Building science and materials part 2

• Latitude


  Relative distance from the equator
• Latitude


  Affects the length of day and night in different parts of the world
• Angle of the sun to the horizon


  Impacts the heating power and ambient temperature
• Angle of the sun to the horizon increasing


  Increases the intensity of solar radiation
• Areas above 250m contour in the UK


  • Wetter and cooler
  • Have poorer soils
  • Less populated
• South-west winds in the UK

  Stormiest and wettest
• Air masses passing over a hill

  Cooled on rising and precipitate moisture as rain or snow on the weather side
• North-east aspect in the UK

  Exposed to coldest spring winds and winter/spring snowstorms
• Enclosed precincts or sites

  May produce unusual and permanent local wind currents, resulting in upward flow of stormwater on impervious surfaces
• Funnel-shaped valley open to south-west or north-east


  Should be avoided as rain may come from one direction and snow from the other
• Valleys running north and south in the UK

  Drier than those running east to west
• Sites at the foot of steep hills

  Deprived of sunshine in the early morning or late afternoon
• Condition 1: A temperature around freezing combined with a RH of 80% can…

  • cause freeze-thaw cycles, leading to expansion/contraction and potential damage.
• Condition 2: Large daytime temperature swings can…


  • lead to thermal stress, especially for exposed roof structures
  • cause repeated expansion/contraction, which can lead to material fatigue
• Solar radiation heats both the ground and the air above
• Air close to the ground

  Further heated by re-radiation from the ground (low temperature or long-wave radiation)
• Glass

  Relatively opaque to long-wave energy, hence a greenhouse can retain heat at night
• Excessive winds

  • Can cause significant lift over aerofoil shapes
  • Repeated bending and flexing can cause material fatigue
• In the UK the common expected wind speed is about 45mph, but in exposed areas it can be much greater
• Relative Humidity (RH) in the UK

  Normally varies from 50% to 80%
• Vapour pressure


  Difference in moisture content between zones causes moisture migration from warmer to cooler side
• Ground mist


  Flows like slow-moving water to collect in valleys and depressions, lowering temperature to frost level
• High humidity


  Reduces the effectiveness of perspiration (sweat) as a cooling mechanism
• Thermal comfort in sedentary occupations


  • Air temperature 16-22°C
  • Relative humidity 40-70%
  • Air movement 0.15-0.5m/s
• Energy flow through a material

  Measured in watts (W), which is joules per second
• Conductivity (k or λ)


  Material's ability to conduct energy, measured in W/m.K
• Resistance (R)

  Inverse of conductivity, depends on material thickness and conductivity, measured in m²K/W
• U value

  Inverse of total resistance, indicates rate of heat energy passing through per square meter per degree of temperature difference, lower values mean better insulation
• Dew point temperature


  Temperature at which air is saturated (100% capacity), below this condensation will occur
• Measures of humidity

  • Absolute humidity or moisture content
  • Vapour pressure
  • Percentage saturation
  • Relative humidity (RH)
• If air is warmed in mechanical ventilation or air-conditioning without adding moisture, the resultant RH may be unacceptably low
• If air is cooled, the RH may be unacceptably high
• Broad requirements for a comfortable and safe internal environment


  • Dry
  • Warm
  • Light
  • Quiet
  • Clean
  • Secure
  • Private
• Supply and disposal services (utilities) contribute to the active creation of the environment
• The combination of building design (passive fabric) and active fabric solutions can reduce energy use from the active services
• Example of multiple components working together

  • Artificial lighting
  • Natural light
  • Colour of the walls
• Passive fabric - the primary concerns:

  • The properties of the material
  • The dimensions, usually thickness
  • The joins and fixings.
• Active fabric (e.g. windows) - primary concerns:

  • Joints and fixings to ensure operation of moving parts
  • The material, shape and dimensions will be determined by their strength and reliability in use, along with considerations for appearance
  • Some form of control is needed to operate when needed.
• Active services


  • Design discipline in its own right
  • Systems within the system as a whole building
  • Outlet links user with supply or disposal system
  • Considerations for location, connections, appearance, noise, access for maintenance
  • Radiator example, the radiator is the outlet, the active distribution would be via heated water contained in the pipes.
• Performance specification


  Defines the expected performance of a building