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Hi @Trobo,
When building a flat roof, even with a low pitch, like 5 degrees, the timber that spans across the roof from wall to wall is still referred to as rafters. These rafters provide the primary structural support for the roof and are what you will install the roof battens onto, followed by your Colorbond roofing. So, even though you're not dealing with a traditional gable or hip roof, the terminology remains consistent for the horizontal members spanning the roof.
If you're looking at span tables, roof rafters are the key term to focus on, as they will help you determine the appropriate timber size and spacing based on the span and load your roof will need to support. You'll need to ensure the rafters are strong enough to handle not just the weight of the roof materials but also any additional loads such as wind or water.
As for ceiling joists, these would typically run horizontally on the inside, parallel to the floor, and are used to support the ceiling lining, if you plan to have one. However, in some flat roof designs, the ceiling joists may also be integrated with the roof rafters, depending on the height and structure you're aiming for.
Beams are usually found on the outer edges of the roof, particularly in skillion or flat roof designs, and serve to support the rafters. For larger spans, you might need a ridge beam or other structural beams to ensure adequate support for the roof, especially if your studio has wide spans between the walls.
It's always a good idea to consult span tables and verify the correct timber size for your specific design to ensure your roof is structurally sound. If you have any concerns, I recommend enlisting a professional's services, such as a structural engineer, to prepare some plans for you.
Please let me know if you have any further questions.
Mitchell
