external walls and roof

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Unit 4

SUPERSTRUCTURE DESIGN

external walls and roof

Mohamed Mohsin - Bahrain


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Strength and stability

External walls fall into two main groups:-

1. structural

make a positive contribution in a structural

integrity of a building,

act in two ways:

load bearing (resist compression)

and/or stabilising. (resist horizontal or oblique forces)

2. non-structural. carry only their own weight

resist horizontal loads( wind loading ).


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Wall properties

1. Weather protection

2. Thermal insulation

3. Durability4. Fire resistance

5. Noise resistance

6. Buildability


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Weather protection

The main function of an external wall,

modifier of the external environment.

Walls must be able to exclude:

rain, wind, snow, frost and sometimes heat and glarefrom the sun.

need to allow naturally ventilated and naturallight to enter the building.


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Thermal insulation

the pressure for better thermal insulationhas mainly been the result of increasedenergy costs.


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Durability

To be durable the external walls of a building must beable to:

withstand the effects of the weather,

withstand physical damage to which they will be

subjected during their life,( e.g. damage fromhumans, vehicles, etc.)

walls will need to be maintained continuously

repainting, cleaning rainwater gutters.

etc


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Fire

The internal walls required to

inhibit the spread of flames, smoke and gases from room to room.

External walls need to

inhibit the spread of flames, smoke and gases from room to room.

contain the fire within the building

All walls fulfill their structural function during a fire until all occupantshave had sufficient time to escape.

Wall materials are normally measured in terms of combustibility andsurface spread (Classes 0, 1, 2, 3 and 4).


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Noise

provide acoustic insulation between the internal and external environment(stated in Hz).

two ways of propagating noise is: through the air (airborne) or by impact (structure borne).

Airborne sound is normally reduced by using materials that are heavy, Impact noise is dealt with using discontinuity. Providing discontinuity by jointing which a weak point in insulating against

airborne sound.

Thermal insulation normally is achieved by the use of lightweight foamed

materials, which are useful for insulating against impact noise butinadequate for airborne noise.

Normally openings, such as windows and doors, are the weakest part of thewall as far as noise.


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Buildability

Using simpler construction methodswithout effecting the quality of the finishedproduct.

Buildability to be considered by:

architects

structural engineers

services engineers


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Types of external walls

Masonry walls

Timber framed buildings

Lightweight profiled and flat sheetcladding


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Masonry walls

constructed of bricks or blocks.

Bricks:

standard size of is 215 x 102.5 x 65mm.

classified by the material they are made from: Clay bricks

Calcium silicate bricks (sand lime)

Concrete bricks

Blocks: made of three main types of materials :-

clay, (hollow blocks)

pre-cast concrete (dense or heavyweight, lightweight)

aerated concrete.


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Bricks


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Blocks


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The construction of masonry walls

Basically there are three main types ofconstruction used for masonry walls.

1. Solid wall

2. Clad walls

3. Cavity walls

4. Layered walls (cavity filled)


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Solid walls

These walls are normally associated withinternal use.

Usually brick thick (102.5mm),


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Clad walls

Solid walls with external porous nature will permit water to migrate from the outside to the

inside.

the application of a cladding material on theoutside face can overcome this weakness(rendering or harling)

way of cladding render tiles,

shiplap boarding /Timber Shingles waterproof coating systems


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Cavity walls

Today almost all externalmasonry walls are built usingcavity construction

basically constructed of two brick thick skins separated by a50mm wide void or cavity.


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Layered walls (cavity filled)

used to

prevent the transmission of moisture throughwalls

install thermal insulation


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DPC in brick walls

Traditional door opening

Scottish door opening

From a thermal insulation pointof view, what is the major defectin figures?


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Modern Door opening

Modern construction overcomes this by closing the cavity withthermally insulated proprietary cavity closers.

The use of plastic extrusions has a double benefit :-

acting as a DPC being strong enough to fix a window of door to the extrusion.


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window opening

the horizontal DPC positioned under the window sill

To provide complete waterproofing the horizontal DPC

and the vertical DPC must overlap.


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Windows opening


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Opening Lintel

lintel Install to support brickwork above the opening

Lintel type

concrete lintels

Pressed steel


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Steel Lintel


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Steel Lintel


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Timber framed buildings

the external walls of the building areconstructed of timber framing

normally rests on a concrete raft foundationand supports timber roof trusses.

The space between the vertical timbermembers (studs) is filled with insulation. The inner face of the studs has sheeting

applied, normally plasterboard. The external face can also be covered in

sheeting, such as ship lap boarding,

A brick skin is normally used, due to the dampnature of the climate. Note the use of a vapour barrier on the inner

side of the wall and a breather membrane onthe outer side.


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Timber Frame

What are theroles of theVapour barrier

and Breathermembrane?


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The role of the Vapour barrier

Vapour barrier

This sheet is imperviousto water in both liquid andvapour state.

