It is always better to have a large rafter rather than be concerned with a sagging roof.
Lumber size for roof truss.
At the end of the day it doesn t matter.
Dead load weight of structure and fixed loads 15 lbs ft 2.
If your project had a rafter length of 8 or less a safe and strong method is to use 2x8 framed 16 on center.
2x4f 2000psif 1100psie 1 8x10 2x6f 1750 psi f 950 psi f 1900 psi e 1 8x10.
The room size will vary depending on the width and slope of the truss.
A gambrel room in attic truss also provides extra living space while giving your roof a barn like appearance.
Spaced sheathing or 1x boards may be reduced slightly.
Douglas fir maximum horizontal roof rafter span for lumber grade selected structural and no.
These trusses the meet building code criteria as specified by structural building components of america sbca and the truss plate institute tpi.
Gable room in attic trusses provide an economical way to add extra living space to your home or garage.
It is strong but shallow maximizing the use of lumber using available and ordinary lumber sizes.
The important point to keep in mind when you use your truss calculator is that every truss calculation is completely unique and is based on the size of your roof and its specific dimensions.
1 ft 0 3048 m.
Every truss designer has his own signature style.
The truss is a framework consisting of rafters posts and struts which supports your roof.
One will like to use a 2 6 1 yellow pine with a certain mending plate where another will like to use a 2 4 msr 2400 with an extra web.
Allowable spans for 2x4 top chord trusses using sheathing other than plywood e g.
Maximum and use lumber properties as follows.
1 psf lb f ft 2 47 88 n m 2.
For example in the rafter span table below the highlighted cell in the 40 live load table indicates that 2 x 8 southern yellow pine joists that have a grade of 2 that are spaced 24 apart can have a maximum span of 10 feet 3 inches 10 3 if designing for a live load of 40 lbs ft 2.
Live load is weight of furniture wind snow and more.
Pre manufactured stock trusses are constructed with spruce pine fir spf or southern yellow pine syp lumber.
Visit the roof framing page for more information on cutting roof rafters and visit the roof pitch calculator for determining rafter lengths based on rise and run.
They are designed at a 4 12 pitch to be spaced 2 foot on center.
Trusses must be designed for any special loading such as.
A stick framed house used 20 643 board feet of lumber while a component framed house including roof trusses used only 15 052 board feet of lumber.
A 4 12 pitch means that the roof rises 4 inches for every 12 inches of run.
I hope this clears up the muddy water of truss design.
There s already been mention of using a prefab set up when appropriate and you can always attempt to negotiate a lower labor fee for larger projects.
