Single Storey Rear Extension on a sloping garden (w/Drawings)

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RoboCap

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Hello all,

I need some advice and clarification on a single story rear extension I want to build.
Firstly, I'm pretty sure I would need Planning Permission based on my current drawings due to a sloping garden causing the height of the extension to exceed 4 meters. Also I have a low pitch due to the (12 degrees) due to a window.
But I would prefer it be able to proceed under permitted development and how it would be possible to achieve this.
(The drawings I did by myself so please advise if there are any problems)
Existing Rear Elevation:
The existing 'extension' (with the door, below the original house) was built before I moved in; It has decking with stairs leading down to the right where there is a concrete block, which leads to some more stairs finally reaching the garden
existing rear elevation.png

Existing Side Elevation:
existing Side elevation.png

Proposed side and rear elevations:
Proposed side rear elevation.png

Side Elevation detail:
side elevation detail.png


side elevation detail annotate.png

Arial View
Top view.png
 
Hello Robo Cap

You bring up a very interesting point, and from the planning local authorities that I have dealt with, there appears to be a degree of ambiguity to the answer. It is all to do with what is ground level. One local authority told me that with regard to permitted development, the height is measured from ground level which is defined as the ground immediately adjacent to the building in question. Where ground levels are not even as in your case, then the ground level is the highest part of the surface of the ground next to the building. Then another told me that ground level was the lowest point within the curtilage of the property in question.

I would simply ring the local planning department and see where they measure from (although, unfortunately you may not get a straight answer. However, most planning authorities, that I have dealt with anyway, will convert a permitted development application to a full householder application, and simply ring you up to ask for an additional fee. That is as long as you were planning on submitting for a certificate of lawful development in the first instance.

Your drawings appear to show two stories, based on the cross section, i.e. building over the existing extension, the authorities would class that as a two-storey extension, even though your just building over an existing one.

PS, as someone that draws plans anyway. I think the plans that you have drawn a very good, definitely better than some plans that I’ve seen drawn submitted for planning applications.
 
Height is measured from the highest ground level - so a point next to the corner of the house. It's national, so there can be no local differences with planner's opinions or policies. So keep within the PD criteria and it's PD.

If you do apply for a LDC, don't show that door at the lower level and treat that as an underfloor void not a room. That avoids any cloudiness with whether it's a storey or not. Afterwards you can do what you like with it.

You don't need to show sections on planning applications. Sometimes it helps not to.

Drawings are OK, but it looks like the eaves and ceiling are too low - the ceiling surely does not match that in the main house? Have you done that to keep to PD? If so I would submit a full application instead and get a better extension.
 
@Aeron Rees

Thank you for the detailed response and advice. Also sorry for any obvious and naive questions I may ask as I'm new to this.
Aeron Rees said:
ring the local planning department and see where they measure from
Click to expand...
Is it possible to have them send someone over to check where my ground level is? Because as you said, there is ambiguity as to where it starts; for example, if I look at the literal corner of the house i.e. the highest point - it is not natural ground but instead a concrete block. So would this be the highst point or do I have to find natural ground?
Aeron Rees said:
the authorities would class that as a two-storey extension, even though your just building over an existing one
Click to expand...
According to Householder Technical Guidance "A single-storey extension must not extend beyond the rear of the original house by more than four metres if a detached house, or by more than three metres in any other case. In both cases, the total height of the extension must not be more than 4 metres."
This references a single storey extension; but as mine would be classed as a two-story extension; what would be the maximum allowable height?
 
