We have an issue with runoff from rain entering the sub-floor of our house (timber frame on posts/piles). The issue is caused by the external ground level being higher than the sub-floor - ideally we would excavate the outside to drop the level and provide fall away from the house, but unfortunately there are some existing features such as shallow plumbing that make this unfeasible. The other issue is the outside ground level overlaps the weatherboards to varying degrees and is causing some rot in areas.

Keen to hear your thoughts on my proposed fix - have attached a sketch below:
1 - Carefully excavate external ground level to expose rotten weatherboards.
2 - Remove bottom rows of rotten weatherboards and replace with a sheet of 6mm cement board coated in bitumen waterproofing membrane.
3 - Protect membrane with a sheet of corflute or polyethelene in areas that will be below ground level.
4 - Backfill against cement board and add fall away from the house.
5 - Pave surface and add in a channel drain to remove surface water.


Any other ideas or suggestions to fix this?