Besides the following:
1. Rebound hammer
2. Ultrasonic Pulse Velocity Test
3. Core Sample
What are other ways to test for voids inside concrete? Would there be a direct X-ray test?
What's the typical slope for a 6 meter by 6 meter metal roof and 12 meter by 12 meter metal roof?
Is the slope double for area that is twice larger?
Is there a rule of thumb formula for the size of metal roof, how fast water move down it?