Guidelines for the Use of Glass inFloors and Stairs

Contents

Introduction

1. Scope

2. Definitions and Descriptions

3. Design considerations

4. Design criteria

5. Glass types

6. Glass strength considerations

7. Post breakage behaviour

8. Selection of glass for slip resistance

9. Framing and installation

10. Building regulations and standards

Appendix 1 Drawing from BS 5395-1

Bibliography

Introduction

Glass floors and stairs are manufactured from a combination ofglasses designed to create a walkable structure in association withstructural supports.

They are designed for pedestrian use only.

The use of glass for these applications allows the interplay oftransparency, reflection and refraction of light.

1. Scope

This Data Sheet covers the use of glass in floors and stairs forpedestrian traffic in internal/external environments anddomestic/non-domestic applications.Comment will be made when the floor has to act as acompartment element in case of fire. It will give the basis of design together with information onselection of glass types and methods of installation.

Detail on anti-slip finishes and other safety matters will be considered.

2. Definitions

NOTE 1: The majority of these definitions have been taken fromEngland Building Regulation K: 2013

NOTE 2: A drawing showing these terms is shown in Appendix 1

2.1 Uniformly distributed load (UDL)

Load, e.g. wind, snow, applied over the entire surface of the pane.

2.2 Concentrated load

Load applied over a small area.

2.3 Normal-use stair

Stair intended for use by all users in or connected to a building

2.4 Private stair

Stair within a dwelling, intended for use only by occupants and visitors.

2.5 Alternating tread stair

A stair with paddle-shaped treads where the wide portion is onalternate sides on consecutive treads.

2.6 Helical stair

Stair in a helix around a central void.

2.7 Spiral stair

Stair in a helix around a central column.

2.8 Nosing

The leading edge of a stair tread.

2.9 Going

The depth from front to back of a tread less any overlap with thenext tread above.

2.10 Rise

The height between consecutive treads

Architectural Glazing Systems SECTION 7July 20137.3

Glass and Glazing Federation

Tel: 020 7939 9100 Fax: 0870 042 4266

While every attempt is made to present up to dateinformation, this Data Sheet, produced by the Glassand Glazing Federation, is issued for guidance butwithout responsibility for any advice given therein oromission therefrom or for the consequences of actingin reliance thereon and all liability on the part of theGlass and Glazing Federation however arising in connection therewith is expressly disclaimed.

2.11 Pitch

The angle of inclination between the horizontal and the lineconnecting the nosings of a stair.

2.12 Flight

Continuous series of steps or a continuous slope between landings

2.13 Stair width

The clear width between the walls or balustrades.

2.14 Tapered tread

A step in which the going reduces from one side to the other.

2.15 Ponding

Deflection of the pane that will allow collection of unwanted water.

2.16 Sacrificial layer

This is a pane of glass that is expressly used to protect thestructural component from damage, e.g. scratching, etc.

NOTE: This type of layer is designed to be easily replaceable

2.17 Redundant layer

This is a pane within the construction that allows the floor/stairtread to continue to support the designed loads should one of thepanes be broken.

3. Design Considerations

3.1 Assessment

Firstly it is necessary to consider the location of the floor/stair caseand whether it spans a dangerous drop. Breakage of the floor/stairtread could result in a fall from a high level or cause injury evenwhen the drop is quite small.

The nature of the building and the likely behaviour of its users mustbe taken into account, with drops in excess of 380mm beingclassified as dangerous. This is especially important whenconsidering glass floors or stair treads.

Other points for consideration are as follows:

• Likelihood of persons walking on the floor/stair tread with wet footwear;

• Application of point or concentrated loadings with hard objects with small contact area, e.g. castors on furniture.

• Thermal stress if artificial lighting is installed beneath the floor/stair tread; or if used in an external application subject to solar radiation.

• Modesty when persons can access beneath the floor or stair;

• When positioned the user has a view of a large exposed area;

• In specific applications the floor may also need to offer appropriate fire resistance.

• Consideration of secondary protection in instances when the floor may be subjected to excess footfall or movements across it, e.g. office furniture, etc.

