How to specify glass balustrades
What a glass balustrade clause has to settle about load, glass, fixings and fire, the standards behind each decision, and how to write it in CAWS and in Uniclass.
Photo: -wuppertaler, CC BY-SA 4.0, via Wikimedia Commons.
How do you specify glass balustrades?
To specify a glass balustrade, state the barrier loading from BS EN 1991-1-1 and its UK National Annex, the glass make-up and its BS EN 12600 safety class, and how the glass is held: base shoe, clamps or posts. Design to BS 6180 so the barrier stays in place if a pane breaks, require fixings and calculations from the installer, and take guarding heights from Approved Document K.
Glass balustrades are usually drawn by the architect and designed by someone else. The glass make-up, the shoe and the anchors are normally finished by a specialist installer, so the clause is really a performance brief: the load the barrier must take, what happens when a pane breaks, what the fixings go into, and the evidence wanted before fabrication. A clause that only names "21.5 mm laminated glass in a base shoe" has skipped the brief and gone straight to an answer nobody has checked.
This guide covers Uniclass Pr_25_71_57_34 Glass barrier panels, the glass infill itself. The shoe, posts, handrail and fixings around it belong to the balustrade system, Ss_25_60_05_05 Balustrade and guarding systems, and that is where most of the performance is written.
What does a glass balustrade clause need to cover?
Some properties are specific to glass balustrades. Others belong in every product clause. A clause that leaves either out gives the contractor room to substitute.
Properties of glass balustrades
- Third-party certificationTest evidence for the system under barrier load.
- FinishGlass tint and base shoe or cap finish.
- Operation methodFixed panels, or note any gate within the run.
- FixingsNever guessAnchors designed for the barrier load into a checked substrate.
- Track and support systemBase shoe, clamps, standoffs or posts.
- Reaction to fire classificationNever guessInterlayers and claddings may matter on balconies.
- Opening configurationGates, returns and breaks in the run.
- Edge treatmentPolished, ground or arrissed exposed glass edges.
- Structural performanceNever guessBarrier loading category from the structural engineer.
- Safety glazing classNever guessBS EN 12600 impact class for the location.
- AccessoriesHandrails, cap rails, end caps and cladding.
- Panel constructionFrameless, clamped or framed infill.
- Joint designGaps between panes and at walls and posts.
- Mass per unit areaPane weight for handling and fixing design.
- Glass manifestationNever guessOnly where people could walk into the glass.
- Nominal sizePane widths and finished guarding height.
- GlazingGlass type, interlayer and glazing wedges or gaskets.
What every product clause needs
- Manufacturer and product referenceNamed balustrade system, or a performance description.
- Product standardGlass standards for toughened, heat soaked and laminated panes.
- Installation methodSystem instructions plus BS 6180 and this specification.
- Technical submittalsGlass and fixing calculations before fabrication.
- Operation and maintenance informationCleaning, inspection of fixings and glass replacement.
- MaterialToughened, heat-strengthened or laminated glass.
- ThicknessLaminate make-up, set by calculation, not by catalogue.
Uniclass Pr_25_71_57_34 Glass balustrades. Not every property applies to every project; where one does not, say so rather than leaving it blank.
Fields marked Never guess depend on the project and should never be filled from a default or a previous job. If the information is not available yet, the clause should say so with a TBC and a reason.
Which decisions does the clause depend on?
Most properties follow from the product you choose. These depend on the project, so they need a decision from the designer before the clause is written.
- 01
Barrier loads
Never guessThe horizontal loads on a barrier come from BS EN 1991-1-1 and its UK National Annex, and they depend on the category of use of the area behind it. A barrier to a private stair, an office floor and a crowded concourse carry very different line, distributed and point loads. The architect does not need to calculate them, but the clause has to name where they come from and who confirms the category. Without that, the installer will price the lightest case and the building control officer will ask for calculations nobody commissioned.
How to decide
- Agree the category of use for each balustrade location with the structural engineer and record it on the drawings or a schedule.
- Require the installer to design glass, shoe and anchors for those loads to BS 6180.
- Ask for calculations as a submittal before fabrication, including glass to BS EN 16612.
- Note where wind load on external balustrades also applies.
Write it asStructural performance: Design to BS 6180 for barrier loads to BS EN 1991-1-1 and UK National Annex, category of use as structural engineer's schedule. Submit calculations before fabrication. - 02
Glass make-up and what happens after breakage
Never guessBS 6180 expects a glass barrier to stay in place if a pane breaks. A single sheet of toughened glass cantilevered from a shoe fails that test the moment it shatters, because nothing is left at the edge. Laminated glass holds together after breakage, and a stiff interlayer or a handrail linking the panes keeps it upright. Toughened plies also carry a small risk of spontaneous breakage from nickel sulphide inclusions, which heat soaking to BS EN 14179-1 reduces. State the BS EN 12600 impact class as well, so the safety glazing requirement is clear.
