week 9 Flashcards
(20 cards)
What defines a flat roof versus a pitched roof?
A flat roof is horizontal or has a slope of less than 10°, while a pitched roof has a sloping surface in one or more directions.
How do climate and weather influence the choice between flat and pitched roofs?
Flat roofs suit dry, hot climates; pitched roofs are preferred in areas with heavy rainfall to shed water effectively.
How are roof structures classified by structural principles?
Roofs are either two-dimensional (spanning mainly in length and depth) or three-dimensional (utilizing length, depth, and breadth to cover larger spans).
What are the typical roof span categories?
Short span (up to 7.6 m), medium span (7.6–24.4 m), and long span (over 24.4 m), with short spans being cheaper and long spans needing structural engineering.
What are common types of pitched roofs?
symmetrical pitch, asymmetrical pitch, mono-pitch, butterfly roof, and lean-to roof, with symmetrical being the most common.
What is a couple roof and what is its structural limitation?
A couple roof uses a pair of rafters pinned at the ridge, which can exert outward thrust on walls under load, risking wall failure.
What characterizes a close couple roof?
Timber trusses are prefabricated, triangulated frames that span entire building widths without needing internal loadbearing walls, unlike traditional cut roofs.
What are the advantages of steel trussed roofs?
Steel trusses provide strength and uniformity for spans up to 15 m, resist warping, are easier to install with modern fixings, and support various roof types.
How does a timber trussed roof differ from traditional cut roofs?
Timber trusses are prefabricated, triangulated frames that span entire building widths without needing internal loadbearing walls, unlike traditional cut roofs.
What are the pros and cons of flat roofs, especially timber and steel flat roofs?
Flat roofs are cheaper, quicker to build, and easier to maintain but are harder to waterproof and prone to leakage; timber flat roofs need joists and fall grading, while steel flat roofs are more durable and dimensionally stable.
What is the primary function of wall cladding on a building?
Wall cladding serves as the external decorative ‘skin’ of a building that provides weather resistance, thermal and acoustic insulation, fire protection, and aesthetic appeal.
What are the two main components of a wall cladding system?
The two components are:
The load-bearing wall system (e.g., lightweight steel or timber framing)
The non-load bearing cladding sheets made from various materials like brick, cement, timber, steel, aluminum, glass, plastics, or vinyl.
Which factors influence the selection of a wall cladding system?
Factors include: material availability, cost, aesthetics, exposure classification (environmental conditions), climatic zones, and compliance with safety, quality, and sustainability standards such as NCC 2022 and AS 1530.4:2014.
What are the critical design loads that wall cladding must resist?
Wall cladding must resist dynamic loads like wind pressure (most critical) and static loads such as the dead load from the weight of the cladding itself.
Why is fire resistance important in selecting cladding materials?
Fire resistance ensures occupant safety by preventing or delaying fire spread. Cladding materials must meet specific Fire Resistance Levels (FRL) such as 90/90/90 according to AS 1530.4:2014 and comply with NCC 2022 fire hazard provisions.
What are the performance considerations when selecting wall cladding?
Key considerations include availability and cost, durability in various environments, fire resistance, weatherproofing quality, breathability (vapour control), embodied energy (sustainability), and thermal/acoustic insulation properties.
What are the advantages and limitations of timber cladding?
Advantages: natural aesthetic, durability (especially hardwood), thermal insulation, and sustainability through carbon reduction.
Limitations: higher maintenance, susceptibility to termites and bushfire risks requiring fire-resistant timber per AS 3959:2018
Why is cold formed steel popular for cladding, and what are its characteristics?
Cold formed steel is popular due to its high strength-to-weight ratio, fire resistance, termite resistance, durability, and sustainability through recycled content. However, it requires corrosion protection and has higher thermal conductivity than timber
What concerns exist around Aluminium Composite Panels (ACPs) in cladding?
Although aluminium is non-combustible, many ACPs contain a flammable polymer core (like polyethylene), posing significant fire risks. Due to past fires (e.g., Lacrosse Tower, Grenfell Tower), polyethylene core ACPs are banned in several Australian states for external cladding.
How do standards and regulations ensure cladding safety and performance?
Standards like AS 3959, AS 1530.4, AS 4055, and NCC 2022 set performance criteria for fire resistance, wind load design, weatherproofing, and material quality. Government regulations also govern installation, fire hazard ratings, and material approvals to enhance safety and durability.
