Roof Truss Deflection

All structural members will deflect or flex under load.

Roof truss deflection.

Allowable deflection is generally expressed as a fraction of the span in inches. Allowable vertical horizontal or other required deflection criteria. Spaced sheathing or 1x boards may be reduced slightly. 2x4f 2000psif 1100psie 1 8x10 2x6f 1750 psi f 950 psi f 1900 psi e 1 8x10.

Criteria for differential deflection from truss to truss or truss to adjacent. Because of this change most trusses designed using tpi 1 2014 will have a lower d l deflection than trusses designed using tpi 1 2007. The weight of non bearing partitions shall be permitted to be ignored for truss design purposes given the following conditions. Deflection is the bending or sag caused by loading.

Generally for roof trusses the deflection in inches due to live load cannot exceed the span in inches divided by 240 l 240 and due to total load l 180. The amount of flex depends on the magnitude of the load applied span of the member and stiffness of the member. Truss that would allow 2 5 16 total load deflection and 1 live load deflection. 610 mm on center.

Dead load live load and in service creep deflection criteria for roofs subject to ponding loads. Spacing a live load deflection limited to l 240 maximum and use lumber properties as follows. For a 35 ft. If a design is known to be good but has excessive deflection it points to another cause.

Codes provide the maximum allowable deflection limits for floor and roof trusses which is based solely on the truss span. The truss is a framework consisting of rafters posts and struts which supports your roof. Increased deflection can lead to a reduction of free height under the bottom chord which might prevent or upset the anticipated usage. Differential deflection tpi 1 6 2 2 1 non bearing partitions.

Deflection provides critical feedback on truss design. A trusses are spaced less than or equal to 24 in. For example the additional deflection of a truss holding doors suspended in a gable of an aeroplane hangar could prevent the smooth operation of the doors. Allowable spans for 2x4 top chord trusses using sheathing other than plywood e g.

This change is due to a new deflection criterion added to ansi tpi 1 2014 to correspond to the limits established in the ibc for deflection due to dead load plus live load d l.