How to decide
- Frameless cantilevered glass: laminated toughened or heat-strengthened glass, with a stiff interlayer, a linking handrail, or both.
- Glass infill held on all sides between posts: post-breakage behaviour is less onerous, but still state it.
- Require heat soaking for every toughened ply.
- Ask the installer to show how the barrier performs with one ply broken.
Write it asGlazing: Laminated heat soaked toughened glass, BS EN 12600 class 1(B)1, to remain in place with one ply broken. Toughened plies heat soaked to BS EN 14179-1. - 03
Support system and fixings
Never guessA base shoe, a set of standoffs and a post-and-clamp system all put the barrier load into the structure in different ways. A continuous shoe needs a deep, sound edge and puts high local forces into the slab. Standoffs on a stair stringer concentrate load at a few bolts. Posts carry the load through their own base plates. The common failure is not the glass but what it is fixed to: screeds, thin slab edges and timber joists that were never checked. The clause should name the substrate and ask for proof.
How to decide
- Decide the support type with the structural engineer before the slab edge or stringer is detailed.
- State the substrate at each location and say the anchors must be designed for it.
- Specify stainless steel anchors of a grade to suit the exposure, and site pull-out tests.
- On balconies, check drainage of the shoe and how the waterproofing is kept intact.
Write it asFixings: Stainless steel anchors designed by installer for confirmed barrier loads, into reinforced concrete slab edge. Site pull-out tests to be witnessed. - 04
Fire on balconies
Never guessInside a building a glass balustrade rarely affects the fire strategy, and fire resistance, smoke control and security ratings do not apply to it. Balconies are different. On a relevant building under regulation 7(2), balconies are among the attachments that have to meet the reaction to fire requirement, with exemptions listed in regulation 7(3). The glass may be fine, but laminated interlayers, cladding to the shoe and handrails can all be caught. Ask the fire engineer how the requirement applies to each part, and record the answer in the clause.
How to decide
- Internal balustrades: state the class only if the fire strategy sets one.
- Balconies on relevant buildings: check each component, including the interlayer, against regulation 7(2) and the 7(3) exemptions with the fire engineer.
- Ask for classification reports to BS EN 13501-1, not product claims.
Write it asReaction to fire: Components to meet regulation 7(2) or fall within a regulation 7(3) exemption, as confirmed by fire engineer. Submit BS EN 13501-1 classification reports. - 05
Manifestation
Never guessApproved Document K asks for manifestation on glazing that people could walk into, where it might be mistaken for an opening. Most balustrades guard an edge at a stair or void, so nobody walks towards them, and manifestation is not needed. A glass screen across a route, a balustrade that turns into a full-height screen, or a low barrier across a landing can be different. Decide it per location and write the reason. A blank field reads as a decision nobody made.
How to decide
- Edge guarding to stairs, voids and balconies: usually not required; say so.
- Glass across a route or forming a screen: manifestation to Approved Document K.
- If manifestation is needed, coordinate its height bands and design with the interior designer.
Write it asGlass manifestation: Not required. Edge guarding, not in a line of travel.
The values under "Write it as" are examples. The right value depends on the location, the use and the fire strategy.
Which standards should the clause cite?
Cite the product standard the declaration of performance refers to, the code of practice for installation, and the test method behind each value you set. A value without its test method cannot be checked against a submittal.
- BS 6180
- Barriers in and about buildings. Code of practice
Design of barriers, including glass barriers, their behaviour after a pane breaks and how infill and handrails work together.
In the clause Use it as the design basis for the whole system: "Design to BS 6180".
- BS EN 1991-1-1 and UK National Annex
- Eurocode 1: Actions on structures. General actions. Densities, self-weight, imposed loads for buildings
Horizontal imposed loads on barriers, set by the category of use of the area they protect.
In the clause Cite it with who confirms the category: "barrier loads to BS EN 1991-1-1 and UK National Annex, category as structural engineer's schedule".
- BS EN 12600
- Glass in building. Pendulum test. Impact test method and classification for flat glass
The pendulum impact test and the classification of safety glass by how it breaks.
In the clause "Safety glazing class: 1(B)1 to BS EN 12600."
- BS EN 12150-1
- Glass in building. Thermally toughened soda lime silicate safety glass. Definition and description
What counts as thermally toughened safety glass and its fracture pattern.
In the clause Cite it for the plies: "toughened glass to BS EN 12150-1".
