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PROPERTY281 Test 1 > L7: Building Envelope > Flashcards

L7: Building Envelope Flashcards

1
Q

What is considered a low-slope roof?

A

Pitch below 25%

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2
Q

What are the basic components of low-slope roofs?

A 
Deck
Thermal insulation
Vapour retarder
Roof membrane
Drainage
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3
Q

What is the minimum slope a roof deck can have and why?

A

2% so it can drain

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4
Q

What can happen if a roof is not drained properly?

A

Progressive structural collapse (puddles = structural deflection cycle)

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5
Q

What are the potential placements of thermal insulation and vapour retarder?

A

Below deck
Between deck and membrane (most common)
Above membrane

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6
Q

How is insulation below deck installed?

A

Insulation –> deck –> membrane –> ballast

Between underside floor framing members - exposes deck and membrane to wide temperature fluctuations and requires ventilation so vapour can escape

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7
Q

How is insulation between deck and membrane installed?

A

Deck –> insulation (2 layers) –> membrane –> ballast

Insulation supports membrane from below (but exposed to temp fluctuations) and protects deck from above from temp fluctuations
Must have topside vents

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8
Q

What are topside vents and why are they required when insulation is between deck and membrane?

A

To let out trapped vapour; without them, insulation decays and blisters/ruptures form in membrane
Located 1 every 100m2

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9
Q

How is insulation above membrane installed?

A

Deck –> membrane –> insulation –> ballast

Insulation protects membrane from temperature and no vapour because membrane is on warm side of insulation

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10
Q

What are examples of ballast?

A

Pre-applied thin concrete layer
Crushed stone
Interlocking concrete blocks (pavers)

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11
Q

What is a common material for insulation above membrane and why?

A

Polystyrene foam panels because it is exposed to water and must maintain qualities when wet

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12
Q

What are the categories of membranes for low-slope roofs?

A

Built-up roof membrane
Single-ply membranes
Fluid-applied membranes

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13
Q

What is built-up roof membrane?

A

2-4 layers of asphalt felt imbedded in bitumen; applied hot and merges into singe membrane

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14
Q

What are single-ply membranes and the two types?

A

Affixed to roof deck by adhesives, ballast or fasteners

Thermoplastic - softened by heat and welded at seams
Thermosetting - cannot be softened so joined by adhesive

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15
Q

What are fluid applied membranes and where are they used?

A

Liquid coats applied with roller/spray gun cure to form rubbery membrane
Used for complex shapes eg. domes

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16
Q

What is a potential problem with fluid applied membranes?

A

They create moisture barriers but if there is a failure and moisture gets in, it causes leaky building

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17
Q

What are the two ways ‘flat’ roofs can be drained?

A

Outer edge towards external gutters

Internal roof drains in roof

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18
Q

How can slopes be created in roofs?

A

Roof structure is sloped
Sloped topping screed on flat roof deck
Tapered insulation on flat deck

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19
Q

What is glass made of?

A

Sand mixed with other materials, heated into a liquid then cooled

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20
Q

What are the 8 types of glass?

A 
Annealed
Tempered
Heat-strengthened
Laminated
Spandrel
Tinted and reflective
Insulating
Low emissivity
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21
Q

What is annealed glass?

A

Cooled slowly in controlled conditions so breaks into large shards

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22
Q

What is tempered glass?

A

Edges cooled rapidly (compression) and core cooled slowly (tension); breaks into small square sections

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23
Q

How much stronger is tempered glass than annealed glass?

A

4 times

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24
Q

How does heat strengthened glass compare to annealed/tempered?

A

2 times stronger than annealed so used when higher stressed but do not require safety factor of tempered

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25
Q

What is laminated glass, what happens when it breaks and where can it be used?

A

Two sheets of glass with a layer of PVB in between not as strong as annealed
Broken shards hold together
Skylights, bullet proof glass

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26
Q

What is spandrel glass?

A

Opaque glass that covers spandrel areas, hiding features

27
Q

What is tinted and reflective light?

A

Chemicals added to reduce glare and solar heat gain; heat absorbed and radiated inside

28
Q

What is the visible light transmission in tinted glass and compared to clear glass?

A

Tinted - 14%-75%

Clear glass- 85%

29
Q

How is heat reducing glass compared?

A

Glazing luminous efficacy (Ke) measures energy-conserving potential; how much heat is blocked compared to light

30
Q

What is reflective coated glass?

A

A type of tinted and reflective glass with metal films attached to the surface which blocks heat and light (lowest Ke)

31
Q

What is insulating glass?

A

Sheets of glass separated by air/gas to improve insulation

32
Q

What is low-emissivity glass?

A

Glass with a metallic coating which reflects light and infrared

33
Q

Why is triple glazing losing its market?

A

Because it is the same as double glazing with a coat of low-emissivity which is much less bulky

34
Q

How is exterior cladding supported?

