Ground level same as proposed DPC?

[AdTee]

Hi folks, 

 

Desperately seeking a solution here!

 

I'm about to embark on a DIY stick-build timber frame 'wraparound' 2 storey extension on a Victorian end terrace cottage. The wraparound part of the extension adds a new front entrance and hallway along the side of the house where ground level slopes from front to rear.

On the drawings, DPC is the standard 150mm above ground, but at the front of the house ground level is pretty much at where the DPC will be. I can't excavate outwards as the build is right against the boundary. As it is, the low cottage ceilings and my increased depth of ceiling joists over the originals, mean I'll have a less than ideal amount of headroom in the hallway. I'd love to be able to drop the floor level further but the high ground level at the front prevents me doing this without going down the tanking route (which I'd rather not). Is there anything I can do here? Aco and some kind of reinforcement/retainer to the boundary? The orange highlight is closer to where I think the cladding is more likely to come out to after cross battening etc (maybe just a few mm overdrawn by me!). 

Thanks in advance.

 

[joe90]

The reason for DPC to be 150mm above ground level is to stop rain “splash” (rain hitting the ground and bouncing up the wall ) but as your cladding over the DPC this won’t be a problem. I would put some vertical slates in the ground at the boundary and fill between them and your wall with 50mm stone to act as a French drain. You will need to create a soakaway at the lowest end.

Edited July 7 by joe90

[AdTee]

39 minutes ago, joe90 said:

The main reason for DPC to be 150mm above ground level is to stop rain “splash” (rain hitting the ground and bouncing up the wall ) but as your cladding over the DPC this won’t be a problem. I would put some vertical slates in the ground at the boundary and between them and your wall with 50mm stone to act as a French drain. You will need to create a soakaway at the lowest end.

Ah that's great, thank you.

[JohnMo]

1 hour ago, AdTee said:

Is there anything I can do here

Have good think - is the right direction to go?

 

You should really move the dpc 150mm above ground level. I would go back to the architect and get a proper solution.

 

[ETC]

Move everything up to the highest level.

[AdTee]

2 hours ago, JohnMo said:

Have good think - is the right direction to go?

 

You should really move the dpc 150mm above ground level. I would go back to the architect and get a proper solution.

 

Thanks. I'll call the architect tomorrow and see what he says. I've only discovered the issue after determining existing floor level and mapping it to the outside flank of the cottage. To match it puts ceiling height in the hallway at 2045mm. Towards the rear of the extension it's planned to step the foundations down to give a more reasonable height, but having modelled it on Sketchup I can see that ground level is still going to make it a bit of a tight squeeze.

Edited July 7 by AdTee
.

[AdTee]

53 minutes ago, ETC said:

Move everything up to the highest level.

Do you mean move block&beam etc up?

[Dave Jones]

on a normal build this would be easy to solve with a tray 1 block above. Effectively moving the DPC 225mm up.

 

On a shed build ....

[Nic]

How do all the designs with flush fitting sliding doors out onto their lovely patios all at the same level etc get round this problem? 🤔

[Dave Jones]

29 minutes ago, Nic said:

How do all the designs with flush fitting sliding doors out onto their lovely patios all at the same level etc get round this problem? 🤔

 

there is specific drainage detail below the cill that needs to be followed. The sides still need a tray in my opinion to be on safe side .

[AdTee]

2 hours ago, Dave Jones said:

 

there is specific drainage detail below the cill that needs to be followed. The sides still need a tray in my opinion to be on safe side .

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. 

[joe90]

@AdTee what did your architect say? Is there anything (fence) on the boundary?  Going back to my reply earlier with vertical slates, you could always do that and lower the ground your side of the slates by 150mm with drainage stone on weed membrane.

 

your splash back is not a problem because your cladding down to DPC level 🤷‍♂️

Edited July 9 by joe90

[AdTee]

@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.  

[joe90]

Is it your fence? When re instating the fence why not use concrete gravel boards, they come in 6” or 12”, if  you use 12” you can put them in so your side is 12” but neighbours side is 6” which gives you the 150mm you need below the DPC (and still use weed membrane and pebbles/stone so no maintenance as you can’t get in there again.)

[AdTee]

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

[Canski]

if it was mine I would put a wraparound DPC below the beam and block and bring it up the external face of the masonry and back in on top of the marmot block below the sole plate. 

[AdTee]

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 🙏

[lineweight]

If that area between the gravel board and the base of the wall gradually gets clogged up with leaves, silt etc over the years, then won't that gravel board act as a convenient dam/retaining wall for damp stuff - potentially bringing the top of that damp stuff up in line with your timber wallplates, which is ultimately what you're trying to protect here?

[joe90]

16 minutes ago, lineweight said:

If that area between the gravel board and the base of the wall gradually gets clogged up with leaves, silt etc over the years, then won't that gravel board act as a convenient dam/retaining wall for damp stuff - potentially bringing the top of that damp stuff up in line with your timber wallplates, which is ultimately what you're trying to protect here?

I take your point but many walls are built too close to clear debris from the gap. At least if concrete posts are used the fence panels can be lifted out and the area cleared, probably only needs doing every few years at most.

[saveasteading]

It will get dirty and clogged , so there has to be enough room to get a hand in to remove the stones annually. Then rinse and return.

I would probably use pea gravel rather than 50mm stones. Use round stones, not jagged.

So move the gravel board further out. 

The perforated pipe should have membrane round it, and an outfall at the end.

[lineweight]

An extra course of Marmox Block could lift the timber plates out of the danger zone.

[joe90]

50 minutes ago, saveasteading said:

So move the gravel board further out. 

I don’t think he can as that’s the boundary 

[saveasteading]

35 minutes ago, joe90 said:

 don’t think he can as that’s the boundary

Good job someone is paying attention.

 

I'll try again.  Aco ( other manufacturers are available) seems to be the proper solution.

Gravel would involve access over the boundary which it is best to avoid.

 

But it isn't a great design. 

 

Have I also missed whether this is a neighbour adjoining, or public land? Will maintenance to wall and roof  be feasible?

 

[AdTee]

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.

[lineweight]

My suggestion to use another row of marmox blocks was that you'd do that but keep the floor level the same. The second row of blocks would be behind the skirting board.