General
1.1 The aim of requirement F1(1) is to protect the health of occupants of the building by providing adequate ventilation. Without adequate ventilation, mould and internal air pollution might become hazardous to health.
NOTE: The guidance in this approved document is not designed to deal with the products of tobacco smoking or vaping.
1.2 The building should provide the ventilation rates given in this section.
1.3 Other ventilation solutions may be used, if it can be shown to the building control body that they satisfy requirement F1(1).
1.4 The ventilation rates set out in this approved document have been designed to meet the indoor pollutant levels in Appendix B where the outside air is of reasonable quality. In areas where the outside air is not of reasonable quality, Section 2 provides guidance on limiting the entry of external air pollutants.
Noise
1.5 Mechanical ventilation systems, including both continuous and intermittent mechanical ventilation, should be designed and installed to minimise noise. This includes doing all of the following.
a. Correctly sizing and jointing ducts.
b. Ensuring that equipment is appropriately and securely fixed, such as using resilient mountings where noise carried by the structure of the building could be a problem.
c. Selecting appropriate equipment, including following paragraph 1.6.
1.6 For mechanical ventilation systems, fan units should be appropriately sized so that fans operating in normal background ventilation mode are not overly noisy. This might require fans to be sized so that they do not operate near maximum capacity when in normal background ventilation mode.
1.7 Account should be taken of outside noise when considering whether openable windows are appropriate for purge ventilation.
NOTE: Although there is no requirement to undertake noise testing, achieving the levels in the following guidance would ensure good acoustic conditions. The average A-weighted sound pressure level for a ventilator operating under normal conditions and not at boost rates should not exceed both of the following.
a. 30dB LAeq,T* for noise-sensitive rooms (e.g. bedrooms and living rooms) when a continuous mechanical ventilation system is running on its minimum low rate.
b. 45dB LAeq,T* in less noise-sensitive rooms (e.g. kitchens and bathrooms) when a continuous operation system is running at the minimum high rate or an intermittent operation system is running.
*The noise index LAeq,T is used in BS 8233, where T is the duration of the measurement. If the noise from the sound source is steady (i.e. fluctuating by up to 3dB), a measuring time of 1 minute will be adequate and the LAeq, 1 min level will be similar to the dB(A) level used elsewhere. lf the noise from the sound source fluctuates more than this, a longer measuring time (T) may be required, but the higher portion of the fluctuating level should be considered, and the sound may attract more attention due to the changes in level.
NOTE: Methods for measuring the sound power level produced by the fan unit of decentralised extract ventilation, centralised extract ventilation and balanced mechanical ventilation with heat recovery systems are described in BS EN 13141.
Access for maintenance
1.8 Reasonable access should be provided for maintaining ventilation systems, including all of the following.
a. Providing access to replace filters, fans and coils.
b. Providing access points for cleaning ductwork.
c. Providing access for the general maintenance of the plant.
The ventilation strategy in this approved document
1.9 The ventilation strategy in this approved document relies on a combination of all of the following.
a. Extract ventilation from rooms where water vapour or pollutants are likely to be released (e.g. bathrooms and kitchens), to minimise their spread to the rest of the building. Ventilation fans may be either intermittent operation or continuous operation.
b. Whole dwelling ventilation to provide fresh air to the building and to dilute, disperse and remove water vapour and pollutants not removed by extract ventilation.
c. Purge ventilation to remove high concentrations of pollutants and water vapour. Purge ventilation is used intermittently and required only for pollutants produced by occasional activities (e.g. fumes from painting).
1.10 Ventilation may be delivered through natural ventilation, mechanical ventilation or a combination of both.
1.11 The ventilation systems in this approved document are examples of systems that comply with Part F of the Building Regulations. Other ventilation systems may be acceptable if they can be shown to meet an equal level of performance.
Performance-based guidance
1.12 Performance criteria for acceptable levels of moisture and pollutants are given in Appendix B. Ventilation rates designed to meet the performance criteria are given in Tables 1.1 to 1.3.
1.13 Ventilator sizes for the whole dwelling are also provided in Table 1.7 to help designers comply with Part F of the Building Regulations in common situations.
1.14 Some ventilation system designs can, in certain circumstances, result in lower ventilation rates than those stated in Table 1.1 and Table 1.2 (e.g. systems with automatic controls). Where lower ventilation rates are proposed, expert advice should be obtained to demonstrate that the solution meets the performance standards in Appendix B.
Equivalent area of ventilators
1.15 The size of background ventilators (including trickle ventilators) is given in this approved document as an equivalent area in mm2, not as a free area. BS EN 13141-1 includes a method of measuring the equivalent area of background ventilator openings.
1.16 Background ventilators should have the equivalent area marked where it will be easy to see from inside the dwelling when installed, to aid verification by building control bodies.
