MPx

On the surface water management...you're likely to get a condition in your planning saying that its got to be dealt with within the plot. Soakaways are the answer but sizing them is a bit of an art form these days with the changing weather patterns (ie deluges giving several weeks worth of average rain in an afternoon.)

Will be interested to see the "right" answers to this, but my layman take is: Have the soil stack in the bathroom rather than bedroom if poss - it will make a noise but can be lessened with boxing in and sound deadening insulation. You only need one 110 pipe with a suitable fall running from the top right corner of the En-suite to the stack in the corner of the Bathroom. The toilets will need their own branch in at 110, but all of the other elements can be run in their individual 40mm/32mm pipe to the nearest point on the 110 and connect in there with an adaptor Of course they all will need their own individual trap near their outlets. The stack needs to run up and out above roof level for venting - and if it was me I'd put an air admittance valve above the outlet of the basin in the en-suite (the furthest element from the stack) and that will stop any gurgling - but many don't seem to bother with AAVs and accept gurgling.

All good points above. We had our last set of soakaways sized "for the 100 year storm". Which happened at least 5 or 6 times over the next decade. In fact I did put in (more than) enough capacity - but still got caught out by the failures. I had 8 downpipes on the house, 2 on the barn and 5 Acos across the drive. My early warning was the one on the front of the barn which would always block first (leaves, helicopter seeds, muck). That was the signal to check the Acos - cos if they blocked, a flash flood was a serious possibillity. Clearing the downpipe head baskets was on my monthly jobs list - and in max drop season could be needed weekly.

Thanks for the welcome Susie. I'll always help if I can....but much more likely to be asking Qs than answering. So much has moved on in the last decade ... and not just the pricing!

Just joined - have already found lots to interest me. We are about to start building our final home to see us out. If you don't want a flat or small house with tiny rooms when you get old, the UK housing market has nothing for you so clearly self build is the (only) way. It will be our first as well as last, but we're not entirely new to the game. I've done major refurbs of houses in my spare time for all of my adult life. The last one had a false start in 2012 when we found more issues than we'd planned for and were in a caravan on site from Feb 2013 to May 2014. The unexpected issues story repeated throughout the refurb and we realised too late we would have been significantly better off bulldozing the original and starting again. We even had to dig up and replace the slab when otherwise half way through! Anyway, although others did "the build" to a water tight shell, and others did the plastering, laid the slabs and installed the GSHP... I did the rest. Heating, plumbing, electrics, tiling, bathrooms, kitchen, hung the doors, etc etc. When we moved back in in 2014 we had 4 rooms and I didn't finish the rest until 2016. Worked on the landscaping thereafter and still had little projects I wanted to do right up until we left a month ago. So I'm incredibly slow....but I do it how I like it. Hoping to follow a similar plan this time with others doing a timber frame Passivehaus for us and then to clad it, etc. before I can take over for fit out and services. We'll see. Not expecting it to be even remotely as easy as that sounds - energy levels approaching 70 are nowhere near the as good as they were in my 50s. We've already been on it for over 2 years just getting through the planning stages - how hopelessly depressing that process is! Anyway, hoping to learn much from the experience and expertise here...