dwtowner

I want to build an extension to infill a corner of my house but there is an inspection chamber in the way. I'd like some advice on what I might have to do to fix this, please. My house is laid out as shown in the first diagram. Yellow for the house, green lines for drain runs (with arrows for direction), and green circles for the inspection covers. IC 1 is the last chamber before it goes off to the mains. IC2/3 take the soil pipes from the house, and the gutters. IC4 provides a rodable change of direction. The pipe between 4 and 1 is approx 9m and is a single run through the foundations. I want to infill the red dotted area (approx 1m wide) , which will be directly over IC4. I don't want to have to leave an access hatch through the floor of the extension to maintain access to an IC in that position. I think that I will have to move IC4 so that it falls outside the red dotted area. Putting it directly in line with the existing long run would put it too far away, but if I put a shallow (<30deg) bend in I could keep it reasonably close to the existing IC. I've drawn this in the second diagram in purple. Is that right? Are there any alternatives? Thanks.

Thanks for your comments Nick. Some useful prompts to think about things again. A few responses. This will be the third SIPs extension to my house, which itself is very insulated, triple glazed, etc., so I think it is in proportion. I've had a very positive experience with SIPs so far - a kit of parts arrives, all nicely numbered, and up it goes in a day or so. I take your point though that maybe its overkill for this slightly smaller extension. The old garage was lower than the existing house so the extra 40cm brings the floor to the same level. thanks, dan

I have a garage-sized outbuilding behind my house for which I have PP to convert into a room, built using SIPs. The existing garage has been there for about 70 years and doesn't have any cracks or issues that I can see with its foundations. The attached diagram shows the existing foundation in orange, relative to the house and surrounding ground. The other attached drawing shows the footprint of the new building in red. The new building will be about 40cm higher than the existing foundation. There is a mature self-seeded Walnut tree about 1.2m from the foundations which our neighbours are very reluctant to remove (technically it is mine so I could, but I quite like it there too). The edge of the left-hand green strip in the diagram is the boundary with my neighbour. There is limited access - about 1.2m width - for heavy machinery to get to the site. I'd like to understand what the options might be for extending or replacing the foundation to make it suitable for the new SIPs room. 1) Rip out the old foundations and pour new foundations. Clean slate to start with, but requires the tree to go, and is very disruptive for the neighbours during the work (their house is only a few metres away). Difficult to get machinery in and spoil out. 2) Leave the existing foundation but use ground screws across the site (through holes drilled in the old foundation) and around the perimeter of the new building, and then put a wooden insulated structure on top to support the SIPs. The tree could stay, and there is less disruption from removing the old slab. 3) Could the old slab be reused, with some new structure built partially on top of it? On the right of the diagram I think I would need to ground screw or do conventional foundation to support the edge, but could I cantilever off the left-hand side to avoid having to do anything else near by neighbour, and to avoid removing the tree? I've got about 40cm height to play with 4) Something I haven't thought of? Finally, any recommendations for a SE who could help with this, in the Bath/Trowbridge area? thanks, dan.