Section 5 New dwellings

New dwellings

  1. Introduction to provisions
    1. Ventilation rates
      1. Ventilation systems for dwellings without basements
        1. Ventilation systems for basements
          1. Ventilation of a habitable room through another room or a conservatory

            Introduction to provisions

            Table 5.1a

            5.1 This Approved Document shows three main ways of complying with the ventilation requirements of the Building Regulations:

            a. providing the ventilation rates set out in paragraphs 5.4 to 5.7; or

            b. following the system guidance set out:

            for dwellings without basements in paragraphs 5.8 to 5.10. This guidance covers all levels of design air permeability. Alternative guidance is also provided for dwellings designed to an air permeability leakier than (>) 5 m³/(h.m²) at 50 Pa where the developer from experience will not construct significantly more airtight dwellings (not better than 3 m³/(h.m²) at 50 Pa); or

            for dwellings with basements in paragraphs 5.11 to 5.13; or

            c. using other ventilation systems provided it can be demonstrated to the Building Control Body that they satisfy the Requirement, e.g. by showing that they meet the moisture and air quality criteria set out in Appendix A.

            5.2 There should be reasonable access for maintenance. This should include access for the purpose of changing filters, replacing defective components and cleaning ductwork.

            5.3 Note that extract fans lower the pressure in a building, which can cause the spillage of combustion products from open-flued appliances (i.e. the combustion gases may fill the room instead of going up the flue or chimney). This can occur even if the appliance and the fan are in different rooms. Ceiling sweep fans produce air currents and hence local depressurisation, which can also cause the spillage of flue gases from open-flued gas appliances or from solid fuel open fires. In buildings where it is intended to install open-flued combustion appliances and extract fans, the combustion appliance should be able to operate safely whether or not the fans are running. A way of showing compliance in these circumstances would be to follow the guidance given in Approved Document J on both the installation of the appliances and tests to show that combustion appliances operate safely whether or not fans are running.

            Table 5.1a Extract ventilation rates

            Table 5.1a Extract ventilation rates

            Table 5.1b Whole dwelling ventilation rates

            Table 5.1b Whole dwelling ventilation rates

             

            Ventilation rates

            5.4 The performance will be achieved by providing the air flow rates set out in paragraphs 5.5 to 5.7. The air flow rates specified are for the performance of the complete installation. The performance of the ventilation devices (and associated components such as ducting for fans) should be tested according to the Standards listed under ‘Performance test methods’ in Table 5.3. All natural and mechanical systems should be fully commissioned, and guidance is given in the Domestic ventilation compliance guide, available from: www.planningportal.gov.uk/ approved documents.

            5.5 Extract ventilation to outside is required in each kitchen, utility room and bathroom and for sanitary accommodation. The extract can be either intermittent or continuously operating. The intermittent rate, and for continuous systems the minimum extract air flow rates at the highest and lowest settings, should be no less than specified in Table 5.1a.

            5.6 The whole dwelling ventilation rate for the supply of air to the habitable rooms in a dwelling should be no less than specified in Table 5.1b.

            5.7 Purge ventilation provision is required in each habitable room and should be capable of extracting a minimum of four air changes per hour (ach) per room directly to outside. Normally, openable windows or doors can provide this function (see Appendix B), otherwise a mechanical extract system should be provided. In other rooms (e.g. kitchens and bathrooms) the mechanical or passive stack extract provisions should be sufficient, although passive stack ventilation will take longer to purge the room.

            Ventilation systems for dwellings without basements

            Diagram 2a

            5.8 The performance required for dwellings without basements could be achieved by following Steps 1 and 2 below. Worked examples for each system are given in Appendix C.

            5.9 For each system, guidance is given for dwellings to cover all design air permeabilities. This guidance is therefore suitable for all dwellings and, for ventilation purposes, it is not necessary for the as-built permeability to be close to the design permeability.