3.2 Specifics

The following can be regarded as 'hazards' that require specialistconsideration:

4. Design Criteria

4.1 General

This non-exhaustive list details the prime consideration:

• Internal or external application;

• Building use category (including change of use)

• Overall size and dimensions;

• Deflection of the glass/system;

• Loading;

• Depth of drop;

• Glass specification;

• Surface finish;

• Fixing substrate;

• Support structure.

Generally the design of glass floors/stair treads ensures thatbreakage of one leaf does not compromise the performance of thecomponent, i.e. the inclusion of a 'redundant' leaf. Therefore a fallis unlikely unless there is total/catastrophic failure of the system.

Two British Standards are relevant to the use of glass in floors andstair treads:

• EN 1991-1-1:2002: Eurocode 1: Actions on structures - General actions - Densities, self-weight, imposed loads for buildings together with the UK National Annex,

Guidelines for the Use of Glass in Floors and Stairs

Hazard

Potential for exposure to water and slipping

Potential for breakage from impact by falling or thrown objects

Potential for glazing failing/breaking

Necessity of refurbishment or replacement

Possibility of deflection that could cause ponding and/or be visually disturbing

Frequency of use and impact on using alternative routes in the building;

Solution

Careful selection of surface finish and appropriate slip resistance

Careful design specification possibly including 'sacrificial' layer.

Consideration of the post-breakage behaviour of the chosenglass specification

Consideration of both glass, glazing design and access.

Consideration of both glass thickness and support stiffness

Careful design specification.

NOTE: This standard specifies the design floor loads for the specificuse of the building

• BS 5395-1:2010: Stairs: Code of practice for the design of stairs with straight flights and winders.

NOTE: This standard refers to the danger of slippage and specifiesminimum coefficients of friction

The loads considered are the uniformly distributed load (UDL) andthe concentrated load. It is usually the concentrated load that willdetermine the glass thickness, so care must be taken to specify thecorrect figure from the national annex of EN 1991-1-1.

Traditional glass flooring has been fully supported by its edges andnever at a mid-point. The strength of the supports must becalculated by a competent structural engineer, with the deflectionof the frame limited to an appropriate value for the glass type.

Glass technology has improved, coupled with the development ofstructural interlayers, e.g. ionomers. This gives greater performanceand provides increased stiffness; therefore alternative supportconfigurations can now be considered.

Using a combination of increased glass and interlayer strength,laminated glass floors can be designed having point support systemsor minimal traditional supports.

5. Glass Types

5.1 General

The type and thickness of glass shall be selected to suit the designtaking into consideration all of the critical factors from the initialassessment.

5.2 Glass types

The following glass types are suitable for installation into floorswithout a drop below:

• Annealed soda lime silicate float glass in accordance with EN 572-9.

NOTE: The required thickness will depend upon size, aspect ratioand loading.

The following glass types are suitable for installation into floors andstair treads with a drop below:

• Laminated annealed safety glass in accordance with EN 14449;

• Laminated thermally toughened soda lime silicate safety glass in accordance with EN 14449;

• Laminated heat soaked thermally toughened soda lime silicate safety glass in accordance with EN 14449.

• Laminated heat strengthened/thermally toughened soda lime silicate safety glass in accordance with EN 14449

• Laminated heat strengthened/heat soaked thermally toughened soda lime silicate safety glass in accordance with EN 14449

NOTE 1: Floors that are subjected to significant levels of solarradiation would usually preclude the use of annealed glass types forreasons of thermal safety;

NOTE 2: Thermally toughened soda lime silicate safety glass shouldbe in accordance with EN 12150;

NOTE 3: Heat soaked thermally toughened soda lime silicate safetyglass should be in accordance with EN 14179;

NOTE 4: Heat strengthened soda lime silicate glass should be inaccordance with EN 1863;

NOTE 5: Thermally toughened safety glass and heat soakedthermally toughened safety glass are available for other glasscompositions, e.g. borosilicate, alkaline earth silicate.

