Designing cross-ventilation through window placement

A client has a new home with generous glass, and the living room is still hot by late afternoon in summer. The windows are there. On the plan the openings look generous, and yet the air hardly moves once the doors are shut. The problem is usually not the number of windows. It is where they are, and whether there is a path for the air to travel through the house from one side to the other.

Cross-ventilation is the movement of air through a space from one opening to another. It is driven by pressure differences that the wind creates on the outside of the building, and by temperature differences that make warm air rise and escape through the high openings. The layout decides whether the air actually crosses the room or simply swirls in the opening nearest the breeze and out again. A builder who understands that can explain a design to a client without reaching for a fan or an air conditioner as the answer to every complaint.

The organising idea of this article is that a room only ventilates well when air has a route in and a route out. The sections below cover the layout decisions, the opening types, the internal route through the house and the mistakes that make a design look right on paper and perform badly once it is lived in. The passive design guidance from the Australian Government’s Your Home resource covers the wider principles. The notes here are about the decisions a builder makes at the design review and on site, before the frame goes up.

Why a breeze needs two openings to do anything useful

When wind meets the face of a building, the pressure on that face rises, and the pressure on the sheltered face falls. Air moves from the high side to the low side, so an opening on the windward wall and another on the leeward wall create a flow through the room. A single window on one wall does far less. Air comes in through the opening and goes back out through the same opening, and most of the room is left where it was. The air is moving, but it is not crossing the space where the people are.

Two openings on adjacent walls can work too, particularly when the wind arrives at an angle to the house. The rule is that the air needs a path from one opening to the other, and the room needs to sit on that path. A room that is open to the breeze on one side and closed on the other is a room that will feel stuffy by the end of a hot day, however large its windows are.

Wind is not the only driver. Warm air is lighter than cool air, so when the room heats up, the warm air collects at the top and wants to leave. A high opening lets it go, and cooler air is drawn in through the lower openings to replace it. This is the stack effect, and it is why a house can move air on a still night when no breeze is blowing at all. It is also the basis of night cooling, where the openings are used to flush the heat out of the building once the outside air has cooled, rather than to hold the heat in until the next afternoon.

Placing the inlets low and the outlets high

The openings that bring air in should sit low in the room, where the people sit and sleep. Cooler air is heavier and it settles low, so an inlet at the bottom of the wall brings the breeze across the body and not over the head. The openings that let air out should sit higher, on the far side, so the warm air collected under the ceiling has a route to leave. A layout that puts both openings at the same height on the same wall is the most common cause of a room that feels still.

The size of the openings matters as well as their position. The flow through a room is limited by the smallest free opening in its path, not by the largest. A big window on the inlet side will not do much if the outlet on the opposite wall is a narrow louvre that cannot pass the air that is coming in. The builder should check the free area on each side, meaning the part of the opening that actually lets air through when it is open, and match the two sides as closely as the design allows.

Placement also depends on the room’s use. A bedroom that is ventilated well during the day may still need its outlet placed so that a sleeper is not in the direct draught, and the designer should think about where the bed will sit as well as where the window will open. A living room that is used in the evening is better served by an inlet on the side that catches the afternoon breeze, with the outlet placed to draw the air through the seating area.

Choosing opening types that let air through

Two windows of the same size can perform very differently, because the free area depends on how the window opens. A sliding window, for example, opens only part of its frame at a time, so the air passes through a limited gap even when the window looks fully open from the street. An awning or casement that opens outward can present most of its frame to the breeze. A louvre opens along its length and can be angled to catch the air. The table below sets out the common types and what each one does for airflow.

Fixed panes have a place in the design, usually for the view and the light, but they are not vents and should not be counted as one when the free area is worked out. Fly screens also reduce the free area, and a heavy security screen placed over an outlet can cut the flow more than the builder expects. Specify screens that let the air through, and check the hardware so the window can be held fully open in the position the design relies on. A window that cannot be held open at the right angle is a window that will be closed by the owner, usually at the first hot afternoon.

Doors count too. A glazed sliding door opens a large part of the wall when it is fully open, and it can be the best outlet or inlet in the house. The same door, kept shut for security or because the owner forgets, can block the route entirely. Where a door is part of the airflow design, say so in the handover notes and think about whether a louvred door or a door fitted with a hold-open device will keep the route clear.

The internal route is part of the design

Air does not stop at the room with the window in it. It travels through the house, and every internal door, hallway and step is part of the route. In an open-plan house the living area is one room and the air moves easily across it. In a house with a series of closed rooms, the air that enters the living room has to go somewhere, and if the only way out is through a closed door, the flow stops. The layout should make the route from the inlet to the outlet clear, and it should not depend on the owner leaving a door open.

