Here is a long section through the proposals with the front and rear elevations added. You can see how the existing ridgeline is preserved and the extension forms a flat roof behind this. The second floor is timber frame with structural steel beams providing the main support back to the party walls. The exact form of the windows has changed since these drawings were done for planning. Incidentally, I'm not sure that you could do this now under permitted development-the new rules insist (since last October) on setting back any dormers from the boundary and eaves. The Planning Portal has some useful guides and tools for assessing terraced houses and what needs permission when you are considering extending. These would have been handy when the regulations were changed!
