GLAZING

GLAZING

Glazing: The act of fixing glass into a frame or surround  in domestic work this is usually achieved by locating the gloss in a rebate and securing it with putty or beading and should be carried out in accordance with the recommendation contained in BS 6262 glazing for buildings.

Timber Surrounds linseed oil putty to BS 544 – rebate to be clean, dry and primed before glazing is carried out. Putty should be protected with point within two weeks of application.

Metal Surrounds – metal casement putty if metal surround is to be pointed – if surround is not to be pointed a non-setting compound should be used.

Double Glazing – as its name implies this is where two layers of glass are used instead of the traditional single layer. Double glazing con be used to reduce the rate of heat loss through windows and glazed doors or it can be employed to reduce the sound transmission through windows. In the context of thermal insulation this is achieved by having a small air or argon gas filled space within the range of 6 to 20mm between the two layers of glass. The sealed double glazing unit will also prevent internal misting by condensation. If metal frames are used these should have a thermal break incorporated in their design. All openin9 ashes in a double glazing system should be fitted with adequate feather seals to reduce the rate of heat loss through the opening ‘clearance gap.

In the context of sound insulation three factors affect the performance of double glazing. Firstly good installation to ensure tightness, secondly the weight of glass used and thirdly the size of air space between the layers of glass. The heavier the glass used the better the sound insulation and the air space needs to be within the range of 50 to 300mm. Absorbent lining to the reveals thin the air space will also improve the sound insulation properties of the system.

In general there are four glazing methods used in fixing glass to an aluminium framing system. The exact glazing pocket geometry and recommended glazing system for each  lidco system.

The glazing methods describe are for vertical glazing only and the four main methods for fixing glass are: Pocket glazing, Rebate and snap on beads, Front glazed plant – on external cap, and wrap – armod channel gasket.

Glass to Glazing Bar

A double – glazed window unit built  using 3/16“ thick glass weighs over five pounds per square foot. Such window unit should be handled with extra care and plenty of hands at least two workers for vertical glass. Any nicks or scratches in the glass will weaken it significantly by compromising the tensile strength of the glass is a little easier to handle as it is less fragile and because its edges are sanded smooth. If you are installing lots of glass, buy the suction cups that professional glaziers used to handle glass units and to place them accurately into their final position in the window frame.

Method Of Weather Proofing The Head And Sill

At corners of the outer frame where the aluminium reveal fins do not meet up, the corner are to be factory tape sealed (waterproof tape) to protect the aluminium reveals. Failure to do so may result in reveals being wet at the corners if water runs down the reveal fin of the window. Most reports of leaking windows can often be attributed to poor installation of the window and / or no proper application of flashing around the window.

For most installations of windows into residential housing the research and development group recommends that flashings always be used at the jambs and sill of the window frame, plumb jamb in both directions. Pack frame at sill and jambs only. Frame must be square and out of twist (essential for smooth operation of sashes) check that diagonal measurements are equal.

1(b) Fixing Aluminium Window To Concrete Frame

Masonry walls should be built well in advance of inserting frames into the wall to protect aluminium. This allows time for the mortar to cure and dry, which reduces the movement of alkalis. The frame is then attached with screws at the bottom, top and sides. A ½ inch gap should be left around the frame. When filled with chalks. This gap separates the inside of the building from the outside reduces wall stresses acting barrier between the mortal and the window frame material. Even so, new hardened mortar that is rewetted by precipitation can still be a source of alkalis. Good coatings should adequately protect aluminium from chemical attack. Two coast of bituminous paints or zinc chromate primer are often used in severe application of the aluminium from the cement-base products. A light coating of petroleum jelly painted onto the surface of the frame is another way to provide temporary protection to the finish during construction. Anything that directs moisture away from the frame reduces alkali exposure. Therefore, if it is possible to separate the frame from direct contact with the mortar by a sheet material (flashing), this can help reduce corrosion as well, plastics, rubbers, and vinyl material resistance to UV degradation and attack by alkalis are all acceptable. If the masonry wall is to be cleaned following construction, the aluminium must not be subjected to harsh chemicals and must be rinsed thoroughly. Clear water should remove any dirt on the wall and any alkalis washed off the building face.
Patent Glazing

Patent Glazing is a non-load bearing framing system mainly used in overhead glazing.

It can also be used in vertical situations.

Its slim profiles allow the full use of natural light in the building. Patent Glazing is a drained and ventilated system of dry glazing comprising a series of longitudinal support members, known as ‘Patent Glazing Bars’, fixed to the building structure, and glass infills, either single- or double-glazed.

