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    Building Construction

    CLADDING

    9/16/2010

    ELA SHARMA

    VEENA .S. NAMBOODIRI

    LOVE CHOUDHARY

    NIMME CYRIAC

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    INTRODUCTIONCladding is an all-encompassing term for the external skin of a building whichkeeps out the weather and provides the buildings aesthetic effect. In low-riseconstruction it may support its own weight but self-weight and wind loading arenormally transferred to the structural building frame. It may form the full

    thickness of the vertical envelope of the building but can simply be the outerlayer with additional layers providing insulation and the internal lining.

    PRINCIPLES OF OPERATIONApart from providing the external appearance of the building, the main functionof cladding is to protect the structure from the weather particularly rain. Thismay be achieved in one of three ways as follows:

    y Porous materials. Porous materials such as brickwork absorb waterduring rain and subsequently dry out. If the wall is of sufficient thicknessand the permeability is reasonably low water will not penetrate during arainstorm. In modern construction a cavity is normally introduced into thewall to provide an additional barrier to the passage of water.

    y Sealed construction. Impermeable cladding materials will only permit thepassage of water at joints. Sealing the joints with gaskets or wet appliedsealants provides a continuous impermeable layer.

    y Rainscreen. As its name suggests, the purpose of the outer rainscreenpanels is to shield the wall from direct rain. The joints between thepanels may allow some water to penetrate but an air gap and airtightbacking wall behind the panels combine to limit this penetration. Thismay be achieved by the drained and ventilated method in which the airgap is continuous and well ventilated to encourage drying out.Alternatively the pressure equalised system may be used in which thegap behind the panels is compartmentalised allowing the air to bepressurised by the wind. The reduced pressure difference across thepanel joints limits water penetration.

    DESCRIPTION OF MAIN CLADDING TYPESThere are many types of cladding available, which are described below,grouped according to type of construction. Some of the categories are clearlydefined but others cover a range of options and some variations could beconsidered to fall in more than one category. The distinction between curtainwalling and some other cladding types is particularly blurred.

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    In some cases weather tightness will always be achieved using the samemethod but in other cases apparently small changes to the design of thecladding will change the cladding from a sealed faade to a rain screen. It isnecessary to appreciate the effect of such decisions on the design of both thecladding and the supporting structure.

    Claddings to buildings can be considered under two classifications:

    1. Claddings fixed to a structural backing.

    2. Claddings to framed structures.

    CLADDINGS FIXED TO A STRUCTURAL BACKING

    materials used in this form of cladding are generally considered to be smallunit claddings and are applied for one of two reasons. If the structural wall isunable to provide an adequate barrier to the elements. A covering of small unitcladdings will generally raise the wall's resistance to an acceptable level.Alternatively small unit claddings can be used solely as a decorative feature,possibly to break up the monotony of a large plain area composed of a singlematerial.

    The materials used are tiles, slates, shingles, timber boarding, plastic boardsand stone facings. The general method of fixing these small units is to securethem to timber battens fixed to the structure backing. Stone and similarfacings, however, are usually secured by special mechanical fixiNG.

    TILE HANGING

    The tiles used in tile hanging can be ordinary roofing tiles or alternatively a tileof the same dimensions. The tiles are hung and fixed to tiling battens. Thebattens should be impregnated to prevent fungi and insect attack so that theiranticipated life is comparable to that of the tiles. Each tile should be twicenailed to its support batten with corrosion resistant nails of adequate length.

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    The minimum lap recommended is 40 mm which would give a gauge of112.5mm using a standard 265 long tile.

    A gauge dimension of112.5 mm is impracticable and therefore a gauge of110mm would be usual.

    It should be noted that if the structural backing is of timber framing a layer ofimpervious felt should be placed over the framing immediately underneath thebattens to prevent any moisture which is blown in between the tiles fromhaving adverse effects upon the structure.

    TIMBER CLADDING

    Timber cladding are usually in the form of moulded or shaped boards fixed tobattens as either a horizontal or vertical cladding.

    Timber claddings will require regular maintenance to preserve their resistanceto the elements. Softwoods are generally painted and and will need repaintingat intervals of 3 to 5 years according to the exposure. Hardwoods aresometimes treated with a preservative and left to bleach naturally; thepreservative treatment needs to be carried out at 2 to 5 year intervals.Western red cedar is a very popular wood for timber claading since it has anatural immunity to insect and fungi attack under normal conditions.

    Plastic boards are a substitute for timber and are fixed in a similar manner.