- BS EN 14179-1
- Glass in building. Heat soaked thermally toughened soda lime silicate safety glass. Definition and description
The heat soak process that reduces spontaneous breakage of toughened glass from nickel sulphide inclusions.
In the clause "All toughened plies heat soaked to BS EN 14179-1."
- BS EN ISO 12543-2
- Glass in building. Laminated glass and laminated safety glass. Laminated safety glass
Laminated safety glass and the requirements on its interlayers.
In the clause "Laminated safety glass to BS EN ISO 12543-2, interlayer type as installer's design."
- BS EN 16612
- Glass in building. Determination of the lateral load resistance of glass panes by calculation
Calculation of glass thickness to resist lateral loads, used by installers to size barrier glass.
In the clause Ask for it in the submittals: "glass calculations to BS EN 16612".
- BS EN 13501-1
- Fire classification of construction products and building elements. Classification using data from reaction to fire tests
The Euroclass system used to show whether balcony components meet the reaction to fire requirement.
In the clause "Submit classification reports to BS EN 13501-1 for interlayer, shoe cladding and handrail."
Confirm the current edition of each standard at every issue. Avoice's State of UK Specifications 2026 found a withdrawn standard cited in 40% of specifications at contract issue.
For the regulations behind these choices, see Approved Document K explained, Approved Document B explained, or search the Avoice Regulations library.
How do you write it in CAWS?
In CAWS, balustrades are written in L30. NBS gives purpose-made and proprietary balustrades separate clauses: purpose-made balustrades for those the architect or engineer details fully, proprietary balustrades for a system from a specialist. Most glass balustrades are proprietary systems completed by the installer, so they go in the proprietary balustrades clause, 560 in the NBS layout. It is a product clause rather than a "type of" system clause in the 100s, and a project with a stair balustrade and a balcony balustrade would usually have two of them, 560 and 561.
The design responsibility is set out in a separate clause near the front of L30, completion of design, which makes the installer finish the design to the stated criteria and submit it. The balustrade clause relies on that, and on the general clauses at the back of L30 for site dimensions, corrosion between dissimilar metals and installation. If the glass itself is written in L40 as well, cross-refer rather than specify it twice.
- Manufacturer
- Submit proposals
- Product reference
- Submit proposals
- Design
- Complete design to clause 107, to BS 6180
- Barrier loads
- To BS EN 1991-1-1 and UK National Annex, category of use as structural engineer's schedule
- Guarding
- Laminated heat soaked toughened glass, class 1(B)1 to BS EN 12600, to remain in place with one ply broken
- Glass thickness and interlayer
- By installer's calculation to BS EN 16612
- Edges
- Flat polished to all exposed edges
- Support
- Continuous aluminium base shoe, surface fixed, drained
- Handrails
- Stainless steel cap rail clamped to top edge, continuous across panes
- Base shoe cladding finish
- TBC Client colour selection outstanding. Resolve before ordering.
- Guarding height
- As drawings, to Approved Document K
- Fixing
- Stainless steel anchors designed for confirmed loads, into concrete slab edge; site pull-out tests
- Reaction to fire
- Components to meet regulation 7(2) or a regulation 7(3) exemption, as fire engineer
- Manifestation
- Not required: edge guarding, not in a line of travel
- Submittals
- Calculations, shop drawings and classification reports before fabrication
Illustrative, not from a real project. One property is left as a TBC with a reason so it can be tracked and closed before issue.
Clauses the type clause relies on
- L30/107
- Completion of design Hands detailed design of glass, shoe and anchors to the installer, with submission requirements.
- L30/130
- Site dimensions Installer measures the slab edges and stair before the glass is cut.
- L30/630
- Corrosion protection of dissimilar materials Isolates stainless steel anchors from the aluminium shoe.
- L30/640
- Installation generally Fixing methods to Z20, and no cutting of structural members unless shown.
Clause numbers vary between NBS versions and practice masters. 560 Proprietary balustrades is the number NBS Source gives for glass balustrade systems; the general clause numbers vary more, so check them against your own L30.
For more on clause structure and checks, see NBS clause writing: common mistakes.
How do you write it in Uniclass?
Uniclass describes the balustrade as a system, Ss_25_60_05_05 Balustrade and guarding systems. The system clause is where the performance lives: the barrier loads, behaviour after breakage, guarding height, the support method, the handrail and the design responsibility. These are properties of the assembled barrier, not of any one product in it.
The glass is written once as a product clause, Pr_25_71_57_34 Glass barrier panels, with its make-up, safety class, heat soak and edges. The system clause points to it. If the same glass infill is used on stairs and balconies with different supports, each balustrade system clause points to the same product, and the thickness can still vary because it comes from the installer's calculation for each case.
