Calculating volume of roof space

[wobbly2]

When calculating the volume of the roof space for the purposes of permitted development do I measure the height from the top of the ceiling plasterboard below to the top of the ridge or to the top of the tiles or to the top of the rafters or some other point?

When measuring the roof length is it taken as being from external wall to external wall elevation i.e. ignore anything that overhangs the walls?

If there are skeilings how do they come into the calculations?

How accurate does the calculation have to be?

 

[lt8480]

You don't measure roof/loft space, you measure added external volume. So anything you add above the existing external finish of the roof counts as added volume.

A roof extension is usually in the form of a dormer, which wouldn't really have or need "overhangs", so not sure what you are proposing on this - do you have a drawings?

The closer you get to the PD volume limit the more accurate you need to be. As basically it is your responsibility to comply with the limit!

If you apply for a Lawful Development Certificate prior to doing the works the LDC doesn't "approve" the proposal, rather it confirms it would be PD if it were built today under today's PD rules.

If you round down and calculate inaccurate volumes it doesn't really help as basically you'll then not be doing what was LDC was confirming would be valid. I.e. if you draw 51 cu.m and cite 50 cu.m the LDC is basically saying 50 cu.m is okay. If you then build 51 cu.m you'll not be compliant with PD regardless of what the drawing showed. Of course whether the council will ever check is that accurately after you have built it or enforce is another question!

Consider future purchasers may also raise queries.

 

[wobbly2]

Apologies, should have said volume.

The overhangs mentioned refer to eaves and tiles extending passed wall on a gable, see attached drawings.

The software used calculates to 5 decimal places, presumably working to 2 decimal places and rounding up would be OK?

I appreciate under declaring the additional roof volume would be wrong but would over estimating be just as wrong with regards to an LDC?

 

[wessex101]

I have always taken it as all the volume of the roof enlargement, so that includes any new eaves/verge roof overhang.

 

[lt8480]

I'm not sure on the technicalities but I would assume it would include overhangs.

Somewhat insignificant though. As assuming this is PD for a detached/semi then your limit is 50 cu.m you will still be under even with the large box dormer option you have drawn.

The smaller dormers likewise are always going to be under 50 cu.m

If you are tight to volume limit then you could change the detail. You don't need eaves etc.

With rounding its also somewhat irrelevant because a Lawful Development Certificate only confirms that what you are proposing would appear to constitute PD and it is not a council "approval" like planning. It is simply just confirmation what you propose would appear to be PD in the council's assessment. You do not have to get a LDC if you don't wish. If what you are proposing is PD you can just build it. Most people simply get a LDC for reassurance.

At the end of the day whatever you build must confirm to the PD rules, whether you make an LDC application or not. Even once you get the LDC through you can change what you build as long as still within the rules of PD.

 

[wessex101]

At the end of the day whatever you build must confirm to the PD rules, whether you make an LDC application or not. Even once you get the LDC through you can change what you build as long as still within the rules of PD.

The LDC I received in the post this morning for a hip to gable conversion says..."The proposed development as shown on plans marked Drawing No. 05.18/PL.1 revision A etc etc. submitted with the application falls within the provisions of Schedule 2, Part 1, Class B, Class C and Class G of the Town and Country Planning (General Permitted Development) England Order 2015 (as amended).

So I would say the LDC is very specific to the application and plans submitted just like a planning application. You can deviate from the plans but the LDC then loses its relevance and you are back to a general permitted development situation where you take the risk that you have interpreted the rules correctly. I suppose you have the reassurance that as long as the changes are "no worse" than the LDC application then you are "probably" on safe ground.

Note to OP: includes large rear dormer (total 47.2m³ dormer and gable new volume) with full height glazed french doors and julliete balcony overlooking about 4 neighbour's gardens. Seems bloody anti-social to me but I don't make the rules.

 

[Nakajo]

[Dons leotard] Except in cases of change of use, LDCs are generally worthless - as the work iteslf is evidence of compliance. That said, they do seem to appease conveyancing solictors, so I suppose that's worth something.

 

[wessex101]

Nice try. I'm not biting and Woody seems to be in one of his quiet periods.

 

[^woody^]

 

[tony1851]

Personally I believe you can discount the volume of projecting eaves and barge boards etc on a dormer, when calculating increase in volume.
There is nothing specific about this in Part B, but the Technical Guidance specifically excludes guttering and bargeboards in Part A, so there is
some sort of precedent there.

 

[^woody^]

The volume is the internal space - "roof space" is actually stated.

 

[tony1851]

The volume is the internal space - "roof space" is actually stated.

I still think it's the overall volume of the enlargement which counts (ie adding the thickness of wall, cheeks and roof), but i see your point about "space".
'Space' is a poor choice of word for a statutory requirement because it can mean anything - probably just woolly thinking on the part of the draftsman.
Had they used "volume" it would have been more concise.
Wonder if there are any appeal court cases on this?

 

[Nakajo]

I doubt that there are, because I doubt that an LPA could be bothered to argue the toss. DIYnot however is a different story; we're here all day.

 

[tony1851]

I doubt that there are, because I doubt that an LPA could be bothered to argue the toss. DIYnot however is a different story; we're here all day.

Well, you might be but I've got work to do - I'm off.

 

[RichA]

In my understanding when one measures area in loft for planning they usually use internal space; and it would be consistent to therefore use internal space when referring to volume.

Of course, IMO neither is logical given that planning typically is more concerned about the external impact of a building.