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Roof height for rear extension on sloping ground

Discussion in 'Building Regulations and Planning Permission' started by Ollie2, 16 Nov 2020.

  1. Ollie2

    Ollie2

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    Hi All,

    I'm planning a single storey rear extension on my 1930s terraced house - 4.5m deep, full width of the house - 6m.

    The house is on naturally sloping land, higher at the front. At the back of the house, there is a 0.7m drop to the patio and then a 0.4m drop to the original ground level (at the point of where the back of the extension will be).

    The extension comes under permitted development if the height of the roof does not exceed 4m, measured from the "original ground level".

    Does anyone know where the original ground level is measured from? Is it the original ground level at the back of the original house? At the back of the planned extension? At the front of the house? From the patio level?

    I'm planning on a flat roof and keen to ensure that I stay within permitted development.

    Thanks,
    Ollie.
     
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  3. DevilDamo

    DevilDamo

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  4. ^woody^

    ^woody^

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    What's the "building in question"?
    The existing building or the proposed building?

    I think that was the OP's question.
     
  5. DevilDamo

    DevilDamo

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    It’s the same principe as that shown on Page 13 of the Technical Guidance.

    If the ground level at the rear of the house is higher than the ground level at the rear of the new extension, then the height is take from the rear of the house as that is the naturally higher level.
     
  6. Ollie2

    Ollie2

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    Thanks for the responses and that is clear. The height should be measured from the natural ground level at the back of the original house where the extension will start from. And the roof height is measured from the eaves at the lowest point of the flat roof, ie at the back of the extension, away from the house.
     
  7. Ollie2

    Ollie2

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    @DevilDamo would roof lights on a flat roof count as part of the total roof height?
     
  8. DevilDamo

    DevilDamo

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    Unless your house is a bungalow, you don’t need to worry about the eaves height. The ‘height’ measurement is still taken from the highest natural ground level anyway. So if from the back wall of the house it slopes down and away, then you take the intersection at the back wall of the house and not the back wall of the extension.

    Rooflights should not protrude more than 150mm above the roof finish/surface. That comes under a different PD class. Although saying that, I’m pretty sure I’ve had taller rooflights accepted via PD.
     
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  10. Ollie2

    Ollie2

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    @DevilDamo the back of the house still drops around 0.7m to the ground level, so that would give me 4m - 0.7m = 3.3m to play with for roof height?

    Ok will look for roof lights that don’t protrude more than 150mm above the roof finish!
     
  11. DevilDamo

    DevilDamo

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    Just to help clarify, can you upload a photo as the maximum eaves height of 3m may also be a sticking point?
     
  12. Ollie2

    Ollie2

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    @DevilDamo will do tomorrow when there's some light!
     
  13. Ollie2

    Ollie2

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    @DevilDamo see attached photo. The sliding door opens into the garden room which is 2.2m from the back of the original house. I measured the natural ground level at the back of the original house from the neighbours side and it’s approx 0.6m from the house floor
     

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  14. DevilDamo

    DevilDamo

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    The overall height of 4m would be measured from the patio level. If your extension is to be within 2m of a boundary, the eaves height should not exceed 3m (from the patio level). Measuring eaves heights are explained on Page 12 of the Technical Guidance.

    It does appear your only option is to seek formal Planning as it’d be almost impossible to meet the PD criteria for what you’re considering.
     
  15. Ollie2

    Ollie2

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    Thanks @DevilDamo. I was reading the guidance last night and that’s what I feared.

    Any guidance on the most cost effective way of getting through planning permission?
     
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