Odd dormer question

[MissUGirl]

Is it possible to extend a dormer horizontally beyond the plane of a roof? The closest example I can find to what I want to do is a 'hipped to gable' dormer, but in my case the floor wouldn't actually begin until the red line shown in the photo.

I have dormers on my second floor already, but they are the traditional type that only start at the roof plane at floor level. I estimate I could add 4ft to the rooms by replacing them with one large dormer of this type.

Is that a mansard roof?

The picture is a hipped to gable dormer.

This is the same building with a Mansard roof. Other than that the Mansard one looks nicer I don't really see the difference.

Structurallly, yes - just need foundation, columns and some steelwork so load transfers directly down. But you might as well then just do a three storey extension.

Sorry, misunderstood what you were asking.

Basically I am asking if a floor can be built on the dormer level that extends outward to the edge of the roof on the floor below, i.e., far beyond the plane of the existing roof.
So there would be a void in between the existing roof and the dormer floor, but from the front it would look as it does in the photo.

I found a better picture of what I want: similar to the white structure in the picture, only mine would be larger than this one (approximately 5m wide x 4ft deep).

I'm assuming the interior floor is level with the bottom of the window in the white structure.

I thought this was called a dormer but perhaps I'm mistaken. If anyone can tell me the correct name for this type of structure I'd appreciate it.

That photo looks like a cantilever structure of some sort - the support for it will be perpendicular to the existing roof, i.e. sticking out at 90 degrees. You'd need to check the planning guidelines locally because projecting out from the original building line - the front wall of the house ignoring any canopy - might not be permitted. If any houses on the same street have front extensions that is an indication that it isn't an issue.

Are you trying to have a roof extension stepping out beyond the existing wall? Like olde world buildings? Called jettying en.m.wikipedia.org/wiki/Jettying

Planning might be a challenge, speak to your local planning office to see if they would outright refuse.

I understand what you mean - a dormer that goes right to edge of the roof without the usual gap (of roof) in front, to give greater floor space inside.

I think you need to speak to your local planning officer and an architect.

Obviously the type of "dormer" (for lack of a better word!) you want is hypothetically possible, but whether it would be permitted and whether it is feasible with your existing structure it isn't really possible to say without more information.

If you read down in the link Rollercoaster posted, you'll see that cantilevers have replaced jettying.

Thanks all! I will do some more research and consult the planning regulations.

Having consulted Rollercoaster's link, I can see that jettying (or its modern equivalent) isn't what I require. The new structure wouldn't protrude beyond the dimensions of the floor below—it would be level (so it would start at the bottom edge of the roof).

The post above from @PCohle describes what I'm after.

So the dormer is directly above the existing external walls? That is my plan for a rear roof extension and is allowed under permitted development regs on the rear of a building. Not on the front (or side if facing a road).

Like this: goo.gl/images/9FfwNL

Note that the original guttering and little bit of roof overhang is usually retained.

So the dormer is directly above the existing external walls?

@Rollercoaster1920 Yes, but the difference with the picture you linked and my proposal is that with mine, the floor of the dormer wouldn't start until about half-way up the height of the dormer (as in the picture in my original post).