I am soooooo stuck!

[AdTee]

Hi folks,

I really need some help on this one please! I've started building and I'm not sure how to progress. Apologies that I've posted recently on this subject (without reply, unfortunately) - I can't work out how to delete it. I wanted to share a few pics/ updated drawings in the hope that it might spark an idea or two.

So, 
It's an end terrace, DIY stick-build timber frame extension, building off of a groundbeam (steels encased in concrete). Wall make-up to be as shown in first pic.
THE BIG SNAG!...
One side wall will sit 100mm from boundary with neighbour and 300mm from their conservatory. Due to a sloping site, finished floor level of half the extension will be 225mm below the bottom of neighbour's conservatory, (and bottom of the conservatory to base of my wall will be 550mm) - see pic/photo 2. Meaning, I need to back fill behind my new wall up to the bottom of their conservatory (fill of approx 200mm wide by 550mm high). I need an alternative to my standard TF at this point but can't fathom it out. The architectural tech had a look this week but isn't sure himself - we bashed out an idea but it's far from perfect, and I'm not even sure it will work (see pic 3). A builder friend (who admits to having little TF experience) came up with another idea (pic 4) but I'm not sure if this will work either. 
MAIN CONCERNS
Drainage/Tanking/DPC's/moisture control/breathability, standing up a TF wall pre-clad and sheathed in cement board (weight/ & this wall also needs to be sealed up against the neighbour's rear brick extension which sits astride the boundary), and I only have the 300mm gap between their conservatory and my wall to get to it)

I'm desperate for a solution as I need to start getting this frame built before the weather turns. Any help to get me on my way will be massively appreciated!

Thanks in advance
Ad

 

Edited September 14 by AdTee

[G and J]

My apologies if I’ve misunderstood but aren’t you effectively building a partial basement without basement suitable methods?

 

 

[AdTee]

2 minutes ago, G and J said:

My apologies if I’ve misunderstood but aren’t you effectively building a partial basement without basement suitable methods?

 

 

Ah I think I see what you mean, but the it's only the one wall alongside the conservatory that's the issue really, as the all the gardens slope down that way. It's a combination of the conservatory sat on made-up ground/rubble fill, and our side flattened out into two levels. 

[G and J]

So you have already built a strip foundation designed to support the build up in your first diagram.  
 

And in effect you need a retaining wall outside of this to prevent bits of next door sliding towards you?

 

Your second diagram seems to be using a block outer skin as a retaining wall. Doesn’t that mean your timber frame is a support for said retaining wall?  If so that doesn’t sound like a good idea. 
 

In your shoes I’d pay an SE to design you a solution.  I’d be too concerned at the risk of building something unsafe, or needing significant remedial work. 

[Mike]

I can't see an easy solution either. You don't want anything that relies on a gravel board to keep the soil away - it will fill up over time - and a 100mm thick retaining wall 500mm high seems inadequate. Theremoblock insn't intended to be used as a wall and the internal ledge would look odd. I'd also not use cement board cladding that close to the boundary due to the difficulty/impossibility of future maintenance (it's not going to be easy to install it in the first place either); since the houses are brick I'd want a brick external leaf, at least on that side.

 

As @G and J suggests, you'll likely need a structural engineer to come up with something that will work with your foundations. Better to take a pause now and get it right, than build something that could cause problems in the future, not least when you eventually want to sell it, even if you can get it past Building Control.

[Redbeard]

+1 to Structural Engineer. If I were your neighbour I'd be worried about the support you are/might be/might not be giving to my conservatory floor/wall, whatever we might feel about the structural solidity of conservatories. I very much doubt BC would sign off without SE recommendations anyway, so the way is pre-ordained.

 

It is an immutable law that building work planned in the winter to allow execution in the Summer will be delayed and take place in the winter. I'd suggest you sigh and accept that possibility, take a step back (to a SE practice) and go from there. And I wish you all the best with the project.

[Redbeard]

...and a tiny bit more detail after connecting more brain cells...

