Calculating loft volume and applying for LDC

KateK · 3 Sep 2018

Hi,

I have a few questions regarding permitted development that I hope someone can help with.

(1) Is the 50m3 PD volume limit for a loft conversion calculated internally or externally?

I've been told by several people it's internally and The Town and County Planning Order 2015 says internally but the Planning Portal says externally.

(2) What supporting documents need to be submitted to obtain an LDC? Is a basic scale drawing good enough or do they require full plans by an architect?

(3) If an LDC is issued and some minor detail is subsequently changed during construction (for example, the size of a window), would this invalidate the LDC?

Thanks for any advice.

^woody^ · 5 Sep 2018

1 internal
2 basic
3 yes

tony1851 · 6 Sep 2018

@ Woody; agree with your response to 2 and 3, but IMO 1 is measured externally.
For example, in theory you could build a dormer with walls (ie the cheeks and front) three feet thick, the roof two feet thick, and end up with an internal increase in space/volume of - say - 30 m³ and an overall (external) volume increase of - say - 60m³ with walls/roof that thick.
This would contavene the rules in Part B, because Planning is concerned with amenity and the external effect/appearance of the dormer.

tony1851 · 6 Sep 2018

@ OP, where does it say in the T&C Planning Order that the volume limit is mesured internally?

^woody^ · 6 Sep 2018

tony1851 said:
For example, in theory you could build a dormer with walls (ie the cheeks and front) three feet thick, the roof two feet thick, and end up with an internal increase in space/volume of - say - 30 m³ and an overall (external) volume increase of - say - 60m³ with walls/roof that thick.

No that is caught by

b) the enlargement shall be constructed so that –
(i) other than in the case of a hip-to-gable enlargement or an enlargement which joins the original roof to the roof of a rear or side extension –
(aa) the eaves of the original roof are maintained or reinstated; and
(bb) the edge of the enlargement closest to the eaves of the original roof shall, so far as practicable, be not less than 0.2 metres from the eaves, measured along the roof slope from the outside edge of the eaves; and
(ii) other than in the case of an enlargement which joins the original roof to the roof of a rear or side extension, no part of the enlargement extends beyond the outside face of any external wall of the original dwellinghouse

Also the wording is actuially "must not increase the volume of the original roof space of the house"

Space is a void

tony1851 · 6 Sep 2018

@woody;

OK, if I have a simple rectangular house measuring 30m x 15m on plan and with an internal roof height of 6m (highly unusual I admit but i'm suggesting these measurements to prove a point).
I could build a dormer with massively thick walls and roof but still keep within the parameters you quote, while still having an internal volume increase of less than 50m³. But outside, with my excessively thick walls and roof, the volume increase over the original roof volume could be well over the 50m³ limit - I could make the walls and roof so thick that the external volume increase could be 100m³ +.
And if the roof plan was big enough, i could still ensure that it was no nearer than 20cm to the eaves/no higher than the original ridge etc.
So i still suggest that the legislation refers to external volume increase.

Nakajo · 6 Sep 2018

Just submit the calculation based on whatever's most favourable.

^woody^ · 6 Sep 2018

tony1851 said:
@woody;

I could build a dormer with massively thick walls and roof but still keep within the parameters you quote,

That's right. You know that Planning Jungle list of loop holes, then get this added to it.

The tech guide specifically mentions volume - which by the dictionary definition, RICS Rules for Measurement, SMM or NRM is the internal area contained, and it specifically mentions roof space. No qualifiers.

Compare that with what the guide says for porches - where it specifically mentioned "measured externally" for the ground area. So a qualification of the measurement could have been added if it was necessary.

Ian H · 6 Sep 2018

If it works out at 55sq/mtrs Just tell them it’s 49.75

tony1851 · 6 Sep 2018

^woody^ said:
That's right. You know that Planning Jungle list of loop holes, then get this added to it.

The tech guide specifically mentions volume - which by the dictionary definition, RICS Rules for Measurement, SMM or NRM is the internal area contained, and it specifically mentions roof space. No qualifiers.

Compare that with what the guide says for porches - where it specifically mentioned "measured externally" for the ground area. So a qualification of the measurement could have been added if it was necessary.

Perhaps we should agree to differ?

wessex101 · 6 Sep 2018

Just another example of our wonderful vague and ambiguous planning guidance. I have always taken it as the external measurements, just to be on the safe side, and to be honest the allowance is pretty generous so it has come close a few times but still been within the permitted volume.

I've seen some appeals where the inspector has said there is no definition within planning legislation for "roof space" so each case should be looked at on its own merits.

I'm not sure why Woody is quoting NRM and SMM, that is completely irrelevant, unless he is pricing the cost of the roof extension. The RICS Code of Measuring Practice deals with definitions for measuring buildings but it does not cover volume, only floor areas. And even that shouldn't be taken as a guide except where specifically referred to in Planning legislation such as CIL floor area calculations. For instance the RICS definition of eaves height is different to the planning definition, but then the planning definition is just weird.

^woody^ · 6 Sep 2018

wessex101 said:
I'm not sure why Woody is quoting NRM and SMM, that is completely irrelevant,

Derrr, it's probably because they describe how to measure.

KateK · 6 Sep 2018

tony1851 said:
@ OP, where does it say in the T&C Planning Order that the volume limit is mesured internally?

Thanks for all the replies. Sorry if I've opened a can of worms but the reason I asked is because I thought it probably was a can of worms.

The T&C Planning Order says:

B.1 Development is not permitted by Class B if—
(d)the cubic content of the resulting roof space would exceed the cubic content of the original roof space by more than—
(ii)50 cubic metres

To me, the "content" is that which is contained, the space inside. As Woody says, "Space is a void." The structure (the walls, the roof) is the container. (Similarly, the content of a can of worms is just the worms, not the can.)

But the Planning Portal says:
All dimensions must be based on external measurements of the building or structure involved and not internal measurements.

Both can't be right. But the former is law and the latter is, what, "advisory"? So as Wessex says, it's all "wonderful vague and ambiguous planning guidance".

The increase in volume measured internally is about 49m3. Including the walls and roof pushes it up to around 57m3. I'd like to do as Nakajo and Ian said but I just worry about the cost of re-doing it if I happen to get a very pernickety BCO.

I'm only going down the LDC route because it seems, in this instance, someone could decide to argue there's ambiguity in what I think is PD.

wessex101 · 6 Sep 2018

You are just calculating the volume of the new dormer, not the entire roof space including the existing roof? 57m³ is bloody huge.

Ian H · 6 Sep 2018

Yes, ours was 49.99mtrs for a dormer and hipped end shifted over 3mtrs.

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Calculating loft volume and applying for LDC

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