    STONE CLADDING

    Stones like marble, quota and slate owing to its smooth surfaces arefrequently used in exteriors as well as interiors of the buildings.The availabilityof these stones in various shades, the possibility of fine polishes that thesurfaces take up and the possibility of cutting the stone makes it a fine

    cladding material.

    The marble slabs generally 15-20 cm thick are fixed on concrete or masonrysurfaces introducing a gap of12 to 25 mm to keep the vibrating surfacesaway. Plaster of paris pads are positioned in such a manner that the joints inthe slabs do not move above the pads. The two adjacent slabs in verticalcourse are joined to each other by means of copper cramps of hooks 3mmdia. The slabs are secured in position by brass cramps turned at 120 to fill into

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    the groove. Rich mortar pads instead of plaster of paris of1 cement, 2 sandare used and also the air gap is filled in with mortar.

    CLADDINGS TO FRAME STRUCTURES

    The methods available to clad a frame structure are extensive and includepanels of masonry constructed between the columns and beams, light infillpanels of metal or timber, precast concrete panels and curtain walling whichcompletely encloses the structure.

    BRICKWORK CLADDING

    Application- Multi storey buildings, where a traditional facade is required.

    Brickwork movement- to allow for climatic changes and differential movementbetween the cladding and main structure, a 'soft' joiint (cellular polyethylene,cellular polyurethane, expanded rubber or sponge rubber with polysulphide orsilicon pointing) should be located below the support angle. vertical movementjoints may also be required at a maximum of12m spacing.

    Lateral restraint- Provided by normal wall ties between inner and outer leaf ofmasonry, plus sliding brick anchors below the support angle.

    PROFILED METAL SYSTEMS :

    Profiled metal sheeting has traditionally been considered as a relatively cheapform of cladding for agricultural and industrial buildings. More recently with awider range of colours and profiles becoming available its use has beenextended to include retail, office, leisure and education buildings. Guidance onthe use of profiled metal is given in BS 5427.

    Profiled sheets of aluminium or galvanised steel may be used in various waysas follows:

    y The simplest form is a single uninsulated skin supported on claddingrails spanning between the main structural columns.

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    y For most structures it will be necessary to incorporate insulation and thiscan be accommodated by using two skins of metal sheeting separatedby a spacer bar and with insulation in the resulting cavity, as shown

    y The need for sheeting rails and spacer bars can be eliminated by usingliner trays which span between columns providing both the internal liningand support for the outer sheets. The liner trays can also be filled withinsulation.

    y Composite panels can be formed from two metal skins separated by alayer of rigid insulation. Mineral wool can be bonded to the skins withadhesive while polyurethane (PUR) or polyisocyanurate (PIR) foams caneither be bonded with adhesive or extruded between the skins, andautohesively bonded to them under expansion. The panels aresupported on sheeting rails and fixed together at the edges only, relyingon composite action between the skins and the core to prevent flexing ofthe panel between the fixing points. The edge joints may be formed bylap joints where the metal sheet overhangs the insulation along oneedge or by tongue and groove joints as shown

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    .

    Systems typically use profiled sheets having a cover width of between 600 and1000mm, and a length of at least 2m. The depth of the corrugations rangesfrom 7mm to 120mm, and the wavelength/pitch from 30 to 350mm. Thespacing of fixings depends upon the wind load and flexibility of the sheet (e.g.depth of profile) and pitch (of roof cladding), but fixings are typically made

    every 250-300mm along the spacers. A maximum fixing spacing is suggestedas being 450mm. Aluminium has a much higher coefficient of thermalexpansion than steel and the thermal movement of aluminium sheets musteither be allowed for in the end lap joint design or controlled by limiting thelength of sheets.

    The simplest fixing technique is to use self-drilling, self-tapping screws withintegral sealing washers through the valley of the profile and into the spacer.However, the fixings can also be made through the crown of the profile, inwhich case an additional spacer may be used to prevent the profile from being

    distorted and the need for an excessively long fixing. To join and seal thesheets together, stitching fixings are used along the side and end overlaps,and these may again be at the peak or trough of the profile.

    A more sophisticated technique is to use a form of hidden fixing. This iscommon with standing seam systems, which also tend to have muchshallower corrugations between the seams. Standing seam sheets lock intofixing brackets which are fitted along the spacers, and overlap the

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    neighbouring sheet. Because these systems are designed to hide the fixings,the sheets will be narrower, and there will not be any intermediate fixings.

    Secret fix cladding systems offer greater weathertightness reliability and finalappearance due to the absence of fixings that penetrate through the outer

    sheet.

