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Staircase design

A couple of things about stairs – 1. They usually take up more space than you would first imagine. 2. There are some quite complex Building Regulations which determine the dimensions to do with width, risers and goings.

https://upload.wikimedia.org/wikipedia/commons/thumb/c/c5/Parana_pine_truck.jpg/800px-Parana_pine_truck.jpg

Parana pines, much used in staircase construction

In terms of embodied energy the use of timber in staircases is far better than metal. However the timber should be sustainably sourced and be FSC woodmarked. One of the traditionally favourite timbers for the manufacture of staircases has been parana pine (Araucaria angustifolia) from Brazil but this is now critically endangered.      see more on Parana pine

A fair number of timber merchants and joinery manufacturers in the UK are still claiming to be supplying sustainably sourced parana pine staircases. However the scientific literature from groups such as Geographical Paper No.180 by J.V.M. Bittencourt , University of Reading, shows the devastating manner in which parana pine has been over harvested and it is difficult to imagine how any real volume of the timber can be available on a sustainable basis.

It is on the IUCN Red List of Threatened Species as a critically endangered species.

‘Since 2001 there has been an official Brazilian ban on log exports of this species. The Brazilian Government is also promoting several initiatives to protect Araucaria genetic resources’


Although many staircases are now supplied as whole systems which are modified for the particular purpose, there are still many occasions when it may be better to revert to traditional joinery, metalwork or masonry. This is particularly true where repairs, changes or extensions are being made to a house or traditional features require matching. The exception to this is spiral stairs where it usually makes sense to utilise a prefabricated system.

Staircase design

The stairs always seem to take up more space than you first imagined (often around 8% or more of the total floor area when you include the associated landings) so it is good to work out a rough size and configuration at an early stage of designing a house. This is particularly true for the relationship of circulation space between different floors. There are several factors which influence the design of stairs:

• the vertical relationship of the landings the stairs serve     see more

One straight flight
At its simplest this involves a straight flight with a landing area at the top and bottom. This is usually the cheapest type to build and is most economical in terms of floorspace, taking up about 10 m² in total (i.e. both floors). Because the lower and upper landing are so far apart horizontally it may be difficult to fit in with the room layout. This is the layout generally used when the lower landing is in the hall or living room near the front door.

The spaces around, under and above stairs can range from grubby little cupboards to opportunities to display all kinds of beautiful artefacts such as plants, pictures works of art, creative lighting etc. This is more true with open tread and spiral stairs where the spaces are more visible.

Not that there is anything wrong with cupboards under stairs but given the non-rectangular, somewhat sculptural shape of stairs it provides a chance to be creative. With long straight flights it may leave space beneath the stairs for a doorway through to another room or a small space for a desk, stereo etc.


Half landing return.

Because of space configurations there is often a half landing and then a turn of 180°.

This allows the top landing to be vertically above the bottom one which may be useful with some types of room layout, especially for external stairs. It’s more expensive to build and takes up about 14 m² of floor plan. It may also be more difficult to arrive at a good design for the spaces below the stairs so it can look a bit poky.


Dogleg

Alternately a turn of 90° may work and this configuration can be particularly useful if you are wanting to link lower and upper floors where the circulation spaces don’t match easily, for instance if you are linking together two existing adjacent properties. Adjusting where the half landing occurs on the stairs can also be used to make adjustments between irregular floor levels. Takes up 12 m² of floor plan.


the aesthetic value of the stairs      see more

Stairs can have several aesthetic components:

They can be beautiful in a purely sculptural way, especially regarding the materials they are made of.

They give a different vertical quality to a space, especially when there is some visual connection between the two storeys they serve:

The book ‘A Pattern Language‘ goes into this in one of its patterns called ‘Staircase as a stage’

“A staircase is not just a way of getting from one floor to another. The stair is itself a space, a volume, a part of the building; and unless this space is made to live, it will be a dead spot, and work to disconnect the building and to tear its processes apart”

The point is also made that people often like to sit on stairs and may use stairs to make an ‘entry’ into a room. So the advice goes:

“Place the main stair in a key position, central and visible. Treat the whole staircase as a room (or if it is outside, as a courtyard). Arrange it so that the stair and the room are one, with the stair coming down around one or two walls of the room. Flair out the bottom of the stair with open windows or balustrades and with wide steps so that people coming down the stair become part of the action in the room while they are on the stair, and so that people below will naturally use the stair for seats.”

