Passive Design Principles: Orientation, Shading, Ventilation & Thermal Mass

Passive design uses the natural environment — sun, wind, shade and thermal mass — to heat, cool and light your home with minimal mechanical energy. Good passive design reduces heating and cooling bills, improves comfort and can reduce the size (and cost) of your air conditioning system. While passive design is largely determined by your house plan, understanding the principles helps you review plans and work with your builder.

Orientation

In Australia (southern hemisphere), the sun tracks through the north. Orientation is the most important passive design element:

• North-facing living areas — receive warm, consistent sun year-round; ideal for living rooms, dining and kitchens; provides passive solar heating in winter
• South-facing rooms — receive cool, indirect light; good for bedrooms (cooler in summer) and studies; minimal heat gain
• East-facing rooms — receive morning sun; good for breakfast areas and bedrooms (warm in the morning)
• West-facing rooms — receive hot afternoon sun; can overheat in summer; minimise windows or use shading

Shading

Correctly sized shading blocks summer sun (high angle) while allowing winter sun (low angle) to enter:

• Eaves — correctly sized eaves shade north windows in summer but let in winter sun; the ideal eave depth depends on window height and latitude
• Pergolas — shade east and west windows; can be deciduous (vines) for seasonal shading
• External blinds — shade west and east windows; retractable for winter sun
• Trees — deciduous trees provide shade in summer and allow sun in winter
• Screens — lattice or slatted screens filter sun while allowing airflow

Cross-Ventilation

Cross-ventilation cools the home naturally by allowing breezes to flow through:

• Windows on opposite walls — air enters one side and exits the other; the most effective cross-ventilation
• Windows on adjacent walls — air flows around a corner; effective in L-shaped rooms
• High and low openings — warm air rises and escapes through high openings (clerestory windows, skylights); cool air enters through low openings
• Casement windows on the breeze side — catch breezes and direct them inside; awning windows on the opposite side let air out
• Stack effect — in two-storey homes, warm air rises and escapes through upstairs windows, drawing cool air in downstairs

Thermal Mass

Thermal mass absorbs heat during the day and releases it at night, moderating temperature swings:

• Concrete slab — a concrete floor slab is the most common thermal mass in Australian homes; absorbs heat during the day and releases it at night
• Brick walls — internal brick walls provide thermal mass; external brick veneer provides some mass
• Stone — stone floors or feature walls provide high thermal mass
• Tile flooring — tiles on a concrete slab provide good thermal mass; carpet insulates and reduces mass effectiveness

Working With Your Builder

Passive design is largely determined by your house plan. When reviewing plans with your builder:

• Check which direction living areas face — north is ideal; east is good; avoid west
• Check window placement — are windows on opposite walls for cross-ventilation?
• Check eave sizing — are eaves deep enough to shade north windows in summer?
• Check west-facing windows — are they minimised or shaded?
• Ask about plan modifications — can the plan be flipped or rotated to improve orientation?
• Consider insulation and sealing — even with good passive design, insulation and draught sealing are essential

Frequently Asked Questions