing of rafters beams and posts according to the loads they will carry.
F stands for the beam s fiber strength in bending which depends on the species of wood.
Most roof framing is 24 on center and you can still build sheds up to 14 with 2 4 rafters at 24 on center.
Also see assumptions for table development.
The image below shows a cross section of our simple 12 x 13 house from the joist span tables section of this tutorial.
Now the example formula is 4 000 1 000 bd 2 9 x 10.
Continuing on from part 3.
Floor beam span tables of residential structural design we will now look at roof rafter and beam design.