Thanks.
A couple of things I've never questioned before. Is there a minimum depth of concrete for foundations and is it always gen1 for single storey and gen 3 for 2 storey?
If you work to approved document A, minimum concrete thickness is 150mm.
Although I've had building inspectors in the past claim that reinforcement is required in any concrete footing less than 300mm thick, so have just worked with 300mm as minimum thickness for a mass concrete foundation.
You can use gen1 for a 2 storey trench fill foundation