Gabriel the Toad

I've started talking to a few builders now, and one to-day was initially very keen on moving the sewer. But then when he saw it was shared with the neighbours' houses (it runs along the front of a row of four houses, of which mine is the second, serving all of them) he went right off the idea, saying it wouldn't be possible to move it. Is that the case? Am waiting to see what the other builders say now...

Thanks for the continuing discussion - it's very interesting. This idea of the sewer diversion sounds great. But I understand the comment about needing "ICs" - inspection chambers? - at direction changes to mean a new manhole at each? That sounds expensive, so am wondering if the number can be reduced. I attach a Google maps image, showing my house (left) and neighbour (with the same extension that I want, already built!) on right. The yellow line represents the existing sewer, which starts at a manhole on my neighbour's drive, and flows right to left to a manhole on mine, then beyond. The green line is an idea for the diversion which would require just two new manholes (and modifications to my existing one too I guess). Is that acceptable or are the changes in direction too sharp, are there any regulations about that? The blue line option would remove the need for another, but would require cooperation from my neighbour, and I'm not sure if it offers any real advantages. The flow down the sewer from next door must be fairly minimal - it only serves a downstairs WC and basin - would this, combined with the additional bends, make blockages any more likely? Can anyone make a rough guess at what such a sewer-diversion project might cost?

Hi, thanks for all the discussion so far! It's giving me lots to think about! When it comes to points about the small size of the extension - the idea is not to increase the value of the house, as I have no plans to sell, and definitely don't want to move. Although turning a poky single bedroom into a reasonably-sized double might increase the value, actually I want a 'hobby room' which is ideally long and narrow (I intend to build a model railway around it!), and when a figure of £30k was mentioned I decided that was acceptable to me. Any other kind of extension would be difficult - house is link-detached so cannot go out sideways. A loft conversion would be possible (some others in the road have done this) but the height of the roof ridge is very low - and I'm 6'1". Extending out backwards might be possible, but the garden is small and a first floor extension there would definitely annoy the neighbours. I did think of 'filling in' the base of the new extension to make a bigger downstairs hallway, but wouldn't find this space very useful, and it would also block some light and views from the living room window. Also the intention is to match the appearance of my neighbour's extension. Re the course of the sewer - this runs along the front of a group of 4 link-detached houses, then into the road. My neighbour's extension did not have to worry about this, as they are on the end of the row, so the sewer commences at their manhole, it doesn't go under their posts. So looking at the Southern Water website, it looks as though I could apply for "build over" permission myself, and pay the £771.60. I'm not sure if I have all the documents they detail on this page though... will have to go through what I have... also unsure what happens if they refuse permission; is the money lost and I have to get revised plans, with the posts moved, and start again?

I've posted a couple of extracts below. Thanks for all the responses so far. It seems the general consensus is to now find some good builders myself, pass them the plans and structural calculations produced so far, and get them to come back with quotes...? Then when I find one, the builder will get me to sign a contract (which I may not fully understand, so will have to get advice on, I suspect), and everything will proceed from there? So if I do that, how much further involvement need the current architect have? They have this "CDM Principal Designer" role, is that still relevant once the design is finalised? When construction has commenced, I guess building control need to be involved to inspect things - does any other inspection process independent of the builder need to be carried out? The structural engineer originally planned to set back the supporting posts so that they were not over the sewer. However I wasn't that happy with that idea - it would look strange, and I was planning the main route to the new 'porch' formed by the extension to be from the side. Engineer queried depth of sewer, which I estimated as "From the 'lip' where the manhole cover sits (ie the level of the underside of the thick concrete cover) to the top of the pipe is 66cm, to the base of the pipe is 80cm". He then worked his figures based on having the posts at the corners. But I suppose if this is refused, then the earlier idea can be returned to...

I've been reading this thread with interest - this seems to be one of the few fora on the internet that goes into these things in any detail. I'm not a self-builder, but am planning an extension. This is the first time I've initiated any building project, and as a complete novice I've been rather (unpleasantly) surprised at the costs of the stages before I get to 'spades in the ground'. It feels rather like HS2! I don't have any previous experience of the process to know whether I'm being, shall we say, overcharged or not, or whether there are ways that I can safely 'cut corners'. My planned extension is very small - a first-floor extension of about 2.5m x 2.5m sticking out above the front door, on stilts, doubling the size of a small single bedroom (copying an identical extension on my next-door neighbour's). A rough estimate by a local builder was that it would cost about £30,000 to build. I hoped that 'preparatory' expenses might be a few thousand. So I engaged an architect to draw up plans, and submit them for planning permission. The cost of planning permission to the council was £528 (standard I think) Fee to architect for plans - £995 + VAT. Then on to: Building Regulation Application - fee to architect £1,450 + VAT Health and Safety CDM Principal Designer role - fee to architect £950 + VAT Structural Engineer (separate company) calculations £600 + VAT Building control approved inspector (separate company) £695 + VAT That's the point that I'm up to now, something over £5,000 spent. I rather thought that by now I'd have all the detailed plans I need, and could call up a few builders, get quotes, and push ahead. But my architect has quoted for continuing the process as follows: Working drawings consisting of further junction details and setting out information. We will also produce an indicative small power/ M&E plan for pricing purposes. £1,950 +VAT Tendering to an agreed list of contractors. We will produce prelims and a pricing schedule to be sent out with the drawings and specifications. We will answer queries that arise during the tender process, analyse the costs once returned and provide a summary. £2,950 +VAT Preparing the contract based on a JCT Minor works, acting as contract administrator, attending site visits and the ongoing CDM Principal Designer role. Our cost for this are TBC as it will depend on the time scales and duration of works on site. Once we have a better feel for the length of involvement on our part we can provide you with a quote for this service. Any site visits will be charged at £120/hr +VAT. The above is based on the approved panning drawings and excludes changes in the design or scope. Interior design and landscape design are excluded. The above also excludes work associated with the building over notice. We would suggest this is submitted by either the builder or engineer [[the 'stilts' will sit over a sewer]] ...so this is another £6,000 for the first two, and "TBC" for the third. Just wondering (a) if these quotes seem reasonable, and (b) if I can shortcut any of this? For example: the "working drawings consisting of further junction details and setting out information. We will also produce an indicative small power/ M&E plan for pricing purposes". Do I need these? What are 'junction details'? I have the "Proposed floor plans" from a previous stage, which have some details (but no dimensions). If the 'small power/M&E' plan refers to electrical and plumbing stuff, this should be quite simple as it will just be moving one radiator, one mains socket, and adding a light fitting. And "Tendering to an agreed list of contractors." - is this anything more than sending out the plans to a few builders and getting quotes? £2,950 + VAT sounds a bit steep for that... Is it a skilled job, or one I could essay myself? Not quite sure what the 'contract administrator' piece is all about, nor how much it is likely to cost. . I did email the architect asking these questions, but they replied to 'phone them and talk it over. But before I do that, I'd like to be a little more confident as to what I'm talking about... Any advice gratefully received!