Stairs on an outside wall can be lit by a tall window: the Victorians often commissioned stained glass work for these. Half landings can incorporate areas to place objects of beauty or window seats. Pattern Language suggests a window affording a Zen view. Landings can be very interesting areas especially if they are part of a gallery which overlooks rooms below or a courtyard.


the cost which can vary enormously     see more

At the cheapest end is the factory made straight flight of timber stairs with closed risers. At the other end is almost anything you can imagine


the type of construction and materials     see more

The main structure of the house may suggest the type of stairs which seem best suited. For instance a very heavy masonry structure may be able to support cantilevered treads. Open risers are often used on modern houses. Timber houses would seldom use masonry stairs for structural reasons.
Stair treads obviously need to be hard wearing and it is almost as if stairs have been divided into two types historically: ones which were meant to be carpeted and ones which were meant to be left exposed.

The carpeted ones (usually with timber risers) were normally with softwood treads which wear down if not covered.
The exposed ones tend to be mainly hardwood but also stone, concrete, terrazzo, steel (usually with a covering such as cork, rubber, timber etc.).

If you are using timber for the stairs then this is an opportunity to show off some of our beautiful native timbers. Because staircases use a relatively small volume of timber it is possible to splash out and use the best. Most people know of ash and oak but there are several more exotic species in terms of colour and grain. Native cherry has slightly pink streaks with yellow markings. Native yew is very exotic in terms of its rich red/brown grain mixed with cream. The fruit woods are light in colour and elm has a rich and charming grain. Alder can have strong streaks of red if treated with oil.


the possibility of stair lifts / lifts     see more

With the growing awareness of Lifetime Homes there is a strong case for considering how stair design might relate to lifts and stair lifts, not necessarily for your own use but also as a way of making a house easier to sell in the future or for the use of a disabled relative. With an ageing population, this will become an increasingly important issue.

The section on Disabled Access indicates how lifts might relate to stairs and landings. In the case of stair lifts there is a case for designing stairs so they may take a stair lift at a later date. This involves the width of the stair, structural support for the lift, adequate space on landings and power supply. It may also have a bearing on the design of service ducts


the Building Regulations

(the Scottish Regulations are different in many respects and are somewhat better illustrated in the Accredited Construction Details part 4.3)

The regulations, (mostly Part K), have a lot to say about stairs.

Below are extracts from the Building Regulations where stairs in houses are termed ‘Private stairs’

Because the relationship between the rise and the going is quite complicated there are 3 methods of achieving the correct result but they all rely on the fact that the pitch of the steps must not be greater than 42°.

This is how it is measured:

The three ways to calculate it are:

  • The maximum rise for steps is 220mm and minimum going is 220mm (but of course with the added proviso that it will not be steeper than 42°)
  • The second way of working it out is having:
    • Any rise between 155mm and 220mm used with any going between 245mm and 260mm; OR
    • Any rise between 165mm and 200mm used with any going between 223mm and 300mm.
  • The third way is to make sure that the relationship between the dimensions of the rise and going is that twice the rise plus the going (2R + G) should be between 550mm and 700mm.

Construction of steps

Steps should have level treads. Steps may have open risers, but treads should then overlap each other by at least 16mm. For steps in buildings providing the means of access for disabled people reference should be made to Approved Document M, Access and facilities for disabled people.

All stairs which have open risers and are likely to be used by children under 5 years should be constructed so that a 100mm diameter sphere cannot pass through the open risers.

