Hi
I'm planning to block-pave around my house to include a patio and a parking area (in total about 65 square metres). Ideally I would have laid the inside blocks directly against the house walls, but that is not feasible for various reasons. I would like your help in finding a solution. I set out in hopefully relevant detail further information below.
The house and ground layout
I have a semi-detached house of solid wall construction built in 1926. The exterior wall lengths are 5.8 + 6.9 + 5.8. If you imagine a rectangle with a smaller rectangle inside, that would approximate a ground plan. The smaller rectangle has a wooden floor supported on joists and piers, with one external wall. The larger "L" has a concrete floor.
There was a 1m wide concrete path which ran around the three sides of the house, apart from a bed for plants which ran along 2m of the front 5.8 wall. A 50cm screed met the concrete. I had the path removed (and some of the blown screed fell off).
The original dpc is slate. At some points it is overlapped by the screed. At others and mostly it was at the level of or below the top of the concrete path. So it was either bridged by the screed, or nowhere near being 150 mm above the original path. (In fact, judging from my property a lot of the houses where I live have their dpcs below the level of the front hard surfaces or plant beds.)
At some point someone has injected a chemical dpc around part of the wall at about 200mm above the slate dpc. I have not removed all of the band of screed from the lower part of the wall, but assume the screed and chemical dpc are connected. (Perhaps I should have removed it before writing this to you.)
Additionally, the only gully (at the back of the house) is less than one brick's course below the slate dpc. And the gas supply is at about the same height as it comes out of the long side wall; it also then turns and runs parallel to the house on a fairly steep gradient towards the front of the house. Last, but by no means least, there is an inspection chamber in the front/side garden at about 3m from the front corner, the top of which is about 25 mm higher than the slate dpc. The pavement is at about the same height as the dpc and starts at approximately 2.5 m from the front of the house, before curving away to about 8 m. And finally, for what it's worth, the back garden level is higher than the dpc by about 50 mm.
My conclusions so far
The things I can't change are the heights of: the slate dpc; the inspection chamber; the gas pipe (or its gradient along the wall); the gully. As things are, I clearly cannot start the paving at the wall.
Having studied your extremely informative and helpful site, I think there would be substantial problems with any of the proposed solutions. The gully is too high for me to slope the paving to channel the water into it without substantially bridging the slate dpc (with the paving laid against the wall). Creating a dry area to channel the water to the gully would fail for similar reasons (and would not take into account the two steps I have to incorporate for the front and back doors). A French drain would have to negotiate two steps and the gas pipe. It also looks like it would be a complicated arrangement to drain the water away from each side the house. A sharply sloping first course of blocks would have to start a little above the dpc to get over the gas pipe (and the blocks would have to remain loose over the pipe).
I'm stuck.
I thought for a while I could simply continue the chemical dpc all around the wall. However, at the back of the house, it would not protect the suspended wooden floor. So I would need to step down from the side to the back and would still have to find some other solution for the back, where the gully is. (An attachment to one of the postings was fairly critical of chemical dpcs as a solution in any case.)
I wonder if a viable option would be to create a trench between the wall and the edging, say 100-200mm wide (with the concrete laid within shuttering to maintain a gap to the wall). I would fill the trench with pea shingle to, say, 60 mm below the dpc (the height of the gully) and let any rain drain away. The soil drains very easily and does not seem to contain any clay. The paving itself would slope away from the house, so most water would be carried away. I assume in any case that with block paving a fair amount of it must drain directly down into the soil, so I wonder if there is any real harm in my proposal. (I saw in the Collins DIY book the author suggested something similar to remedy a situation in which a path or patio had already been installed above the dpc; ie cutting a trench into the edge of a pre-existing path or patio.) What worries me about this is that you make no mention of such a possibility (that I could see)!
What do you think? How would you deal with the problem?
Kind regards,
Tim