Extract ventilation
1.17 Extract ventilation to the outside should be provided in all of the following spaces.
a. Kitchens.
b. Utility rooms.
c. Bathrooms.
d. Sanitary accommodation.
1.18 Extract ventilation can be intermittent or continuous.
1.19 Minimum extract ventilation rates in litres per second (l/s) for intermittent operation extract systems are given in Table 1.1. Minimum extract ventilation rates for continuous operation extract systems are given in Table 1.2.
1.20 Extract ventilation terminals and fans, not including cooker extract hoods, should be installed to comply with both of the following conditions.
a. As high as is practicable in the room.
b. A maximum of 400mm below the ceiling.
1.21 Where a cooker hood is used to extract to the outside, the height of the extract hood above the hob surface should be either as specified in the manufacturer’s instructions or, if no specification is available, between 650mm and 750mm.
Table 1.1 Minimum extract ventilation rates for intermittent extract systems
Diagram 1.1 Minimum kitchen extract ventilation rate in cases where a cooker hood extracts to the outside(1)
Diagram 1.2 Minimum ventilation rate for kitchen extract where a cooker hood does not extract to the outside(1)
1.22 Minimum extract ventilation rates for continuous extract systems are specified in Table 1.2. A continuous rate is given for the general operation of the fan and a high rate for when additional extraction is required.
Table 1.2 Minimum extract ventilation rates for continuous extract systems(1)
Whole dwelling ventilation
1.23 Supply air for the dwelling should be delivered through one of the following means.
a. Continuous supply fans.
b. Background ventilators.
1.24 The minimum whole dwelling ventilation rate for the supply of air to the habitable rooms in a dwelling should meet both of the following conditions.
a. A minimum rate of 0.3 litres per second per m2 of internal floor area (this includes all floors, e.g. for a two-storey building, add the ground-floor and first-floor areas).
b. A minimum rate determined by the number of bedrooms, as specified in Table 1.3.
Table 1.3 Minimum whole dwelling ventilation rates determined by the number of bedrooms
1.25 Internal doors should allow air to flow through the dwelling by providing a minimum free area equivalent to a 10mm undercut in a 760mm wide door. Doors should be undercut to achieve one of the following.
a. If the floor finish is fitted: 10mm above the floor finish.
b. If the floor finish is not fitted: 20mm above the floor surface.
Purge ventilation
1.26 A system for purge ventilation should be provided in each habitable room.
1.27 Purge ventilation should be capable of extracting at least four air changes per hour per room directly to the outside.
NOTE: In order to demonstrate compliance with Part O of the Building Regulations it is likely that higher purge ventilation rates than those given in paragraph 1.29 will be required.
1.28 Purge ventilation should be delivered through one of the following means.
a. Openings (e.g. windows or doors).
b. A mechanical extract ventilation system.
1.29 Where purge ventilation is delivered through openings in a habitable room, the minimum opening areas in Table 1.4 should be achieved. The values in Table 1.4 are based on BS 5925, which assumes all of the following.
a. Single-sided ventilation.
b. An urban environment.
c. A wind speed of 2.1 metres per second (m/s).
d. A temperature difference of 3°C between the air inside and outside the building.
1.30 Depending on the dwelling design or the external climate, it may be possible in certain circumstances to achieve four air changes per hour with smaller openings. If smaller openings than those given in Table 1.4 are specified, expert advice should be sought to ensure that the design complies with requirement F1(1).
Table 1.4 Purge ventilation openings
1.31 Hinged or pivot windows with an opening angle of less than 15 degrees are not suitable for purge ventilation.
Performance testing
1.32 The air flow resistance of all components should be considered when specifying ventilation systems. The complete assembly, as installed, should be designed to meet the performance standards of this approved document. The performance of the separate components should be measured according to the relevant parts of BS EN 13141 and other relevant standards. The relevant test standards for common equipment types are given in Table 1.5.
Table 1.5 Performance testing standards
Control of ventilation
1.33 Ventilation should be controllable. Controls may be either manual (i.e. operated by the occupant) or automatic.
1.34 Background ventilators should be at least 1700mm above floor level, to reduce cold draughts, but still be easy for the occupant to reach.
NOTE: Background ventilators are intended to normally be left open.
1.35 Continuously running fans should be set up to operate without occupant intervention but may have manual or automatic controls for selecting the high rate of operation. Any manual high rate controls should be provided locally to the spaces being served, e.g. bathrooms and kitchens. Automatic controls might include sensors for humidity, occupancy/usage and pollutant release.
1.36 Controls based on humidity sensors may be installed in moisture-generating rooms (e.g. kitchen or bathroom) but should not be used for sanitary accommodation, where odour is the main pollutant.
1.37 Other types of automatic controls might be suitable. Where present, automatic controls should operate according to the need for ventilation in the space. Background ventilators with automatic controls should also have manual override.
