Ed_

It seems to go away. No signs of flooding or waterlogging. The gradient is minor but still that would prevent any sort of flooding, the water would just run off. In the end there is a road at the lowest point, and if it gets that far it will enter the drains.

Houses. This is an urban area. All the houses up the hill, so far as I can tell, drain to back garden soakaways.

The foundations will be down to the clay, it's a basement so will be a sort of raft. Soakaway can be downhill and I could put it 15m-20m away I think. You are right, best to dig a hole and see what happens first.

It says to a depth of 300mm below the invert pipe. That will be fairly shallow, within my made ground layer. From part H the depth seems quite clear, but when I read about soakaways and percolation tests, a lot of the Information suggests I should conduct the test in the undisturbed layer, ie the clay below the made ground. I feel reasonably content that doing the test in the made ground will give me a representative result, and if successful a working system like the existing one, but I am hardly an expert.

No...

100mm. Attenuated to 2l/s, I think.

Doing a demolish and rebuild. Existing rainwater went to a soakaway, which unfortunately had to be removed. I have 1-2m of made ground over clay. Clay is, apparently, essentially impermeable. Don't bother with a percolation test they say. All well and good but I've been quoted £25-30k for connection to the surface water drain - 8m away across a quiet residential road! I'm sure I can find a cheaper quote, but got me back to thinking about soakaways. Clearly the existing soakaway worked, I'm on a very slight slope and I guess the water percolates through the topsoil/made ground downhill, slowly adsorbing, evaporating and eventually ending in the river. The advice on a percolation test seems to be to dig it at the level of the soakaway. If I choose a broad flat soakaway design, I'm sure I could bring this above the top of the clay layer and reasonably expect it to drain adequately. Is there anything wrong with this logic? It seems percolation tests aren't exactly very well controlled.

My understanding is that having the insulation on the outside is better for condensation, as it means the concrete is warm. Insulation on the inside and the concrete is cold so the condensation point moves to inside the wall, potentially.

I've been round the internal v external debate so many times. You are right but I can't work out what to do about the cold bridge through the ground floor slab. How effective is a bit of external plinth insulation going to be to stop that? At least external is continuous. Maybe I am worrying about nothing. Will add a drawing later to help!

It would, it just needs to be thicker obviously. I'm limited to 100mm insulation where the timber frame joins the slab at ground floor level, to give a drip edge to the timber frame insulation. So 250mm EPS for example is quite a step out and probably won't look great, hence why I was thinking PIR as the thickness needed for PIR above ground is about the same as EPS below ground.

I am building a walkout basement, this means that down the sides the ground level will slope, from top of basement at front to floor level of the basement at the back. I'm struggling to understand how to detail the above and below ground insulation. i think I need to use EPS below ground and PIR is not suitable. As it's below ground, I need less, so 150mm EPS is ample, but that won't work above ground, so I thought I'd use 150mm PIR above ground and that works about roughly equivalent. The issue I'm struggling with is how to detail the transition given the slope? Can I just butt them up, render over the top to just below ground level and put in a french drain? Should I cut the insulation to match the slope (with lots of wastage) or just get as close as practical using blocks? I was planning on just adhering directly to the concrete.

Not really an option unfortunately, can't impact drive due to proximity to sewer in the road, and anything else is expensive. If I have to I will put the Insulation on the inside, it's not the end of the world, just trying to work out whether it is internal or external because a lot of decisions depend upon it and it's not turning out to be a straightforward decision.

The other sides are battered back, so traditional formwork. I have 1m to the boundary, so 350mm piles and 250mm insulation doesn't leave me much working room!

I likely need to pile one side of my basement as can't batter back. Will be CFA piles in concrete. I would like to use external insulation, mainly to avoid cold bridging at the ground floor slab. If I have a line of piles, can I place insulation against that, then cast concrete against the insulation? Is that practical? I know concrete cast against piles is fine but can't get my head around what happens with insulation in the mix as well. Any experience gladly received!

About 2.5 weeks is the stand-up time it appears, it has now started to collapse! Nice to know I wont be spending money for no reason.