@^woody^

^woody^ said:
Height is measured from the highest ground level - so a point next to the corner of the house.
Click to expand...
As replied above, If I look at the literal corner of the house i.e. the highest point - it is not natural ground but instead a concrete block. So would this be the highest point or do I have to find natural ground?
^woody^ said:
If you do apply for a LDC, don't show that door at the lower level and treat that as an underfloor void not a room. That avoids any cloudiness with whether it's a storey or not.
Click to expand...
In removing the lower level door, would the extension be regarded as single storey or two storey from the drawings?
^woody^ said:
it looks like the eaves and ceiling are too low - the ceiling surely does not match that in the main house?
Click to expand...
The original house has a ceiling of 2.7m, the extension has a finished ceiling height of 2.4m. So I believe they aren't too low. Also the eaves being higher would result in a lower pitch than the already low 12 degrees, making it a virtually flat roof if I am understanding your comment correctly.
 
You need to determine where the 'natural' ground level is. If you are saying that the side ground at the top of those steps was built up after the house was built ie unatural, then you can't use that as the base line.

However if the ground at the front is higher and is natural, then you would argue that the ground at the side is natural too and the house has been cut into the ground.

An under floor void is not a story unless it's a story height and will be used as some sort of room. The unique position of that house means that you can argue it's not a story but a necessary means of building at first floor level. As long as you don't show it as something that looks like it can be a room.

If the extension ceiling height is 2.4 then that's fine. It just looked a bit cramped and out of proportion. Probably best to take remove those horizontal dim lines and put them below the extension.
 
@^woody^

^woody^ said:
If you are saying that the side ground at the top of those steps was built up after the house was built ie unatural, then you can't use that as the base line
Click to expand...
Yes, the steps and the concrete side ground highlighted in green was built after the original house. Therefore it can be assumed that natural ground is further below.
However, this poses the problem of the 4m height limitation.
side elevation mesurements-1.png

As you can see, when using an estimated natural ground floor as well as using the 4m height limtation; the extension will be too low and require a step-down. Therefore, would it be logical to assume I will need planning permission based on my current drawings?
 
Yes, looks like planing permission will be needed. In which case, think about having that underfloor space as a proper room, as for the little extra cost it may be worth it.
 
As Woody said, you will require planning permission for that extension. Just some other things to consider. With a CLD, the planners do not make a site visit and do not consult neighbours, either the development would have been lawful or not. However, with a householder planning application, such as the one that you would be submitting, the Local Authority will consult your immediate neighbours, usually the ones to either side and the rear of yourself. They will also make a site visit to determine any potential impact themselves, they don’t necessarily need you to be there when they do that, however they will probably ring in advance to ask you to leave like a side gate opener something.

If you have not already done so, it’s usually courteous to let the neighbours know of your proposal, as the last thing you want is them to object, even though it should not influence the overall planning decision, it won’t help either.

It is also worth considering the Party Wall Act. From your drawings it does not look like this act will apply, but, for example if you are building foundations within 3 m of a neighbouring properties foundations, and your foundations were lower, you have to notify that neighbour.

Finally, as I’m sure you’re already aware, you can do that via the local authority or via an approved inspector, and either go for fully approved plans or a building notice.

Cheers
 
@^woody^
@Aeron Rees

Thank you again for all you extremely useful information and help in showing my current drawings would require planning permission.
However, now I'm wondering if it is even worth it to go with planning permission, as all I need is a simple kitchen extension (through finding the 'natural' ground level proves difficult). I could reduce the extension height by using a flat roof with a potential step down, thus meeting PD.
However, when looking at my council's (Sheffield City Council) fees, i'm quoted £180 for Building Control application (according to: planning and development building regulations Table) and only £206 for planning permission from the online application. So what would you do in this situation?
 
Hello

Yes, a flat roof is a potential solution, I personally prefer the GRP fibreglass ones, but there is a great deal of choice out there these days.

I would personally stick with what you’ve got, just place a full householder application in at £206, only £103 more than the CLD, a relatively small amount in the grand scheme of an extension building process.

Then you will have to pay the appropriate fee for the building regulations once the planning has been approved, which I’m sure it will be, fingers crossed.
 
I’m sure you realise already, but just to make sure, the total building control fee would be £360. Either an approved plan application for £180, followed by an inspection for £180. Or £360 for the inspection and building notice at the end.
 
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