NOTE: Where a combustion appliance is installed, any automatic controls must also ensure that the ventilation provided meets the requirements of Part J of the Building Regulations.
Ventilation systems for dwellings with basements
1.38 In addition to paragraphs 1.12 to 1.37, the performance required for ventilation systems for dwellings with basements would be achieved by following the guidance in paragraphs 1.39 to 1.41.
1.39 A dwelling that includes a basement connected to the above ground parts of the dwelling by a large permanent opening (e.g. an open stairway), may be treated as a multi-storey dwelling when following the guidance in this approved document for dwellings without basements.
NOTE: If a basement has only one exposed façade, the guidance for natural ventilation given in this approved document would not be appropriate. In such cases, expert advice should be sought.
1.40 A dwelling with a basement that is not connected to the rest of the dwelling above ground level by a large permanent opening should be considered as follows.
a. The part of the dwelling above ground level should be considered separately.
b. The basement should be treated separately as a single-storey dwelling above ground level.
c. If the basement has no bedrooms, it should be treated as having one bedroom when calculating the ventilation required for the purposes of meeting the ventilation standards.
1.41 A dwelling that is only a basement should be treated as a single-storey dwelling above ground level. In such circumstances, the guidance for dwellings without basements should be followed. The guidance on natural ventilation, however, is not appropriate for a dwelling that is only a basement.
Ventilation of a habitable room through another room
1.42 If a habitable room does not contain windows that can be opened (e.g. an internal room), the requirement to provide adequate ventilation can be met using paragraphs 1.43 and 1.44. This guidance can be used if the room is ventilated through either of the following.
a. Another habitable room.
b. A conservatory.
1.43 The habitable room or conservatory should have openings to the outside to provide both of the following.
a. Purge ventilation with a minimum total area given in paragraph 1.29, based on the combined floor area of the habitable rooms (or the habitable room and the conservatory).
b. Background ventilation of at least 10,000mm2 equivalent area.
1.44 Between the two rooms there should be a permanent opening with a minimum area of 1/20 of the combined floor area of the two rooms (see Diagram 1.3).
Diagram 1.3 Two habitable rooms treated as one room for ventilation purposes
System-specific guidance
1.45 Paragraphs 1.46 to 1.73 give guidance for the types of ventilation system listed in Table 1.6.
Table 1.6 Types of ventilation system
NOTE: For situations outside the scope of Table 1.6, expert advice should be sought for the design, sizing and position of ventilators to provide effective ventilation.
NOTE: As defined in Appendix A, less airtight dwellings are dwellings which have one of the following.
a. A design air permeability higher than 5m3/(h·m2) at 50Pa.
b. An as-built air permeability higher than 3m3/(h·m2) at 50Pa.
1.46 Where a dwelling has natural ventilation and a measured air permeability that differs from the design air permeability, so that it is defined as a highly airtight dwelling, one of the following applies.
a. Expert advice should be sought.
b. A continuous mechanical extract ventilation system should be installed by following the guidance in paragraphs 1.60 to 1.66.
NOTE: Continuous mechanical extract ventilation systems are available as decentralised options.
An intermittent extract fan may be replaced with a decentralised continuous mechanical extract ventilation system fan. Natural ventilation with background ventilators and intermittent extract fans (guidance suitable only for less airtight dwellings)
Intermittent extract
1.47 Intermittent extract fans should be fitted in all wet rooms. For kitchens, utility rooms, bathrooms and sanitary accommodation, the extract rates in Table 1.1 can be met using an intermittent extract fan.
1.48 If a wet room has no external walls, the intermittent extract fan should extract at four air changes per hour to meet the purge ventilation standards in paragraphs 1.26 to 1.31.
1.49 For sanitary accommodation, extract rates can be met using windows by following the purge ventilation guidance in paragraphs 1.26 to 1.31.
1.50 Any automatic controls (e.g. humidity control) for intermittent extract should have a manual override to allow the occupant to turn the extract ventilation on or off.
1.51 In a room with no openable window, an intermittent extract fan should be provided with controls which continue to operate the fan for at least 15 minutes after the room is vacated.
Background ventilators
1.52 All rooms with external walls should have background ventilators. If a habitable room has no external walls, paragraphs 1.42 to 1.44 should be followed.
NOTE: A window with a night latch position is not adequate for background ventilation, due to the following.
a. The risk of draughts.
b. Security issues.
c. The difficulty of measuring the equivalent area.
1.53 If the dwelling has more than one exposed façade, the area of background ventilators on each façade should be similar, to allow cross-ventilation.
1.54 If an exposed façade is close to an area of sustained and loud noise (e.g. a main road), then a noise attenuating background ventilator should be fitted.
