# Tanking versus excavation on a sloping site?



## Vanilla (28 Sep 2010)

We're thinking of building on a sloping site. We're still waiting to find an architect but in the meantime I wondered if anyone has any ideas or experiences of building on a sloping site.

We're looking at an upside down house with the living areas on the first floor. The two options we need to decide between would be having a 'buried' back to our ground floor and be able to walk in the back door. Or excavate the back, have windows in the back of the ground floor and a bridge to the back door. Hope that makes sense. 

Personally I like the idea of a buried ground floor ( at the back only) but I'm worried about the cost and efficacy of tanking. Any input would be welcome.


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## RKQ (29 Sep 2010)

Vanilla said:


> The two options we need to decide between would be having a 'buried' back to our ground floor and be able to walk in the back door. Or excavate the back, have windows in the back of the ground floor and a bridge to the back door. Hope that makes sense.


I know exactly what you mean, I have successfully designed a number of upside-down-homes. There is a third alternative. Dig a 1000mm path at the back of the house with a retaining wall - this acts as your main line of defence. It should be cheaper than tanking and theres no risk of the tanking failing. No windows on the back of the ground floor, unless absolutely neccessary.

It really depends on the site and its levels. IMO Your home should add to the landscape not scar it with a 2.5m excavation.

Well done for imbracing your side and designing accordingly. I don't think you'll regrete it. My designs worked really well and I'm still quite proud of them.


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## onq (29 Sep 2010)

Vanilla said:


> We're thinking of building on a sloping site. We're still waiting to find an architect but in the meantime I wondered if anyone has any ideas or experiences of building on a sloping site.
> 
> We're looking at an upside down house with the living areas on the first floor. The two options we need to decide between would be having a 'buried' back to our ground floor and be able to walk in the back door. Or excavate the back, have windows in the back of the ground floor and a bridge to the back door. Hope that makes sense.
> 
> Personally I like the idea of a buried ground floor ( at the back only) but I'm worried about the cost and efficacy of tanking. Any input would be welcome.




I'd suggest you consider creating a decent sheltered courtyard and bridge over, otherwise you will be costing for tanking or a "box in a box" to ensure its dry.

However the object of the exercise is to keep earth away from the wall of the house so you need to excavate three sides of a hole, stabilise the ground forming the "walls" and build the house within it, draining the courtyard to the "front". You'll also need to protect from falls into the courtyard.

If you want to see what happens when it all goes wrong in difficult site conditions, follow the current court case between Sheridan the film maker and De Blacam and Meagher, multi-award winning RIAI-registered architects.

OTOH, if you appoint an archtiect with some sense, he may suggest a drained cavity to the rear, within a retaining wall structure, and with storage and utility spaces arrayed along it to limit any fallout from water ingress to servant spaces.

Detail design with heavy ramifications if it all goes wrong cannot really be entered into on AAM - too many variables - but the above outline some basic choices.

BTW had you considered the ODOS solution in Wicklow?
Raise the house on columns out of the ground!

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon                 as a defence or support - in and of itself - should  legal        action    be      taken.
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## johnnyg (29 Sep 2010)

Channel 4's Grand Designs last week had a lovely house built under an old barn into the side of a hill and it looked lovely. it was the first passive accedited house. Worth a look: http://www.channel4.com/programmes/grand-designs/episode-guide/series-7/episode-14


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## Vanilla (2 Oct 2010)

I saw the Grand Design house- it was lovely ( except for the hideous disney-esque ruins on top) but thankfully I don't think we'll need to go underground to get planning!

The ODOS house is beautiful- thanks for drawing my attention to it. It reminds me of the 30's Eileen Gray type architecture- the design for a Centre de Vacances in France. Beautiful, but I fear, out of reach. 

Interesting that both architects replying said not to tank, but to have a retaining wall. I kind of wanted a real walk-in back door, rather than a bridge but I don't want to regret it later either.


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## cack (8 Oct 2010)

Do'es anyone know if you build into a slopping site are any windows in the back at the highest part of slope first floor or spilt level ground floor and if they could be considered ground floor and you put a 1m path along the back instead of tanking would that change this.


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