Impermeable membranethat block air to inter

Placed in the inner side

Preventing the passageof the water vapour that iscontained in air

Function of Vapour Barrier

Protect envelop structure

Prevent air leakage

Maintaining interiorhumidification


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Vapour barrier


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The role of the Breather Membrane

Breather Membrane

Water Resistance material

Used outside under theexterior finish material

Shed moisture and restrict rain Allow water vapour to pass

Act as wind barrier

Allowing moisture with cavityto escape out side

Breather Membrane must have:

Water resistance

Water Vapour permeability

Air Barrier properties


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Lightweight profiled and flat sheet cladding

Used in frame structural to formthe outer walls and often the roofas well.

used for low cost, low qualitybuildings

single sheet cladding had:

no insulation,

limited life expectancy

little visual attraction

Todays sheets are made in awide range of materials, colours,finishes, size and profile


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Typicalsteelprofiles


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Component Elements of sheet Cladding

External Cladding:

Normally steel or aluminum

Breather membrane

Spacer:

Spacer bar to Protectthermal insulation

Vapour Barrier

Impervious to water bothliquid and vapour

Acoustic absorption

Internal lining


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typical detail in a vertical wall.


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Typical of the construction from thebottom of a foundation


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Detail at a gutter (eaves)

The main component elements

Portal frame

Cladding railsFixed at 90 to the portal frame.

Cladding

Gutter lapped by the roof cladding and the

flashing. noted the continuity of the insulation

under the gutter.


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Gutter
http://www.ambiancerestorations.com/images/Install_Gutters.jpg


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Gutter


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Question

What type of problems do youthink the owner of a building

would have, to maintain a hiddengutter?

Would this problem be removedby the use of half-round gutters?

Bit h d f


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Bitched roofRidge detail.


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Detail of Corner of a building.


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Ventilation duct penetrates the cladding.


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Why is the cladding profile different fromthat shown in the previous cladding details?


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Composite Panels


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Question

Sketch the symbols for the followingmaterials:

brickwork concrete

DPC & DPM soil insulation blockwork


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Symbols ofmaterials


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W ll i l ti


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Wall insulation


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Ground supported concrete slab withinsulation located below the screed

Ground supported concrete slab withinsulation located below the slab


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Type of Cladding

Profile metal sheet

Flat metal sheet

Rainscreen

Curtain Walling

R i l ddi


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Rainscreen cladding

The rainscreen, as its name

suggests, is designed to deflectrainwater from the buildingsfacade.

A Rainscreen system allows theflow of air into the system

ventilating the cavity. This allowsany water which penetrates thepanel joints to flow down the backof the panels and out at the base

Rainscreen consists of an outerpanel, a cavity and an inner leaf.

Normally, the internal leaf of thebuilding is constructed inreinforced concrete or concreteblock


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Rainscreen Cassette Panels


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Terracotta RainScreen Cladding

From ItalyTerra: mean earthCotta: mean cooked/baked

use of terracotta tiles, usedas a rainscreen.

In this method of claddingthe metal panels, arereplaced with terracottatiles.

water which penetratesbetween the terracotta tilebeing drained away by thewaterproof membranebehind the tiles.


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Curtain Walling system


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Curtain Walling

The traditional curtain wall isa frame of aluminum withmullions and transoms quitesimilar to large framedglazing except that the wallsform an independentenvelope around the mainstructure and are generallynot resting on the concretestructure but only connectedto it.


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Curtain Walling


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Curtain walling systems

Curtain walling systems are:1- Framework (Stick )2- Unitised frame

They are presented to site in three basic ways.:

Framework (stick ): of site-assembled componentswhich is used to support pre-assembled infill panels.

sections of prefabricated wall which are transported to

site as unitised frames, often preglazed.

prefabricated unitised frames, often pre-glazed, whichare hung on a site-assembled carrier framework.


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Stick curtain walling systems Stick systems are installed on site, component by component

They get their name from the fact that the vertical structural mullions(sticks)

normally using a pressure plate and face cap.

That a building has to be unoccupied during refurbishment.

Stick systems allow on site adjustment, but the performance of thesystems is dependent upon the quality of the installation in what areoften uncontrolled conditions.

In conclusion, stick systems are economical and, if correctlydesigned, detailed and installed, extremely reliable. They are,however, slow to assemble, which may not suit certain fast trackprojects.


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Unitised curtain walling systems

installed as a series of factory-assembled frames, usually withinterlocking mullions and transoms.

The glazing panels and spandrels are usually factory-glazed andseals are also applied or prepared in the factory

Advantages fabrication in controlled environment, very rapid assembly on site (speed of installation,) minimal on site labour, lower installation costs.

Disadvantages

expensive storage and shipping costs, the need for very careful site handling, require longer lead limes. expensive lifting equipment on site.


