General

3.1 When building work in an existing dwelling includes work on ventilation, for example:

a. adding a habitable room

b. adding a wet room

c. replacing part of the ventilation system, including extract fans the work should meet the relevant standards in this approved document.

3.2 When other building work is carried out that will affect the ventilation of the existing dwelling, for example:

a. replacing a window or door

b. doing energy efficiency work

the ventilation of the dwelling should either:

a. meet the standards in the relevant approved document

b. not be less satisfactory than before the work was carried out.

NOTE: Ventilation through infiltration should be considered to be part of the ventilation provision of a dwelling.
Reducing infiltration might reduce the indoor air quality of the dwelling below the standards given in Appendix B.

3.3 For common types of work, the requirements of paragraphs 3.1 and 3.2 may be demonstrated by following the guidance detailed below.

a. For installing energy efficiency measures excluding window replacement, paragraphs 3.6 to 3.13.

b. For installing energy efficiency measures including window replacement, paragraphs 3.6 to 3.13 and 3.14 to 3.16.

c. For replacing windows only, paragraphs 3.14 to 3.16.

d. For the addition of a habitable room, paragraphs 3.17 to 3.20.

e. For the addition of a conservatory, paragraphs 3.21 to 3.24.

f. For the addition of a wet room, paragraphs 3.25 to 3.29.

g. For refurbishing a kitchen or bathroom, paragraphs 3.30 to 3.32.

h. For work done to improve the ventilation of the dwelling that was not triggered by the building work in (a) to (g), section 1 should be followed.

3.4 Other ventilation solutions than those detailed here may be used, as long as it can be demonstrated to a building control body that they comply with the requirements of paragraphs 3.1 and 3.2.

3.5 When a building undergoes a material change of use, Part F of Schedule 1 to the Building Regulations applies to the building or part of the building that has changed use. Guidance in Section 1 should be followed.

NOTE: Ventilation equipment is considered to be a ‘controlled service or fitting’ and providing or extending this equipment in or in connection with a building is considered to be building work.

NOTE: Some building work does not need to be notified to the local authority. Details of such work are set out in the Manual to the Building Regulations.

Installing energy efficiency measures

3.6 Many existing dwellings are ventilated through infiltration rather than purposeful ventilation. Energy efficiency measures carried out on existing dwellings might reduce infiltration and cause the dwelling to become under-ventilated.

Building work should not reduce the ventilation provision of the dwelling unless it can be demonstrated that the ventilation provision after the work is carried out meets the minimum standards of requirement F1(1).

3.7 When carrying out energy efficiency measures to an existing dwelling, an assessment should determine what, if any, additional ventilation provision is needed, based on the estimated impact of the work. The assessment should be carried out by one of the following means.

a. Applying the simplified method in paragraphs 3.8 to 3.13.

b. Seeking expert advice, which may include carrying out an air permeability test that follows the procedures given in Approved Document L, Volume 1: Dwellings.

NOTE: Following BSI PAS 2035 is considered to be an adequate means of demonstrating compliance with paragraph 3.6.

Simplified method

NOTE: The simplified method set out in paragraphs 3.8 to 3.13 is designed to apply to an existing dwelling that is assumed to have adequate means of ventilation through a combination of purposeprovided ventilation and infiltration. If the property differs significantly from this assumption, the requirements of paragraph 3.6 must still be met. This should be demonstrated through seeking expert advice or using another suitable method.

3.8 When carrying out energy efficiency measures on an existing dwelling, Table 3.1 should be used to calculate the number of major and minor energy efficiency measures involved. This calculation should include all of the following.

a. Energy efficiency measures fitted since the original dwelling was constructed, to consider accumulation of measures.

b. Energy efficiency measures planned.

NOTE: Where specific energy efficiency measures are not included in Table 3.1, the most similar category should be chosen instead.

