Stack effect
As air gets warmer it becomes less dense and so more buoyant. This means that warm air has a tendency to rise.
This effect can be used to naturally ventilate buildings. Cooler outside air is drawn into buildings at a lower level, it is warmed by sources of heat within the building (such as people, equipment, heating and solar gain), and then rises through the building to vent out at a higher level.
A positive pressure area is created at the top of a building and negative pressure area at the bottom. This process can take place without mechanical assistance, simply by introducing openings at the bottom and the top of buildings. It is known as the stack effect or stack ventilation.
Stack ventilation can be particularly effective as a means of naturally ventilating tall buildings that include vertical spaces which rise throughout their height, for example buildings with central atriums. This can be useful in deep buildings, where cross ventilation may not be sufficient to penetrate to spaces in the heart of the building.
The effectiveness of stack ventilation is influenced by:
- The effective area of openings.
- The height of the stack.
- The temperature difference between the bottom and the top of the stack.
- Pressure differences outside the building.
The stack effect is a relatively weak force in many buildings (although it can be strong enough to fly a kite in large buildings) and so it may be necessary to have large openings with minimal resistance.
The pressure will vary through the height of the building, with the outside pressure being higher than the inside pressure at the bottom of the building, but the inside pressure being higher at the top. As a consequence, there will be a neutral plane, which is the level at which the internal and external pressure are equal. Above the neutral plane the internal air pressure will be positive and so air will tend to exhaust to the outside. Below the neutral plane, the internal air pressure will be negative and air will tend to be drawn into the building. This requires careful design to ensure that the neutral plane is above the spaces that need to be ventilated from the outside.
Stack ventilation is not appropriate for all building types, and as the stack effect requires that the internal temperature is higher than the outside temperature, it may not always provide a sufficient cooling effect by itself and additional mechanical cooling may be necessary. In particular, rooms adjoining the warmer part of the stack may experience poor ventilation and unwanted heat gains. In addition, there may be conflicts between the requirement for large unrestricted openings between the outside and the heart of the building, and requirements for security, privacy, noise control, fire compartmentation, and so on.
Designing natural ventilation can become extremely complex because of the interaction between cross ventilation and the stack effect as well as complex building geometries and complex distribution of openings. This can require computer analysis.
NB: Approved document F, Ventilation, defines 'passive stack ventilation' (PSV) as, ‘…a ventilation system using ducts from terminals in the ceiling of rooms to terminals on the roof that extract air to the outside by a combination of the natural stack effect and the pressure effects of wind passing over the roof of the building.’
NB: Stack ventilation can also refer to secondary ventilation stacks used to overcome air pressure changes in pipework in high-rise buildings. For more information see: Secondary ventilation stacks in tall buildings.
[edit] Related articles on Designing Buildings
- Computational fluid dynamics.
- Cross ventilation.
- Dynamic thermal modelling of closed loop geothermal heat pump systems.
- Energy targets.
- Face velocity.
- Natural ventilation.
- Passive building design.
- Secondary ventilation stacks in tall buildings.
- Single-sided ventilation.
- Solar chimney.
- Thermal comfort.
- Types of ventilation.
- U-values.
- Natural ventilation.
- Ventilation.
- Warm roof.
- Windcatcher.
Featured articles and news
The UK's Modern Industrial Strategy: A 10 year plan
Previous consultation criticism, current key elements and general support with some persisting reservations.
Building Safety Regulator reforms
New roles, new staff and a new fast track service pave the way for a single construction regulator.
Architectural Technologist CPDs and Communications
CIAT CPD… and how you can do it!
Cooling centres and cool spaces
Managing extreme heat in cities by directing the public to places for heat stress relief and water sources.
Winter gardens: A brief history and warm variations
Extending the season with glass in different forms and terms.
Restoring Great Yarmouth's Winter Gardens
Transforming one of the least sustainable constructions imaginable.
Construction Skills Mission Board launch sector drive
Newly formed government and industry collaboration set strategy for recruiting an additional 100,000 construction workers a year.
New Architects Code comes into effect in September 2025
ARB Architects Code of Conduct and Practice available with ongoing consultation regarding guidance.
Welsh Skills Body (Medr) launches ambitious plan
The new skills body brings together funding and regulation of tertiary education and research for the devolved nation.
Paul Gandy FCIOB announced as next CIOB President
Former Tilbury Douglas CEO takes helm.
UK Infrastructure: A 10 Year Strategy. In brief with reactions
With the National Infrastructure and Service Transformation Authority (NISTA).
Ebenezer Howard: inventor of the garden city. Book review.
The Grenfell Tower fire, eight years on
A time to pause and reflect as Dubai tower block fire reported just before anniversary.
Airtightness Topic Guide BSRIA TG 27/2025
Explaining the basics of airtightness, what it is, why it's important, when it's required and how it's carried out.
Construction contract awards hit lowest point of 2025
Plummeting for second consecutive month, intensifying concerns for housing and infrastructure goals.
Understanding Mental Health in the Built Environment 2025
Examining the state of mental health in construction, shedding light on levels of stress, anxiety and depression.
The benefits of engaging with insulation manufacturers
When considering ground floor constructions.
Lighting Industry endorses Blueprint for Electrification
The Lighting Industry Association fully supports the ECA Blueprint as a timely, urgent call to action.