I agree with Tani - asking your planning officer is the best way to check what is possible in your particular circumstance. If you have had planning approval then you will have the name of the case officer who dealt with it - that is the best person for you to talk to, as they will already know your project. For your legal situation on the freeholder side then you need to check your title deeds. You should be able to get a copy of these from the land registry if you can't find your own copy. Alternatively speak with your conveyancing solicitors who might have some information stored from your purchase, or be able to advise you.

I have three of these in a loft--side-by-side and quite large. Besides the summer sun baking in, my furniture was beginning to fade. The cost of blinds was pretty steep, so I opted to use light-cream drapery panels with a rod pocket sewn into both ends and thin tension rods to hold them taut. Works like a charm! I still have plenty of light--a softer, diffused light. And the light fabric reflects most of the heat. Plus, the UV damage has stopped. Another bonus--the fabric acts as an insulator in winter so there's much less radiant cold off the glass. A win-win, and the whole arrangement cost less than $100.

We will have a 2.8m ceiling and Westin have advised their Stratus ceiling extractor would work - in fact they don't set a height limit just say it should be set at the highest point in the room. Might work for you? We also have two skylights but our other one runs the other way so as to best allow light into the internal seating area (where your utility is) - so ours won't match at all! if you want symmetry though, why not push your other one over to the side as well- wouldmake lighting the dining table easier!

Interesting question, and at least from my point of view, possibly more complex to answer than you may realize ... I suspect, but currently don't either have the time or mathematical rigor to fully model this from first principles, that a lantern will get you more light in a north-facing situation. This is for a combination of reasons: Reflection / Transmission ratios depend on the angle of incidence; steeper (i.e. "head on") means more transmission. Since the panes of a lantern are more-inclined than a flat rooflight (even on a pitched roof), expect more light through. For north-facing windows (i.e. permanently shadowed), it's _ambient_ light that counts - i.e. the more or less even brightness of the blue sky (or, less-bright evenly overcast sky ...). A roof lantern, with panes facing two or four different directions, is again "catching" more ambient light at steeper angles (transmitting it inside). Ambient light (blue sky) is polarized to a strong degree, and reflection/transmission also depends on polarization (strongest: 90 degrees from the Sun, or - "generally northwards"). On some times of the day, ambient sky polarization may be such that a flat rooflight will reflect a larger proportion of light than at others. Again, the differently-oriented panes of a lantern would balance this out more. If indeed your geometry is such that the roof opening would not be in the shadow all day long but receive some sunlight at some hours ... then a pitched-north-facing flat rooflight would be oriented disfavourably at such hours (away from the sun, so getting the light at shallow angles, reflecting much). I'm not a technical consultant for this kind of advice (only have a physics background, which makes me a decent smart-*ss on such questions), and I can't say out of my head if a lantern would give you twice-as-much light in your situation, or only 10%-more-light. And then, the glazing (coated, and how ? double/triple glazing ? water-white glass or ordinary "greenish" float glass?) also plays a role. If you want it quantified, contact a professional. Right-to-light surveys commonly do such calculations (if for a slightly different reason ... how much light do I loose if that five-storey block of flat is being built on my doorstep ...). Also ... an alternative, in some situations, may be an extension with a ridged roof (i.e. two opposite pitches), and then two flat rooflights (facing east/west). Large roof lanterns don't come cheap after all.