I'm 1m to the boundary. The current neighbour building is 2.5m and new ones will be 1-1.5m. Many reasons for a basement: More space - urban plot so footprint limited. Ground slopes- front is 2.5-3m above back, basement spans this slope so GF is ground level at front and basement is ground level at back. I have made ground with possibility of a slightly mobile slope so would likely have needed deep foundations anyway. As it is walkout it both becomes cheaper to build and more functional than a traditional basement. Hopefully.

No, this actually is the neighbour's, not me trying to cover up! 1m made ground over stiff clay (site of a former brickworks, 100 years ago), but with a severely sloped section that probably needs to be levelled for a piling rig to work, just out of shot to the left on my picture. This is my new focus, seems to me if I need to pile why not weld them up (or similar) and that is my boundary. Ring beam on top to put the rest of the house on and insulate inside. I'd been avoiding this as it seems like a retrofit basement method and i'd thought that implied high cost, but it could be the best solution for my constraints.

Fabulous @Gus Potter, been scratching my head for weeks over this one and don't think I'd have ever worked it out myself. Looks like a temporary works engineer will be my next call.

@Pendicle How did you assess the slope angle?

Learn something new everyday, rubber duck excavator! Would you mind sharing details of the piling firm you used with me? I don't think I'm too far away.

I've looked into kingpost, but at first study it looks like being no cheaper. Still have to mobilise the piling machine, piling mat etc. Additionally probably need a crane because how else do you get an 8m long steel into a narrow hole, then need to pay for concrete for the panels and probably some sort of gravel to back fill the reverse side... Seemingly everywhere i look people (professionals even) are doing this sort of thing without a retaining structure, are they just risking it or am I missing something? I don't intend to just risk it.

I am excavating a basement and due to the confined plot there is not enough room to batter back at what I believe to be a safer battering angle, which seems to be 45 degrees at best from any seeminly scientific source I can find, therefore I had imagined I had to create a retaining wall. Said retaining wall, in piles, is going to cost in the region of £30k. What is giving me pause is that almost every picture I see on industry website, e.g. waterproofing specialists, shows bare earth battered at 60+ degress and seemingly without any safety measure, for example: And then the neighbouring plot to mine have done almost the identical excavation to me, and left it like this: I see how this could be safe whilst excavating with a digger, as no one is in the collapse zone, but how about doing any work under it? To me, it seems unlikely the bank would suddenly collapse, it will probably be fine, but thats not good enough when the consequences could be death? Just looking for views and experience on whether there are ways for a contractor either to safely build a retaining wall behind this or to erect shuttering for a basement, or whether my gut feel that it has to be a proper retaining wall or similar is correct. Thanks!

The advantage of private is if you choose someone who is accepted by your warranty provider they can share reports and you save some cash. Protek won't take LABC. That said, my architect said LABC are better than private since the building safety act, as private providers have gone very risk averse and LABC are more pragmatic. Your mileage may vary.

I've been to see the construction of the viaduct and tunnel through the Chilterns, very impressive. However the project is full of aberrations, like the bat tunnel. Spending £100M on 1km is ridiculous, I'm sure you could achieve the same result with a much more modest structure like netting or bat scarers when the trains are due or whatever. But give the problem to a company employing large civil engineering consultancies working predominantly in concrete and you will get sold a concrete tunnel and clearly no one at HS2 is sufficiently incentivised to keep costs down. Try that solution at a private company and you'll be off the project immediately, someone else will be found for a more effective solution, and they are still working to the exact same regulations.

I was asked for a demolition and construction environmental management plan. Something the neighboring 10 property development was not asked for and I couldn't find any other examples of a single property development being asked for this. Unfortunately, I'd been too distracted by fighting to remove other unnecessary conditions like an ecological impact assessment that my architect was just waving through. I believe there is a conflict of interest as architects will often be able to charge to discharge preconditions so there is no interest in them trying to negotiate them away. Certainly not from mine. I regret not spending longer arguing them.