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Raising the floor had crossed my mind. Russell, the steps down are a mix of practical and asthetic. We have a step down from the the old cottage of 175mm to increase the ceiling height from 2m (would've been a lower ceiling than the cottage ceilings due to increased joist depth), and then another step of 250 to create a split level kitchen/diner. This will still leave a good step or two down into the garden from FFL due to the sloping site.

I've emailed the SE, fingers crossed he can fit me in and can design a working solution. Love your ethos, G&J! Will certainly push for it if the SE can deliver in time. Its not even an old wall, just rubble they threw up against the fence. I would say probably 150-250mm looks like original ground, but it's scrappy at best. Its their AAV. We've made a new connection to the main sewer (we were connected to a shared run via the pipe the that the grey 110mm finally connects into), and discovered on excavation of our unused soil vent pipe (against back wall of house) that they had tapped into it when they had their extension built. We're removing our SVP and the AAV was the choice they made for venting rather than doing any major works. They can access the valve via a small panel in the return of the fence. Yep, you're right, it should've been sorted earlier. I just took my eye off the ball on that one as so many problems kept arising. Only yesterday did the water company finally sleeve holes in the neighbour's sewer run to prevent sewage seaping out and under my foundations. Formwork would certainly be a good way of shutting away the problem. I'd be a bit nervous about any further excavation so if would be great if it could be achieved without much of that! Russell, I hadn't considered ICF before. Will look into it.

Thank you everyone for your thoughts - it really makes a difference when it feels like you're just running aroud in the dark. Taking this back to the SE is good advice that I shall follow. The gravel board retainer on the wall detail is a for small section on the other flank. Unfortunately the neighbour's conservatory builders had piled the back fill up against the fence that was there. Shame they didn't put a proper retainer in at the time. The architectural tech suggested adding piers to a 100mm block wall, although they would need to be internal and this would be tricky with the timber frame inner wall. Flank foundations are 152x152 uc23 steels in concrete making a total groundbeam size of 352x352, and sat on 3 pads along that side, 2m deep at the garden end due to a tree, then 1.2m, and 1m as they move toward the house. When I mentioned my concerns of the proximity of the conservatory to the SE last year, he said that a lightweight masonry wall would be ok, so hopefully he can come up with something that works. We had so much trouble below ground with historic footings, sewage leaks from the neighbours, and 5 different victorian drain runs, that sadly I wasn't focussed on this impending issue. We have full planning. On the last visit from the private BCO, she said she was happy for block on that wall as long as it was brought up in render as it was built. She said it would be like building against a garden wall (my mind was set racing around moisture, ventilation etc at this point!). Fortunately, I'm not particularly concerned about the neightbour in question as I've just dicovered they've built the darn conservatory without regs anyway (it has become their kitchen extension!). In case of having to shelve the project for winter (shudders at the thought of zero insulation, and being without central heating as the boiler was in the old demolished kitchen!), would the b&b floor need protecting from the elements? Thanks.

Ah I think I see what you mean, but the it's only the one wall alongside the conservatory that's the issue really, as the all the gardens slope down that way. It's a combination of the conservatory sat on made-up ground/rubble fill, and our side flattened out into two levels.

Hi folks, I really need some help on this one please! I've started building and I'm not sure how to progress. Apologies that I've posted recently on this subject (without reply, unfortunately) - I can't work out how to delete it. I wanted to share a few pics/ updated drawings in the hope that it might spark an idea or two. So, It's an end terrace, DIY stick-build timber frame extension, building off of a groundbeam (steels encased in concrete). Wall make-up to be as shown in first pic. THE BIG SNAG!... One side wall will sit 100mm from boundary with neighbour and 300mm from their conservatory. Due to a sloping site, finished floor level of half the extension will be 225mm below the bottom of neighbour's conservatory, (and bottom of the conservatory to base of my wall will be 550mm) - see pic/photo 2. Meaning, I need to back fill behind my new wall up to the bottom of their conservatory (fill of approx 200mm wide by 550mm high). I need an alternative to my standard TF at this point but can't fathom it out. The architectural tech had a look this week but isn't sure himself - we bashed out an idea but it's far from perfect, and I'm not even sure it will work (see pic 3). A builder friend (who admits to having little TF experience) came up with another idea (pic 4) but I'm not sure if this will work either. MAIN CONCERNS Drainage/Tanking/DPC's/moisture control/breathability, standing up a TF wall pre-clad and sheathed in cement board (weight/ & this wall also needs to be sealed up against the neighbour's rear brick extension which sits astride the boundary), and I only have the 300mm gap between their conservatory and my wall to get to it) I'm desperate for a solution as I need to start getting this frame built before the weather turns. Any help to get me on my way will be massively appreciated! Thanks in advance Ad

It's the wall highlighted in yellow on the plan.