3.9 Diagram 3.1 should then be used to determine the category that the works result in.

Table 3.1 Energy efficiency measures

3.10 If the method in Diagram 3.1 results in the work being categorised as Category A, it is likely that the energy efficiency measures have not reduced the ventilation provision of the dwelling below the requirements of F1(1) so no further ventilation provision is necessary.

3.11 If the method in Diagram 3.1 results in the work being categorised as Category B, it is likely that the ventilation provision of the dwelling has been reduced below the requirements of F1(1). Further ventilation provision should be provided by one of the following means.

a. Natural ventilation, by following the system-specific guidance in paragraphs 1.47 to 1.59. It is assumed that any existing purpose-built ventilators are in working order and that the equivalent area has not been compromised.

b. Continuous mechanical extract ventilation, by following the system-specific guidance in paragraphs 1.60 to 1.66.

c. Mechanical ventilation with heat recovery, by following the system-specific guidance in paragraphs 1.67 to 1.73. To avoid unintended air pathways, existing background ventilators should be covered or sealed shut.

3.12 If the method in Diagram 3.1 results in the work being categorised as Category C, it is likely that the ventilation provision of the dwelling has been reduced significantly below the requirements of F1(1). Further ventilation should be provided by one of the following means.

a. Natural ventilation, by following expert advice for the design, sizing and positioning of ventilators to ensure adequate ventilation provision.

b. Continuous mechanical extract ventilation, by following the system-specific guidance in paragraphs 1.60 to 1.66.

c. Mechanical ventilation with heat recovery, by following the system-specific guidance in paragraphs 1.67 to 1.73. To avoid unintended air pathways, existing background ventilators should be covered or sealed shut.

3.13 Appendix D provides a checklist for determining the ventilation provision in an existing dwelling. It may be used before energy efficiency measures are carried out to establish whether an existing dwelling complies with the requirement for adequate means of ventilation.

Replacing windows

Existing windows with background ventilators

3.14 If the existing windows have background ventilators, the replacement windows should include background ventilators. The new background ventilators should comply with both of the following conditions.

a. Not be smaller than the background ventilators in the original window.

b. Be controllable either automatically or by the occupant.

If the size of the background ventilators in the existing window is not known, the ventilator sizes in paragraph 3.15 may be applied.

Existing windows without background ventilators

3.15 Replacing the windows is likely to increase the airtightness of the dwelling. If ventilation is not provided via a mechanical ventilation with heat recovery system, then increasing the airtightness of the building may reduce beneficial ventilation in the building. In these circumstances, it is necessary to ensure that the ventilation provision in the dwelling is no worse than it was before the work was carried out. This may be demonstrated in any of the following ways.

a. Incorporating background ventilators in the replacement windows equivalent to the following.

i. Habitable rooms – minimum 8000mm2 equivalent area.

ii. Kitchen – minimum 8000mm2 equivalent area.

iii. Bathroom (with or without a toilet) – minimum 4000mm2 equivalent area.

b. If the dwelling will have continuous mechanical extract ventilation, installing background ventilators in any replacement windows which are not in wet rooms, with a minimum equivalent area of 4000mm2 in each habitable room.

c. Other ventilation provisions, if it can be demonstrated to a building control body that they comply with the requirements of paragraph 3.2.

NOTE: If it is not technically feasible to adopt the minimum equivalent areas set out in paragraph 3.15, the background ventilators should have equivalent areas as close to the minimum value as is feasible.

3.16 When windows are replaced as part of the work connected with a material change of use, Section 1 of this approved document should be followed in addition to paragraphs 3.14 and 3.15.

Addition of a habitable room (not including a conservatory) to an existing dwelling

3.17 The requirement for adequate ventilation can be met if background ventilators are used as follows.

a. If the additional room is connected to an existing habitable room which now has no windows opening to the outside, paragraphs 1.42 to 1.44 should be followed

b. If the additional room is connected to an existing habitable room that still has windows opening to the outside, the following conditions apply.

i. If the existing habitable room has a total background ventilator equivalent area of less than 5000mm2, paragraphs 1.42 to 1.44 should be followed.

ii. If the existing habitable room has a total background ventilator equivalent area of at least 5000mm2, both of the following should be provided.