1.55 If fans and background ventilators are fitted in the same room, they should be at least 500mm apart.
1.56 The minimum total area of background ventilators in each room should follow the guidance in Table 1.7.
1.57 The total number of ventilators installed in the dwelling’s habitable rooms and kitchens should be at least the following.
a. Four ventilators if the dwelling has one bedroom.
b. Five ventilators if the dwelling has more than one bedroom.
1.58 If the dwelling has a kitchen and living room which are not separate rooms, at least three ventilators of the same area as for other habitable rooms in Table 1.7 should be provided in the open-plan space.
Table 1.7 Minimum equivalent area of background ventilators for natural ventilation(1)
Purge ventilation
1.59 For purge ventilation, follow paragraphs 1.26 to 1.31.
Continuous mechanical extract ventilation
1.60 A continuous mechanical extract ventilation system could consist of one of the following.
a. A central extract system.
b. Individual room extract fans.
c. A combination of a central extract system and individual room extract fans.
1.61 If an exhaust air terminal is located on a façade that is exposed to the prevailing wind, measures should be taken to minimise likely wind effects. Solutions could include the following.
a. Ducting to another façade.
b. Use of constant volume flow rate units.
c. Seeking expert advice.
Ventilation rates
1.62 The total combined rate of continuous mechanical extract ventilation in the dwelling should be at least the whole dwelling ventilation rate in Table 1.3.
1.63 Each wet room should have a minimum continuous mechanical extract ventilation high rate as given in Table 1.2.
Background ventilators for continuous mechanical extract ventilation
1.64 Where continuous mechanical extract ventilation is used, background ventilators should satisfy all of the following conditions.
a. Not be in wet rooms.
b. Provide a minimum equivalent area of 4000mm2 for each habitable room in the dwelling.
c. Provide a minimum total number of ventilators that is the same as the number of bedrooms plus two ventilators (i.e. a one-bedroom dwelling should have three background ventilators, a two bedroom dwelling should have four background ventilators, etc.).
1.65 If a habitable room has no external walls, paragraphs 1.42 to 1.44 should be followed.
Purge ventilation
1.66 For purge ventilation, follow paragraphs 1.26 to 1.31.
Mechanical ventilation with heat recovery
Ventilation rates
1.67 For dwellings using mechanical ventilation with heat recovery, each habitable room should have mechanical supply ventilation. The total supply air flow should be distributed proportionately to the volume of each habitable room.
1.68 Mechanical supply terminals should be located and directed to avoid draughts.
1.69 The minimum total continuous rate of mechanical ventilation with heat recovery is the whole dwelling ventilation rate in Table 1.3.
1.70 For dwellings using mechanical ventilation with heat recovery, each wet room should have a minimum continuous mechanical extract ventilation high rate as given in Table 1.2.
1.71 Mechanical ventilation with heat recovery systems should be designed to avoid the moist air from the wet rooms recirculating to the habitable rooms.
Background ventilators
1.72 To avoid unintended air pathways, background ventilators should not be installed with mechanical ventilation with heat recovery.
Purge ventilation
1.73 For purge ventilation follow paragraphs 1.26 to 1.31.
NOTE: The efficiency of mechanical ventilation with heat recovery systems should improve as the dwelling becomes more airtight.
Installation of ventilation systems
1.74 Ventilation systems should be installed to meet both of the following conditions.
a. Comply with the guidance in this approved document.
b. Not compromise the performance of the system.
1.75 Adequate space should be available for access to maintain ventilation equipment.
1.76 Rigid ducts should be used wherever possible.
1.77 Flexible ductwork, where installed, should meet all of the following conditions.
a. Only used for final connections.
b. Lengths should be a maximum of 1.5m.
c. Meet the standards of BSRIA’s BG 43/2013.
1.78 Any flexible ducts should be installed so that the full internal diameter is maintained and flow resistance is minimised. This is achieved by taking both of the following actions.
a. Pulling the duct taut.
b. Ensuring that ductwork does not pass through orifices with a smaller diameter than the duct itself.
1.79 Ductwork installations should be designed and installed to minimise the overall pressure losses
within the system by taking all of the following steps.
a. Minimising the overall length of duct.
b. Minimising the number of bends required.
c. Installing appropriately sized ducts for the air flow rate.
1.80 Each air terminal should have a free area of at least 90% of the free area of its associated duct.
1.81 Duct connections should be both mechanically secured and adequately sealed to prevent leaks. Rigid connectors and jubilee clips should be used for flexible ducting to ensure a good seal.
1.82 The installer should make a visual inspection to confirm both of the following.
a. There are no obvious defects.
b. All packaging has been removed.
1.83 Mechanical ventilation systems must be commissioned in accordance with an approved procedure. Appendix C of this approved document includes a completion checklist and commissioning sheet, which the system installer should complete to demonstrate compliance. See Section 4 of this approved document.