This is mainly about pitch and dimensions but also includes other aspects such as guarding, handrails and ‘spread of flame’ concerning the materials of the surfaces surrounding the stairs. Below is an on-line calculator to help work out the dimensions of stairs. It is based on the Building Regulations Approved Documents formulas for calculating a straight flight of stairs. Note that the variables can all affect each other so you may need to play around a bit. There are four main constraints built into the calculations and they must all apply

  • the actual slope of the stairs, which must never exceed 42º
  • the maximum rise on a step. This must not exceed 220mm
  • the minimum going on a step, which must not be less than 220mm
  • the sum of twice the riser plus the going (2R+G) which must lie between 550mm and 700mm
There is also a big section on ‘Means of warning and escape‘ under Fire Safety which is to do with how directly and safely you can get from an upper floor down to a ground floor and out of the building. It can determine much of the design and layout of stairs including fire doors and protected stairs.

Straight stair calculator

The live spreadsheet below works on the assumption that you have a fixed floor to floor dimension (total rise) but you may want to vary the number of steps and their size and the slope. You can input the number of risers you want and their goings and the spreadsheet then checks whether they conform to the Building Regulations. Enter your guestimate values into the green boxes and then the red text comments indicate whether the necessary conditions are met. Other values such as riser height and pitch get calculated. If the conditions are not met you need to try different goings and risers.

Notes:

  1. Stairs are limited to 36 consecutive risers in a flight unless there is a change in direction. See para 1.14 in the Approved documents.
  2. Risers are not allowed to exceed 220mm
  3. It is important to work to 0.1 of a mm.  (or better) because cumulative error on many steps can become significant
  4. The greater the going the shallower the pitch of the stairs. You can’t have a combination of the maximum risers (220) with the minimum goings (also 220). It makes it too steep (over 42 deg). Longer goings make for shallower but longer stairs.
  5. If this result does not fall within 550-700 try adjusting the risers (via the number of risers) and the goings. The formula comes from the Building Regulations.
  6. if this is above 42 degrees then try increasing the going (or increasing the number of risers to make them smaller)
  7. The total length is the horizontal distance from the nosing on the top landing to the position on the lower landing directly below the lowest nosing. See diag. below

The 2000mm headroom rule can be reduced under certain circumstances for loft conversions. (see part K , page 7)

These calculations give you results as if there were no nosings on the treads. That is fine because you can simply add nosings to the steps afterwards without altering the basis of the calculations. However doing so can affect two things: both the headroom and the lower landing width will be reduced marginally. The headroom must always be 2000 min. and the width of the landing is determined by the regulations.

Headroom (with exemption for loft conversion)

A headroom of 2m is adequate on the access between levels (see Diagram 2). For loft conversions where there is not enough space to achieve this height, the headroom will be satisfactory if the height measured at the centre of the stair width is 1.9m reducing to 1.8m at the side of the stair as shown in Diagram 3.

Width of flights

No recommendations for minimum stair widths are given. Designers should bear in mind the requirements for stairs which:

  • form part of means of escape. Reference should be made to Approved Document part B: Fire safety;
  • provide access for disabled people. Reference should be made to Approved Document part M: Access and facilities for disabled people.

Length of flights

Stairs having more than 36 risers in consecutive flights should make at least one change of direction between flights of at least 30° (see Diagram 5).

Landings

Landings should be provided at the top and bottom of every flight. The width and length of every landing should be at least as great as the smallest width of the flight. The landing may include part of the floor of the building.

To afford safe passage landings should be clear of permanent obstruction. A door may swing across a landing at the bottom of a flight but only if it will leave a clear space of at least 400mm across the full width of the flight (see Diagram 6). Doors to cupboards and ducts may open in a similar manner over a landing at the top of a flight (see Diagram 7). For means of escape requirements reference should be made to Approved Document part B: Fire safety.

Landings should be level unless they are formed by the ground at the top or bottom of a flight. The maximum slope of this type of landing may be 1 in 20 provided that the ground is paved or otherwise made firm.

Stairs designed to BS 585-1:1989 Wood stairs.

Specification for stairs with closed risers for domestic use, including straight and winder flights and quarter or half landings, will offer reasonable safety.

Also:

Stairs designed in accordance with BS 5395-2:1984 Stairs, ladders and walkways.

Code of practice for the design of helical and spiral stairs will be adequate.

Stairs with goings less than shown in this standard may be considered in conversion work when space is limited and the stair does not serve more than one habitable room.

