Disclaimer: Here, we will provide an interpretation of the approved document as we read it. This includes consultations with customers and trade bodies. However, it is essential that you refer to the published approved document for its guidelines on how to comply with the building regulations. We have included the section references within the document for you to easily reference the approved document directly. We have also tried to break the document down so that particular questions you may have can easily be identified.
Part K (comprising regulations 64 – 68) of the Building Regulations sets out the requirements for the provision of ventilation of buildings, taken directly from the Building Regulations (Northern Ireland) 2012. Any person who intends to demonstrate compliance with the Building Regulations by following the guidance given in the technical booklet is advised to ensure that the regulations below are current on the date when plans are deposited or notices given to the district council. All Parts of the Building Regulations NI should be read in conjunction with Part A.
The requirements of regulation 65 will be met where a ventilation system is provided that, under normal conditions, is capable of limiting, the accumulation of moisture which could lead to mould growth, and the accumulation of pollutants originating within a building which would otherwise become a hazard to the health of the people in the building. This is achieved by replacing “stale” indoor air from a building with “fresh” outside air.
Using trickle vents normally fitted to window casement or frame the following routes can be used.
New dwellings are specified according to two standard designs of air permeability
a) in the default option, the guidance assumes no air permeability and therefore no infiltration, resulting in the building’s ventilation being reliant only on the installed ventilation provisions. Provides for adequate ventilation provision for dwellings of all air permeability and be particularly suitable when intending to construct a more airtight dwelling.
b) The guidance assumes an infiltration of 0.15 air changes per hour (ach). Provisions are less than option (a) as infiltration contributes to the total amount of ventilation. This option is most appropriate when designing to an air permeability greater than 5 m3/(h.m2) at 50 Pa
This Technical Booklet adopts the following
a) Intermittent or continuous extract ventilation from rooms where most water vapour and/or pollutants are generated to provide local control and minimise general spread to other areas
b) Whole building ventilation to provide fresh air to the building and to dilute and disperse residual water vapour
and pollutants not dealt with by extract ventilation as well as removing water vapour and other pollutants that are released throughout the building. Whole building ventilation provides nominally continuous air exchange.
c) Rapid ventilation throughout the building to aid removal of high concentrations of pollutants and water vapour released from occasional activities such as painting and decorating or accidental releases such as smoke from burnt food or spillage of water.
This can be delivered by a Natural, mechanical or Hybrid ventilation system.
Naturally ventilated buildings, it is common to use a combination of ventilators to achieve this strategy (e.g. for dwellings it is common to use intermittent extract fans for extract ventilation, trickle ventilators for whole dwelling ventilation and windows for rapid ventilation).
Mechanically ventilated, air-conditioned buildings, it is common for the same ventilators to provide both local extract and whole building/dwelling ventilation.
So, how can the requirements of Document K be delivered?
New Buildings
Method 1 – providing the ventilation rates set out in paragraphs 2.5 to 2.7; or
Method 2 – following the system guidance set out –
(i) for dwellings without basements (ii) for dwellings with basements
Select the ventilation system model
System 1 – Background ventilators and intermittent extract fans.
System 2 – Passive stack ventilation (PSV).
System 3 – Continuous mechanical extract (MEV).
System 4 – Continuous mechanical supply and extract with heat recovery (MVHR).
Method 3 – using other ventilation systems
Using Method 2 – System 1
Determine the total equivalent ventilator area ¬ see tables below for a dwelling with any design air permeability. The lower table may be followed for a dwelling designed to an air permeability greater than 5 m3/(h.m2) at 50 Pa which recommends less ventilation provisions.
Follow (a) or (b) as appropriate depending on the number of storeys –
a) for multi¬storey dwellings, and single storey dwellings more than four storeys above ground level – use the total equivalent ventilator area from Step 1; or
b) for single storey dwellings up to and including the fourth storey above ground level – add a further 10000 mm2 to the total equivalent ventilator area from Step 1, preferably shared between several rooms.
System 2 – Passive stack ventilation (PSV)
Step 1 – Determine the total equivalent ventilator area from the tables above (¬ see Table 2.3 for a dwelling with any design air permeability). Alternatively, the guidance in Table 2.4 may be followed for a dwelling with a designed air permeability greater than 5 m3/(h.m2) at 50 Pa which recommends less ventilation provisions,
Step 2 – Make an allowance for the total air flow through all PSV units. As an approximation assume each PSV unit provides an equivalent area of 3000 mm2.
