Roof trusses are a key component of a construction project that uses timber framing. But their design must take place only when other elements of the construction are planned, and various things must be taken into account. It takes knowledge and skill to design a safe, effective system of roof trusses.

In this guide, we walk you through how timber roof trusses are designed using CAD software to define what is needed.

Step 1: Model the walls, floors, ceilings, main beams and roofing

Trusses require other objects for support in the building model. Walls, floors, ceilings, beams and roofing can all function as beating components to some extent, so they must be in place before trusses are added. The load bearing must be carefully planned and calculated, particularly for more complex projects.

Step 2: Generate the truss areas

The truss areas are generated by any objects that limit the truss volume. Limiting objects should meet end walls snugly and all connections between trusses should meet the girder.

Step 3: Generate the truss members

The truss members are generated with user-defined rules to meet the necessary requirements. The designer must check the truss type and member parameters as well as the grade of the materials being used.

Step 4: Check all the connections

Connections between truss members must be defined. Truss member framing means adding connections between the members but everything inserted manually must be checked. The designer must check the fastener types and their codes to verify the capacity of the connection.

Step 5: Check all supports

There must be physical connection between all supported and supporting objects. Every single one of these connection must be correct, so the designer should check all supports and add connections where necessary. They must also check bearing all heights and the positioning of beams and contacts to ensure no bad support relation during engineering.

Step 6: Generate truss labels and drawings

Once everything is checked and verified, it’s time to create the truss drawings with member labels.

Step 7: Generate the internal pressure area

Internal pressure area means internal space limited by exterior walls as well as interior ceilings and roofing. If a ceiling is permeable, the roof limits the internal pressure area.

Step 8: Generate wind loads

This is an important step for roof truss design. The building code is the defining factor for the generation of wind codes. It incorporates the main wind direction and the meaning of exposure and enclosure parameters must be considered.

Step 9: Add additional line, point and area loads

These can be modelled manually. Loads should be modelled on the same drawing-model pair in which the bearing object exists. To apply line or point loads to bottom chords, the load must first be applied to the ceiling then moved into contact with the bottom chord.

Step 10: Run the engineering

Engineering can be run for any number of trusses or rafters. All trusses are mechanically tested and confirmed or flagged for manufacturing purposes.

Step 11: Check the engineering results

These can be viewed as a 3D model or 2D drawing. Stress indices are shown for each member and changes can be made where indicated.

Step 12: create the engineering printouts

Engineering results are displayed in printouts. Once everything is checked and confirmed, roof truss manufacture can begin.

Get in touch

If you’re looking for a timber truss and roof company, then Gosford Timber and Truss is a name you can trust. Contact us on 0409 437 201 or visit us at www.gosfordframentruss.com.au for more information.

We service MacMasters Beach, Hardys Bay, Fountaindale, Umina, Terrigal, Gosford, Pretty Beach, Bateau Bay, Patonga, Avoca, surrounding areas, Killcare, Ettalong, Copacabana and surrounding areas.