Permitted Development - where exactly is the ridge line (highest part of the roof)?

[Naknah]

I'm planning a full width L-shaped dormer loft conversion (to an Edwardian terraced house) under permitted development rights and I'm trying to find every possible cm for head room in the main part of the roof as we're right on the 2m threshold that is, for us, the difference between enough and not enough!

My house has (original) decorative ridge tiles similar to those shown in this photo and I'd like the dormer roof to be level with the top of the decorative bit if possible (the tiles would be removed) as this would gain us a few cm. One of the PD requirements is "No extension to be higher than the highest part of the roof". In the technical guidance document it says "The highest part of the roof of the existing dwelling house will be the height of the ridge line of the main roof." but I can't find anything explaining exactly where the "ridge line" is. What I'm wondering is whether the "ridge line" on my house is the top of the decorative bit of the ridge tile or the bottom. I'm probably overthinking this and it is obviously the top but I'm just not sure.

Not that it means anything but one of my neighbour's has a dormer that is built to the top of the decorative bit (that's what gave me the idea!)

This thread shows a dormer that is the sort of height mine would be although the OP has rounded ridge tiles rather than decorative ones.

Thanks for any help!

 

[Naknah]

 

[John D v2.0]

Speaking for common sense it's the lower height, however you really need the view of your council planning department if you want safety. Put in an application to confirm PD with a lawful development certificate in that case.
If you like going for risks, you can go on the principle of asking for forgiveness. Even if it's technically a breach, it might go down as too minor to warrant enforcement.
On another note that's a very nice roof, try to keep it's features if possible!

 

[^woody^]

The ridge is the tile. Those decorative bits are called f̶i̶n̶i̶a̶l̶s̶ and are not the ridge line.

Edit:

Crested ridges as per below

 

[Naknah]

Oh thank you but that's not my roof! Ridge tiles are the same though.

I thought a finial is

 

[Naknah]

Oops... what I was trying to say is that I thought a finial is the pointy bit on the end of a ridge line, like in this photo:

I really expected answers telling me that I was a plonker for thinking it is anything other than the top-most bit of the ridge tile (i.e. the top of the decorative bit) so this has been very useful!

 

[freddiemercurystwin]

I would expect the ridge to be akin to the apex which I would interpret as the point where the two roof planes meet which (give or take an inch will be top of the ride tile

The ridge is the tile. Those decorative bits are called finials and are not the ridge line.

I'm pretty certain the finials are the bits at each end of a ridge not the bits protruding off the ridge tiles, the tiles are just decorative ridge tiles. But I agree that the ridge line is a point where the two roof planes cross.

 

[wessex101]

I was going to patent a ridge tile with 2ft high cocks combs! I could corner the market in low headroom loft conversions.

 

[Naknah]

So my neighbour is just in breach of planning regulations rather than being a clever... err... person! I really don't want to lower the ceiling at a cost of £4k to get 10cm

 

[noseall]

They are called crested ridge.

 

[Chri5]

Since the backside of the roof will come off for the dormer you could raise the front roof a bit to get extra head room.

Pretty sure thats a full plaining application, although everyother loft conversion firm (round my way) do it.

I take it you've added in the loss of height that the steels and supporting floor loft structure causes?