Dampness and figuring out original ground levels

[Lithgae]

Hi,
House has had dampness in the hall and around the room on the other side of the wall in the picture. There are a lot of contributing factors, some of which I have dealt with (leaking gutters, leaking drain and downpipe (removed at time of the picture), and still to do (lift floor in room as I think the solum has been filled and is not ventilating).

I also suspect that the ground levels may have been raised at the front of the house in the eighties, or whenever the driveway was added. Its complicated by the fact that house was modified at some point in the late 1800's and the bay window and porch added (to the right in the photo), and I suspect at that time the floor inside of the existing part of the house was lowered, probably to get Victorian high ceilings. The vent in the picture actually angles down, and the floor level inside is about level with the top of the vent outside. I suspect the original outside ground level was at the top of the vent, because this appears to be where the sandstone block ends, and it looks like it is rubble that has been rendered over below this point.

I was digging down today to fix the drain and noticed that there is a stone plinth that was under the ground, and I was wondering if this is where the original ground level was (after it was lowered and porch added in 1800's)? Does anyone have any knowledge or experience of this, should the flat plinth I am pointing to in the picture normally be above ground?

https://www.dropbox.com/s/flq58gvotntwwrr/2018-11-04 15.15.57.jpg?dl=0

 

[malcolm]

Missed this post, It is difficult to tell from the photo. I work on the principal that interior floors or any woodwork like joists ought to be a bit above exterior ground level. Is that possible to achieve (even by digging a trench or something?).

 

[Lithgae]

Missed this post, It is difficult to tell from the photo. I work on the principal that interior floors or any woodwork like joists ought to be a bit above exterior ground level. Is that possible to achieve (even by digging a trench or something?).

Its probably possible, but what I am worried about is disturbing the footings, from what I have read that is something that should be avoided. My difficulty is knowing where the original ground levels were. I've been trying to source old photographs of the street to get an idea of how the front of the house looked before the driveway. At minimum I am going to slope the ground away from the wall and form a trench drain about a metre away, using gravel to level off. This would at least ensure any surface water would run away from the house.