Developed as a two edged supported system, Patent Glazing is an economic alternative to four edge support curtain walling.

Essential features

Key to the Patent Glazing system is the design of the aluminium section that provides continuous support to the long edge of the glass or composite infill panel. In addition to supporting the infill it is designed to incorporate: seatings to provide continuous support to the sides of the glass pane cap or wings, to retain the glass pane and impede direct water penetration without restricting thermal channels or grooves under the seating, to collect and drain away any water that may penetrate beyond the wings and cap fittings, for attaching the load bearing element to the structure.

The glazing bars project either internally or externally to the glass on a roof application and are traditionally T-shape in cross section, although hollow box sections are also used.

Supported:

The Patent Glazing bars support the self-weight of the system, stress caused by wind and snow loads.

These loads are transmitted to a secondary structure and through to the structural frame. Such systems are used for canopies, northlights and large multi-pitched roofs such as atria.

Self supported:

The system can bridge a 6m gap, extend to any length, and support the self-weight of the system and stress caused by wind and snow loads.

These loads are transmitted directly to the structural frame without the need for additional steel or timber supports.

Such systems are used for hipped lantern and sky lights, rectangular, pyramid, octagonal or multi-faceted features.

Design criteria

The design of a Patent Glazing system must be in accordance with BS 5516 Design and installation of sloping and vertical patent glazing.

Patent Glazing is a non-load bearing system, not designed to take any structural loads of the building.

However, it must be structurally strong enough to support wind loads, snow loads and the self-weight of the installation. Allowance must also be made for building movement, maintenance loads and safe access for internal and external cleaning.

The infill glass panels must withstand the stress and deflection caused by wind and snow loads. The correct choice depends on pane size, dimensions, support and loadings.

It is strongly recommends that the use of laminated glass in single-glazing or as the inner pane of a sealed unit where it is necessary to minimise the risk of glass falling down after breakage.

Given the loadings, the bar span between structural supports, bar centres and degree of slope, one will calculate:

• The glass thickness or double-glazing unit configuration
• The correct size of glazing bar Most Patent Glazing systems were designed and tested on the basis that the glazing bars are set at 600mm centres. This can be increased, but needs to be correctly designed by the contractor / Building engineers. Where the bar span exceeds the available glass size, or to meet safe handling requirements, joins can be made in the length of glazing in the form of a silicone joint, or a non-structural transom or ‘H’ frame per-pendicular to the glazing bars.

Weather-resistance

There are no standard tests for the weather-resistant properties of Patent Glazing. If the design recommendations of BS 5516 are followed, good weather-resistance is achieved.

The minimum recommended pitch for Patent Glazing is 15°. Where the slope is less than 15° care must be taken to ensure the integrity of weather-resistant properties and to avoid the build-up of dirt in the drainage channels.

Openings

Opening lights provide natural ventilation in Patent Glazing and, where necessary, smoke ventilation compliant with BS 7346 : Part 1.

These lights can be mechanically or remotely operated. If necessary they can also be linked to the building management system.

Building tolerances and movement

In order to ensure the accuracy required to achieve the best appearance of the completed installation, it is necessary to establish specific limits for dimensional and positional tolerances of the supporting structure at an early stage.

Guidance on structural tolerances can be found in BS 5516. Allowing for building tolerances means that the structural opening and fixing areas in a building, will not always be plumb, square and true dimensionally. Also, during a building’s lifespan, the fixing points and openings may be subject to movement. Thus, when designing a Patent Glazing application, consideration must be given to such tolerances.

Glazing

The glass infill panel is a key contributor to the building’s internal environment. Patent Glazing systems can incorporate most of the glass types and configurations in laminated form from the SAINT-GOBAIN GLASS range:

• SGG CLIMAPLUS sealed units to reduce heat loss
• SGG SOLAR CONTROL to decrease dependence on air-conditioning
• SGG STADIP SILENCE to reduce noise, especially impact noise from rain.

The glass predominantly determines thermal performance of an installation, however the frame may conduct heat and bridge this insulation.

Unless the frame is thermally improved, condensation may occur as well as heat loss.

Double-glazed units used in sloped applications should be stepped at the bottom edge to allow drainage. The upper glass pane of the unit extends beyond the lower glass pane.

Fabrication

Patent Glazing bars are cut from sections of extruded aluminium alloy 6063-T6 to BS 1474. Normal finishes are polyester powder coated or anodised. Fasteners are either stainless steel to BS 304515 Grade A2 or mild steel bright zinc plated.

Gaskets are extruded thermo plastic rubber quality 98625 BS 4255: Part 1:1986 Grade C.