    SMALL CLADDING PANELS

    Cladding panels vary widely in size and materials used. This section describescladding panels that are too small to span between the main structural framingmembers and are either supported by a backing wall or secondary framingmembers.

    Small overlapping units such as tile hanging and weatherboarding have notbeen included in this category. Most of the cladding panels described in thissection may be fixed with sealed joints but may also be used as rainscreenpanels. The method of achieving weathertightness will affect the design ofboth the cladding and the supporting structure.

    These materials are most likely to be used for commercial buildings althoughthey may also be used for over-cladding existing structures including blocks offlats.

    Various forms of cladding panel which can be supported on timber battens or

    metal rails are available. This method requires a backing wall to support thefixing rails and it will usually be necessary to incorporate insulation in the wall,generally in the cavity between the cladding panel and supporting wall. Thisform of cladding may be used for new construction but is particularly suitablefor upgrading existing buildings.

    For new construction the supporting rails can be made of heavier section sothat they can span between floors. This allows the use of a lightweight internallining.

    Panels may be fixed to the supporting rails using screws, rivets, structuraladhesive, a screw-fixed pressure plate, or the edges of the panels may befolded, punched and hung onto pins through the supporting rail.

    A range of materials may be used for the cladding panels as follows

    y Fibre cement sheets are manufactured in thicknesses between 5 and10mm and in sizes up to 1220mmx3050mm. Both cellulose and glass

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    fibres may be used and a wide range of finishes is available includinguntreated, various types of paint and resin bonded aggregate. Sheetsare normally supplied to site ready cut to size and with predrilled fixingholes. Similar panels may be manufactured using fibre reinforcedcalcium silicate, resin laminate and glass reinforced polyester.

    y Panels may be made from both aluminium and steel sheet and may begiven increased stiffness by folding the edges or adding stiffeners eitherwithin or at the back of the panel.

    y Thin composite metal panels may be formed from two layers ofaluminium separated by a layer of polyethylene giving an overall panelthickness of 3 to 8 mm. The composite action of the layers gives astronger panel than the aluminium alone. Panels can be used as flatsheets but can be bent to form curved panels or folded to form sharpcorners if the inner layer of aluminium is first cut along the line of thefold.

    y Thick composite panels may be formed from aluminium or steel stripseparated by a core of insulation. These panels differ from thoseproduced from profiled metal in that they are manufactured asrectangular panels and may have flat faces. The edges of the panelsmay incorporate grooves to facilitate fixings, which can then be hiddenby gaskets. Alternatively a pressure plate fixing system can be used.

    Stone has traditionally been used as masonry to form an external facingmaterial for buildings but is now being increasingly used as a non loadbearingcladding as a result of developments in stone processing which allow stone to

    be cut into thin panels.

    Stone types used for cladding are granites, marbles, hard limestones, slates,quartzites, limestones and sandstones that offer a range of colours andsurface textures with good durability. Stone is covered in detail in

    LARGE CLADDING PANELS

    Cladding panels with sufficient strength to span between discrete fixing pointson the main building frame, often as storey height panels, may bemanufactured from reinforced concrete or as pre-assembled curtain wall.Glass fibre reinforced polyester and glass fibre reinforced cement wereintroduced in the 1960s and 1970s respectively but have now largely fallen outof use. Some composite metal panel systems may be used to spanhorizontally between columns and strictly fall into the group but in otherrespects are as described above.

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    Precast concrete can be used to produce loadbearing cladding panels but theyare normally non-load bearing. Guidance on their use is given in BS 8297.

    Precast concrete cladding systems come in three forms:

    y

    Small units supported on brackets and used to fill gaps betweenconventional glazing systems,y Larger mullion and spandrel units which cloak the structural frame

    members, often to form a window opening within each bay. Units arenormally supported on bearing pads on the concrete floor slab, withpacking shims providing vertical adjustment. Horizontal restraint andadjustment is provided by angle brackets and adjustable bolts,

    y Full bay-width, storey-height panels with cast (punched) windowopenings. Panels are of a sufficient size and stiffness to be able to spanhorizontally or vertically between structural frame members without

    requiring any intermediate support.

    Panel-to-panel joints are either weather sealed with single or double wet-applied seals or left open (but baffled to prevent direct water ingress).Concretepanels/units can be produced with a variety of smooth and coarse finishes orfaced with factory-set natural stone, clay brick or tiling systems. They can alsobe made from carefully selected materials to give the appearance of stone.