 

The detail you need includes the make-up of what is effectively your footing wall (from a load-bearing and moisture control/management p.o.v) and the make-up of the back-fill so that it provides adequate support for the neighbour's conservatory. However well you get on with the neighbour it might be tainted slightly if their conservatory starts getting close with your extension. I think the masonry wall detail you have sketched can be amended and built, and the stud wall too, but the 'interface' of the stud wall and its cladding with the masonry wall needs to be *designed* and built exactly as per the design. Are you on a Building Notice? I take it you have not submitted a Full Plans app, since the plans are evolving now. Have you had an inspection yet?

[AdTee]

Thank you everyone for your thoughts - it really makes a difference when it feels like you're just running aroud in the dark. Taking this back to the SE is good advice that I shall follow. 

The gravel board retainer on the wall detail is a for small section on the other flank. 

Unfortunately the neighbour's conservatory builders had piled the back fill up against the fence that was there. Shame they didn't put a proper retainer in at the time. The architectural tech suggested adding piers to a 100mm block wall, although they would need to be internal and this would be tricky with the timber frame inner wall. 
 

22 minutes ago, Redbeard said:

...and a tiny bit more detail after connecting more brain cells...

 

The detail you need includes the make-up of what is effectively your footing wall (from a load-bearing and moisture control/management p.o.v) and the make-up of the back-fill so that it provides adequate support for the neighbour's conservatory. However well you get on with the neighbour it might be tainted slightly if their conservatory starts getting close with your extension. I think the masonry wall detail you have sketched can be amended and built, and the stud wall too, but the 'interface' of the stud wall and its cladding with the masonry wall needs to be *designed* and built exactly as per the design. Are you on a Building Notice? I take it you have not submitted a Full Plans app, since the plans are evolving now. Have you had an inspection yet?

Flank foundations are 152x152 uc23 steels in concrete making a total groundbeam size of 352x352, and sat on 3 pads along that side, 2m deep at the garden end due to a tree, then 1.2m, and 1m as they move toward the house. When I mentioned my concerns of the proximity of the conservatory to the SE last year, he said that a lightweight masonry wall would be ok, so hopefully he can come up with something that works. We had so much trouble below ground with historic footings, sewage leaks from the neighbours, and 5 different victorian drain runs, that sadly I wasn't focussed on this impending issue.

We have full planning. On the last visit from the private BCO, she said she was happy for block on that wall as long as it was brought up in render as it was built. She said it would be like building against a garden wall (my mind was set racing around moisture, ventilation etc at this point!). Fortunately, I'm not particularly concerned about the neightbour in question as I've just dicovered they've built the darn conservatory without regs anyway (it has become their kitchen extension!).

In case of having to shelve the project for winter (shudders at the thought of zero insulation, and being without central heating as the boiler was in the old demolished kitchen!), would the b&b floor need protecting from the elements?

Thanks.
 

[G and J]

Don’t know about the need to protect the b&b but to me, with focus and a kind autumn weather wise I would be tempted to go for a watertight timber frame well before Xmas (but then, as my old Irish farmer friend used to say, I am like a cock at a gooseberry!).  You are almost out of the ground so things could happen pretty quickly, funds allowing, especially as you’ve already got an SE engaged and invested.

 

Go for it!  And take no prisoners.

[Bozza]

You are right to stop and get professional experts to identify a solution.  My instincts are that some form of higher wall with basement style tanking and drainage is going to be the best solution, other than redoing the the foundations for the lower section to bring it up to same height as neighbours.

 

 

[Russell griffiths]

Ditch all your previous ideas. 
go and look at some ICF block ideas. 
either build that entire wall out of icf blocks, or build one or two courses as high as you need. 
 

build them up from your ground beam to the height you need and core fill with waterproof concrete. 
then tank the outside as though it is below ground level, you can either carry on and build your TF from the top of the icf or continue up in icf. 
 

if you continue up in icf you can pour every couple of courses and reach over to apply a waterproof render to the outside as you go up. 
 

also, why is your floor stepped, can you not lift the lower floor up to match the higher portion, not clear in the photo why it is stepped. 

