Glazing Systems

Glazing systems are the framed and frameless glass in a building's envelope: windows, sliding and hinged doors, shopfronts, window walls, curtain walls, structural silicone glazing and point-fixed glass. Skylights and atrium roofs have their own page. A system is the glass, the frame, the gaskets and seals that hold the glass and keep water out, the internal drainage, the anchors to the structure, and the perimeter seal to the surrounding wall.

Glass type matters to safety and to how glass breaks. Annealed (float) glass breaks into large sharp shards. Heat-strengthened glass is about twice as strong and breaks into larger pieces that tend to stay in the frame. Toughened (tempered) glass is four to five times as strong and breaks into small cubes; it can break spontaneously from nickel sulphide inclusions unless heat-soak tested. Laminated glass holds together when broken. Insulated glass units (IGUs) are two or three panes sealed around the edge with a dry air or gas space; the edge seal is their life. Double glazing became standard in British housing from the 1980s, in Australian commercial work through the 2000s, and more widely in Australian housing after the energy provisions tightened.

Era tells the story: steel windows with putty glazing in pre-war and mid-century buildings; single-glazed aluminium in Australian and American stock of the 1960s to 1990s; stick curtain walls with captured glass in offices of the 1970s and 1980s; four-sided SSG in the late 1980s and 1990s; unitised systems and IGUs from the 2000s.

What shortens life:

• Water held in the glazing rebate because weep holes are blocked or omitted, which destroys IGU edge seals from below.
• West and north elevations in Australia (west and south in the northern hemisphere), where UV and thermal cycling age seals and gaskets fastest.
• Coastal air on aluminium finishes, steel anchors and stainless fittings.
• Missing sill flashings and end dams on window walls, sending water into the slab edge and the unit below.
• Frame deflection under wind and building movement on long spans, which works seals loose.
• Poor cleaning practice: abrasive cleaning and scrapers scratch glass and damage coatings and seals.

Water infiltration

Glazing leaks at a small number of predictable places: the perimeter seal between frame and wall, the sill where it meets the slab or opening below, end dams at sill ends, splice joints in stick curtain wall mullions, transom-to-mullion joints, stack joints in unitised systems, and glazing pockets that cannot drain. Most systems are designed to let some water past the outer seal and drain it out again; leaks occur when the drainage path is blocked, missing or overwhelmed.

IGU edge seal failure

Moisture enters the cavity of an insulated unit through a failed edge seal. The first sign is fogging or condensation between the panes, then a white bloom or residue on the inner faces, and on low-emissivity units, a hazy or corroded coating. Thermal performance falls and the unit cannot be repaired, only replaced.

Gasket shrinkage and seal ageing

Dry gaskets shrink back from corners, leaving gaps where water enters the glazing pocket. Wet seals harden and lose adhesion. On capped systems, the cap can loosen as pressure plates relax.

Glass breakage

Thermal stress breaks annealed and some heat-strengthened glass when part of a pane heats faster than the rest: shading from deep frames, internal blinds close to tinted glass, and edge damage concentrate the stress. Nickel sulphide inclusions break toughened glass spontaneously, often years after installation and without any load; non-heat-soaked toughened glass at height can release a whole pane of fragments. Impact and edge damage from installation or building movement account for most other breaks.

Structural silicone adhesion loss

On SSG, the silicone bond is what holds the glass on. Poor surface preparation, incompatible materials, inadequate bite (bond width) or cure at installation can leave bonds that pass a visual check but have little strength. Loss of adhesion lets glass move, leak and in the worst case detach.

Anchor and bracket corrosion

Curtain wall and window wall anchors fix the system to the slab edge. Water reaching them through failed perimeter seals or slab edge joints corrodes carbon steel components, and dissimilar metal contact corrodes aluminium. They are concealed behind ceiling and floor finishes.

Steel window corrosion

Steel windows rust where paint fails, and rust at the glazing rebate jacks the glass and cracks it. Steel frames built into masonry rust at the sill and jamb and crack the surrounding brick or stone.

From the street and from aerial imagery

• Misted or hazy panes in a pattern across an elevation: IGU seal failure, often concentrated on the most exposed faces.
• Replaced panes visible as a different tint or reflection, a record of breakage or seal failure.
• Broken or taped panes; netting or protection below a curtain wall.
• Gaskets visibly shrunk at corners, caps missing or displaced, black streaking below gaskets.
• Staining or efflorescence at sills and on the slab edge below window walls.
• Rusting steel windows with cracked panes; cracked masonry at window jambs.

Close up on site

• Blocked or absent weep holes in sills and transoms.
• Wet seals hard, cracked or peeling; gaps at gasket corners; gaps at the perimeter seal.
• On SSG, a visible change in the silicone line, staining behind glass, or glass that moves when pressed.
• Glass type markings in the corner of each pane (toughened, laminated, heat-soak); absence of markings on panes required to be safety glass.
• Hardware loose, corroded or failing; doors and sashes not closing.

