Help with ground level/dpc/dpm

[cdbe]

My extension is coming up to floor level and I need to deal with the high ground level along the boundary:

I've drawn what I think is the usual way to do it:

I'm just wondering if there's anything else I can/need to do to avoid water penetration? The height of the channel drain is fixed - halfway up the first brick (as it has to clear a pipe further round). Would it be better to put the dpc on the fourth course then (if necessary) I could put a cavity tray and weep holes to drain into the channel while maintaining the 225mm clear cavity.

Also, how do I protect/cover the dpm internally where it rises above the floor slab, is it just a matter of being careful till it gets covered by the dot and dab?

Any suggestions appreciated.

 

[bobasd]

some of the info you ask about should have been in the BCO submitted drawings - thats if your doing it on the books?
typically, your benchmark is the main house DPC.
BCO is your friend, not your enemy. they have a history of knowledge to share with DIY'ers or Builders.
a glance at your pic shows up a few possible questions - why not get a heads up on site from someone like a BCO or a Builder?

do you have a good relationship with your fence neighbours?

 

[^woody^]

Do those drains have a back-fall to the house?

I would not put an open surface drain in that location to get filled with crap and not be accessible. Sort out a retaining something to hold the ground back, and then form a hard surface with a fall.

Re: post above, be careful about asking the building inspector what to do. Generally they hate that. They check things not design things.

 

[bobasd]

i get what your saying but we've got long time relations with local BCO's - two of them worked on the tools a few years back.
i understand that they are reluctant to be quoted but i've found them approachable now an then, and watched them gently ease DIY'ers out of expensive to cheaper possibilities

 

[cdbe]

Thanks both, it's a building notice so no detailed drawings. BCO isn't due back till I've prepped for the floor slab and I want to get this sorted asap, and I suspect that he would (as he seems to be quite helpful) suggest something along the lines of: fence down, proper retaining wall to separate the 2 levels etc - which would cause me some difficulties with the neighbours.
House dpc is lower than I'm proposing (and inner leaf is a further 2 courses lower than outer) so I'll be stepping down where extension meets house.
I'll have 150mm between (extension) wall and fenceposts, enough for 130mm acco drain but nothing else - as for maintainence access, I agree it will be challenging but I'm sure the the neighbours will let me lift the fence panels every now and then for a clear out and there's no trees nearby to block it with leaves. I will try and set some vertical flags under the gravel boards to keep next doors flowers beds out.
Woody, most of the 4" pipes are just ducting to extend the airbricks to vent the existing house suspended floors. One of them is a (unused and capped) soil pipe which I've put in as we may build a garden room (which may have a WC in), in the future!

I do think a cavity tray draining the cavity outwards before it even gets to the inner leaf and dpm would be no bad thing:

 

[Ian H]

What about replacing those first 3 fence posts with a extra couple of concrete gravel boards to retain the ground?

 

[^woody^]

Thanks both, it's a building notice so no detailed drawings. BCO isn't due back till I've prepped for the floor slab and I want to get this sorted asap, and I suspect that he would (as he seems to be quite helpful) suggest something along the lines of: fence down, proper retaining wall to separate the 2 levels etc - which would cause me some difficulties with the neighbours.
House dpc is lower than I'm proposing (and inner leaf is a further 2 courses lower than outer) so I'll be stepping down where extension meets house.
I'll have 150mm between (extension) wall and fenceposts, enough for 130mm acco drain but nothing else - as for maintainence access, I agree it will be challenging but I'm sure the the neighbours will let me lift the fence panels every now and then for a clear out and there's no trees nearby to block it with leaves. I will try and set some vertical flags under the gravel boards to keep next doors flowers beds out.
Woody, most of the 4" pipes are just ducting to extend the airbricks to vent the existing house suspended floors. One of them is a (unused and capped) soil pipe which I've put in as we may build a garden room (which may have a WC in), in the future!

I do think a cavity tray draining the cavity outwards before it even gets to the inner leaf and dpm would be no bad thing:

View attachment 164481

That tray is serving no purpose.

 

[cdbe]

That tray is serving no purpose.

Ok. I won't bother with it - will the standard arrangement be ok, assuming I can somehow lower the (very) adjacent ground level?

 

[tomfe]

Set your dpc higher on the external skin on that side then cavity tray on the internal skin above your external dpc.

I'd like to know about those drains though.

 

[cdbe]

I've managed, with a bit of hand digging, to concrete some vertical slabs under the fence gravel boards which has effectively separated the two ground levels and leaves a 180mm gap for my aco drain:

I think I'll put the inner leaf on ready to do the floor slab and discuss dpc height with the BCO when he comes to check that.

The "drains" are mostly just soil pipe to extend the airbricks to telescopic vents at the front of the extension. One of them is a capped off 6m length of soil pipe that runs across the extension back under the floor of the existing house near an existing soil pipe that we can connect into in case we build a garden room (with WC) beyond the extension.