As an engineer myself I will bet London to a brick that the engineer who signed off the design for this house had a disclaimer or notes on the approval drawing about general access under the house and the storage of flammable materials within. If he didn't he's a Numpty.
I forgot to mention above that the flanges on the beams provide some stiffness against turning moments in the horizontal plane and must be anchored correctly to the support columns or stumps.
This type of flooring system sucks balls when you have steel screw or driven pile systems (C-channel) and steel purlins with fully adjustable all thread that makes securing and levelling up the floor structure idiot proof.
Not affected by moisture, mould, rot, termites and much better performance in the event of a fire (although some wood derived structural beam systems claim better performance).