Edited September 15 by Russell griffiths

[ProDave]

So just what is next doors conservatory sitting on?  It looks like the remains of a dry stone wall or some rubble just piled up.

 

Honestly that should have been sorted right at the start before you even laid your foundations.

 

My suggestion is build some formwork and pour a concrete slab against all that rubble to stabilise it, but whatever you do it needs some prefessional input.

 

Who's vent pipe and AAV is that?  It will become inaccessible.

[G and J]

46 minutes ago, Russell griffiths said:

ICF block ideas

Each time I’ve seen pics of an ICF house there’s always steel rods sticking up out of the slab to fit the polystyrene over.  I get that they are great for basements but isn’t it too late to do ICF with AdTee’s foundations?

[Russell griffiths]

1 hour ago, G and J said:

Each time I’ve seen pics of an ICF house there’s always steel rods sticking up out of the slab to fit the polystyrene over.  I get that they are great for basements but isn’t it too late to do ICF with AdTee’s foundations?

Nope, drill the holes in the foundation, minimal needed as it’s not a basement, resin fill and fit some short starter bars. 
 

[AdTee]

I've emailed the SE, fingers crossed he can fit me in and can design a working solution. 

 

4 hours ago, G and J said:

Don’t know about the need to protect the b&b but to me, with focus and a kind autumn weather wise I would be tempted to go for a watertight timber frame well before Xmas (but then, as my old Irish farmer friend used to say, I am like a cock at a gooseberry!).  You are almost out of the ground so things could happen pretty quickly, funds allowing, especially as you’ve already got an SE engaged and invested.

 

Go for it!  And take no prisoners.

Love your ethos, G&J! Will certainly push for it if the SE can deliver in time.

 

4 hours ago, ProDave said:

So just what is next doors conservatory sitting on?  It looks like the remains of a dry stone wall or some rubble just piled up.

 

Honestly that should have been sorted right at the start before you even laid your foundations.

 

My suggestion is build some formwork and pour a concrete slab against all that rubble to stabilise it, but whatever you do it needs some prefessional input.

 

Who's vent pipe and AAV is that?  It will become inaccessible.

Its not even an old wall, just rubble they threw up against the fence. I would say probably 150-250mm looks like original ground, but it's scrappy at best.
Its their AAV. We've made a new connection to the main sewer (we were connected to a shared run via the pipe the that the grey 110mm finally connects into), and discovered on excavation of our unused soil vent pipe (against back wall of house) that they had tapped into it when they had their extension built. We're removing our SVP and the AAV was the choice they made for venting rather than doing any major works. They can access the valve via a small panel in the return of the fence.

Yep, you're right, it should've been sorted earlier. I just took my eye off the ball on that one as so many problems kept arising. Only yesterday did the water company finally sleeve holes in the neighbour's sewer run to prevent sewage seaping out and under my foundations. Formwork would certainly be a good way of shutting away the problem. I'd be a bit nervous about any further excavation so if would be great if it could be achieved without much of that!

Russell, I hadn't considered ICF before. Will look into it.

Edited September 15 by AdTee

[AdTee]

4 hours ago, Bozza said:

You are right to stop and get professional experts to identify a solution.  My instincts are that some form of higher wall with basement style tanking and drainage is going to be the best solution, other than redoing the the foundations for the lower section to bring it up to same height as neighbours.

 

 

Raising the floor had crossed my mind. Russell, the steps down are a mix of practical and asthetic. We have a step down from the the old cottage of 175mm to increase the ceiling height from 2m (would've been a lower ceiling than the cottage ceilings due to increased joist depth), and then another step of 250 to create a split level kitchen/diner. This will still leave a good step or two down into the garden from FFL due to the sloping site.

Edited September 15 by AdTee

[G and J]

4 hours ago, Russell griffiths said:

Nope, drill the holes in the foundation, minimal needed as it’s not a basement, resin fill and fit some short starter bars. 
 

Can that be done into a steel and concrete beam?  I guess the SE will decide.