6 Glass Strength Considerations

6.1 General

The final glass specification should have sufficient strength towithstand the appropriate floor loadings given in the UK nationalannex to EN 1991-1-1:2002.

In addition it is important to consider the deflection of the finaldesign, particularly when the glass is supported on less than fouredges. In such cases it is possible to consider glass specificationsthat have sufficient strength, but results in a floor that unnervespeople due to excessive deflection.

6.2 Selection of glass for use in floors

Glass should be provided that is suitable for normal pedestrian useand so can be walked upon safely and with a degree of confidencewithstanding the relevant design loads from EN 1991-1-1:2002.

It is never feasible to ensure that glass will not fracture undersufficiently extreme abuse. Consequently a redundant ply of glass ina laminated construction is imperative to provide the appropriatelevel of post fracture behaviour.

Contact with hard objects such as glass, metal and stones shouldbe avoided at all times.

Over a period of time the top surface is likely to deterioratedepending upon the amount of pedestrian traffic and type offootwear used.

NOTE: The incorporation of a sacrificial top layer means that whenthe visual deterioration becomes unacceptable, only the sacrificiallayer requires replacing.

The top surface finish of the glass can be modified to achieve anappropriate level of slip resistance.

Tables 1 to 5 provide some suggested glass types that havesufficient strength for a number of load cases.

Guidelines for the Use of Glass in Floors and Stairs

U D L(kN/m2)

1.5

2.5

2.0

4.0

4.0

Concentratedload (kN)

2.0

2.7

3.0

3.6

4.5

Glassthickness

15

15

19

25

25

Specificuse

Domestic

Office

Restaurant

Retail

Museum

Thickness of annealed glass complying with EN 572-9

Table 1 – Thickness of annealed glass, without a drop below,uniformly and continuously supported, with a size of 1500 x 1000mm

6.3. Selection of glass for use in stairs

To ensure the safe use of stairs there are specificrecommendations for the width, rise and going, which can befound in BS 5395-1.

A summary of these dimensions is shown in table 5.

Note*: For regular two-way traffic, the minimum stair clear width is1000mm

Note**: For hospitals, the minimum stair clear width is 1200mm

Once the appropriate size and geometry of the stairs have beendecided, the advice given in 6.2 relating to conventional glass floors,can be applied to stair design.

NB: Exposed nosings of glass stair treads can be particularlyvulnerable to damage. For high pedestrian foot traffic areas it isrecommended that nosings be protected to avoid accidentaldamage of any exposed glass edges/corners.

7. Post breakage of glass

7.1 Annealed glass floors

Providing that the glass floor is designed, manufactured andinstalled in accordance with this Data Sheet, and then if breakageoccurs the glass is likely to lock together. This will mean that thereis no penetration that will allow a drop into the space below.

Guidelines for the Use of Glass in Floors and Stairs

U D L(kN/m2)

1.5

2.5

2.0

4.0

4.0

Concentratedload (kN)

2.0

2.7

3.0

3.6

4.5

Glassmake-up

19 + 19

25 + 15

25 + 19

25 + 25

25 + 25

Specificuse

Domestic

Office

Restaurant

Retail

Museum

Thickness of annealed laminated glass complying with EN 14449

Table 2 – Thickness of laminated annealed glass, supported along all four edges, with a size of 1500 x 1000mm

U D L(kN/m2)

1.5

2.5

2.0

4.0

4.0

Concentratedload (kN)

2.0

2.7

3.0

3.6

4.5

Glassmake-up

12 + 12

15 + 15

15 + 15

19 + 19

19 + 19

Specificuse

Domestic

Office

Restaurant

Retail

Museum

Thickness of laminated thermally toughened glass complying with EN 14449 and EN 12150

Table 3 – Thickness of laminated toughened glass, supported along allfour edges, with a size of 1500 x 1000mm

U D L(kN/m2)

1.5

2.5

2.0

4.0

4.0

Concentratedload (kN)

