Do you need planning permission for a VELUX window?

Permitted development is the set of works the government lets you carry out on a house without asking the council first. Roof windows are covered by it, but only while they keep within a handful of measured limits. Get outside any one of them and the right falls away, and you are back to a full planning application.

The three that matter for a VELUX unit are straightforward:

• Projection. The window must not stand more than 150mm proud of the plane of the existing roof. A standard roof window sits almost flush in the slope, so this is rarely a problem. A raised kerb-mounted unit on a flat roof is where you can trip it.
• Height. No part of the finished window can be higher than the highest part of the existing roof. In practice that means keep it below the ridge, which is where anyone would put a roof window anyway.
• Side elevations. If the window faces a side boundary and its lowest edge is less than 1.7 metres above the floor of the room, it has to be obscure-glazed and either fixed shut or restricted so it only opens above that 1.7 metre line. This is a privacy rule, meant to stop a new window overlooking next door.

None of these stops a normal loft or extension roof window on the front or rear slope of a house. They exist to catch the awkward cases: the unit that stands too proud, the one that peers over a boundary, the one bolted above the ridge line.

The permitted development right is switched off entirely for certain buildings and certain locations. If any of these applies to you, treat a roof window as needing permission and check with the local authority before anyone orders glass.

• Flats and maisonettes. Permitted development for roof alterations applies to houses, not to flats. If you own the top flat in a converted Victorian villa, the automatic right does not cover you.
• Listed buildings. A roof window in a listed roof needs listed building consent, and that is a stricter test than ordinary planning. The council will care about which slope it goes in and whether it can be seen from the street.
• Conservation areas. Permitted development for roof windows is curtailed on the principal elevation, and often more widely, inside a conservation area. Around here that catches Clifftown, with its Victorian estate, and Leigh Old Town, whose fishing-cottage core runs from the thirteenth to the eighteenth century.
• Article 4 Directions. This is the one that surprises people. An Article 4 Direction lets a council remove permitted development rights street by street. The Leigh Cliff and Leigh conservation areas both carry one that covers changes to roofing materials and windows, so a roof window that would be permitted development three streets away needs a planning application there.

If you are in Leigh, or in any conservation area, the safe assumption is that you will have to apply. A quick call to Southend-on-Sea City Council planning, quoting your postcode, will tell you which regime your roof falls under before you commit to anything.

These two get run together constantly, and they are separate approvals with separate purposes. Planning is about whether the building may change how it looks and sits in its surroundings. Building Regulations are about whether the work is sound, warm and safe. You can be clear of one and still owe the other.

A new roof window, or an existing one made larger, is notifiable under Building Regulations even when no planning application is needed. Two parts of the regulations bite. Part L sets a ceiling on the U-value, the rate at which heat leaks out through the unit on a cold night, so the glazing has to meet a thermal standard. Part K covers safety glazing and guarding, which matters where the glass is low down or within reach. On our installations we make the Building Control notification to Southend-on-Sea City Council, or to the relevant authority if you are outside the city, so the paperwork is handled rather than left to you.

The catch worth knowing is what the regulations do not police. Part L caps the U-value for winter, but it sets no limit on the G-value, the share of the sun’s heat the glass lets through in summer. A roof window can pass Building Regulations comfortably and still cook the room under it in July.

Once you know whether you need permission, the decision that actually shapes how the room feels is the glass, and it barely shows up in either approval. Southend faces south across the Thames Estuary, so a great many rear roofs here look straight at the sun with an open horizon and reflected light coming up off the water. Put a clear-glazed VELUX in that slope and you have added a solar collector to the room.

Clear double glazing sits at a G-value of around 0.6, meaning roughly sixty per cent of the sun’s energy comes through as heat. Solar-control glazing brings that down to around 0.3 for the same size of opening, which halves the heat without making the room dark. Neither planning nor Building Regulations will ask you which one you fitted, so on a south or west-facing roof it is worth deciding for yourself. This is the whole basis of our VELUX window installation work: orientation first, then the glass specification, then the unit. If glare and summer heat are the reason you are adding rooflight in the first place, the glass matters more than the model number, and our solar-control glazing page sets out the figures in full.

Start by working out which regime your roof is in. Note whether you live in a house or a flat, whether the building is listed, and whether your street sits in a conservation area or under an Article 4 Direction. If none of those applies and the window will stay within the 150mm projection and below the ridge, it is almost certainly permitted development and no planning application is needed. If any of them does apply, budget for a planning application and check the detail with the council before ordering.

Either way, remember the two things the planning question leaves out: the Building Regulations notification, which we handle, and the glass specification, which decides whether a south-facing roof window is a pleasure or a problem. If you want us to look at the orientation and the paperwork together, ring 01702 898232 or request a quote, and we will tell you which permissions your roof needs and what glass belongs in it.