This is going to be long so thank you in advance if you take time to read and answer.
The house is about 1890, 3 storey, stone base and brick built, the 3rd floor is of breeze block construction. It faces Southwesterly towards the coast and all windows are at the front. One chimney breast is open the other is capped and sealed.
It has been rendered and internally damp-proofed in various areas due to high ground levels running along the entire length of the rear wall. The suspended floor has been taken out and a concrete subfloor added then covered by slate tiling (much of which has come loose due to what I think is damp in the subfloor). When the floor was lowered I don't know as I am aware that this would have affected the internal Vandexing if it was lowered after this was done.
My problem is that I want to remove the slate floor but I know that in order to do this I must deal with the back wall which I believe is causing damp to come in under the concrete floor. The house has been built abutting the boundary wall which then holds back a sizeable amount of very wet earth in my neighbours garden. The wall is at ceiling height along the entire back of my house and the soil is about 4 ft up the wall. This acts as a wick bringing water into the brickwork of my house which the previous owners dealt with my Vandexing but as the floor seems to have been lowered at a later date I think this has now failed and is causing water to move under the concrete floor.
I cannot find evidence of a DPM and I need advice as to how to try to find it. I have checked behind the skirting boards but the concrete goes right to the edges of the room with nothing sticking up that looks like a DPM. If there isn't one I know I must dig up the floor and start again but due to the off road location of the house I really want to avoid this for cost and labour reasons.
I know the right thing to do would be to dig a trench in the garden, membrane the wall and backfill but because the the house has been rendered and vandexed there is no chance of the house ever drying out. I know I should take all the render off the house internally and externally and restore breathability but I just do not have the money to do that and I am not sure the house value would make it worth it so I am wondering if my plan be sounds like an option
Plan B consists of dealing with the subfloor if there isn't a DPM by digging up and replacing then using Newton membranes along the back and sides of the walls to create a sealed unit a bit like a basement. I would then put stud walling along the back wall and batten and board the rest. With regard to ventilation I already have large dehumidifiers fitted in both kitchen and bathroom and passive vents in all other rooms. We also have lateral penetrating damp throughout the middle floor which I am hoping to fix by patching the render in the spring. I have a budget of £20k but was hoping to put I a new kitchen aswell.
Am I going down the right track or is there a better way of doing this? Any advice would be greatly appreciated.