    FULLY SUPPORTED METAL SHEETING

    Copper and lead sheeting may be used for cladding but are expensive andhence only used to a limited extent where required for appearance on prestigebuildings. Due to its weight and low strength lead must be fully supported,usually by plywood boards. Due to its cost, copper is used in thin sheets thatalso need continuous support.

    CURTAIN WALLING

    Curtain walling is a form of vertical building enclosure which supports no loadother than its own weight that of ancillary components and the environmentalforces which act upon it. Although the term is sometimes restricted to metalframed curtain walls, the above definition embraces many differentconstruction methods and materials including non-loadbearing precastconcrete.

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    Description of curtain walling types

    The classification of types of curtain walling varies but the following terms arecommonly used:

    y Sticky Unitisedy Panellisedy Spandrel panel ribbon glazingy Structural sealant glazingy Structural glazing

    Stick system curtain walling

    The general arrangement of a stick system curtain wall is shown as

    Horizontal and vertical framing members (sticks) are normally extrudedaluminium protected by anodising or powder coating, but may be cold-rolled

    steel (for greater fire resistance) or aluminium clad with PVC-U. Members arecut to length and machined in the factory prior to assembly on site as a kit ofparts: vertical mullions, which are fixed to the floor slab, are erected firstfollowed by horizontal transoms, which are fixed in-betweenmullions. Mullions are typically spaced between 1.0 and 1.8m centres. Intothe framework are fitted infill units, which may comprise a mixture of fixed andopening glazing and insulated panels (which may have metal, glass or stonefacings). These units are typically sealed with gaskets and retained with a

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    pressure plate, screw-fixed every 150-300 mm, although hammer-in structuralgaskets are used for some stick systems. The pressure plate is generallyhidden with a snap-on cosmetic cover cap or overlapping gaskets. The screwfixings can be exposed by removing the cover, which is typically produced insix metre lengths for vertical framing elements. Fixings must be secured to

    the correct torque to retain the glazing/infill panels and to ensure propercompression of the gaskets for weather sealing.

    Stick curtain walling is very common and versatile and can be used foranything from glass towers tens of storeys high to single storey shop fronts.Because of the number of joints in stick curtain walling it is generally very goodat accommodating variabilitys and movement in the building frame. It is alsosuitable for irregular shaped buildings. Assembly is slow compared with pre-assembled systems and performance (e.g. weather tightness) is dependent onknowledgeable installers who are familiar with the assembly and sealing

    procedures for the particular system. Some pre-assembly of stick curtain wallframes is possible by the use of ladder frames.

    Many manufacturers (systems suppliers) produce standard sticksystems. Insulated panels, usually designed for the project, may be faced withanything from aluminium or steel sheet, to glass or expensive stonecomposites. Some companies produce project-specific bespoke systems -either designing frame profiles from scratch for each job, or using standarddetails for some parts of the frame and simply altering some small aspect togive the appropriate structural properties or appearance. The type, complexityand budget of the project will normally determine whether a standard (i.e. off-the-shelf) or bespoke curtain wall is used.

    Stick system curtain walling may be erected in one of three sequences:

    y

    Stick system wall, method 1.

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    y Stick system wall, method 2.

    y Stick system wall, method 3.

    Unitised curtain walling

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    Unitised systems comprise narrow, storey-height units of steel or aluminiumframework, glazing and panels pre-assembled under controlled, factoryconditions, Mechanical handling is required to position, align and fix units onto

    pre-positioned brackets attached to the concrete floor slab or the structuralframe. Unitised systems are more complex in terms of framing system, havehigher direct costs and are less common than stick systems. The smallernumber of site-sealed joints in unitised curtain walling simplifies and hastensenclosure of the building, requires fewer site staff and can make such systemscost effective. If construction joints interlock consideration must be given tohow damaged units could be removed and replaced. The reduced number ofsite-made joints compared with stick systems, generally leads to a reduction inair and water leakage resulting from poor installation.

    Panellised curtain walling

    Panellised curtain walling comprises large prefabricated panels of bay widthand storey height, which connect back to the primary structural columns or tothe floor slabs close to the primary structure Fixing the panels close to the

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    columns reduces problems due to deflection of the slab at mid span, whichaffect stick and unitised systems.Panels may be of precast concrete orcomprise a structural steel framework, which can be used to support mostcladding materials (e.g. stone, metal and masonry). Structural steel panellisedwalls are known as truss walls in North America. Aluminium or galvanised

    steel skins are generally fixed to the frame with insulation in the cavity. Thewall construction is then completed by a plasterboard lining and externalcladding.Joints may comprise gasketted interlocking extrusions, gasketsbetween separate extrusions or wet applied sealant.

