Trickle Vents - Meeting regulations

The Building Regulations in England and Wales require ‘that there shall be adequate means for ventilation provided for people in the building. It however now differentiates between windows for residential installation in either a Replacement or New build application.

Replacement windows

If the window being removed has trickle vents fitted, then the replacement window should also have them – to the same level of performance.

The ventilators fitted to the replacement window should therefore offer at least the same capacity as the ventilators fitted to the removed window.

Typically these ventilators will be either 4000mm2 or 2000mm2 in their geometric free area.

Where it is not possible to ascertain the capacity of the outgoing vents;

• Habitable rooms should have a minimum of 5000 mm2 EA*
• Wet rooms should have a minimum of 2500 mm2 EA*

*Equivalent Area EA, figures will vary for Scotland, Northern Ireland and Eire.

If the window being removed did not have trickle vents fitted, it is recommended to provide the background ventilation in the replacement window, due to the health benefits.

Additional Guidance for Replacement Windows within England and Wales

The Building Regulations Requirement F1 – Means of ventilation, states:

There shall be adequate means of ventilation provided for people in the building.

When assessing a property for replacement windows the following should be considered regarding the use of trickle ventilators and other forms of ventilation within replacement windows:

• Trickle ventilators are not mandatory unless the existing windows have them, however it is always good practice to consider their use when replacing windows. Alternatively ventilators may be replaced by an air brick.
• Replacement ventilators must be no smaller in geometric open area than the existing ventilators. If the geometric area is not known, habitable rooms should have trickle ventilator of 5000mm2 equivalent area and wet rooms should have 2500mm2 equivalent area.
• Although not mandatory, increasing ventilation by the provision of new or additional ventilators to maintain good air quality should be considered between the supplier and the customer (ref: GGF publication “Advice to consumers regarding ventilation when replacing windows”).
• Two stage locking handles are an acceptable form of trickle ventilation, where security is not compromised and draughts will not create a problem. This would usually mean not on the ground floor.
• The provision of permanent ventilators for combustion appliances is a different matter and compliance with Approved Document J is mandatory

New Houses

Ventilation levels within a house or dwelling are dependant upon a number of factors. Guidance tables can be found within Approved document F – or alternatively ventilator manufacturers maybe able to assist.

England and Wales

Basic requirement is 5,000 mm2 EQA for a habitable room.
Overall calculations are by floor area.

Total equivalent ventilator area (mm2) for a new dwelling with any design air permeability (EQA)

Total equivalent ventilator area (mm2) for a new dwelling with a designed air permeability leakier than (>) 5 m3/(h.m1) at 50 Pa (EQA)

This is based on two occupants in the main bedroom and a single occupant in others. For a greater level of occupancy, assume a greater number of bedrooms. For more than five bedrooms, add 10000 mm2 per bedroom.

Building Regulations Part F (England & Wales)

A systems approach

Due to the increasing complexity of the Regulations, ventilation strategies and system design must be considered at the earliest stages of building design.

3 three ventilation types:

"Whole Building" background ventilation to provide fresh air to dilute and disperse low levels of water vapour and pollutants, usually by the provision of background ventilators or mechanical supply ventilation.

"Local extract" extract ventilation in rooms where most water vapour or concentrated pollutants are released.

"Purge" rapid ventilation for the rapid dilution and removal of high concentrations of pollutants from occasional activities, usually by opening windows as set out in Appendix B of Part F.

Approved Systems of Ventilation

Background Ventilation & Intermittent Extract:

This method requires background ventilators with at least 5000 mm2 EQA in habitable rooms with external walls and a combination extract and background ventilators with at least 2500 mm2 EQA installed in wet rooms.

Passive Stack (PSV) & Background Ventilation:

This method requires the installation of a stack system into wet rooms/kitchens with background ventilators with at least 5000 mm2 EQA fitted in all habitable rooms with external walls and background ventilators with at least 2500 mm2 EQA installed in wet rooms not containing PSV units. Open flued appliances still require air supply as given in approved document J.

Continuous Mechanical Extract Ventilation:

Continuous mechanical extract ventilation is an alliance of a central extract unit and trickle ventilators to ensure fresher air is drawn through the property. All habitable rooms require 2500 mm2 of equivalent area to ensure property does not dry out.

Continuous Mechanical Supply & Extract,with Heat Recovery:

No requirement for trickle vents.

The performance for each “System” approach set out in Part F are the minimum requirements needed. The occupant’s health could be at risk if they are compromised.

Systems may be manually or automatically controlled. For each system air must be able to flow through the dwelling. The Regulations make provision for this via internal door undercuts to maintain a minimum gap of 10mm above the finished floor. This provides a 7600mm2 permanent opening when a door is closed.

E.g. System 1 – Intermittent extract fans and background ventilators. This is the most commonly used system in the UK.

Where can it be used?

It is suitable for use in houses and flats or apartments with multiple façades. In some circumstances, especially in dwellings with a single façade.

How does it work?

The system comprises of background ventilators, fitted to windows and extract fans fitted in moisture producing areas or “wet rooms” (kitchens and bathrooms). The background ventilators provide the whole building ventilation and also supply air to the intermittently operated extract fans which provide the extract ventilation.

How are ventilation rates calculated?

Guidance on minimum provisions for extract and whole building ventilation is set out in tables of Approved Document.

The whole building ventilation rate for background ventilators is determined by a number of factors:

• Dwelling floor area
• Number of bedrooms, occupants, storeys and number of façades.

What benefits does it offer?

• Simplicity
• Operation familiar to most occupants
• Straightforward installation
• Inhabitants control

What difficulties could we encounter?

• Perceived high running costs
• Noise potential of low quality or poorly installed fans
• Single façade dwellings require additional background ventilators fitted at low level

Specific Ventilator requirements - approved F1 revised document 2006

• Ventilator areas are now described in terms of equivalent area, as opposed to the geometric measurement.
• Where replacement windows are fitted, these must have Ventilators if the old units contained them. Ideally vents should be fitted in all cases.

Performance-based Guidance introduced

• What level of ventilation should be sufficient, rather than how it should be achieved.
• The designer has the freedom to use whatever ventilation provisions suit a particular building.

Standard Requirements

• All Vents to be Marked with Equivalent Area in a visible location.
• All trickle vents must now be tested to BS13141-1:2004.

Ventilator Location

• Ventilator should be typically located at 1.7 metres from finished floor level, this is to avoid the potential discomfort of draughts.
• Single façade properties where both ‘High’ and ‘Low’ level ventilation is required, low level should be approx, 1 metre below the high level ventilation.
• When using intermittent extract fans, the frame vent should be located at least 0.5 metre’s from the extract fan.

Vent opening configuration and method used to calculate equivalent area @ 1Pa.Tested to EN 131141.

• New Build Dwelling – The trickle ventilation requirement for a house is based upon the overall floor area and number of bedrooms. (Dependent on ventilation method used.)
• Existing Dwellings – Trickle ventilators supplied in all rooms, 5000mm2 minimum in habitable rooms, 2500mm2 in wet rooms.
• Regulations now apply to Conservatories and Extensions