Decking foundation advice required

[ColytonJohn]

Hi folks,

I'm about to install a deck in a corner of a garden where the soil is very soft (but not waterlogged). The height will be no more than 300mm but, due to being near a railway line that sees the garden regularly visited by rats, I want to eliminate any possibility of them gaining access to the void beneath the deck which would be an open invitation for them to nest (as regularly happens beneath neighbourhood sheds).

Furthermore one part of the deck will need to support a large octagonal summerhouse which will need more substantial foundations that the rest of the decking.

To eliminate access to the void (and as I don't want posts set in concrete) my thought is to lay a perimeter strip foundation of concrete and use concrete block to raise the height above ground to which bearers would be attached either on end or via a wall plate but the concern I have is that this may be overkill and form a tank that will retain any rainwater that dripped through the gaps between decking boards (although I will cover weed barrier with gravel forming a kind of soak away).

Alternatively I could set posts on concrete pads with anti-vermin net stapled to the bearers and sunk into the ground (but the aesthetic doesn't appeal much).

Any thoughts on this would be greatly appreciated.

Cheers,

John