Protection (T4) Flashcards
1
Q
Building as a system
A
requires designers to consider the interactions between the for primary elements comprising the system
2
Q
protection for buildings
A
- Building envelope (enclosure system)
- Occupants (humans, animals and/or plants)
- Building services (electrical/mechanical systems)
- External environment (site with its landscape and services infrastructure and micro-climate)
3
Q
Integrated dynamic system
A
- Large number of materials, components equipment, and assemblies must be properly integrated or achieve a high-performance building
- Most performance problems involve the building envelope.
4
Q
Functions of the building envelope
A
- Waterproof to wind-driven moisture
- Permit access in and views out
- Admit natural light
- Avoid summer overheating
- Retain heat in winter
- Be free from damp and condensation
- Provide adequate ventilation
- Permit entry of electricity, fuel and water supplies and exit of waste
- Provides structural support
5
Q
Physical mechanisms associated with climate and weather
A
For primary mechanisms
- Heat flow = conductive, convective and radiative
- Air flow = air flow across and within the building envelope due to air leakage and ventilation
- Moisture flow = flow of water and vapor across and within the building envelope
- Solar radiation = influence of solar radiation on the opaque and transparent envelope components
6
Q
Rain and moisture penetration
A
- Includes moisture vapour and snow
- Permanent damage mainly occurs to finishes rather than the construction (unless major errors are made)
- In solid walled construction rainwater soaks in, spreads and then evaporates
- Traditional details seek to protect vulnerable aspects & locations
- Long term water penetration associated with timber failure (rot) and corrosion of metallic components
- Guidance available in Building Regulations Part C2 - resistance to moisture
7
Q
Factors affecting ‘as-designed’ envelope performance
Regulatory and planning constraints which must be considered
A
- Structure
Approved document part A – structure (loading, ground movement, disproportionate collapse) - Containment of fire
- Approved documents part B – fire safely
- British standards e.g. BS 476-10:2009
- Conservation of fuel and power
- Approved document L (specifies backstop U-values and minimum carbon compliance targets)
- Ventilation
- Approved document F (specifies acceptable means of ventilation and minimum rates)
8
Q
Factor’s affecting ‘as-built’ envelope performance
A
- Integrated design must consider real-world constraints inclosing construction methods, buildability and quality control during construction phase
Quality assurance = two main objectives - Clean robust brief, integrate quality control during design and construction
- Construction sequencing, on-site checks, compliance testing
9
Q
House construction methods
A
- ‘traditional’ methods = typically masonry
- Modern methods of construction (MMC)= offsite manufacturing
- Others = alternative, hybrid, natural or more sustainable
10
Q
Traditional methods of construction
A
- Masonry = defined as brick and block construction
- Built in situ using fired clay bricks or concrete blocks and mortar
11
Q
MMC
A
- Off-site production methods
- Advantage = factory conditions, fewer material delivers, reduced construction time, reduced labour, reduced energy use
- Model: timber, straw and hemp panel system that can be produced, then delivered and erected on-site.
- Timber ‘cassettes‘(e.g. Facet Homes); major components of superstructure are manufactured offsite
- Structural insulated panel (SIP) are a lightweight sandwich construction method
- Common aim = reduction in construction time on site
12
Q
Insulating cavity walls
A
- HW block – 100mm filled cavity = U=0.32 W/m2K
- LW block, 75mm filled cavity U=0.35 W/m2K
- Remedial filled cavity wall
- Installer drills a small hole then blows insulation into the cavity, when finished they will then fill the holes
13
Q
Timber frame detail
A
- Mineral wool insulated stud wall system
- Polystyrene foam insulated floor system
- External wind barrier membrane
14
Q
Suspended concrete floor (‘block and beam’)
A
- Used in areas with a high-water table or on sloping sites
- Usually insulated internally
- Continuous external insulation retains the thermal mass of the floor slab with in the thermal envelope
15
Q
Roof insulation
A
- Cheap
- Easy to apply
- Cost effective
- Thickness 150mm
- U-value ≈0.25W/m2K
16
Q
Thermal conductivity
A
Thermal conductivity (𝝀) and thermal resistance (𝑹) are inversely related, so the higher the conductivity the lower the resistance will be
17
Q
Conductivity
A
The rate of one-dimensional heat flow through a linear depth of a uniform material of thickness 𝑥 [m], per unit temperature difference [K]
Units: [W/ (m.K)] 𝜆
18
Q
Thermal Resistance (𝑹)
A
A measure of the resistance to heat flow through unit area of a material of thickness (𝑥).
R = x/𝜆
19
Q
u-value
A
- Inverse of the R value
- Overall thermal transmittance through a wall is referred to as the wall U-value
- Unit: W/m2K
- Rate of heat flow, through a 1m2 area of a homogenous layered structure per degree [K] temperature difference
- The U-value includes both heat conduction through the solid layers of the materials as well as the convective transfer occurring due to the air boundary layer at the surface(s) of the construction
20
Q
Conductivity
A
- The thermal conductivities of inert gases such as argon can vary by a factor of 104 from those of pure metals such as copper.
- Pure crystals and metals have the highest thermal conductivities and gases and insulating materials the lowest
21
Q
Building envelope = areas of heat loss
A
- Non-insulated roof
- Failing windows
- Single pane windows
- Poor sir-tightness sealing
- Thermal bridges across insulation plane
- Moisture damage to insulation
- Uninsulated cavities or solid masonry walls
22
Q
conclusion 1
A
- Insulation is the key to reducing the heating energy demand of dwellings in temperate (UK) and cold climates (e.g. Northern Europe).
- Ventilation is essential, but this should not be via leaks in the thermal envelope.
- Masonry construction predominates in many countries but timber frame is more common in others, and is increasing in the UK, detailing is critical.
- Thermal bridges and unwanted infiltration (air leakage) must be avoided.
23
Q
conclusion 2
A
- Post-completion testing is increasingly undertaken – buildings need to perform in accordance with the design intent
- House builders struggle to build to the minimum standards set by Building Regulations, designs need to be checked for buildability and quality assurance procedures implemented.
