Background ventilation in old buildings came from chimneys and naturally air-leaky construction
Higher sealing standards, such as Passivhaus, drive down construction air-leakage to avoid heat loss .
3 Modern buildings are heavily insulated to retain heat
Some Causes of Overheating
1 Uncontrolled Solar gain through windows / glazing
Solar radiation passes through the glazing and heats objects and surfaces - in-turn, they emit heat to raise the overall room temperature.
2 'Caravan Syndrome':
Summer overheating through conventional construction
Holiday caravans rapidly overheat when exposed to constant summer solar radiation
A contemporary shaded or un / intermittently sun-lit timber frame wall
Within the context of the current climate, conventional walls cause few overheating problems.
The same wall circa 2050 subject to increasingly constant solar radiation
• Walls of conventional timber frame construction including mineral fibre infill insulation are likely to be problematic as climate change results in more intense summers.
• In addition to high ambient summer temperatures, constant exposure to solar radiation heats up the surface of the brickwork and, through conduction, transfers the heat to the space within.
• Time taken for the heat to appear on the inside of the wall will be typically 7 hours - resulting in overheating during the late afternoon and early evening.
• In transferring the heat to the interior during the warm daylight hours, the construction type provides inadequate thermal buffering / lag /decrement delay
Even conventional masonry cavity walls will be subject to overheating
Chronic overheating is more pronounced in roof spaces
• Loft spaces have always been subject to high temperatures in summer
• The Sun's angle of incidence is closer to the perpendicular - causing more intense radiation
• Rooms in the roof have accentuated the problems of heat transfer through lightweight fabric and structure
3 Internal Gains
People, Appliances, Lighting
4 Inadequate or poorly controlled Ventilation
Some buildings have no, or ill-conceived, ventilation systems
The noise and fumes from adjacent traffic inhibit the opening of windows
Ventilation rates through the century:
Home ventilation rate circa 1900 = 2.0 air changes per hour (ACH)
Home ventilation rate circa 1970 = 0.7 ACH
Home to Passivhaus standard 2015 controlled ventilation rate = 0.4 ACH
5 The urban 'Heat Island Effect'
Heat absorbed by the urban fabric during the day is re-radiated during the night - providing little respite from a hot atmosphere.
In turn, purging ventilation through buildings works barely at all where there is so little difference between inside and outside temperatures.
Windows to the front elevations of these two identical 1960s houses are subject to very different amounts of solar gain during the day
House types are often repeated throughout a 'housing estate'.
It is likely that one type template will be located facing in a number of different directions.
Windows facing the SW and W are likely to experience higher levels of solar gain penetration than other orientations late in the day.
6 Exposed thermal mass without the potential of night time 'purging' ventilation
The sun's radiation is absorbed into exposed thermal mass eg stone tile flooring
When the room temperature drops at night the heat is re-emitted
If ventilation is unavailable the heat will be trapped overnight in a well-insulated, well-sealed building.