Climate and the building
Climate is the usual weather of a place over many years. A good building works with its climate.
- Hot and dry: thick walls, small windows, courtyards, light colours.
- Hot and humid: big shaded openings, raised floors and deep eaves for air flow and rain.
- Cold: thick insulation, compact shape, windows facing the winter sun.
The sun: in summer at noon the sun is high, in winter it is low. A roof overhang (eave) of the right depth blocks high sun and lets low sun in. Orientation means which way the building faces. Thermal mass (heavy walls) slows heat so that rooms stay steady through the day.
Draught and ventilation
Ventilation is planned fresh air through a room. It removes smell, moisture and stale air, and cools us in hot weather.
A draught is unplanned air leaking in through gaps. It makes people feel cold and wastes heating.
- Cross ventilation: wind enters one opening and leaves from another. Place openings on opposite or adjacent walls.
- Stack effect: warm air is lighter, so it rises and leaves by a high opening while cool air enters low. It works even without wind. A taller height gives a stronger pull.
- Mechanical ventilation: fans when natural air is not enough.
How much air? Air changes per hour (ACH) tells how many times the whole room air is replaced in one hour. Fresh air per hour: Q = n × V (m³/h). In litres per second, Q (m³/h) = L/s × 3.6.
Colour in buildings
Colour does three jobs.
- Heat: a light surface reflects most sunlight (high reflectance, for white about 0.8), a dark one absorbs it (reflectance about 0.1). Heat absorbed = (1 − reflectance) × sunlight. A white roof can stay many degrees cooler.
- Light: light walls bounce daylight deeper into a room. Dark walls make a room look dim and need more lamps.
- Feeling and meaning: warm colours (red, orange, yellow) feel lively and close; cool colours (blue, green) feel calm and spacious. Colour also marks exits, danger and direction, and helps people with low vision tell a door from a wall.
Good colour plans mix: a light roof, calm walls in rooms for rest, strong colours for signs.
Try it: cool-roof test
Try it. Put two similar tins in the sun, one wrapped in white paper and one in black paper. Put a thermometer in each (or touch them after 20 minutes). Predict which is hotter, then check. Then use the 3D house and tick the dark roof to see the room temperature go up.
Key formulas and definitions
- Fresh air per hour: Q = n × V (m³/h)
- Air changes per hour: n = Q ÷ V
- Q (m³/h) = Q (L/s) × 3.6
- Heat absorbed = (1 − reflectance) × sunlight
- Units: W/m² for sunlight, m³ for room volume
Worked examples
1. A room 4 m × 5 m × 3 m needs 6 air changes per hour. How much fresh air per hour?
V = 4 × 5 × 3 = 60 m³. Q = n × V = 6 × 60 = 360 m³/h.
2. Sunlight 800 W/m² falls on a white roof (reflects 0.8) and a dark roof (reflects 0.1). Compare the heat absorbed.
White: (1 − 0.8) × 800 = 160 W/m². Dark: (1 − 0.1) × 800 = 720 W/m². The dark roof absorbs 4.5 times more.
3. Four people each need 8 L/s of fresh air in a 48 m³ room. Find the ACH.
4 × 8 = 32 L/s. In m³/h: 32 × 3.6 = 115.2 m³/h. n = 115.2 / 48 = 2.4 air changes per hour.
Common mistakes
- Thinking more windows always means a cooler room: windows on only one wall give little air flow.
- Mixing up draught and ventilation: one is leakage you cannot control, the other is planned.
- Making eaves too deep in a cold place: you then lose the low winter sun.
- Painting a roof a dark colour in a hot place without checking the heat it absorbs.