Inside the building

• Water staining, swollen floor finishes and mould at sills and at the base of window walls.
• Condensation on frames and glass on cold days, more than the glass type should allow; draughts at sashes and joints.
• Corrosion at accessible anchors in ceiling voids at the slab edge.

In the records

• Breakage log, especially repeated spontaneous breakage of toughened glass.
• Leak logs that recur at the same floor or the same mullion line.
• Glass schedule, heat-soak certificates, SSG adhesion test records and warranties.
• Façade inspection reports and ordinance filings.

Findings are graded by what they demand: safety (can hurt someone now), failure (failed and damaging the building), condition (distress present and progressing), lifecycle (renewal due on age and exposure), deadline (a regulator or ordinance sets the date), check (investigate before sizing works) and nil (cosmetic or stable).

A façade engineer leads; a glazier assists with glass identification and opening of glazing pockets.

• Visual survey of every elevation, close up from building maintenance units or rope access where defects are suspected, recording broken, misted and replaced units and seal condition.
• Glass identification from markings and with a polarising filter or edge-stress viewer to confirm toughened glass; heat-soak status from records.
• Field water testing to locate leak paths: a nozzle test under AAMA 501.2 or a chamber test under ASTM E1105 in the United States, and test methods under AS/NZS 4284 practice in Australia, done before any remedial design.
• Adhesion testing of sealants and structural silicone by the hand pull method in ASTM C1521, with bond width and depth measured.
• Opening up of glazing pockets, sill drainage and a sample of slab-edge anchors behind ceilings and floor finishes.
• Thermography to show air leakage, failed IGUs and thermal bridging at frames.

The report should identify the system and glass types, leak paths found by testing, IGU and seal condition by elevation, SSG adhesion results, anchor condition, and any glass that must be made safe.

• Drainage restoration: clear weeps, reinstate baffles and end dams, which often stops leaks without resealing.
• Reseal and regasket: replace perimeter seals, cap seals and gaskets; on stick curtain walls a wet-sealed overlay of joints can extend life.
• IGU replacement unit by unit, or reglazing of whole elevations where failure is widespread.
• SSG remediation: supplementary mechanical retention (toggles or caps) where adhesion is doubtful, or full reglazing.
• Toughened glass risk: replace with heat-soaked or laminated glass where breakage history or location warrants; interim protection below.
• Anchor repair: replace or supplement corroded anchors, which requires access through finishes.
• Replacement or overclad: full replacement of the system, or a new system over the old on curtain walls, when frames, seals and glass are all at end of life or an energy upgrade is wanted.
• Steel windows: strip, treat and repaint, reglaze with matching sections, or install secondary glazing on heritage frames.

Investigation is a lump sum with rates per water test and adhesion test. Resealing and regasketing are measured by linear metre; IGU replacement per unit; reglazing and replacement by façade area. Access by building maintenance unit, rope access or swing stage, and out-of-hours work in occupied buildings, are often the largest components.

Two-part lines are normal: testing first, then works sized from the results. Reseal and regasket are repairs and maintenance; IGU and system replacement are lifecycle; safety glazing upgrades and ordinance findings are code compliance; make-safe is immediate.

• Australia. The National Construction Code calls up AS 1288 for glass selection and installation and AS 2047 for windows and external glazed doors; insulated glass units are made to AS/NZS 4666, and Section J sets energy performance for glazing. On strata buildings, windows are commonly lot property and the façade common property, which complicates whole-building replacement.
• United Kingdom. Approved Documents K (safety glazing and protection from impact), L (energy), B (fire) and Q (security in dwellings) apply; glazing follows the BS 6262 series, curtain walling BS EN 13830, toughened glass BS EN 12150, heat-soaked toughened glass BS EN 14179 and insulating glass units BS EN 1279. The Centre for Window and Cladding Technology publishes the working standards for curtain walling.
• United States. International Building Code Chapter 24 governs glass and glazing; ASTM E1300 sets load resistance, ASTM C1048 heat-treated glass, ASTM E2190 insulating glass units and ASTM C1401 structural sealant glazing; safety glazing follows 16 CFR 1201. Façade ordinances include windows and curtain walls in the periodic examination; New York's Cycle 10 runs from February 2025 to February 2029.

• Shop drawings and the glass schedule, with glass types by location.
• Heat-soak certificates for toughened glass, and SSG adhesion test and compatibility records.
• Breakage log and leak log by location.
• Previous water testing, façade inspection reports and ordinance filings.
• Warranties for IGUs, sealants and systems, with dates.
• Window maintenance and hardware service records.
• Façade access strategy and the certification of the equipment that serves it.