Hi all. My (mostly) DIY timber frame extension build is slowly progressing, with the block and beam floor now in. However, I’m currently stuck on the details of one of the walls and wondered if anyone here has had to deal with a similar situation, or could perhaps offer any suggestions? My architect has yet to come back to me with a solution. It’s an extension to an end-terrace cottage and all new walls will be timber, sheathed in cement board and clad in steel. On one side, the neighbour has a brick-built extension projecting 3m. It's astride the boundary and the party wall will form a part of my build (will become my internal wall). Beyond this, they also have a 4m long conservatory (that sits about 300mm in from the boundary, solid plastic walls to the sides), and my extension will continue parallel to this, and beyond. At first glance, the tricky parts are: 1. If I build a completely timber wall here, I’d have to clad it before standing it up, and if anything went awry, I’d never be able to get to it as there wouldn’t be room between the two buildings. I'm also concerned about the risk of fire in their conservatory, but that's a conversation for another day! 2. my ground beam and subsequent floor level is below their conservatory floor and footing (looks like pads at the corners but hard to tell) - the ground beneath the conservatory is mostly loose rubble, doesn’t seem particularly solid, and I need to backfill behind my wall to shore it up. Ideally, I’d build this wall in block and bring it up the inside face of the brick party wall (which is where the timber frame was drawn to sit). I’d then build the timber frame inside of this block wall and treat the blockwork as cladding, giving me an outer skin which would hopefully be maintenance-free. This raises a few more issues, however: 3. The first few courses of block would be below ground on the neighbour’s side, adding pressure and moisture (once backfilled) to the wall. I think I’d need to tank it part-way, and add an intermediate pier, as at over 3m high and 4.5m wide a full block wall would be quite slender. 4. I couldn’t tie the blockwork into the frame due to a.) having to build the block wall first and b.) the sheathing, wrap and battens already being on the timber when the frame is erected. I’ve been looking at the TRADA drawings below, trying to work out if there is a happy medium between the two. It would be great if I didn’t have to build such a high wall but maintenance remains a concern. All suggestions greatly appreciated, thanks.

I'm building it myself onsite, so for me it's the best overall system.

Ah I see. I'll look at the plans and see if that works. Thanks.

Yep my plan is to wrap the perf pipe in a non-woven geotextile to prevent silt ingress. I'll also be able to lift the fence panels out periodically for inspection. Unfortunately I can't fit in another row of Marmox blocks as it would raise the floor level and it's tight on headroom as it is (keeping first floor levels in line with those inside the cottage). I've installed both ACOs and perf pipe land drains elsewhere around the property. I like that the process of clearing the ACO's is uncomplicated, but my thinking is that the pipe wouldn't fill up with debris, especially if it fills most of the void. Neighbour is adjoining btw. Maintenance will be possible. Roof is flat.

Architect is happy to go down the gravelboard/drain route. I suggested perforated pipe wrapped in a geotextile to prevent the channel silting up which he's also happy with. I can then top that with stones too. Thanks for all your help guys 🙏

Great idea, thanks! It's not my fence, but I'll be the one replacing it, so could def do this.

@joe90 Have left messages, and awaiting a reply. There's a fence (which I'll take out during works) and then a roughly 2.5m wide tarmac'd section between that and the neighbour's house, so it's accessible from a build point of view. There'll already be an excavation there down to the top of the groundbeam which will be helpful, and there's a run of pin kerb/edging on the neighbour's side holding back the tarmac a few cm from the fence. It doesn't become such an issue after a couple of metres as the ground continues to slope down towards the rear of the cottage.

From reading previous Buildhub threads, I get the impression that splashback isn't such a concern across level threshold doorways, especially as they're often paired with a combo of drainage channels and cavity trays in adjacent masonry walls to raise the DPC. I've gone down the timber frame route as there's restricted width, and for me it's a much easier DIY material.

Do you mean move block&beam etc up?