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Building Regulations - Approved Document F (Ventilation)

Approved Document F provides guidance on meeting building regulations that specifically apply to ventilation. It states that adequate ventilation needs to be provided to prevent excess condensation buildup which could damage the structure of the property. It also ensures then, that air properly flows through the property maintaining good levels of indoor air quality. 

When building a new property it is important to comply with requirements in building regulations for installation, inspection, testing, commissioning and provision of information when installing fixed ventilations systems in your new and existing property. Approved Documents provide guidance on how to meet these building regulations.

Each new room in a house should have adequate ventilation for general health reasons. The type of room will determine how much ventilation is required.

When inserting a new internal wall care should be taken not to make any other matters, such as ventilation, worse. If a new room is being created as a result of the addition of an internal wall then care should also be taken to ensure that the existing room is ventilated adequately. The general rules for ventilating a room are:

Purge - this is achieved by opening the window. The opening should have a typical area of at least 1/20th of the floor area of the room served, unless it is a bathroom which can be any openable size.

Whole building - this is also known as trickle ventilation which can be incorporated in to the head of the window framework, or by some other means. The area varies on the type of room:

Both of these forms of ventilation are normally required, however alternative approaches to ventilation may also be acceptable, subject to agreement with the building control body.

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

In England and Wales, requirements for ventilation are contained in Approved Document F and can be downloaded from www.planningportal.gov.uk. The Building Regulations Approved Document F 2010 considers ventilation through a combination of infiltration and purpose-provided ventilation. Regulations are constantly being reviewed, with the aim to improve building standards, so it is worth checking the Planning Portal website for any updates to Building Regulations.

Infiltration
A uncontrollable air exchange between the inside and outside of a building.

Purpose-Provided Ventilation
A controllable air exchange between the inside and outside of a building.

Approved Document F looks at different systems for ventilation. The performance rates for each of the “System” approaches set out in Approved Document F are the minimum requirements needed to ensure that adequate air quality is provided for people indoors. The occupant's health could be at risk if these ventilation rates are compromised.

The following systems are outlined which satisfy the performance standard:

Approved Document F - System 1 - Background Ventilation & Intermittent Extractor Fans

The most common approach to meeting the Building Regulations Approved Document F is intermittent extract fans with background vents (i.e. trickle vents in the windows). Extractor fans are located in the bathroom, ensuite, kitchen and utility room. They must comply with providing the following ventilation airflow rates for intermittent extract minimum rates.

Table 5.1A - Extract Ventilation Rates

 

 

 

 

 

 

 

 

 

In addition, background ventilators (trickle ventilators) must comply with the total ventilator area (mm²) depending upon the design air permeability:

Use table A for a dwelling with any design air permeability or B for a building with a design air permeability >5m³/(h.m²) @50Pa

Ventilation Table A

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Ventilation Table B

 






















Intermittent extractor fans can be operated with a number of different control functions: fan operates in conjunction with a light switch, remote switch, pull cord, humidistat, PIR (presence detector) or timer. Intermittent fans are not the most energy efficient way due to the heat loss incurred.

In addition, if they are not switched on, the property is not being adequately ventilated. The fans must be regularly maintained in order to work effectively and minimise sound levels.

Approved Document F - System 2 - Passive Stack Ventilation

Passive stack is a non-mechanical approach to ventilation, where air vents are located in various locations around the dwelling. Using the principle of convection, currents allow the movement of air through the ducts.

Unfortunately with passive stack airflow rates are very much weather dependant with a risk of over or under ventilating. In addition, background vents must be installed.

Approved Document F - System 3 - Mechanical Extract Ventilation

System 3 covers continuous mechanical extract ventilation (MEV). This can be either a whole house centralised MEV system, or localised decentralised MEV fan.

The centralised MEV system is typically located in a loft space or hallway cupboard. Multiple ducts run from the unit to the kitchen, bathroom, ensuites and other wet rooms of a property to simultaneously draw moisture laden air from these wet rooms to control humidity levels.

Decentralised MEV (dMEV) are individual room fans which operate continuously to draw moisture from either the bathroom, kitchen, utility room or other wet room. Continuous mechanical systems should include either manual or automatic controls (i.e. humidity sensors) to operate on between trickle and boost modes.

They should always provide the minimum whole building ventilation rate, which can be calculated in the following steps:

Step 1: Determine the whole dwelling ventilation rate in Table 5.1b taking into account note a:
Extract Ventilation Rates - Table 5.1A

 

 

 

 

 

 

 

 

Building Regulations - Table 5.1B







 

 

 

 

 

Step 2: Calculate the whole building extract rate from Table 5.1a by taking the ‘Continuous extract minimum high rate’. e.g. if an individual dMEV fan is fitted in the kitchen, bathroom and utility room, the total minimum high rate would be 13l/s, plus 8l/s for the bathroom and 8l/s for the utility room = 29l/s.

Step 3: The required extract rates are as follows:

The continuous extract minimum high rate (i.e. the boost rate) should be at least the greater of Step 1 (higher than the trickle rate).

For any design permeability, controllable background ventilators having a minimum equivalent area of 2500 mm2 should be fitted in each habitable room,. As an alternative, where the designed air permeability is leakier than (>) 5m³/(h.m²) at 50 Pa background ventilators are not necessary, but see cautionary advice in paragraph 5.10 of approved document F.

Approved Document F - System 4 - Mechanical Extract Ventilation with Heat Recovery

Mechanical Ventilation with Heat Recovery (MVHR) is covered under System 4 of the Building Regulations, Approved Document F. Heat Recovery ventilation provides fresh, filtered air, energy efficiency and a comfortable all year round climate. Stale, moist air is extracted out of the wet rooms of a home.

These include the kitchen, bathrooms, utility and en-suite rooms. MVHR systems should always provide the minimum whole building ventilation rate, which can be calculated using the same steps as System 3 above. The required airflow rates are as follows:

Background ventilators are not required with System 4.

Alternative Means

The Building Regulations Approved Document F include other systems these require European certification by a Technical Approval body and must meet the requirements F1. Approved Document F section 4.17 states.

“Other ventilation systems and devices, perhaps following a different strategy (e.g. Positive Input Ventilation) may provide acceptable solutions, provided it can be demonstrated to the Building Control Body (e.g. by a BBA Certificate) that they meet Requirement F1.”

The EnviroVent Range of Positive Input Ventilation systems are accredited with BBA certification: 03/4043. These are sophisticated whole house ventilation systems, which dilute, displace and replace high humidity levels to control condensation and mould growth.

Trickle vents are not required, provided that the whole house ventilation rate is met in Table 5.1B of Part F and the requirements of the BBA certificate are met.. It is recommended that extract fans are installed if there is a remote wet zone that is located away from a central hallway.

Positive Input Ventilation is an all year round system that is a cheaper option than heat recovery ventilation. Systems can also be extremely energy efficient, taking advantage of the benefit of solar gain from the loft space and providing heat distribution.

This can save around 10% of annual heating costs per year. With lower humidity levels, the dust mite population is also reduced, a major trigger for asthma sufferers. Indoor air quality is improved to transform a stale, humid atmosphere into a fresh, healthy, condensation-free environment.

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