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Curtain wallCladding with

Aluminium and glass


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Bridge

Spandrel glass as viewed


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Spandrel glass as viewedfrom the inside

Steel structureWithout glazing

vision glass as viewedfrom the inside


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Spandrel glass as viewed

from the outside

vision glass as viewedfrom the outside

Anchoring


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Anchoring


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Curtain wall anchoring

Anchor clips- typical stick applications


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Spandrel Glass


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Opaque glass used for covering the bands of wallaround the edges of floors

Spandrel Glass

4 3 2 1 (Glass surface order)


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Cladding System


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Cladding System

Stick System

1-Anchors 2-Mullion 3-Horizontal rail( gutter section at window head)

4-Spandrel panel (may be installed from inside building) 5-Horizontal rail (window sillsection) 6-Vision glass (installed from inside building) 7-Interior mullion trim

Other variations: Mullion and rail sections may be longer or shorter than shown

Vision glass may be set directly in recesses in framing members, may be set withapplied stops, may be set in sub-frame, or may include operable sash.


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Unit System and Unit-and-Mullion System

(A) Unit SystemSchematic of typical version 1-Anchor 2-Pre assembledframed unit. Other variations: Mullion sections may be interlocking spilt type ormay be channel shapes with applied inside and outside joint covers. Units may beunglazed or may be Pre-plazed .Spandrel panel may be either at top or bottom ofunit.

(B) Unit-and-Mullion SystemSchematic of typical version1-Anchors 2-Mullion(either one-or two-story lengths) 3-Pre assembled unit-

lowered into place behind mullion from floor above 4-Interior mullion trim. Othervariations :Framed units may be full-story height (as shown)either unglazed orpre-glazed, or may be separate spandrel cover units and vision glass units.Horizontal rail sections are sometimes used between units.


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Panel System and Column Cover and SpandrelSystem(A) Panel SystemSchematic of typical version 1-Anchor 2-Panel Other variations:Panels may be formed sheet or castings, may be full story height (as shown) orsmaller units, and may be either pre-glazed or glazed after installation.

(B) Column Cover and Spandrel SystemSchematic of typical version

1-Column cover section 2-Spandrel panel 3-Glazing infill. Other variations:

Column covers may be one piece or an assembly, may be of any cross-sectionalprofile, and either one or two stories in height. Spandrel panel may be plain,textured or patterned. Glazing infill may be a pre-assembly, either glazed orunglazed, or be assembled in place.

Unitized: finished glazed panels shipped to


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Unitized: finished glazed panels shipped to

jobsite ready for installation

F t f h i th t


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Factor of choosing the system

The choice between stick and unitisedsystems is dependent on a number offactors:

1. The cost,2. site access

3. construction timetabling,

4. the overall design and structural requirements.


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The methods ofStructurally Bonded of Curtain Walling

Structural Glazing


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Structural Glazing

It is a system of bonding glassto an aluminium window frameutilizing a high-strength, highperformance silicone sealant.

No mechanical retention such

as beads, clips or bolt fixings

It is a uniform large glazedsurfaces, not interrupted bytraditional frames or any othersupporting or fitting system

projecting out of the frame.

the glass is fixed to a support,which in turn is attached to astructural element of thebuilding,

Bolted Glazing


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Bolted Glazing

holds the glass bymeans of visible metalparts and covers asmall part of the glasssurface.

For small or mediumglazing not exceeding7m in height and 50m in

length, rigid boltedsystem can be used.


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Fin Supported Glazing


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Fin Supported Glazing

Glass fins are used toachieve the all glass clarityrequired by designers whilemeeting the structuralrequirements of the glazing

system

A glass fin replaces a frameor mullion and must be

assessed as to size andthickness and securely fixedor supported at the headand sill.

Cable Supported Glazing


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Cable Supported Glazing

In these systems stainlesssteel or carbon fibre highstrength cables are usedto transfer loads to the

main structure.

Cables systems creategreater levels of openness,

visibility & natural light andenhance the dramaticappearance of thebuilding.

Suspended Glazing


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Suspended Glazing

This method of providing aframeless glazing facade is to fixtogether a matrix of toughenedglass lites, hung from the buildingstructure

allow designers to glaze large

openings in buildings, withoutusing metal frames or mullions, tocreate light and space withminimum visual barriers.

The glass faade is hung from thebuilding structure like a curtain.The top tier panels are connected

to the structure by adjustablehanger brackets and lower panelsare connected by special fittings attheir corners.

Traditional Glazing


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Traditional Glazing

The traditional framed glazing using wood

Roof GlazingP t t Gl i S t


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Patent Glazing Systems

Patent Glazing isthe most widelyused product inoverhead glazing

It consistsessentially of aseries oflongitudinalsupportingmembers (glazing

bars), and aninfilling of glass orother suitablematerials.


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Patent Glazing


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Patent Glazing


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external walls and roof

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