- Description
- Frameless glass balustrade to balconies, base shoe supported, with cap rail
- Design
- Installer to complete design to BS 6180
- Barrier loads
- BS EN 1991-1-1 and UK National Annex, category of use as structural engineer's schedule
- Glass infill
- Pr_25_71_57_34 Glass barrier panels (GP01)
- Post-breakage
- Barrier to remain in place with one ply of any pane broken
- Support
- Continuous aluminium base shoe, drained, surface fixed to slab edge
- Handrail
- Stainless steel cap rail, continuous
- Guarding height
- As drawings, to Approved Document K
- Fixings
- Stainless steel anchors designed for confirmed loads; site pull-out tests
- Manufacturer
- Submit proposals
- Product standard
- Plies to BS EN 12150-1 and BS EN 14179-1, laminated to BS EN ISO 12543-2
- Material
- Laminated heat soaked toughened glass, clear
- Thickness
- TBC Installer's calculation to BS EN 16612 not yet submitted. Resolve before fabrication.
- Safety glazing class
- 1(B)1 to BS EN 12600
- Edge treatment
- Flat polished to exposed edges
- Nominal size
- Pane widths to setting-out drawing
- Reaction to fire classification
- Interlayer classification report to BS EN 13501-1 submitted
- Glass manifestation
- Not required
Illustrative. Performance of the finished system sits in the system clause; properties of the product sit in the product clause.
Glass barrier panels carry no NBS reference in Avoice's data, so head the product clause with the Pr code alone, and do not mix CAWS and Uniclass references in one specification.
What goes in the spec, and what goes in the schedule?
The specification defines each type once. The schedule and drawings say where each type goes.
In the specification
What the product is and how it performs and is installed. Written once per type.
In the schedule or drawings
Where each type goes and how much of it. Changes with every plan revision.
Write each balustrade type once with a type mark (for example BL01) and let the drawings show where it runs and how high it stands. Heights and loads change with location, so the schedule must carry them, and the clause must say where they come from.
What are the common mistakes?
Most problems are a missing property, a property filled with the wrong kind of value, or a decision left silently open.
- A glass thickness with no load. "21.5 mm laminated" means nothing without the barrier load it was sized for. Name the category of use and ask for calculations.
- Monolithic toughened glass on its own. When it breaks, the edge is open. Use laminated glass, a linking handrail, or both, and say what must survive a breakage.
- No heat soak. Toughened glass can break with no impact at all. Ask for heat soaking to BS EN 14179-1 on every toughened ply.
- Fixings left to site. A shoe bolted into screed or a thin slab edge will not carry the load. Name the substrate and ask for pull-out tests.
- Balcony fire rules missed. On relevant buildings, interlayers, shoe cladding and handrails can all fall under regulation 7(2). Check with the fire engineer and record the outcome.
- Heights written into the clause. Guarding height varies by location. Put it on the drawings and point to Approved Document K from the clause.
How Avoice helps
Avoice's spec writer drafts balustrade clauses from your drawings, and makes the gaps in a design-and-build package visible instead of hiding them behind a thickness.
- Drafts from your drawings
It reads the balustrade types (BL01, BL02) and their locations from the plans and sections, and drafts the L30 or Uniclass clause with the support, glass and handrail those drawings show.
- Leaves the engineering as TBC
Where the category of use, the glass thickness or the fire engineer's view on a balcony interlayer is not yet known, the clause says TBC with the reason, and each item lands in the project TBC register to close before tender.
- Writes in your format
CAWS or Uniclass, adapted from your practice's master clauses, so your completion of design wording and submittal lists stay intact.
- Checks the clause against the drawings
QA/QC flags a balustrade on a section with no type mark, a clause that cites BS 6399 or another withdrawn standard, or a cross-reference to a design clause that is missing from L30.
- Keeps evidence and regulations to hand
Data sheets and classification reports sit in the Product Room linked to the clause, and Approved Documents B and K are in the Avoice Regulations library for checking heights and balcony fire rules.
Related guides: How to specify stair nosings, How to specify fire doors, How to specify sealants.
Software can draft and check. The designer still chooses the product and is responsible for the specification.
For more on the evidence behind product choices, see the role of manufacturer product data in specification writing.
Draft your glass balustrade clause in Avoice
Upload your drawings and schedules. Avoice drafts the clause in CAWS or Uniclass, cites the standards and flags anything your information does not settle.
This guide is for general education and is not professional advice. Check current editions of standards and Approved Documents, the manufacturer's data, and the requirements of your project before relying on any clause.