On the face of it you’d think that taking the roof across to replace the hip roof to the side would be the best option. Afterall, it gives the most area, right?

Sure, the alpine look may be what your want, but gables won't give you much useable space.

The trick is to remember that everything under 1800 headheight is really only good for desks or cupboards, and that's to the sides of the gable.

And where the gable meets the ceiling in the main space creates a corner you'll be at risk of banging your head.

So whever you can, go for a flat roof dormer.

Positives

• The ensuite will be larger and have good headheight throughout.
• A simpler floorplan is most likely, which results in regularly shaped, spacious rooms.
• A full gable lets the new staircase go further to the back of the house, so less likelihood for it to project into the main room.

Negatives

• If it uses up all your additional volume then the dormer face to your room will have to be brought back into the house to stay within limits, which makes the main room smaller.
• The area to the front of your house is below 1.8m high, so can only be used for storage to the eaves.
• Planning may not like it. Afterall, gable ends are a much more prominent extension, especially as seen from the front and the sides where you have the community views to consider. If you’re in a conservation area then less chance of getting the go-ahead from the council.