Skylight and rooflight fitting in Gwaun-Cae-Gurwen

Gwaun-Cae-Gurwen is a village, and also a community, within Neath Port Talbot county borough. The electoral ward had 2,910 residents at the 2011 census. The Welsh Language Board reported in 2009 on how many residents could speak, read or write Welsh, and the figure it gave was high. The Welsh form of the village name runs together as a single word, Gwauncaegurwen.

Local history gives the village a landlord. At one time almost all of the land called The Waun belonged to the Jones family, who also owned the Pwll-y-Wrach Estate. Both farmhouses connected to that estate are still standing. The Welsh primary school used to stand on Heol y Dŵr, which means Water Street, and that is where the Pwll y Wrach estate is based.

Swansea is 14.15 road miles away, and the village lies north of it, comfortably within our 30-mile area. Close neighbours where we also work include Garnant, Brynamman and Glanamman, and Cwmllynfell is nearby too.

What comes next describes house types in general, whatever the village. A pre-war terrace with a narrow rear slope usually takes a single roof window. A semi from a later decade tends to leave space for two, or for a roof window and a tube with a dome. A flat-roofed extension is a candidate for a rooflight or a lantern.

Roofs vary from street to street and house to house, and an extension or a loft conversion can change a roof that started out standard. The survey is where the real roof gets measured, and no figure is quoted until it has happened.

Planning decisions for the village rest with Neath Port Talbot Council. Gower's AONB lies well away from here, so it has no bearing on work in the village. Whether a rooflight on a house is permitted development or needs an application depends on the details of the house, and every test is set out in our guide to skylight planning in Wales.

That guide also deals with the exceptions: flats and maisonettes, houses where a council has taken householder rights away, and listed buildings. When a roof is near the line of a rule, you can ask the council's planning team for a view, or apply for a Lawful Development Certificate to have the answer on paper.

Building Regulations take their own route, apart from planning. The Welsh Government's guidance on roof lights says that a new one will generally need approval, because cutting the opening usually means altering how the roof is built, and the roof then has to bear the unit's weight. Swapping a window like for like is building work as well, and the new glass has targets to meet under Approved Document L (Wales). A roof window should reach 1.4 W/m²K or Window Energy Rating Band B, and a rooflight on a kerb 2.2 W/m²K.

You choose the approving body: Neath Port Talbot's building control team, or a registered building control approver. When a job needs a notification, we send it for you.

Glass has its own safety guidance in Wales, Approved Document N. It marks out critical locations in walls and partitions, from the floor up to 800 mm, where glazing should break safely, be tough enough for the knocks it might take, or be made of small panes.

Ventilation is the other quiet requirement. Where an old window carried trickle vents, its replacement should offer vents at least as large, controllable by the person living there or automatically. We settle that detail with the old window in front of us. Enlarging an opening or making a new one brings in a limit on glass: Approved Document L (Wales) says the total area of windows and doors should not exceed 25% of the home's floor area.

The bathroom comes first because it shows up every weakness. A roof window over a bath or shower wants glazing that holds its heat and a fan that clears the air. A top-hung sash swings out above your head, and a centre-pivot rolls over so the outer pane can be cleaned from inside. VELUX also lists safety lamination, a laminated inner pane so glass does not drop into the room after accidental breakage. Over a bath, that is a sensible thing to want.

A stairwell has no outside wall to borrow light from. A sun tunnel picks up daylight on a small roof dome and carries it down a reflective tube to a ceiling diffuser, so it can serve a landing even when the roof space has nothing spare for a window. From outside it is only a dome, and rain leaves it quickly.

Back extensions usually have flat roofs. The two candidates are a flat roof rooflight and a roof lantern, and each does better when the roof falls away so water can move off. If you want a lantern on an extension that is yet to be built, the planning question goes to the council at survey. The warmth side is covered under energy-efficient rooflights.

Changing an old roof window starts with a code. VELUX lists every size by width and height, and the size code stamped on the metal plate at the head of the sash, easy to read with the window open, tells you both. The plate has been fitted since 1968, so even an old window gives you something to read. With the code and the pitch of the roof, a like-for-like change in the same opening is easier to plan, and the new unit still has to reach the Welsh figures.

People ask us about rooflights that have clouded between the panes. That points to a failed sealed unit, and we take on misted rooflight replacement as well as new fittings.

Once the roof has been looked at, a fixed written quote comes to you, and a written 10-year workmanship guarantee covers the finished job. The visit costs nothing. Call 01792 929062 or use the booking form.