Background ventilators of at least 12,000mm2 equivalent area between the two rooms.
Background ventilators of at least 12,000mm2 equivalent area between the additional room and the outside.

3.18 As an alternative to paragraph 3.17, to ventilate the additional habitable room, one of the following methods could be used.

a. A single-room heat recovery ventilator. The supply rate to the additional room should be determined as follows.

i. Establish the whole dwelling ventilation rate from Table 1.3.

ii. Calculate the room supply rate required from the following equation.

(whole dwelling ventilation rate × Room volume)/(Total volume of all habitable rooms)

b. If the dwelling already has mechanical ventilation, the centralised system could be extended into the additional room.

3.19 For purge ventilation in a new habitable room in a dwelling, paragraphs 1.26 to 1.31 should be followed.

3.20 For a new habitable room in a dwelling, ventilation location should follow paragraphs 1.9 to 1.31, performance testing should follow paragraph 1.32 and controls should follow paragraphs 1.33 to 1.37.

Addition of a conservatory to an existing building

3.21 The guidance in this section applies to conservatories with a floor area that exceeds 30m2. Conservatories with a floor area that does not exceed 30m2 are exempt from the Part F requirements.

3.22 The general ventilation rate for a new conservatory and, if necessary, adjoining rooms could be achieved using background ventilators. The guidance in paragraphs 1.42 to 1.44 should be followed regardless of the ventilation provisions in the existing room adjacent to the conservatory.

3.23 For purge ventilation in a new conservatory, paragraphs 1.26 to 1.31 should be followed.

3.24 For a new conservatory, performance testing should follow paragraph 1.32 and controls should follow paragraphs 1.33 to 1.37.

Addition of a wet room to an existing dwelling

3.25 When a wet room is added to an existing dwelling, whole dwelling ventilation should be extended and extract ventilation should be provided by one of the following means.

a. Intermittent extract, as specified in Table 1.1, and a background ventilator of at least 5000mm2 equivalent area.

b. Continuous extract, as specified in Table 1.2.

c. Single-room heat recovery ventilator, as detailed in paragraph 3.26.

3.26 If a continuously running single-room heat recovery ventilator is used in a wet room, it should use the minimum high rate given in Table 1.2 and 50% of this value as the continuous rate. A background ventilator is not required in the same room as the single-room heat recovery ventilator.

3.27 Internal doors should allow air to move within the dwelling by providing a 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.

3.28 For purge ventilation in a new wet room, paragraphs 1.26 to 1.31 apply.

3.29 For a new wet room, ventilation location should follow paragraphs 1.9 to 1.31, performance testing should follow paragraph 1.32 and controls should follow paragraphs 1.33 to 1.37.

Refurbishing a kitchen or bathroom in an existing dwelling

NOTE: If a combustion appliance is installed in a kitchen or bathroom where building work is carried out, Part J of the Building Regulations must be considered.

3.30 Where building work is carried out in a kitchen or bathroom, any existing fans (including cooker hoods, where they extract to the outside) should be retained or replaced. Appropriate checks should be made to determine whether any retained ventilation devices are working correctly.

3.31 If there is no ventilation system in the original room, it is not necessary to provide one in the refurbished room. However, additional ventilation may be necessary if refurbishment work is likely to make the building less compliant with the ventilation requirements of the Building Regulations than it was before the work was carried out. The guidance in paragraphs 3.6 to 3.13 should be followed for refurbishment that includes energy efficiency measures and paragraphs 3.14 to 3.16 should be followed for window replacements.

3.32 If an extractor fan or cooker hood is replaced and it uses the existing cabling, this does not need to be notified to a building control body (see section 1(a) of Schedule 4 to the Building Regulations).

Section 3: Work on existing dwellings