The equivalent ventilator area required for the dwelling is the value found in Step 1 less that calculated from Step 2.
Background vent locations for PSV
Background ventilators should be located in all rooms with external walls except the rooms where a PSV is located, There should be background ventilation of at least 5000 mm2 equivalent area in each habitable room and 2500 mm2 equivalent area in each wet room not containing a PSV.
Background ventilators should be located to avoid draughts, typically 1.7 m above floor level.
System 3 – Continuous mechanical extract (MEV)
Background ventilators
For any design air permeability, controllable background ventilators, having a minimum equivalent area of 2500 mm2, should be fitted in each room other than in rooms from which air is extracted.
As an alternative, where the designed air permeability is greater than 5 m3/(h.m2) at 50 Pa background ventilators are not necessary.
Where background ventilators are fitted they should be:
a) located to avoid draughts,
b) Typically, 1.7 m above floor level
c) A minimum of 0.5 m away from fans fitted in the same room
d) Manually adjustable or automatically controlled.
System 4 – Continuous mechanical supply and extract with heat recovery (MVHR)
No background or trickle ventilators required
Alternative ventilation system can be used, provided it can be demonstrated to the district council that it satisfies Part K, e.g. by showing that it meets the moisture and performance -based ventilation requirements.
Ventilation of a habitable room through another habitable room or conservatory
Background ventilation, of at least 8000 mm2 equivalent area must be installed and there being a permanent opening between the two habitable rooms.
Adding a habitable room to the building
Background ventilators should be used
i) if the additional room is connected to an existing habitable room which now has no windows opening to outside, the guidance is as for new build or
ii) if the additional room is connected to an existing habitable room which still has windows opening to outside but with a total background ventilator equivalent area less than 5000mm2, the guidance is as for new build or
iii) if the additional room is connected to an existing habitable room which still has windows opening to outside and with a total background ventilator equivalent area of at least 5000mm2, there should be background ventilators of at least 8000 mm2 equivalent area between the two rooms and background ventilators of at least 8000 mm2 equivalent area between the additional room and outside.
Adding a wet room to the building
Whole building and extract ventilation can be provided by a background ventilator of at least 2500 mm2 equivalent area; or
Adding a conservatory to the building
the guidance is as for new build
Refurbishing a kitchen or bathroom
The building work it should not make any existing provision less compliant with the regulations.
Ventilation of replacement windows
Completed building work should not create a new or greater contravention with other applicable requirements than before commencement of the work.
Where the original windows were not fitted with trickle ventilators and the room is not ventilated adequately background ventilation should be provided in the form of trickle ventilators to assist with the control of condensation within dwellings and improve indoor air quality.
In all cases where trickle ventilators are to be fitted, the new ventilation opening should not be smaller than was originally, and it should be controllable.
Where there was no ventilation opening, or where the size of the original ventilation opening is not known, the following minimum sizes should be adopted –
Dwellings:
habitable rooms – 5000 mm2 equivalent area
kitchen, utility room and bathroom (with or without WC) – 2500 mm2 equivalent area
Buildings other than dwellings:
occupiable rooms: for floor areas up to 10 m2 – 2500 mm2 equivalent area
greater than 10 m2 at the rate of 250 mm2 equivalent area per m2 of floor area;
kitchens (domestic type) – 2500 mm2 equivalent area
bathrooms and shower rooms – 2500 mm2 equivalent area per bath or shower and
sanitary accommodation – 2500 mm2 equivalent area per WC.
Location of background ventilators
Background ventilators should be located to avoid draughts, typically 1.7 m above floor level
Background ventilators should be located in all rooms with external walls, with at least 5000 mm2 equivalent area in each habitable room and 2500 mm2 equivalent area in each wet room.
If the dwelling has more than one exposed wall, to maximise the air flow through the dwelling by encouraging cross ventilation, it is best to locate similar equivalent areas of background ventilators on opposite (or where this is not possible, adjacent) sides of the dwelling.
Technical booklet K – Ventilation
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