Attic Truss Bottom Chord

About the bottom chord.

Attic truss bottom chord.

Attic trusses are popular over garages or anywhere people want to increase living or storage space without adding another floor to their structure. For traditionally spaced trusses the bottom chord is cut out of 2x4 or 2x6 dimension lumber but can also be cut out of 2x8 2x10 2x12 and even lvl material for roof trusses. Removal has left them extremely vulnerable to collapse due to spreading especially under snow loads but also under just the load of the roof itself. The horizontal beam of the triangle of a bottom chord is used in this simple triangle truss construction.

Change the bottom chord depth to match your floor structure depth for floor 2. Factors that determine the size of the bottom chord include on center spacing dead loads applied to the truss span and if there is any pitch applied to the bottom chord. On the general panel of the roof truss specification dialog. The bottom chord therefore carries combined stress of both tension and bending of the truss.

Top chord live load snow and other temporary loads top chord dead load roofing materials weight of the truss itself other permanent items attached to the roof bottom chord live load storage or living space and bottom chord dead load. Those trusses were engineered with a heavy critical dependency on the bottom chords which are in tension. Truss capacity is listed by pounds per square foot based on the following load rating criteria. A triangle is the simplest form of a truss and the bottom chord is the base piece.

The roof system is basically a hinge now. Check the box beside attic truss. In this case 11 7 8 will be used. The bottom chord is increased and loaded for live loads similar to floor systems in residential spaces.