    The advantages of using panellised systems stem from the high utilisation offactory prefabrication, which allows better control of quality and rapidinstallation with the minimum number of site-sealed joints. However to be costeffective a large number of identical panels is required.Panellised systems areless common and more expensive than unitised construction. The size and

    weight of panels is limited by the practicalities of manufacture, handling,storage, transport and erection.Some authors do not differentiate betweenunitised and panellised systems, but panellised construction may havesignificant internal steel structure to support the extra weight, or may consist ofprecast concrete panels with openings for windows.

    Spandrel panel ribbon glazing

    Spandrel panel ribbon glazing is a long or continuous run of vision units fixedbetween spandrel panels supported by vertical columns or the floor slabs, .

    Glazed areas may comprise:

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    y Several standard windows fixed together on site by joining mullions,y Pre-glazed, bay width, factory-assembled frames, ory Individual framing sections and glass infill panels which are site

    assembled.

    Ribbon glazing is often used in conjunction with spandrel panels, that is,horizontally spanning prefabricated or precast concrete units. It may also beused with spandrels comprising upstand walls faced with rainscreen panels.Care needs to be taken when detailing interfaces with adjacent elements.

    Ribbon glazing/spandrel panel construction generally results in buildingshaving a horizontal banded or strip appearance.

    Structural sealant glazing

    Structural sealant glazing is a form of glazing that can be applied to stickcurtain wall systems and windows, particularly ribbon glazing. However it canalso be used in unitised and panellised systems. Instead of mechanicalmeans (i.e. a pressure plate or structural gasket), the glass infill panels areattached with a factory-applied structural sealant (usually silicone) to metalcarrier units which are then bolted into the framing grid on site. External jointsare weathersealed with a wet-applied sealant or a gasket,.

    These walls are attractive to architects as they offer a smooth or semi-smoothfacade.

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    Structural sealant glazing has been used in the USA for around 30 yearswhere it was initially site applied direct to the framing. However, this is nolonger acceptable due to difficulties of application and replacement and allstructural silicone joints are now made in a factory.

    Glass replacement/resealing must be undertaken in a controlled environmentusing the correct materials. All elements used in the construction must becompatible with the silicone sealant.

    Structural sealant glazing systems can have sealant on two opposite sides oron all four-sides with or without the weight of glass supportedmechanically. Generally, the glass is mechanically supported to reduce thesize of the sealant bead.

    Structural sealant glazing can be used to create a building exterior that is freefrom protrusions, but the framing system will be visible at night whenbacklit. Structural sealant glazing is more widely used on prestige buildingsand may be produced as a standard system, or on a project-by-projectcustomised basis. The framing members are often more widely spaced thanfor traditional stick systems.Any of the previous types of curtain walling andribbon glazing could incorporate structural silicone glazed elements.

    Structural glazing - bolted assembly

    Sheets of toughened glass are assembled with special bolts and brackets and

    supported by a secondary structure, to create a near transparent facade orroof with a flush external surface.

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    A multitude of discreet or prominent secondary structures can be designed(e.g. space frame, rigging or a series of mullions) which support the glazingthrough special brackets. The joints between adjacent panes/glass units areweathersealed on site with wet-applied sealant.

    Structural glazing - suspended assembly

    Here the glass is fixed together with corner, rectangular, patch plates and thewhole assembly is then either suspended from the top or stacked from theground and wet-sealed on site,

    Suspended glazing systems utilise the minimum amount of framing for a givenglass area and are used as glazing features on prestige buildings, but also forprestige atria on otherwise simple buildings.

    Glass fins may be used to brace the assembly. In some designs a light trussstabilises the wall and transfers wind loading, while the weight of the glass istransferred through the corner plates and suspension system

    Curtain walling applications

    Stick curtain walls are used on larger office developments but may also beused on some low-cost office or industrial units, typically for one small part,such as an entrance. Unitised or panellised curtain walling systems aregenerally adopted where the additional expense of factory assembly iscompensated by faster installation. They are only economic where a largenumber of similar units or panels is required. The highest-cost bespoke curtainwalling systems will generally only be used on prestige buildings, large orsmall.