            5.10 In addition to this guidance, for each system alternative guidance is provided for dwellings with as-built air permeabilities leakier than (>) 3 m³/(h.m²) at 50 Pa. It is recommended that this option is selected only if designing to an air permeability leakier than (>) 5 m³/(h.m²) at 50 Pa and if the person carrying out the building work has previous experience of closely matching design with as-built air permeability levels. If the alternative guidance is followed, and it is subsequently found that either

            • the tested air permeability for that dwelling is tighter than or equal to (≤) 3 m³/(h.m²) at 50 Pa, or
            • if the dwelling is not tested, but another dwelling of the same dwelling type tested under regulation 43 is tighter than or equal to (≤) 3 m³/(h.m²) at 50 Pa,

            it may be necessary for the BCB to ask for more air permeability testing to be carried out to ensure all dwellings in the sample are provided with adequate ventilation.

            Step 1: Select one of the following four ventilation systems (illustrated in Diagram 2a).

            System 1: Background ventilators and intermittent extract fans. Guidance on minimum provisions for extract and whole dwelling ventilation is set out in Table 5.2a. Note that it includes separate guidance for dwellings with habitable rooms having only a single exposed facade.

            System 2: Passive stack ventilation (PSV). Guidance on minimum provisions for extract and whole dwelling ventilation is set out in Table 5.2b.

            System 3: Continuous mechanical extract (MEV). Guidance on minimum provisions for extract and whole dwelling ventilation is set out in Table 5.2c.

            System 4: Continuous mechanical supply and extract with heat recovery (MVHR). Guidance on minimum provisions for extract and whole dwelling ventilation is set out in Table 5.2d.

            Step 2: See Table 5.3 for guidance on performance test methods for the products chosen.

            Diagram 2a Ventilation systems

            Diagram 2a Ventilation systems

            Diagram 2b Single sided ventilation

            Diagram 2b Single sided ventilation

            Table 5.2a System 1- background ventilators and intermittent extract fans (for additional Information see Table 5.3 and worked examples c1 and C5 in Appendix C)

            Table 5.2a System 1- background ventilators and intermittent extract fans (for additional Information see Table 5.3 and worked examples C1 and C5 in Appendix C)

            Table 5.2a System 1- background ventilators and intermittent extract fans (for additional Information see Table 5.3 and worked examples c1 and C5 in Appendix C) continued

            Table 5.2a System 1- background ventilators and intermittent extract fans (for additional Information see Table 5.3 and worked examples C1 and C5 in Appendix C) continued

            Table 5.2a System 1- background ventilators and intermittent extract fans (for additional Information see Table 5.3 and worked examples c1 and C5 in Appendix C)

            Table 5.2a System 1- background ventilators and intermittent extract fans (for additional Information see Table 5.3 and worked examples C1 and C5 in Appendix C)

            a href=”http://cms.thebuildingregulations.org.uk/wp-content/uploads/2016/04/Table-5.2b-System-2-Passive-Stack-Ventilation-PSV-for-additional-information-see-table-5.3-and-worked-examples-C2-and-C6-in-Appendix-C-continued.png” rel=”attachment wp-att-7884″>Table 5.2b System 2- Passive Stack Ventilation (PSV) (for additional information see table 5.3 and worked examples C2 and C6 in Appendix C) continued

            Table 5.2b System 2- Passive Stack Ventilation (PSV) (for additional information see table 5.3 and worked examples C2 and C6 in Appendix C)

            Table 5.2b System 2- Passive Stack Ventilation (PSV) (for additional information see table 5.3 and worked examples C2 and C6 in Appendix C)

            Table 5.2b System 2- Passive Stack Ventilation (PSV) (for additional information see table 5.3 and worked examples C2 and C6 in Appendix C)

            System 2- Passive Stack Ventilation (PSV) (for additional information see table 5.3 and worked examples C2 and C6 in Appendix C) continued 2

            Table 5.2b System 2- Passive Stack Ventilation (PSV) (for additional information see table 5.3 and worked examples C2 and C6 in Appendix C) continued 2

            Table 5.2c System 3- Continuous mechanical extract (MEV)(for additional information see Table 5.3 and worked examples C3 and C7 in Appendix C)

            Table 5.2c System 3- Continuous mechanical extract (MEV)(for additional information see Table 5.3 and worked examples C3 and C7 in Appendix C)

            Table 5.2c System 3- Continuous mechanical extract (MEV)(for additional information see Table 5.3 and worked examples C3 and C7 in Appendix C)