Handrails for stairs

Stairs should have a handrail on at least one side if they are less than 1m wide. They should have a handrail on both sides if they are wider. Handrails should be provided beside the two bottom steps in public buildings and where stairs are intended to be used by people with disabilities. See Approved Document part M: Access and facilities for disabled people. Elsewhere handrails need not be provided beside the two bottom steps.

In all buildings handrail height should be between 900mm and 1000mm measured to the top of the handrail from the pitch line or floor.

Handrails can form the top of a guarding if the heights can be matched.

Guarding of stairs

Flights and landings should be guarded at the sides (see Diagram 11) in dwellings – when there is a drop of more than 600mm;

Except on stairs in a building which is not likely to be used by children under 5 years the guarding to a flight should prevent children being held fast by the guarding. The construction should be such that:

  • a 100mm sphere cannot pass through any openings in the guarding; and
  • children will not readily be able to climb the guarding.

The height of the guarding itself should be as shown in the diagram 11 below

Pedestrian guarding

There may be other situations around stairs where guarding is required:

Siting

Guarding should be provided where it is reasonably necessary for safety to guard the edges of any part of a floor (including the edge below an opening window), gallery, balcony, roof (including rooflights and other openings), any other place to which people have access and any light well, basement area or similar sunken area next to a building. Guarding should also be provided in vehicle parks, but not on any ramps used only for vehicle access. Guarding need not be provided to such places as loading bays where it would obstruct normal use.

Design

Any wall, parapet, balustrade or similar obstruction may serve as guarding. Guarding should be at least the height shown in Diagram 11. Guarding should be capable of resisting at least the horizontal force given in BS 6399-1:1996. Where glazing is used in the guarding, reference should be made to Approved Document N: Glazing – safety in relation to impact, opening and cleaning.

For further guidance on design of barriers and infill panels, reference should be made to BS 6180:1995Code of practice for protective barriers in and about buildings.

Where buildings are likely to be used by children under 5 years the guarding should prevent children being held fast by the guarding. The construction should be such that a 100mm sphere cannot pass through any opening in the guarding and so that children will not readily be able to climb it. Horizontal rails for such guarding should be avoided.

Spiral staircases

Spiral and helical (centreless) stairs are attractive in several ways

  • They can be extremely elegant and visually satisfying. This is partly the spiral shape itself and partly the visual connection which can be created between the two or more floors. They can also introduce an element of novelty. Spiral stairs are quite sculptural and can sometimes intrigue the mind as to exactly what holds them up. They can be an opportunity for creative lighting, especially in the way shadows of the circling steps can be used.
  • Sometimes they will allow stairs to fit into a space which would be difficult for conventional stairs. However it can work the other way because of the greater width of the treads which is usually required by the Building Regulations.

Considerations

There are several constraints to take into account and they involve the slightly complex geometry of spiral stairs:

  • Is there enough space for them to fit in?
  • Will the turn of the stairs allow for the upstairs landing to be in the right place?
  • Will the upstairs landing work when headroom over the stairs is taken into consideration?
  • Are half landings required?
  • If there is a centre pole, how is it supported?
  • If it is centreless then what supports the whole of the stair structure
  • Is fire proofing between storeys an issue?
  • Do you want a factory made kit system or a custom design?

Space requirements

Most of the factory made systems have good on-line information about the dimensions of their various models and you can establish pretty quickly whether there is enough space.

If you are wanting custom made spiral stairs then the Building Regulations are quite complicated and there are some calculations to do. Basically the regulations are there to make them as safe as normal straight stairs in terms of risers, going, headroom, guarding (handrails etc.), numbers of steps in a run, landings and width of treads.

How much turn?

There is a complex relationship between the going, the riser and the width of the stairs and this determines how much the stair turns. It is, for instance, possible to design a narrow spiral staircase to rise by 2.5 metres with only a bit more than half a turn. But the question arises as to whether you are heading in the right direction when you reach the top. If not you may need a large and awkward landing to get facing the right way. If you have wider going (treads) then you will complete more of a circle.

Headroom and landings

The headroom you need over the stairs may eat into the area of the landing above. There are minimum areas stipulated by the regulations.