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    Choice of curtain wall type is never straightforward. Dominant factors are:

    y Costy Appearancey Timescale

    y Access limitations

    The lowest cost is often achieved with a standard aluminium-framed sticksystem. Generally, costs increase with complexity, although factory assemblyalso increases costs. Increasing the number of non-standard items willincrease cost, not only due to the additional material cost but also due toadditional design work required to integrate the component(s) within thesystem and possibly because of the need for project testing.

    The importance of appearance will depend upon the desired image that thebuilding is to project. A building situated in a highly visible or prestigiouslocation may demand the use of more expensive materials, perhaps stone-faced insulated panels or a structural sealant or bolted glazing system with noexternal protrusions to interrupt the facade. A building facade may bedesigned to compliment, or contrast with, the surrounding built environment.

    Time-scale is important because there may be contractual limitations on thetime available for assembling the facade. A site-assembled stick system hasthe advantage that installation can start quickly, but it may then proceed moreslowly than with factory-assembled units. However, systems requiring factorypre-assembly must be carefully planned so that units are available when

    construction of the facade is planned to start, but the units must not bemanufactured or delivered too soon or storage costs will be incurred. Notethat whilst the smaller number of site-made joints in pre-assembled systemssimplifies installation and weatherproofing, far greater attention to themanufacturing and erection tolerances of both structure and cladding isrequired.Other factors that are important include the ease ofmaintenance. Replacement of a glazing unit in a ribbon glazing system mightbe undertaken by a local glazier, whilst in a structural sealant glazing systemthis might require a specialist contractor, maybe the original

    contractor. Systems such as structural glazing must be designed so thatbreakage of a glass unit does not cause progressive failure of the facade. Thismay increase the cost of these systems.

    The architect may select several different types of curtain wall for a building -for example ribbon glazing at the back of the building, a standard stick systemfor the front of the building, and a prestige suspended glazing for the

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    atrium. Efforts should be concentrated on the construction interfaces duringthe design development and testing phases to reduce the risk of subsequentbuild ability and performance problems.

    MASONRYMasonry is the predominant form of wall construction for low rise housing andis widely used in all types of building although on large structures it is oftenused for small areas with less labour intensive cladding materials being usedfor large areas of faade. The wide range of materials available means that itcan be suitable for both low-cost industrial buildings and prestige structures.

    Masonry is a composite construction of individual brick or block units built upin horizontal, overlapping layers (courses) and bonded and sealed with mortar(sand, cement, and lime or plasticizer). Bricks may be manufactured from clay,

    calcium silicate or concrete and blocks are normally concrete or stone.

    Cavity wall construction is used almost without exception for external wallsbecause it provides an increased degree of thermal insulation and protectionagainst water penetration compared with a solid wall of the same overallthickness. In modern construction the external leaf is normally a non loadbearing cladding 100mm thick and the units are chosen primarily for theirappearance, durability and cost. The load bearing structure may be a steel,concrete or timber frame or an inner leaf of load bearing masonry.The innerleaf of a cavity wall may consist of concrete blocks, concrete or an insulated

    panel typically consisting of a timber frame with plywood or plasterboardsheathing. Where masonry is used for the inner leaf the requirements for theunit are normally low density (for insulation), adequate strength and low cost.An inner leaf is typically 100mm thick but this may be increased to improveinsulation or strength. Thermal insulation (typically mineral fibre quilt) is oftenrequired within the cavity to comply with Part L of the Building Regulations.

    In load bearing masonry and non-load bearing low rise construction themasonry will support its own weight but the external leaf needs to be tied tothe inner leaf and structural frame to give it lateral stability. In non-structural,multi-storey applications the weight of the masonry should be transferred tothe frame at each storey level. In the past this was often achieved bysupporting the wall directly on the floor with brick slips on the edge of the floor.Current practice is generally to support the wall on metal angles. These shouldbe adjustable, particularly in the lateral direction to ensure alignment andadequate bearing of each panel of masonry.

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    OTHER TYPES OF CLADDINGWeatherboarding and tile hanging are traditional forms of cladding which aregenerally confined to housing. PVC and fibre cement panels are now availableas alternatives to timber for weatherboarding. Tile hanging may use traditionalclay or concrete tiles, or slates of natural stone or fibre cement.

    Rendering may be used as a decorative or weatherproofing finish on masonrywalls but may also be used on a lightweight background. Traditionally thiswould be wooden lath but this has now been replaced by metal mesh that mayeither be expanded metal or a lightweight welded mesh. This form of claddingis not widely used and is generally restricted to housing.

    The cladding types described in this Section are established methods. Newsystems or developments of existing systems using new materials arecontinually being produced, a recent example being the use of titanium and

    terracotta.