BUILT ENVIRONMENT JOURNAL

Getting stair construction right

Stair construction must fulfil the requirements of Approved Document K to ensure it is safe for its intended use

Author: Amy Allen

25 March 2021

There is no guarding at all in this case so anyone could have a fall, while the handrail is too high © Amy Allen

The technical guidance for stair construction included in pp13-26 of Protection from falling, collision and impact: Approved Document K defines and sets requirements for all aspects of design including pitch, rise, going and guarding. It states that "stairs, ladders and ramps shall be so designed, constructed and installed as to be safe for people moving between different levels in or about the building."

There are three classifications of stair for those in or outside a building, and all depend on use of the building or area, or the intended use of the specific stair. These classifications are: private, utility, and general access. Each has a specific definition in Appendix A of the approved document, as follows.

  • Private stair: this is intended for use by one dwelling.
  • Utility stair: this is designed to be used for escape, maintenance access, or purposes other than general day-to-day circulation.
  • General access stair: this is intended for all users of the building on a day-to-day basis as a normal route between levels.

Some buildings may have multiple stairs with different classifications; for example, the main day-to-day stair in the front-of-house area of a cinema is designed as general access, while further, utility stairs serve as a means of escape.

These classifications differ in terms of requirements for rise, going and pitch. A utility stair may have a rise of up to 190mm compared to a general access stair, which is limited to 170mm. Because the utility stair is permitted a larger rise, it can take up less space in the floorplan of a building. However, if a utility stair is mistakenly designed when a general access stair is required, it can have consequences in terms of space.

Construction details

Further requirements for staircase design and construction are grouped into those for dwellings, those in buildings other than dwellings, and those in common areas in blocks of flats. However, they are required to be level and consistent in formation for the entire flight in all buildings.

Failure to comply may increase the risk of the user stumbling or tripping on risers that are inconsistent in height. This may seem an obvious requirement, but inconsistent stair heights are often found when refurbishing existing buildings.

A typical instance is where the stair doesn't quite fit, either due to being measured incorrectly, or where other work such as floor insulation installation has affected storey height. The top or bottom riser may not be consistent with the main flight if it has been modified to fit.

A key requirement in all situations other than dwellings is that risers should not be open or require contrasting nosings. Open risers – that is, a staircase with treads and no risers – are acceptable in domestic dwellings but should be limited to a 100mm rise, with the treads overlapping by at least 16mm; this is to prevent a small child, for instance, slipping through the gap. Consequently, if you had a rise of 220mm, some form of horizontal subdivision would be needed to limit the depth to less than 100mm.

We often find this to be a significant issue for homeowners who may have installed a modern-style stair and have trouble understanding why they need to carry out remedial works or can't have the design they'd planned to use; this frequently arises with minimalist floating stairs. Approved Document K's requirements are not intended as a barrier to design, but we must ensure each stair is safe for all people who may use it. We have seen inventive ways of addressing these safety concerns that maintain a modern feel.

The stair width and length required in Approved Document K is intended to be suitable for everyday use in a domestic situation. However, in a non-domestic building, it is important to consult Approved Document B for guidance on means of escape, to ensure any stair is sufficient to accommodate people leaving in the event of a fire.

The stair width and length required in Approved Document K is intended to be suitable for everyday use in a domestic situation. However, in a non-domestic building, it is important to consult Approved Document B for guidance on means of escape, to ensure any stair is sufficient to accommodate people leaving in the event of a fire.

Handrails and guarding

Another essential aspect of stair construction is handrails and guarding, which are critical to help prevent falls. The handrail can form the top of the guarding if the heights can be matched, but it is important still to think of the two features as separate to ensure their respective objectives are achieved if they are combined.

A handrail is for users to hold as they ascend or descend the stairs, and there are therefore requirements in Approved Document K for its size and shape. A guarding, meanwhile, is intended to prevent falling. We sometimes see instances where the two elements are combined, but the top of the guarding is insufficient to act as a handrail, often being too small or of an irregular shape that can't easily be held.

Handrails should be positioned between 900mm and 1,000mm from the pitch line; in all buildings other than dwellings there should be a handrail to each side of the flight and landings, and in every instance where the stair is more than 1,000mm wide.

Guarding should be provided in all instances where there is a fall risk of more than two risers in non-domestic instances, and a height of more than 600mm in private domestic dwellings.

In buildings that may be used by children younger than five, it's essential that the guarding is designed so it cannot be readily climbed or for children to be held fast. It is therefore critical to ensure that all openings are less then 100mm, as per the design requirements for open risers, and that horizontal railings aren't used where a foothold could be formed. Typical examples that present issues for compliance include tensioned-wire guarding designs where openings are usually a lot larger than 100mm and the wire is horizontal or follows the pitch.

Spiral and alternating tread

These forms of stair design are less commonly used, but can save space. Alternating treads are a midway design between a typical stair and a ladder, often used with domestic loft conversions, bed decks and other small areas where space is restricted.

Familiarity is an important aspect for building control surveyors to consider because alternating, space-saving stairs feel unusual compared to regular staircases, and may present safety issues as a result.

Meanwhile, BS 5395-2: 1984 offers design guidance on spiral stair construction, detailing requirements for specific situations and occupancies.

Competency evidence

During an inspection at Level 2 of the Building control inspections competency, you would typically be expected to record issues of the kind shown in the photographs below.

Faulty stair construction example one

The top riser being significantly lower than those on the remainder of the flight presents a falling risk. The only remedy would be replacement.

Faulty stair construction example two

A door frame installed on the line of the bottom step; this door location isn't acceptable as the door will swing across the step, which means there is no landing. The door in this case was relocated to the top of the stair ensuring a clear landing space between the stair and door.

You should apply knowledge of standards and regulations to site scenarios, and advise where work is incorrectly constructed.

Protection from falling may seem like an obvious requirement, but we frequently identify these issues in our site inspections, whether in the form of an ill-constructed detail or simply as an inappropriate design feature. The 100mm opening rule is intended to safeguard young children specifically, but stair and guarding design and construction generally aims to protect all occupants of a building. It is a critical factor in ensuring that buildings are safe and fit for a wide range of users.

admin@assentbc.co.uk

Related competencies: Building control inspections, Legal/regulatory compliance

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