2.0

2.7

3.0

3.6

4.5

Glassmake-up

10 + 10 + 10

12 + 10 + 12

12 + 10 + 12

15 + 10 + 15

15 + 10 + 15

Specificuse

Domestic

Office

Restaurant

Retail

Museum

Thickness of laminated toughened / heat strengthened / toughened glass complying with EN 14449, EN 12150 & EN 1863

Table 4 – Thickness of laminated toughened / heat strengthened /toughened glass, supported along all four edges, with a size of 1500 x 1000mm

U D L(kN/m2)

1.5

2.5

2.0

4.0

4.0

Concentratedload (kN)

2.0

2.7

3.0

3.6

4.5

Glassmake-up

10 + 10 + 10

12 + 12 + 12

12 + 12 + 12

15 + 15 + 15

15 + 15 + 15

Specificuse

Domestic

Office

Restaurant

Retail

Museum

Thickness of laminated toughened glass complying with BS EN 14449 & BS EN 12150

Table 5 – Thickness of laminated toughened glass, supported alongtwo 1500mm edges, with a span between supports of 1000mm

Stair category

Rise (mm) Going (mm)

Stair clear width (mm)

Table 5 – Recommended sizes for straight stairs and winders

Private stair

200 250 400 800*150

Normal-use stair

180 300 450 1000*150

Min. Max. Min. Max. Min.

However, broken glass should be replaced immediately and accessprohibited.

7.2 Annealed laminated floors/stair treads

Providing the glass floor/stair tread is manufactured from laminatedannealed glass, and is suitably supported around the perimeter, thepost fracture behaviour is one that retains a significant degree of itsinherent strength and is likely to resist displacement or penetration.

These qualities make this particular specification advantageouswhen the glass is located inside a building and is still required toperform the function of supporting people.

7.3 Thermally treated laminated floors/stair treads

When considering laminated thermally treated glass there is oftenthe potential for a reduction in overall glass thickness.

It should be noted that a reduction in thickness will be followed byan increase in glass deflection, and can be particularly noticeablefollowing the fracture of one of the plies in the laminateconstruction.

Failure of any single ply in the specifications considered in tables 2& 4 will rarely be critical when solely considering the ability of theremaining glass to withstand the appropriate load, as all suchconstructions have a “redundant ply.”

This is unlikely to be the case following any additional ply failure.However with the development of structural interlayers givingstronger performance and providing increased stiffness, animproved post breakage characteristic can be realised.

Table 3 relates to laminated thermally treated glass construction,incorporating a heat strengthened ply. This is advantageous whenconsidering the post breakage behaviour should fracture of atoughened ply occurs.

NB: Irrespective of glass make-up in all cases a replacement panelshould be prioritised immediately following fracture.

NOTE: The ability of a broken pane to remain in situ is dependentupon the loads being applied, the glass type, the support condition,the number of fractured plies and the type of interlayer in theconstruction. The manufacturer should be consulted forinformation on the post fracture behaviour.

8 Selection of glass for slip resistance

As the surface of glass has a smooth fire polished finish there is avery low friction grip between glass and most footwear even innormal dry conditions.

Should the surface of glass become wet, there is the potential foran extremely hazardous condition, which requires considerationalongside strength and post fracture behaviour.

Sandblasting is a common technique used to provide slip resistanceeither by an all-over treatment or by deep sandblasting to raisedots on the glass surface.

A ceramic frit containing a fine hard grit can be applied and firedinto the top surface to provide a reduced risk of slipping.

Floors near entrance areas may be walked upon by people withwet footwear with external floors presenting the highest risk ofslipping. For these and other hazardous areas the slip resistanttreatment is critical.

For external floors, deflection inherent in the glass may lead toponding when large sizes are considered.

BS 5395-1:2010 Stairs. Code of practice for the design of stairswith straight flights and winders, makes reference to the danger ofslippage and specifies minimum coefficients of friction that couldequally be applied to glass floors

9 Framing and Installation

9.1 General

Traditional glass flooring should be fully supported by its edges and never at a mid-point, see figure 1.

