Approved Document K:
Building regulations and skylights

This is Sunsquare’s practical guide to understanding what English building regulations’ Approved Document K means for skylight installation projects. We hope the advice it contains proves valuable to architects, specifiers, surveyors and dabblers alike.

Approved Document K covers protection from falling, collision and impact around stairways, ramps, ladders, doors, windows, balustrading and barriers. It also comprises guidance – previously part of Approved Documents N and M until April 2013 – on safety of glazing and roof access in residential dwellings.

While we have endeavoured for utmost accuracy in this article, we always advise thorough consultation of official documentation and local building control authorities before commencing any work.

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Skylights and roof access – guidance on stairs, ladders and ramps

Skylights are often used to provide simple and secure access to flat rooftop terraces or gardens. They can also provide a means for maintenance access on a less frequent basis.

To ensure people can move safely between different levels in or about a building, see Requirement K1. It covers design, construction and installation guidance for stairs, ladders and ramps. It provides specifications for steepness, handrails, headroom, length and width as well as rise and going.

To follow the building regulations properly, your first question should always be: why is roof access required? The justification for roof access informs which aspects of the building regulations apply and which safety measures you should employ. If it’s going to be used infrequently, for maintenance only, the requirements will differ from a skylight meant to provide regular rooftop access.

Maintenance access

Generally speaking, the level of safety provisions required will depend on the nature of the building and its predicted uses.

A public building would require a higher standard of safety compared to a residence where roof access is reserved for maintenance professionals only. The first scenario offers the possibility of many more users – some of whom would be unfamiliar with the building’s layout. The other assumes professional users taking greater level of care at reduced intervals.

If in doubt, follow the one month rule. In cases where stairs or ladders are used a minimum of once per month, follow guidance for private stairs in dwellings or industrial stairs and ladders. Where maintenance access is needed less often, portable ladders – covered under 2007 Construction Regulations – may be an acceptable alternative.

Terraces or regular roof access

Anything notably over and above the aforementioned one month minimum will entail a more permanent and secure installation.

Naturally, what is appropriate for the project at hand will vary depending on your scheme. It is recommended that you consult with your Building Control Officer for absolute confirmation. However, a permanent flight of stairs is widely deemed to be the most appropriate solution for roof access via skylights.

Now, there are several elements you should be aware of in order to achieve total compliance with building regulations.

Headroom

Space is a key issue as regards moving between levels in a building. Approved Document K provides strict guidance on size and specification to ensure safety of passage.

KEY NUMBERS

• A minimum headroom of 2m is required for access between floors
• A private stair in one dwelling permits a maximum pitch of 42 degrees
• Every 50mm of roof construction depth requires 56mm added to the length of the opening
• Where opening width accommodates double stair width, minimum internal skylight length reduces to 2.4m for a 900mm landing
• A skylight with 2m external and 1.8m internal dimension with a conventional stair will not comply!
• Consider the final step of a flight of stairs to an access skylight as a landing
• The minimum tread width for the top of a skylight access flight of stairs is 400mm
• Measure the going at the centre of the tread
• Specify a minimum width of 50mm at the narrow tread end
• Minimum barrier height in single family dwellings for stairs, landings, ramps and edges of internal floors is 900mm
• For external balconies and roof edges, minimum is 1100mm
• In residential and public buildings: 900mm for flights, otherwise 1100mm

• A stair going of 220mm & short landing area of 400mm affords 860mm headroom – too little!

WARNINGS

The thickness of the building’s roof construction affects attainable head clearance directly. As roof thickness is variable and often substantial – with set requirements for insulation and structural load – special care should be taken. Ensure enough space in the roof and skylight is available that the 2m headroom permitted is achievable at the maximum pitch.

To be in compliance, the landing must be same width as the stairs at minimum. The recommended minimum for stair width in England is between 600mm and 800mm, depending on circumstances and the ruling of your building control authority.

In the event of a skylight not providing a clear opening, you should factor in the headroom of both the partially open skylight frame and the internal ceiling.

Getting around headroom: box skylights

If you’re having trouble achieving the requisite clearance with a traditional sliding skylight frame, a box skylight is an option for adding extra headroom.

Compared to hinged products, box skylights are the definitive choice for providing skylight access to rooftop areas, mainly as a result of the height they add above ceiling level.

