Ground levels. Help me to dig!

[Willsa]

After discovering yet more horrors in my house (the concrete floors are much, much worse than I'd have ever imagined) I need to find a way to alleviate the rain under the floor slab. It will help no end once I get the whole of the ground flooring replaced

The dry rot "drinks" under the floor and then comes up via the cracks in the floor to eat everything in sight. There's tendrils in the screed everywhere...

Here's a pic: (that's my front door threshold chewed on at some point)




I won't get rid of the fungus for as long as it has plentiful access to water.
One of the jobs is to lower the ground outside that seems rather high but here's the catch:

 

[Willsa]

The area closest to the house was concreted over and also a concrete path leading all the way up to the house.
I've started digging up the concrete and I hit a wet, black earth underneath. Have to admit, will be easy to dig further!

I'm somewhat confused by the fact that the original ground seems to have been pretty high too?

Here's my dig and the slate DPC circled. The slates were level with concrete:

 

[Willsa]

I'm planning on an empty, grated over trench to separate the walls from the cloggy wet earth.

I know some of you have done that! How deep do I dig?
How to go about building a retaining wall?

 

[Willsa]

No wonder the floor rotted and this house has had concrete for as long as! The joists must have been earth-level. Certainly looks like it!

The under the floor void is very deep though, I can see brick dwarf walls waaaay below the earth levels.

 

[MatthewC]

I'm planning on an empty, grated over trench to separate the walls from the cloggy wet earth.

I know some of you have done that! How deep do I dig?
How to go about building a retaining wall?

Some of your dampness is due to rainwater bouncing off the concrete and keeping the base of the wall very damp so I'd go with the trench. You only need 100mm depth of gravel, with about 250mm width and the surface at least 150mm (preferaby more) below the level of the floors inside. If the exterior ground level is level with, or above, the floor level then you are better off with a French drain which is a new ballgame (Google it).

 

[Zebra]

I'm planning on an empty, grated over trench to separate the walls from the cloggy wet earth.

I know some of you have done that! How deep do I dig?
How to go about building a retaining wall?

Look at the thread "The Zebcolm Trench" in the Projects section of this forum. https://www.periodproperty.co.uk/forum/threads/the-zebcolm-trench.17575/

 

[Lacan07]

The area closest to the house was concreted over and also a concrete path leading all the way up to the house.
I've started digging up the concrete and I hit a wet, black earth underneath. Have to admit, will be easy to dig further!

I'm somewhat confused by the fact that the original ground seems to have been pretty high too?

Here's my dig and the slate DPC circled. The slates were level with concrete:
View attachment 10386


View attachment 10387

The air brick in the photo is pretty good indicator of how high the external ground level is, its not too bad but yes, definitely dig it out. If it were me I'd get a skip and take the lot out and not bother with trenches.

 

[88v8]

Here's my dig and the slate DPC circled. The slates were level with concrete:
View attachment 10386

The airbrick should be two courses above ground.
If you dig out, or rather when you dig out, put the top-soil aside and dig out the sub-soil and then put the top soil back.
I know that the garden may not be uppermost in your thoughts at the moment, but plants do not grow well in subsoil