A

At each storey by the frame

35
Q

What do curtain walls support?

A

Internal portion supports loads and external portion does not support any loads

36
Q

What are the primary functions of cladding?

A

Keeping water out
Preventing air leakage
Controlling light, heat radiation, heat conduction and sound

37
Q

What are the conditions required for water to penetrate cladding?

A

Water present at outer face
Opening for water to pass through
Force to move water through opening

38
Q

How are walls made watertight?

A

Keeping water away from the wall - deep overhangs but unavoidable in high rise

Barrier wall approach to eliminate openings - covering gaps but requires secondary defences eg. drainage

Eliminate or neutralise forces

39
Q

What are the 5 forces that can move water through an opening and how are they overcome?

A

Gravity - do not slope inwards
Momentum - cover over joints or labyrinth
Surface tension - provide a drip
Capillary action - opening wider than a water drop so it cannot bridge it
Air pressure differences - rainscreen

40
Q

What is surface tension?

A

Water can move horizontally by holding on to a surface

41
Q

What is capillary action?

A

Water travelling horizontally through small openings by ‘holding on’ to both sides

42
Q

How does air pressure differences move water?

A

If pressure is different, wide travels through and can carry water

43
Q

What is a rainscreen and how does it work?

A

Air barrier against back up wall which equalises pressure between inside and outside with small air currents that pass in and out

44
Q

Why must air pressure systems be compartmentalised?

A

To accommodate for different air pressures at different parts of the building cladding

45
Q

What are the secondary functions of cladding?

A 
Resisting wind forces
Controlling water vapour
Adjusting to movement (thermal, moisture, structural)
Resisting fire
Weathering gracefully
Ease of installation
46
Q

What are 5 cladding systems?

A 
Masonry veneer
Stone panels mounted on steel subframe
Stone cladding on steel trusses
Precast concrete curtain walls
Metal (aluminium) and glass
47
Q

How does masonry veneer cladding work?

A

Supported on a steel shelf angle (each storey) and tied to a structural back up wall with brick ties

48
Q

What are two types of structural backup wall used in masonry veneer cladding?

A

Concrete masonry unit (CMU) - preferred, stronger

Light-gauge steel frame - lightweight, deflection

49
Q

Where are soft joints placed in a masonry veneer cladding system and what do they do?

A

At the bottom of shelf angle and vertically at regular intervals
Allows independent movement of veneer and frame

50
Q

What must be put in masonry veneer cladding to allow moisture to escape and from where?

A

Weep holes

The air cavity between the veneer and the backup wall

51
Q

What makes up a stone panels mounted on steel subframe cladding system?

A

Vertical steel members transfer vertical and horizontal loads from panels to frame
Horizontal aluminium fits in slots on panels
Gaps filled with backer rods and sealant
Non-structural backup wall provides air barrier for thermal insulation, wiring, interior finish

52
Q

What makes up a stone cladding on steel trusses cladding system?

A

Prefabricated sheets of stone mounted on structural steel trusses (transfers load to frame)
Sealant, backer rods, non-structural backup wall

53
Q

What makes up a precast concrete curtain wall cladding system?

A

Precast panels (rebar or prestressing) typically full floor height and adds considerable load to building frame

54
Q

Why is aluminium the metal of choice in a metal and glass cladding system?

A

Protects against corrosion and can have a variety of surface finishes and shapes

55
Q

What are thermal breaks?

A

Put in aluminium to reduce rapid conduction of heat and avoid condensation inside

56
Q

What are the modes of assembly for a metal and glass cladding system?

A

Stick system
Unit system
Panel system
Column-cover-and-spandrel system

57
Q

What is a stick system and what are the components?

A

Shipped in low bulk pieces and assembled on site

Vertical mullions
Horizontal rails
Spandrel panel
Glass
Interior mullen trim
58
Q

What is a unit system?

A

Factory assembled large shipping bulk erected by crane

59
Q

What is a panel system?

A

Homogeneous units formed from metal sheet with custom-made die/mould; economical for large number of identical panels and has large shipping bulk

60
Q

What is a column-cover-and-spandrel system and what are the components?

A

Custom design each time

Column cover section
Spandrel panel
Glazing infill

61
Q

How can glazing be installed?

A

Inside or outside (inside for taller buildings - bottom half of mullion installed after glass)

62
Q

How does the rainscreen principle apply to a metal and glass cladding system?

A

Outer and inner gaskets in mullions and horizontal rails to stop water penetration; inner gasket if outer fails, acts as an air barrier
Water drained through weep holes

63
Q

Why must a metal and glass cladding system provide for thermal expansion and how is it done?

A

Aluminium expands twice as much as glass during thermal expansion

Gaskets provide flexibility between glass and aluminium
Vertical - telescoping joints
Horizontal - rails cut shorter (interrupted by mullions; mullions cannot be cut because they are continuous over the building)

PROPERTY281 Test 1 (12 decks)

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