Where you put windows, and which way they face, changes how hard your aircon works. Planning them well can reduce the heat before you pay for cooling it.

We give no savings figures. Results depend on your plan, orientation, use and equipment, and your designer should size choices for your house.

01Think about direction

Windows facing east and west let in low sun that is hard to block. Windows facing north and south are often easier to shade.

Ask your designer which way each window faces and what shades it. Direction decides how hard a window is to shade. Example: a window facing west gets low afternoon sun that a short overhang cannot block. Why this works: choosing positions early lets the design use the easy sides for glass.

02Size and number

More glass is not always better. Large openings on the hot side can add heat and glare, while smaller openings can still give light and air.

Ask your designer to explain why each window is the size it is. Window size should follow need, not habit. Example: a smaller window placed high on a hot wall can still bring in light and let hot air out. Why this works: you keep the light and air while limiting the heat that enters.

03Glass and shading

The type of glass, the frame and the shading all matter. Overhangs, screens and blinds can reduce the heat that reaches the room.

Ask for the shading to be drawn on the elevations, so you can see it before it is built. Shading is easier to judge when you can see it. Example: an elevation that shows the overhang over each window helps you notice where a window will stay in sun. Why this works: you can fix a problem on paper, where changes cost nothing.

04Help the aircon

Rooms with aircon need tight doors and windows, and the aircon should not fight with open openings. Ask which rooms will be cooled and how they are sealed.

Keep the aircon unit and its pipes in a place that is easy to service. Aircon works best in a sealed room. Example: a bedroom with a window left slightly open lets cooled air escape and raises the bill. Why this works: planning which rooms are cooled lets you seal only those rooms and keep the others open to air.

05Mind privacy and security

Windows must also protect privacy and keep the house secure. Ask your designer about screens, grilles and frosted panels where they are needed.

A well-placed window can give light and air without exposing the room to the street.

Windows also affect resale and daily life. Ask your designer to explain how each opening will feel from the inside, not only how it looks from the street. Windows are a balance between light, air, privacy and safety. Example: a frosted panel on a street-facing bathroom window gives privacy while keeping daylight. Why this works: deciding the trade-offs on paper avoids retrofits after the house is built.

06Questions for your designer