Figure 1 Example of glass floor

9.2 Glass floors/stair treads

As glass technology has improved coupled with the developmentof structural interlayers giving stronger performance and providingincreased stiffness, alternative support configurations can now beconsidered. Using a combination of increased glass and interlayerstrength, laminated glass floors can have point support systems orminimal traditional supports.

The final glass specification should have sufficient strength towithstand the appropriate floor loadings given in the UK nationalannex to BS EN 1991-1-1:2002. In addition it is important toconsider the deflection of the final design, particularly when theglass is supported on less than four edges. In such cases it ispossible to consider glass specifications that have sufficient strength,but results in a floor that unnerves people due to excessivedeflection

9.3 Frame and Installation

The frame should provide continuous support to the perimeter ofeach individual element of glazing, and must be capable ofwithstanding both the design loading and the self-weight of theglass without excessive deflection.

The frame may be of metal, masonry or wood and the glass mustbe cushioned from it by 3mm thick neoprene rubber or othermaterial with a Shore A hardness of 60.

Guidelines for the Use of Glass in Floors and Stairs

The clearance between the edge of the glass and the frame, orbetween adjacent glasses, should be 3mm minimum and infill stripsof a material such as wood, cork or neoprene, should be insertedto finish just below the upper surface of the glass.

To provide a flush finish a compatible high-grade synthetic rubber,polysulphide or silicone sealant can be used as a top pointing

9.4 Supporting structure

The strength of the supports must be calculated by a structuralengineer, with the deflection of the frame limited to an appropriatevalue for the glass type

10 Building Regulations and Standards

The Building Regulations, see Bibliography [1], cover stairs but doesnot cover floors. None of the regulations say anything about glassin these applications. However, the regulations are not materialspecific so they can be applied to glass.

British Standards BS 5395 – Parts 1 and 2 cover the specificationand design of stairs. The use of glass treads is not covered by thesestandards.

Appendix 1 Drawing from BS 5395-1

• Bibliography

B1 United Kingdom Building Regulations:

England –

Approved Document K: 2013 – Protection from falling, collision and impact – Parts K1, and K2

Wales –

Approved Document K – Protection from falling, collision and impact – Parts K1

NOTE: Formerly England & Wales AD K

Scotland –

Building (Scotland) Regulations Technical Handbook – Domestic and Non-Domestic – Section 4 - Safety

Section 4.4 – Pedestrian protective barriers

Section 4.8 – Danger from accidents

Northern Ireland –

The Building Regulations (Northern Ireland) Statutory Rules– Technical Booklet H – Stairs, ramps, guarding and protection from impact

B2 British Standards

BS 5395-1: 2010: Stairs. Code of practice for the design of stairs with straight flights and winders

BS 5395-2: 1984: Stairs. Code of practice of helical and spiral stairs

B3 European Standards

EN 14179-2: Glass in building – Heat soaked thermally toughened soda lime silicate safety glass – Part 2: Evaluation of conformity/Product standard

EN 1863-2: Glass in building – Heat strengthened soda lime silicate glass – Part 2: Evaluation of conformity/Productstandard

EN 12150-2: Glass in building – Thermally toughened sodalime silicate safety glass – Part 2: Evaluation of conformity/Product standard

EN 12600: Glass in building – Pendulum test – Impact test method and classification for flat glass

EN 13024-2: Glass in building – Thermally toughened borosilicate safety glass – Part 2: Evaluation of conformity/product standard EN 14179-2: Glass in building– Heat soaked thermally toughened soda lime silicate safety glass – Part 2: Evaluation of conformity/Product standard

EN 14321-2: Glass in building – Thermally toughened alkaline earth silicate safety glass – Part 2: Evaluation of conformity/product standard

EN 14449: Glass in building – Laminated glass and laminated safety glass – Evaluation of conformity/Product standard

EN 15682-2: Glass in building – Heat soaked thermally toughened alkaline earth silicate safety glass – Part 2: Evaluation of conformity/product standard

EN 1991-1-1: EUROCODE 1: Part 1-1, General actions – Densities, self-weight and imposed loads

Guidelines for the Use of Glass in Floors and Stairs