Damp joist - external ground level

[benst86]

Recently moved into a Victorian terrace. There is damp on the rear corner wall (see photos). Looking under the floorboards at the rear of the house, the rear joists that runs parallel to the rear wall is also damp (not sure if you can see it from the photo, but you can see watermarks on it, along with what I assume is white mould on top). The ground below the house is dry. I think I can see a slate DPC, but I’m not sure.

Now from researching on this forum, I assume this damp is being caused by the high external ground level. The previous owners had laid a patio on top of an existing one. I am guessing this was done around 4-5 years ago. The internal floorboards are below the external ground level. The photos show this. There is concrete under the stone around the edge of the patio, and it also slopes towards the rear of the house. So I think rainwater has nowhere to go, except sitting against the brickwork.

in terms of solving the damp, am I correct in saying that water is soaking through the brickwork and making the joist damp?

how low does the ground need to be lowered? Could I just dig out a trench to the required depth and fill with stone/an aco drain (save lowering the entire patio level), or should I just do the whole lot?

Assuming that solves the issue, how long for the wall / joists to dry out?

cheers

 

[bobasd]

Best practice would be to lower the whole patio concrete 150mm below any DPC. Or, at least, remove the top patio.
Could be that removing the top patio is not deep enough, & both patios will have to come up?
Or, you could try your suggestion for an Aco drain - but where would the Aco discharge to? At the moment it looks like a French drain is in place.
Where do you think you can see a DPC - there should be one but i cant see it in the pics?

Your pics show what could be rotting joist tails seated on a probably rotting timber plate - you will need to remove floor boards to expose the timber plate and fungal damage.
The plate and maybe some joist ends will have to be cut out, and new arrangements made where all joist ends are wrapped in DPC material.
The soil in the void looks damp in your pics.
The skirting will probably need replacing.
The plaster hacked off to 1m in height.

 

[Nige F]

Assuming that solves the issue,

There is also the issue of air bricks ( lack of )