Rooflights and skylights fitted in Treharris

Deep Navigation Colliery began as Harris's Navigation Pits. Its shafts were the deepest of their time in South Wales, some sunk to 760 yards (695 metres) to reach the Nine Feet Seam, and the pit stayed in production until 1991. An older row of houses keeps its character from the street: the slate, the ridge line, the chimneys. A roof window cut into the front slope changes that picture, and the rules take notice.

In Wales, putting a rooflight into the roof slope of a house inside a conservation area is not permitted development. It needs a planning application. What matters is the boundary, because a house outside it is not caught. The council holds the maps; DataMapWales also publishes a conservation area boundary layer that shows where lines run.

A conservation rooflight is the product line made for this kind of roof. Our guide to rooflights in conservation areas in Wales goes through how an application is approached, and the planning side is yours to decide on with the council.

A listed house is its own category. Listed building consent is needed where the work would affect the building's character as a building of special architectural or historic interest, and it covers work inside as well as outside. The council that handles planning handles that application too, and even small work can need it. Read listed building consent for rooflights in Wales before you commit to a design.

When a house is not in a conservation area and not listed, the questions become simpler: what is on the roof, how it slopes, what holds it up and which room is below. That is the territory where a roof window can be the right answer, and the survey would deal with those in the usual order.

If you are unsure where your house stands, put the question to the council's planners, who can answer it, and ask about a Lawful Development Certificate if you want the answer formal. That is worth having before money is spent on a design.

At the survey, bring what you know about the house: whether it is listed, whether it has been extended, and anything the council has told you. Those facts shape the whole job, and it is easier to learn them before the quote than after it.

Working from a room under the roof has become ordinary, and a roof window decides how that room feels. A large pane in the slope gives a lot of daylight and a view of sky. It also puts a bright rectangle behind or beside a screen, and in the afternoon that glare can be the main complaint.

Blinds are the cure, and the choice is wide. A blackout blind is for a room where you sleep. A lighter blind can take the glare off a desk without turning the room dim. Which blinds fit which windows is for the maker's own list to say, and we check it for the model we suggest.

Rain is the next thing to hear. A roof window is close to your head, and rain on glass can be loud. VELUX lists a rain noise reduction option among its glazing choices, though not every window or glazing variant has it. If the room is for calls, raise it at the survey and we check what the window you want can take.

If the window is replacing an older one that had trickle vents, the new window's vents should be at least as large. That keeps the room's ventilation no worse than it was.

Energy comes last. Approved Document L (Wales) gives 1.4 W/m²K as the figure a roof window should meet, or Window Energy Rating Band B. Read it on the specification of any window you compare, because the figure tells you something the price does not.

Think about where the desk goes before the window does. A desk under the lowest part of the slope puts the screen close to the glass, while one at the gable end can sit beside it. Moving the desk costs less than moving a window, so the survey starts from the furniture you already own.

For the other side of the job, our guide to roof window planning permission in Wales sets out when a roof window is permitted development and when it is not.