Instead of working via a hinge mechanism, box skylights tend to utilise sliding glass sections. Therefore be careful to ensure the stair is positioned in such a way that the thresholds meets where the box skylight ends up when in the open position.

Compliance of stairs and landings

Approved Document K also provides guidance on the minimum dimensions permitted in the rise and going of permanent flights of stairs.

Key Information

Compliance of special stairs and tapered treads

When installing a flight of stairs incorporating tapered treads, the rise and going should be designed with the same requirements as those covered above.

If using consecutive tapered treads, the going should be identical on each. If, however, you are using a stair consisting of both tapered and straight treads, the going of the tapered treads should never be below that of the straights’.

KEY INFORMATION

Compliance of alternating tread stairs

Approved Document K recommends alternating tread stairs only in loft conversions where there’s not enough space for a full flight of stairs, or the stairs give access to only one habitable room.

They should, in other words, be a last resort. Use them only when a conventional stair won’t suffice and when steeper pitch and lesser demand on space are strictly needed. Building authorities are unlikely to accept budgetary justifications alone.

Using alternating tread stairs to a converted loft, or single habitable room, is justified by assumptions about user intention. There is an expectation that these stairs would be used by a limited number of people. It is for this reason they are not recommended to be used as a means for regular terrace or rooftop access.

WARNINGS

Approved Document K does not explicitly cover roof terrace access. However, industry expertise suggests an alternating tread stair would not satisfy safety standards in most circumstances. Seek advice from your local authority before settling on an alternative to a full flight of stairs.

Compliance of terraces, guards and barriers

Covering several aspects of safety barrier requirements, section K3 of the guidance recommends pedestrian guarding to be installed wherever reasonable around any part of a roof – including skylights and other openings.

Whether a rooftop access skylight needs barriers is ultimately dependent upon choice of product, its specification and its placement on the roof.

KEY NUMBERS

• Minimum barrier height in single family dwellings for stairs, landings, ramps and edges of internal floors is 900mm
• For external balconies and roof edges, minimum is 1100mm
• In residential and public buildings: 900mm for flights, otherwise 1100mm

Using skylights as safety barriers

If permitted by the specification and orientation of the skylight product, as well as the layout of the building, hinged access skylights can be safely used with minimal barriers provided.

In some instances, for example, the opening section of the skylight can act as an appropriate barrier while in open position. As long as the product meets the minimum requirements of size and glazing safety laid out in Approved Document K and Approved Document N, there should be no foreseeable issue.

Using the skylight itself as a barrier is also viable in cases where a skylight is installed next adjacent to a wall. If, when the skylight is fully open, the wall and glass combine to form barriers along both lengths of the opening, then a balustrade at the rear is all that is required to meet compliance standards.

Removing the need for safety barriers with box skylights

If installing barriers or balustrades around a skylight feels like too much effort, box skylights provide an ideal solution. With their physical structure above roof line, the glazing of the skylight should itself form a barrier to prevent injury by falling.

Glazing: protection against impact

Installed glazing, its design and the materials used therein, must comply with building regulations, particularly Requirement K4: Protecting against impact with glazing. There are three principles to look for in terms of glazing compliance. The guidance states that any glazing likely to be regularly interacted with by people in a building should, if broken:

• Break in a manner which is unlikely to cause injury
• Resist impact without breaking
• Be shielded or protected against impact

The most common solution for skylight compliance is the adoption of toughened safety glass. Designed to fracture into small, less dangerous fragments upon breaking impact, they provide an optimal route to reducing risk of harm.

Toughened safety glass of higher specification provides an attractive option. Heat soak tested, this form of glazing is designed to combat the risk of glass fractures occurring as a result of nickel sulphide inclusions formed in the toughening process.

We also recommend the use of glazing with a laminated interlayer, manufactured to capture fractured glass as it falls, preventing its escape from the frame and reducing the possibility of injury.

For more information on recommended glazing for skylights, read our short guide on the subject.

Summary

Any project involving skylight installation must take the above information from Approved Document K into account if they wish to maintain safe, happy customers and avoid falling foul of the local authority. In particular, specifiers and architects should take care around providing:

• the appropriate level of access for intended purposes
• the right amount of headroom and opening space
• the correct specification of stairs and landings
• appropriate safety measures around protecting from falling
• reduced risk of harm from potential breakage of glazing

We recommend referring to Approved Document K in full when in doubt about the full-compliance method for implementation of any of the above measures and features.