Half landings

Half landings may be necessary in some cases such as when adjacent floor levels differs by something other than a storey height. This will then involve a specially made half landing which may not work well with a kit stairs.

Support

Each tread needs supporting and fixing at both ends unless it is cantilevered off a centre post. This can be done a number of ways.

If there is a centre pole it can support the centre end of the treads but it also needs fixing top and bottom. Usually the bottom of the pole has a plate which is fixed directly to the floor. The top of the pole can go up to the floor above (or a structural element incorporated in the ceiling) or it can be fixed to the upper floor, in which case it needs a lateral support which may also serve as the upper landing. This is the most usual configuration.

The outer ends of the treads are often fixed to each other using the ballustrading which supports the handrail. This gives added strength and rigidity to the whole structure.

If the stairs are centreless then there are basically three ways  to support the treads

  • a support wall under the tread ends
  • a structural curved string to both sides of the steps, rigidly fixed at the top and bottom
  • a method of rigidly fixing succeeding treads to each other at both ends so that they effectively form a string similar to stairs with a centre pole.

It may be possible to support the outer ends of treads on surrounding walls either by fixing to them or cantilevering out from them. If they are cantilevered then the stairs can be centreless or there can be a pole, or the steps can be stacked on top of each other.

The Building regs on spiral stairs

The Building Regulations for straight steps generally apply to spiral stairs but there are special methods for measuring curved stairs and design is based on BS 5395-2:1984. As of 6th April 2013, part K of the Approved Documents was updated and simply tells you to use BS 5395-2:1984 to design spiral stairs without giving as much detail as the previous Approved Document (the Part K 1998 with 2000 Amendments – which is now archived).

For steps with tapered treads the going should be measured as follows:

  • if the width of flight is narrower than 1 m measure in the middle
  • if the width of flight is 1 m or wider measure 270mm from each side

The going of tapered treads should measure at least 50mm at the narrow end.

Where consecutive tapered treads are used a uniform going should be maintained.

Where a stair consists of straight and tapered treads the going of the tapered treads should not be less than the going of the straight flight – these treads should satisfy paragraphs 1.1 to 1.5.

Spiral stair calculator (narrow)

This calculator is based on Part K 1998 with 2000 Amendments which in turn uses BS 5395-2:1984

Enter your guestimate values into the green boxes and then the red text comments indicate whether the necessary conditions are met. Other values such as riser height and pitch get calculated. If the conditions are not met you need to try different goings, etc.

The radius is the radius of the outer (larger) curve on the stair. The width is the width of the treads.

Notes for above calculator

  1. Having more risers than the minimum may make for a less steep stairs. The risers will be smaller and the formula (2x riser + going) will allow for longer goings
  2. Controlling by the radius helps to fit the stair within a limited space whereas controlling by the amount of turn may be more important so that the landings are positioned correctly
  3. Adjusting the width affects where the centre line of the steps is and hence the pitch. Note that there is no minimum set width except that means of escape from fire and disabled access should both be considered. Bear in mind that the going on steps is measured to the edge of the nosing (see diagram 1 in section 1 of the Approved Documents part K)
  4. Adjusting the goings affects the pitch and the overall length of the stairs
  5. The formula (2x riser+ going) is included in the building regulations and is intended to make for a comfortable and safe stride
  6. The pitch is measured along the centre line of the nosings
  7. If the width at the narrow end is too low you may be able to adjust this by increasing the radius of the stair, having longer goings or setting a lower stair width
  8. The total angle turned will affect the position of landings and which way you are facing when you reach the top (or bottom) of a flight. You may be able to make adjustments by having an extra piece of triangular landing to create the necessary amount of turn
  9. The 2000mm headroom is measured above the pitch line. It can be reduced slightly for certain loft conversion configurations
  10. Bear in mind that after you have calculated the stairs you will need to allow something extra in width for things like the thickness of handrails (and space for hand movement), balustrades, stair construction etc.

Spiral stair calculator (wide)

This calculator is based on Part K 1998 with 2000 Amendments which in turn uses BS 5395-2:1984

Enter your guestimate values into the green boxes and then the red text comments indicate whether the necessary conditions are met.

