moving / extending drains

morning all, just doing a bit of light digging in preparation for a new porch. I need to reposition a rainwater downpipe - please see attached photo. After that s-trap thingy the drain looks like it goes off deep into the ground. I had anticipated having to dig down to intercept it somewhere ouside the new porch area, but I suspect that will involve a lot of digging. My question is can I simply install a new rainwater gully outside the porch and then connect it back to the drain that I've already exposed? If I remove that s-trap there's sufficient depth to keep all of the pipework below the porch floor-slab. My BCO will be out to seethis later in the week and I'm just trying to get an idea of what short-cuts might be acceptable. Is it OK to have drainage components under the porch or is the general principle that everything should be completely external? thanks in advance for any thoughts/guidance
Nick

There is no problem in having pipes beneath a building.

It is also rather unusual to see a trap ('s' bend) on a storm pipe.

Do you know where this pipe runs to?

thank you noseall. Not sure exactly where it goes but it seems to be aiming diagonally across that photograph. Off to the right out of picture are a couple of manhole covers so I assume it connects into the main drain somewhere in that region.

From what you say I reckon I can save some time here then - run the pipe from the new gully back to that exposed pipe, just need to lintel over it where is crosses the wall of the new porch I guess.

Can I ask your advice on a related thing please .... I've done a bit more digging since taking that photo. BCO wants me to dig down to the same level as the footings on the neighbouring wall. I've done that and have found a trickle of water seeping out of the blockwork - see new photo. Seems a bit odd to me, given that it is not open ground on the other side of that wall - it's my neighbour's garage, part of which he's had converted to a utility room. The wall and adjacent ground seem generally dry. Should I be asking my neighbour to check his plumbing? Maybe this is normal drainage - I guess water has to find its way somehow and we are talking about 1.5m below ground here. Maybe I'm worrying about nothing .... any thoughts?

I'd be inclined to test the gulley, (get someone to tip a bucket of water down it and see if it appears in one of the manholes), depending on depth, maybe easier to reroute pipe outside footprint of new build. If you'd rather not do that, then i'd suggest you remove the 'S' bend, and replace with a 90deg bend over to new gulley position. Use a 'Bottle' gulley, rainwater drainage is less likely to block, but access for jetting would be easier from a bottle gulley IMO.

The pipe coming from the wall above the existing gulley, what is it? Looks like it might be a safety discharge from a boiler. (Will need moving!) If there is a boiler the other side of the wall will the proposed build affect the flue position? Also the service running through 1st picture may need diverting to remove it from under the proposed new porch....

Is that a lead water service in the 2nd photo? They are inclined to leak having been there for a number of years. It may be possible there is a leak under your neighbours building, wouldnt be the first time i've seen that. If they've a water meter, check for movement with ALL taps etc shut firmly off. If no water is being drawn and the dial moves, then fair chance of a leak.

hugh jaleak, thanks for the reply.

I'd rather avoid a major re-routing - my neighbours did this same porch project and they ended up removing a mega amount of ground to sort out the drains. If the BCO is happy with me removing the s-bend and coupling back into that pipe from the new gully then I think that's the way to go. Yes, the pipe you see is a boiler dishcarge which can be routed out through the new porch without too much difficulty. The boiler is a couple of metres behind that door and has a rear flue which takes it out of the wall at right angles to the one you can see in the photo. The services you can see are not lead but are some hard plastic material. The higher diagonal one is the electric, the lower services are water - the two lower pipes was a surprise as I was expecting mains water only, so what the 2nd feed is I don't know. I think the electric feed will be OK as it's low enough to be clear of the new floor structure - well it might be in the sub-base but certainly no higher.

Will get my neighbour to check his water meter but I suspect not a leak on his mains as his feed is on the opposite side of the property. The water seepage smells slightly off - not full on foul water but not fresh! I'm wondering if his drains are OK as they will be not too far from this location. Question is would I be wrong to ignore the seeping water? I've since removed more material and it really is quite isolated and is coming out of the joint which is one course up from the concrete footing. it doesn't seem to be saturating the ground or causing any sort of problem. The ground is heavy clay, so I was thinking that water dispersal below ground might be a bit patchy with some pooling in certain areas maybe. Basically I'm trying to convince myself to ignore it and crack on with the porch!