Stairwells can help. Warm air rising in a stairwell collects at the top, and a high opening or roof light above the stair can draw air through the lower floor on its way out. The same principle works with a high vent in a hallway that connects the rooms. The mistake is to design a stairwell that is closed off by a door at the bottom, or a hallway that ends in a closed bedroom with no other way out.

Matching the layout to the site and the breezes

A generic plan cannot tell you where the breezes come from, so the design has to start with the site. Note which way the warm-season winds usually arrive, and look at what sits between the house and those winds. Neighbouring buildings, fences, mature trees and the terrain can all block a breeze that would otherwise reach the house. A lot that looks open from the street may be sheltered on the side that matters most.

Once the breezes are known, the layout can be set. The main living rooms and the bedrooms that are used most in warm weather should sit on the path of the breeze, with inlets on the side that catches it and outlets on the sheltered side. Rooms that are used less, such as a laundry or a storeroom, can be placed where they do not block the route. The aim is a layout where the cooling air has a clear line through the spaces people actually occupy.

Each step leaves a record that the designer and the owner can check. The site notes show why the openings were placed as they were, the sketch shows the route, and the schedule of openings shows the free area on each side. If the owner later asks why a room is hotter than expected, the file answers the question rather than leaving it to guesswork about the installer.

Glazing and shading come before the airflow

Ventilation can move heat out of a building, but it cannot stop heat arriving through glass that faces the afternoon sun. A large west-facing window will let in heat that the openings then have to remove, and on the hottest days the openings may not be enough. The guidance on windows, doors and skylights from Your Home is clear that the glass choice and the shading shape how much heat enters the building in the first place. Good airflow is the second line of defence, not the first.

That is why the window placement and the shading should be designed together. Eaves, external blinds, screens and landscaping can keep the sun off the glass while the openings keep the air moving. A builder who designs the openings for airflow and then leaves the glass unshaded has solved half the problem. The client will blame the ventilation, and the ventilation will not be the cause.

Working in heat on the site

The same principle matters on the site. A building that has good through-airflow is easier to work in during the build, and a crew working in a shed-like frame with no openings will feel the heat much sooner. Airflow is not a substitute for the controls the work requires, though. The Safe Work Australia guidance on working in heat sets out the expectations for managing heat exposure, including water, shade, breaks and the way the work is planned. A breeze through the frame helps, but it does not replace a plan for the hottest part of the day.

A worked example from a Hunter region project

A builder in the Hunter region has finished a slab-on-ground house for a family with two children. The openings are on the street side, which is where the designer placed the living room and the view. In the first summer the owner reports that the rear rooms are hot until late in the evening, and that the living room is uncomfortable in the afternoon. The builder visits on a still evening and finds that the only openings that can take a breeze are on one wall.

The builder proposes two changes. A louvred window goes into the rear wall of the living room, low on the wall and placed on the path of the afternoon breeze. A high vent is added in the hallway, and the internal door between the living room and the hallway is fitted with a hold-open device so it stays clear. The owner also agrees to fit external shading on the west-facing glass, which the builder had raised at handover and the owner had put off.

The changes are small beside the cost and disruption of reopening a finished wall. The lesson the builder takes to the next design review is simple. Openings that face the view will be used, but openings on the breeze side will move the air. A house that is designed to be cooled naturally needs both.

Checking the design before the frame goes up

The design review is the cheapest place to catch a layout that will not ventilate. Before the frame is set, the builder can walk the plan with the designer and the owner and check the route from the inlet to the outlet in each main room. The review does not need specialist software. It needs the plan, the site notes and a clear view of the openings that will be used.

• Does each main room have openings on two faces, or on adjacent walls that can catch the breeze?
• Are the inlets low and the outlets high, with the outlets on the far side from the inlets?
• Is the free area on the outlet side matched to the inlet side, and do the screens and hardware keep it open?
• Does the route through the house stay clear when the doors are shut, or does it depend on the owner?
• Has the glazing been shaded so the openings are not asked to remove heat that should never have entered?

Fans are a separate question, and the decision about ceiling fans is covered in ceiling fans and passive cooling. A fan moves air that is already in the room, so it works best when the layout has already got air moving through the building. Mechanical ventilation and heat recovery systems are another separate question, covered in mechanical ventilation and heat recovery in homes. The window layout is the foundation both of those systems depend on.

For the wider picture of how builders keep their own knowledge current in NSW, the PointCPD guide to how NSW builder CPD works sets out the topics and the records that go with them.

Questions builders ask

• Passive design
• Ventilation
• Windows

Published 3 October 2026. General information for builders, not legal, financial or engineering advice for a specific job. Check current requirements with the relevant regulator or standard before relying on them.