The glass and the edge are two separate questions
A guard rail protects people from falling off something or through something. A properly rated walk-on unit removes the second risk, but it does nothing about the first.
When a homeowner asks whether a walk-on rooflight needs a rail, they are often picturing a rail around the glass, like the fence round a hole in the pavement. That is rarely what the regulations are after. A walk-on skylight is designed to be stood on: it typically has a thick laminated top pane, continuous support round its edge and a load rating declared by its maker. Once it is installed flush in a terrace or courtyard, it behaves like the paving around it, and nobody puts a balustrade round a paving slab. The page on whether you can walk on a rooflight explains how that rating differs from an ordinary flat unit, and the details vary from one product to the next.
The real question is about the space the glass sits in. If the walk-on rooflight turns a flat roof into somewhere people go, or sits beside a sudden change in level, then the edge of that space may need guarding whatever the glass is made of. That is a Part K matter, and it is decided by the drop and the use, not by the rooflight.
What Approved Document K asks for at a roof edge
Part K of the Building Regulations covers protection from falling. For a house, guarding at the edge of an external balcony or a roof that people use is set at 1,100 mm high in the approved guidance.
Approved Document K is the government guidance that shows one way of meeting Part K in England. It asks for guarding where it is reasonably needed for safety at the edges of floors, balconies and roofs to which people have access, and it names rooflights and other openings in a roof among the places to consider. For dwellings, the guidance gives 900 mm for internal floors and stairs and 1,100 mm for external balconies and the edges of roofs. The same guidance expects guarding in a home likely to be used by young children to be hard to climb and to have no gaps that a 100 mm sphere could pass through.
Whether a particular edge needs guarding at all depends on the height of the drop, how people use the space and how easy it is to reach. Those are judgements for your designer and Building Control on the actual site, and the guide to Building Regulations for walk-on rooflights puts Part K alongside the structural and thermal points. Where a new or replacement rooflight is notifiable, we handle the Building Control notification as part of the job.
When the roof itself becomes a terrace
A flat roof with a walk-on rooflight in it is not automatically a roof terrace. It becomes one when you give people a way on to it and a reason to stay.
Behind the terraces of Romsey, Petersfield and De Freville, the flat roof of a rear extension is often reachable from a first-floor window or a new door off a landing. A roof that is only ever reached for maintenance is treated very differently from a roof you step out on with a coffee. Once the roof becomes a place people use, the open edges usually need guarding to the external height, and the whole build-up changes: the waterproofing, the decking or paving, the drainage and the walk-on unit all have to work together. The guide to walk-on rooflights for roof terraces covers that build-up.
There is a planning side too. A rail or balustrade that turns a flat roof into a usable terrace can change how the house overlooks its neighbours, and that is often where permission comes in. The answer on planning permission for walk-on rooflights goes into that, and it is sensible to check with the council before you commit to a design.
Standard rooflights on a roof people use
The rooflights that most need thought are the ones that are not walk-on. A standard flat skylight on a roof that people reach is exactly the kind of opening the guidance has in mind.
An ordinary flat rooflight is built to carry snow and wind, not a person. If a roof has both a terrace area and a standard unit, someone stepping back to take a photograph could end up on glass that was never meant to take them. The usual answers are to replace that unit with a rated walk-on one, to keep it outside the area people use with a fixed barrier between, or to guard round it. Which of those is right depends on the layout, and it is one of the choices we set out in the written light plan before any work starts. The comparison of walk-on and standard flat rooflights helps with that decision.
Lightwells, basements and garden drops
Walk-on glass at ground level is usually there to replace an open lightwell, and in that case it can take away the need for a railing rather than add one.
An open basement lightwell is a sunken area next to the house, and Part K expects the edge of that kind of drop to be guarded where people could fall into it. Covering the well with a rated walk-on unit, flush with the garden or front path, closes the drop entirely. That is one reason the approach suits Victorian houses with lower-ground rooms, where an open well would otherwise need a railing along the front path. Where the glass stops short of the full width, or a stair runs down beside it, the remaining open edge still needs looking at. There is more in the guides to walk-on glass over basements and walk-on glass in courtyards and gardens.
| Where the glass sits | Rail round the glass? | Edge guarding? |
|---|---|---|
| Rated unit in a used roof terrace | Not normally | Usually, 1,100 mm |
| Standard unit on a used roof | Often, or keep it out of reach | Usually |
| Rated unit over a lightwell | Not normally | Only for open edges left |
| Roof reached only for upkeep | Not normally | Site specific |
The table is a general guide to how these cases tend to be treated, not a ruling on any one house. Building Control decides on site.
Where a rail goes, and what it does to the light
A balustrade is not only a safety item. On a flat roof it also casts a shadow, and on some orientations that shadow crosses the glass for part of the day.
A solid parapet or a close-boarded rail on the south side of a terrace throws a band of shade north across the roof in winter, when the sun is low over Cambridge. If the walk-on rooflight sits right behind it, the room below can lose much of its direct sun between November and February. A glass balustrade, or moving the rooflight a little further from the guarded edge, keeps more of that light. In summer the same rail does little, because the sun is high. We plan the rail line and the rooflight position together so that the light lands where you want it in the room below. The light planning page shows how that works by orientation, and the walk-on rooflight installation hub covers the rest of the job.
Questions people also ask
Can a glass balustrade meet the 1,100 mm guidance?
Glass balustrades are widely used for external guarding and can be designed to the height and loads Part K expects. The glass, fixings and base all need to suit the barrier loads, so the specification comes from the balustrade maker and your designer, and Building Control confirms it.
Does a walk-on rooflight need a rail while it is being fitted?
During installation the opening is a real fall hazard, so it is protected until the unit is bedded and secure. That is site safety rather than the permanent guarding Part K deals with.
Does a parapet wall count as guarding?
It can, if it reaches the required height above the finished terrace surface. Raising the floor level with decking or paving reduces the effective height of an existing parapet, so measure from the new surface, not the old roof.
What about a walk-on rooflight on a balcony?
A balcony already has an open edge, so its guarding is needed with or without the glass. The answer on walk-on glass on a balcony covers the rest. To see how a walk-on unit would light your own room, book a light survey.
