crooksey

Spend the money now, lay a pipe over 400m, wont cost as much as you think and problem solved (for life).

you could always approach the farmer, ask if you can site the septic tank on his land as well, then simply allow the other neighbours to route through your land on a sealed pipe. If you can negotiate £10k off the asking price, 5k, for the farmer and 5 for the tank works, you may have a quick solution.

Fine in the UK with a drainage field. Most of the time though building regs/planning will get involved and heavily question/advise against it.

Depends, if it goes to a drainage field also on your property, it will be a nightmare. Do you have a ditch/stream within your boundary you can discharge to, or a big enough garden? My advice, if you really like the property, consult a drainage engineer (or a local sewage company who empty spetic tanks) and ask for a quote and percolation testing to install a new sewage plant and drainage field. You can then find out 1) if its even fee-sable and 2) roughly what its going to cost. If you have a stream/ditch/river within the boundary, I could blindly estimate the supply and install of a sewage plant for £7-£10k.

How old is your existing house? Are you sure you have a structural slab and not a floor screed? Screed over PIR is generally a better option for a retro fit, and screeds also offer better thermal conductivity, personally I am not a fan of liquids, but look at modified sand and cement screeds, like Mapei Topcem or PCT Xtreme.

You are clearly very concered on heat loss, if the front door is the only point holding you back on going for UFH, its worth considering. If you are going for radiators, you could consider a H5 panel with a wood burner boiler, this will take excess heat out of the wood burner and use it to "top up" the output from your ASHP. I considered this for a long time (even purchased the panel) but then decided to just put new PIR, UFH and screed down. Pleased I did it now as can get away with 35C flow temps from the heat pump even at -3 outside and maintain 25 degrees inside.

Why not just replace the front door and raise the floor height further, is that an option? Have you got enoguh height in the doorways to add 140mm (this would be 70mm PIR, screed and finished flooring)?

A well constructed house with proper floor insulation should never need "chill removal" even on tiled floors. Works fine for every job I have been on and had zero issues.

fit bathroom loops on the same adjoining areas, if its a new build well insulated house it will be no issue. Hallways and corridors tend to get the most UFH demand (if you set your stat correctly). So if you run them off the same loops they are next to, you eliminate the short cycling issue.

Not the best to have the DPC breached, but probably not going to cause you any issues. Lots of times now I see gangs use wider DPC that flaps over both sides of the brick, then cut it back on the face brick once BC have signed it off

The way drainage fields usually work is they have to be level, so if the new area is much lower, it generally won't work as expected. If water level is 1.5 below ground, the outlet probably be at 1.65m below ground level. Its hard to comment more without seeing the drawings and the site, but the extension of the drain-field would need to be level with the existing. If you have overflow to a field drain, and this is allowed to stay in under the extension with building control, then I honestly don't see why they are insisting on an extension to the existing drain field?

16m2? Is that the size of the drainage filed being extended? Or is he wanting 16m2 of crates installing? (as thats huge). Soakaway crates are usually calculated in m3. Usually you are not allowed to mix a soakaway for rainwater to anything foul related (e.g. septic tank). As heavy rain can flood the tank etc. If for whatever reason you are, I would add a NRV from the new soakaway to the existing one, or add an NRV after the tank, before the soakaway.

Not without written approval and usually an increase in foul water costs or a one off payment.

SUDS regulations. BCO will sometimes allow a soakaway within 3m, all depends on the site, the reason and the amount of rain. Plot 8 borders the road, depending how big the flat roof is, the new run off from this roof is going to be minimal. Speak to the local authority, if you are just dealing with rainwater run off, you have a waterbutt for the new extension, they should allow a small soakaway closer to the boundary where your property joins the road, there will be no future building there, and we are talking tiny amounts of water. If you have a patio now where your new extension will be, you aren't even diverting more rain to ground, simply diverting it.

With rain doing that to your trenches, I am presuming you are discharging to a stream or ditch?

What did the percolation test come back with, when you say not suitable what was its value? From a contractors point of view, install a shared plant, pipe to river. If it was my house, I would want my own STP with its own discharge. If I was selling, install cheapest STP on my land and pipe into the existing shared output (if building control allow it). This could be done in 2-3 days, landscaping afterwards may be costly though.

Its not too hard, aeration encourages break down, allowing water to settle will leave solids at the bottom and a clear water layer on the top to be pumped out. Many old septic tanks and brick chamber tanks can be simply aerated that will produce the same quality of water as some sewage plants.

Any decent bathroom fitter deals with this on a daily basis and its never an issue, you are building from scratch, I am sure you can design it accordingly.

You generally don't have a drain outside for each bathroom item, one drain/soil pipe that takes it all, looking at that your utility sink could also go through the wall into that as well. Generally, you design a house so that a soil-pipe comes in, then goes straight up,so rooms above can also use it (bathrooms/en suites etc). Bottom right SVP I would have that go into a big curve, no need for access there, you can rod from the manhole in bottom left. If you wan't one crack on, but you want as few manholes as possible (for visual reasons anyway).

Twin chamber tank, then soakaway then drainfield? Should be twin chamber tank and then drain-field for a traditional tank (not sure if the rules in Scotland are different). Surface water should not really be going into the tank, if it is, it means silt and leaves can also get in, it also means the smell coming from downpipes could be horrendous. Also means in an extreme downpour, there can be too much water in the tanks and cause untreated effluent to enter the drain-field causing it to block. With all the rain we had last year, this has probably happened.

+1 Depending how thick the concrete is and if this area will get any vehicle traffic (during construction so large vehicles). You may want to construct a brick chamber, two courses of engineering brick in water bond. I would only suggest this if the area is getting considerable traffic though, as probably be 3-5 days work with a temporary diversion for the pipes required as well. I was on a job where this was required as there was regular tractors near this area, and the owner of the existing pipe specified, also meant the new chamber had no flex in it with the older fixed pipes.

Remove LVT and glue, latex screed again (2-3mm) then tile. Amtico or LVT is by no means a cheaper option, I have seen and installed LVT into kitchens £100k + kitchens.

Latex is just a 2-3mm skim coat on the floor to make it ready to accept LVT, you usually never remove it, if you had new LVT again in 10 years, they would re-skim with another 2-3mm of latex. You can remove it, but its like tile adhesive, sticks like **** (when applied properly).

Just to add, you can pay private building controllers for a "plan check service". The route you could go down is: 1) Get proper system design done (after percolation testing) 2) Submit the design for a plan check to building control/approved inspector, I imagine this would cost in the region of £1000 3) If building control pass the plan check, they can also then submit the design to the local water authority for comment (this is what's done in a normal building regs application pre commencement for a new STP). 4) If all of the above come back good, submit it all to a bundle to the EA, then they will have everything they need to make a decision.

Just an FYI, if you have a solid tank at the moment, you can have "septic tank conversion units" installed, to make it work as a sewage plant. usually requires a full clean down, inspection and install, not horrendously expensive. Less than £5,000 if your tank is solid, can be as low as £3k depending on circumstances.