dormer window vs. velux

self_builder

We have a choice between a dormer window or a velux-type window in our bathroom. Which would you choose from an insulation and airtightness point of view? It would be a passive dormer window (u-value 0.8-glass and frame), not sure if I can get passive/triple glaze velux or cost of them?
Thanks

sinnerboy

The additional roof and side cheek walls required for a dormer increases the amount of surface area to lose heat from .

You can get triple glazed velux windows.

So from an energy saving point of view the velux wins. But not from an internal -space-in-the-room point of view and possibly too not from an external / architectural point of view . A well proportioned and located dormer will improve an elevation.

BryanF

+1 with SB
both dormers and roof-lights have their own detailing issues. with current levels of insulation the dormer can read quiet heavy/fat in an elevation. with rooflights you tend to struggle to get good insulation overlap.

muffler

+1 from me also in relation to the above.

Slig

Velux type rooflight will also be substantially cheaper and allow more light into the room