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Help! Detached House - 6m single storey rear extension on sloped garden??

Discussion in 'Building Regulations and Planning Permission' started by noob17, 2 Aug 2020.

  1. noob17

    noob17

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    Hello All,

    I am trying to understand the rules regarding the 4m ceiling height ruling for a single storey rear extension. The problem i face is that the house is on a downward hill so there is a drop of about 900mm from the patio (3m) to garden.

    We are trying to submit planning permission to build a 6m single storey rear extension and am struggling to figure out the best way to do it.

    Ideally would like to have flat roof and then basically have some steps coming down into the garden.

    Is the 4m from the back of existing house? Or back of new extension?

    My garden slopes down and to the left. So can i measure from the highest point? Or lowest point?

    Have added a picture of the back of the house for reference. Basically the raised patio is about 3m and we would eat an additional 3m into existing garden space.

    Any advice/help would be much appreciated.
     

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  3. DevilDamo

    DevilDamo

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    The 4m is the external ‘overall’ height above natural ground level, so not your internal floor to ceiling height.

    As defined with the PD guidance...

    Height - references to height (for example, the heights of the eaves on a house extension) is the height measured from ground level. (Note, ground level is the surface of the ground immediately adjacent to the building in question, and would not include any addition laid on top of the ground such as decking. Where ground level is not uniform (for example if the ground is sloping), then the ground level is the highest part of the surface of the ground next to the building.)

    The 6m is the external depth/length from the original rear wall of the house, so not to include any previous extensions. A 6m rear extension includes the Neighbour Consultation Scheme via the Prior Approval route.
     
  4. noob17

    noob17

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    Thanks for that, I was aware that was how the height was calculated. I had read through the Pd.

    the confusion is with the following piece:
    “then the ground level is the highest part of the surface of the ground next to the building”

    is this referring to the ground next to the existing house (which is higher given the slope) or is it from the back of the new extension which is lower?

    thanks
     
  5. DevilDamo

    DevilDamo

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    The extension would connect to the original house so if that’s higher than the new rear wall, then you take the highest part.
     
  6. noob17

    noob17

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    Sorry just to be clear.

    From the height of extension at the original house and the base of the extension at the back of the extension?

    or height and base by the the original house?

    thanks
     
  7. DevilDamo

    DevilDamo

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    I don’t follow your first part as that would indicate taking levels from two different heights.

    At the back of your house, you have some kind of raised patio. If somebody asked you to measure the height of that existing rear single storey bay window, you’d measure from the patio. So the height of your new extension would be measured from that same level.
     
  8. JP_

    JP_

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    If you are getting planning permission, rather than using permitted development, I don't think it should not matter, so long as you are not making the root line higher - and even that might be accepted if there is good reason and it doesn't affect anybody else. But judging by the big box dormer next door, you have nothing to worry about (IMO)
     
  9. noob17

    noob17

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    ok thank you. I think I know what you are saying now.. I have had the following feedback from one of the architects which seems to contradict my thinking....

    "
    The first is the fact that you have a large drop. The 4m height is definitely taken from the natural ground level at the further point of the extension.

    The second issue is that, under permitted development/prior approval process, any rear projections on the back of the existing house will have an impact on how the local authority calculates the depth of the extension. For example, on the rear of the property there is already an original projecting bay window, which forms part of the original rear of the house. Because of this, you would not be able to build a 6m extension (this is a grey area and a technicality, which can be found on the permitted development technical guidance).

    Ultimately, given the site conditions and the fact that there is the rear bay projection which forms part of the original rear wall, my belief is that you will have to submit a householder planning application for the applications to the house. I do not believe you will be allowed to build out by 6m, however, you would have a good chance with a 4m rear extension. The extension would have to be stepped lower down, which means you will have steps internally leading into the extension. Please find attached a little sketch, FYI.

    The only way of knowing what you can do is to have a pre-app meeting with a planning officer or just to submit an application and try your luck.

    I've had a long look around the area and I cannot see any extensions which are 6m deep. The majority are 3-4m in depth."

    he also sent the following diagram as a proposal:



    I am not sure I agree with him. Would be good to hear your thoughts on this... Was really hoping for a 6m extension! The neighbour has a 4m single storey and 6m basement extension below the single storey!
     

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  11. Notch7

    Notch7

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    That means the side extension PD rules come into play.
     
  12. DevilDamo

    DevilDamo

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  13. noob17

    noob17

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    Thank you. I imagine the following proposal should be achievable? Subject the ruling about the dormer. See pics.

    hopefully I have interpreted everything correctly.
     

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  14. DevilDamo

    DevilDamo

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    Apart from the 4m would be where your first 2.8m dimension is. But you should ignore the PD rules if your extension is to cover the bay window.
     
  15. noob17

    noob17

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    Ah ok,

    So I would start off with 4m and then end with approx 5.2m at the back of the extension. As you said, the 4m is counted from highest adjacent land which would be the back of the current house.

    So what the is the best way to go forward, the architect seems certain the 6m will be refused. Im not too familiar with PD/non-pD. Would appreciate some advice and guidance on how to proceed!

    ----

    Additionally, looking at the neighbour, they have a 4m back extension single storey and then a 6m basement below the single storey extension which protrudes more than the single storey. See attached.

    Am hoping that because the neighbours have had this approved since 2007, we can push for our normal 6m.
     

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  16. noob17

    noob17

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    Ok, i am officially losing my mind now.

    I spoke to the local council planning department who said that the 4m rule only applies to pitched roof where the 4m would be the height of the pitch and the pitch would end at 3m high.

    Am i missing something??
     
  17. DevilDamo

    DevilDamo

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    Correct.

    You would not be able to utilise PD due to the presence of the existing rear bay. So any extensions to the rear would require PP.

    Incorrect. Although the 3m eaves height is the thing that would have caught you out anyway. Sounds like they’re getting confused with the PD rules for outbuildings within 2m of a boundary.

    Your only option is to submit a formal application of which the design is to meet Local Plan policies and design guidance. The fact the neighbour has already extended will help go in your favour. No point talking about the PD rules anymore as they would not apply to you.
     
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