How To Install Temporary Roof Supports
Vertical shoring against the top chord of the joist is most certainly the least expensive choice.
How to install temporary roof supports. Make sure that the beams support the roof well and are not left loose or wobbling. I would never install temporary shoring of open web joists on their bottom chord. We provide a nationwide installation service supplying to a broad customer base our shrink wrap encapsulation system for their projects. The temporary support that you use will need to have a firm footing in order to hold up the weight.
Use 2 inch carriage bolts to secure the posts to the mounting brackets. Place the wood on the floor or ground and hold in place with small screws. Attaching the two with bolts every foot or two 50 cm. Once it is plumb mark the position on the porch roof.
These pieces act as the bases that hold the legs of the support beams. I did not interpret your question as whether to support the open web joist on their top or bottom chord. The ideal height of such beams should be 2 10 foot longer than the distance between the roof and the ground. Once both of the brackets are secured set a post into them.
Bring in the temporary beams and install them in place. Install another bracket in this position. Use several bolts at the ends of the wider lumber 7x2. For a perpendicular support you should use square pieces of 3 4 inch plywood or other scraps of wood that are at least 10 inches wide.
Stand a post up in the bracket and hold a level on its side. Continue installing porch roof supports.