            Table 5.2c System 3- Continuous mechanical extract (MEV)(for additional information see Table 5.3 and worked examples C3 and C7 in Appendix C) continued

            Table 5.2d System 4- Continuous mechanical supply and extract with heat recover (MVHR)(for additional information see Table 5.3 and worked examples C4 and C8 in Appendix C)

            Table 5.2d System 4- Continuous mechanical supply and extract with heat recover (MVHR)(for additional information see Table 5.3 and worked examples C4 and C8 in Appendix C)

            Table 5.2d System 4- Continuous mechanical supply and extract with heat recover (MVHR)(for additional information see Table 5.3 and worked examples C4 and C8 in Appendix C) continued

            Table 5.2d System 4- Continuous mechanical supply and extract with heat recover (MVHR)(for additional information see Table 5.3 and worked examples C4 and C8 in Appendix C) continued

            Table 5.3 Performance Test Methods

            Table 5.3 Performance Test Methods

            Ventilation systems for basements

            5.11 For a dwelling which includes a basement that is connected to the rest of the dwelling above ground by a large permanent opening (e.g. an open stairway), the whole dwelling including the basement should be ventilated in accordance with paragraph 5.8 (for dwellings without basements) and treated as a multi- storey dwelling. If the basement has only a single exposed facade, while the rest of the dwelling above ground has more than one exposed facade, ventilation systems 3 and 4 are preferred, following the guidance in paragraph 5.8. If systems 1 or 2 are to be used, seek expert advice.

            5.12 For a dwelling which includes a basement that is not connected to the rest of the dwelling above ground by a large permanent opening:

            a. the part of the dwelling above ground should be considered separately and ventilated in accordance with paragraph 5.8. If the part of the dwelling above ground has no bedrooms, assume it has one bedroom for the purpose of determining ventilation provisions; and

            b. the basement should be treated separately as a single-storey dwelling above ground level in accordance with paragraph 5.8. If the basement has no bedrooms, assume it has one bedroom for the purpose of determining ventilation provisions. The guidance on natural ventilation given in the Approved Document may not be appropriate for this situation and expert advice should be sought.

            5.13 A dwelling which comprises only a basement should be treated as a single-storey dwelling above ground level in accordance with paragraph 5.8. The guidance on natural ventilation given in the Approved Document may not be appropriate for this situation and expert advice should be sought.

            Ventilation of a habitable room through another room or a conservatory

            Diagram 3

            5.14 In a habitable room not containing openable windows (i.e. an internal room) the requirement will be met if the room is ventilated either through another habitable room (see paragraph 5.15) or through a conservatory (see paragraph 5.16).

            5.15 A habitable room not containing openable windows may be ventilated through another habitable room (see Diagram 3) if:

            a. there is, from the habitable rooms to outside, provision for both:

            i. purge ventilation, one or more ventilation openings, with a total area given in Diagram 3 based on at least the combined floor area of the habitable rooms; and

            ii. background ventilation of at least 8000 mm² equivalent area; and

            b. there is an area of permanent opening between the two rooms as given in Diagram 3 based on at least the combined floor area of the habitable rooms.

            5.16 A habitable room not containing openable windows may be ventilated through a conservatory (see Diagram 4) if:

            a. there is, from the conservatory to outside, provision for both:

            i. purge ventilation, one or more ventilation openings, with a total area given in Diagram 4 based on at least the combined floor area of the habitable room and conservatory; and

            ii. background ventilation, a ventilation opening (or openings) of at least 8000 mm² equivalent area; and

            b. there are openings (which must be closable) between the habitable room and the conservatory for:

            i. purge ventilation equivalent to paragraph 5.15a(i) above; and

            ii. background ventilation equivalent to paragraph 5.15a(ii) above which should be located typically at least 1.7 m above floor level and need not be within the door frame.

            Diagram 3 Two habitable rooms treated as a single room for ventilation purposes

            Diagram 3 Two habitable rooms treated as a single room for ventilation purposes

            Diagram 4 A habitable room ventilated through a conservatory

            Diagram 4 A habitable room ventilated through a conservatory