Sloping ground-Rear extension

[ea2020]

I have seen other posts regarding building an extension on sloping ground but would like further clarification as I am now in the same situation.

Basically I have spoken to the planners who are confusing and I would like to clarify this before I submit my drawings.

We are currently proposing to build a rear single storey extension. As we exit the kitchen at the rear of the property there are concrete steps across the fill width of the house which then lead to a lawn which is more or less flat. The level change from the kitchen door to the lawn is approx. 900mm.

Now when we build the rear extension the rear wall of the new extension will be more or less where the lawn is. So under PD the maximum eaves height can only be 3m and should be measured from the base of the outside wall. Now if we do this then we will be losing a lot of internal head room and our ceiling height will be approx. 1850 after accounting for the roof structure.

The PD technical guidance states the following:

Ground level is the surface of the ground immediately adjacent to the building in question. Where ground level is not uniform (e.g. if the ground is sloping), then the ground level is the highest part of the surface of the ground next to the building.

The above statement is OK when looking at the rear of the extension, i.e. near the existing kitchen. The overall height of the extension cannot exceed 4m. So when this is taken from the higher level we are OK in this aspect.

However the problem lies with the eaves whereby we would be measuring from the base of the rear wall of the new extension. Am I interpreting this correctly or I am measuring the eaves height incorrectly and will lose 900mm of internal headroom.

Can I take the base of my measurement for the eaves height from the highest level which is right outside the existing kitchen?

I want to avoid a step in the extension at all costs and also a sloping ceiling.

Please clarify if my interpretations are correct. Many thanks for your help.

 

[nickjb]

It reads to me like your interpretation is more or less correct. This part, anyway:
Can I take the base of my measurement for the eaves height from the highest level which is right outside the existing kitchen? Which you can.
If the rear of your house is already 900mm above ground level then you will lose that 900mm from all of your extension if you don't want a step down into the extension. Three options: Have a step, have a low ceiling, go for planning permission instead of PD. If you really don't want a step then full planning is the way to go. Are neighbours likely to complain? Any reason to think you won't get it? Planners are normally OK with rear extensions as long as they aren't huge and overbearing.

 

[^woody^]

All height dimensions are taken from a single point on the highest existing ground adjacent to the proposed extension

 

[ea2020]

Thanks woody.

So to clarify then;

When you mean adjacent can that mean the ground outside the existing kitchen door which will be the proposed extended kitchen?

Or is the adjacent defined as the ground outside the extension? I.e. in this case the lawn.

If the eaves height is measured from a reference point which is the highest ground (in this case the ground outside the kitchen door) then surely my eaves would be greater than 3m?

 

[^woody^]

If your extension has three sides, it's the ground immediately adjacent to the external wall on any one or all three of those sides.

 

[ea2020]

Nickjb

In your previous post you mention

Can I take the base of my measurement for the eaves height from the highest level which is right outside the existing kitchen? Which you can.

If the rear of your house is already 900mm above ground level then you will lose that 900mm from all of your extension

Where the rear wall of the new extension will finish in relation to the rear wall of the existing house there is a 900mm level change.

But I thought based on the PD tech guidance notes the eaves height is measured from the base of the rear wall of the proposed extension. If based on what the PD tech guidance says then I will 900mm down on head height.

How is it then possible to measure the eaves height from right outside the kitchen which is 900mm higher up?

Thanks

 

[ea2020]

Woody,

Is it the external wall of the original house or is the external wall of the proposed rear extension?

Can i therefore use the level right outside the kitchen door as the reference point?

I will be putting up a sketch later on tonight so if you pass by on the board then please do take a look.

Thanks.

 

[GeoffJ]

Do not let the PD vs planning permission argument get in the way for good design.

I know there is also a chicken 'n' egg argument - but that is about compromise that should come later.

Just check out some of the terrible rear extensions you see riding the trains through that place called suburbia.

Geoff

 

[^woody^]

Measure the height from anywhere in the red area - immediately adjacent to the new extension walls. Not the yellow areas.

 

[ea2020]

All,

Please see attached pdf which highlights my proposal.

Is there anyway without creating a stepped floor that I can maximise the headroom?

I am applying for prior approval for a 6m extension so obviously a FPA would be out of the question as the 6m would be refused.

Many thanks for all the earlier replies, much appreciated.

 

[unclebob1]

I have the same setup, patio was built up above "Natural Ground Level". The importance of this being that if they believe (as they did for me) that the ground had been built up to make a flat patio, the height would be from whatever it was before it was built or some compromise if this could not be accurately determined.
Harrow council made me step down for 5.75m PD build.

So i ended up taking the hit on steps, added two steps in the existing house to keep the floor level on the existing/extension joint. The extension/rear back room is the same, with the steps between the existing hallway and entrance to the rear room (with a platform between the door and first step).

 

[^woody^]

Is any of the ground around the extension 900mm higher than the other ground?

If it is, I can't see what the problem is.

 

[ea2020]

Woody,
If you mean the ground around the extension as being outside the extension and as highlighted red in you sketch above then no.

Around the extension (the red zone) the ground is virtually flat.

 

[tony1851]

It's difficult to say from your diagram. Height has to be measured from 'natural ground level'. If the floor of the house at the front is the usual 150-200mm above ground level there, it suggests that the natural ground level is sloping down left-to-right. If that's the case, the patio at the rear will probably have been built up. I suspect the natural ground level may be somewhere between the higher and lower dimensions you have been referring to.
It needs someone on site to give you a proper indication of where the natural ground level is.

 

[freddiemercurystwin]

How about a photo?