This means that the interior is not disrupted at all and up to 40% of your costs can be saved. No other systems are as robust, maintainable and guaranteed as ours. We do not treat the underneath surface of the roof as it is not necessary.
There is no health hazard if it is left untouched unless you actively drill, saw or break into the roof. Splits or cracks can be sealed with a solvent-based varnish or similar. If you are looking to do work to the underside of the roof from the interior of the garage, then you would be best finding a separate contractor.
Any work of this type should be done with the doors and windows open, and a mask should be worn.