With spiral stairs of a metre or more in width things get quite complicated because the steps have to be checked in two places for steepness and size. (see diag. 8 above) This means there are effectively seven variables which can all affect each other. The best way is to simply play around with the calculator and get a feel of the dynamics. Values such as riser height and pitch also get calculated.

Notes for above calculator

  1. Having more risers than the minimum may make for a less steep stairs. The risers will be smaller and the formula (2x riser + going) will allow for longer goings
  2. Controlling by the radius helps to fit the stair within a limited space whereas controlling by the amount of turn may be more important so that the landings are positioned correctly
  3. Remember that the space needed for the stairs will be slightly larger than the radius because of handrail, banisters etc.
  4. This should be 1000mm or more. If you want it less then use the other calculator above
  5. Increasing the width has the effect of creating a larger difference between the two goings which get measured and this can cause the outer (2R+G) formula to exceed its limit.
  6. Adjusting the goings affects the pitch and the overall length of the stairs
  7. The (2x riser + inner going) formula comes from the Building Regulations and must be satisfied at both going measurement points (270mm in from the end of the steps). The pitch is also measured at both points
  8. The spreadsheet works by first setting the inner size of the step and then checking to see if the outer size is OK
  9. The total angle turned will affect the position of landings and which way you are facing when you reach the top (or bottom) of a flight. You may be able to make adjustments by having an extra piece of triangular landing to create the necessary amount of turn
  10. The 2000mm headroom is measured above the pitch line. It can be reduced slightly for certain loft conversion configurations
  11. The amount of turn may be a more important factor than the space available. If so use this part of the calculator (after first using the very top part where you input the floor to floor height and number of steps)
  12. Increasing the width has the effect of creating a larger difference between the two goings which get measured and this can cause the outer (2R+G) formula to exceed its limit.

Note that the radius of the stairs might be much greater than the stair width.

With the riser dimension it is necessary to work to fractions of a millimetre since the cumulative effect of many stairs can make a large difference to the overall floor to floor dimension.

10 comments to Staircase design

  • bobthebuilder

    Thanks Gideon, British Standards tend to disappear pretty quickly when they are made freely available on the net.

    You have to spend the best part of £100 to buy this one.

    This all goes back to the Thatcher years when “there is no such thing as society” meant that agencies such as British Standards got privatised. This was theft of public information into the private realm.

    But what do you expect from that type of government.

  • Gideon viljoen

    Hi – this is brilliant. THANKS!

    Your link to the BS5395 doc doesnt work though..

    Best
    Gideon

  • M Hopper

    A straight staircase against right hand wall (going up)ground floor to first floor (1970s house)eight feet floor to ceiling, 14 steps, need to know minimum height from front of step to ceiling.

  • Vivienne Mitchell

    Has anybody got any information on who can come and build me a helical staircase or two, preferably good and cheap. Lincolnshire area. many thanks.

  • Fadi

    Hi,
    Thank you for your post. I am designing a helical staircase for a university project, it is composed of 3 parts that get steeper. The risers are respectively 90mm, 105mm, 129 mm. Unfortunatly, if I refer to Part K, the minimum rise should be 150mm. Des this vary BS 5395-2 ? Is there a minimum rise value at all for helical staircases?

    Thank you

  • bobthebuilder

    Hi Carl,

    Not quite sure what you mean by deviation.
    The maximum rise for steps is 220mm and minimum going is 220mm
    But if you mean ‘can you stretch the rules a bit’ then the answer is maybe. You can sometimes get what is called a ‘relexation’ of the building regulations. A relaxation is most often given when changes are being made to existing buildings when a slight ‘bending’ of the rules might lead to some other major gain. E.g. headroom is sometimes relaxed.

  • carl jenkins

    Is there a maximum permissible deviation for the dimensions of each tread / riser?

  • Graeme

    Hi, iwould like to find out about the requirements for supporting a double winder newel post fir stairs leasing to loft, by suspending from a structure above? Supporting from below places the newel right in the middle of the existing srairs. any advice on this approach? Thanks

  • Stephanie

    Thank you so much for this spreadsheet!

  • Mike Earley

    The stair spreadsheet was just want I needed. Everything is included. Perfect – thank you

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