How does the cost of a dormer loft conversion increase compared to a Velux only?

An individual dormer window does increase the cost of the conversion; however, these do provide additional space within the conversion and, in some cases, are a requirement. Where dormer windows are not required, a number of Velux windows can be used and combined to create larger banks of windows that will allow more light into a room than a dormer window. A large bank of the larger Velux windows will often be comparable in cost to that of a single dormer window.