Building Regulations - Wales

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.

There are three ways of complying with the Welsh Building Regulations:

a) Providing the ventilation rates
b) Follow the system guidance set out for dwellings without basements. For all levels of design air permeability. Guidance is also provided for dwellings  designed to an greater air permeability > 5 m3/(h.m2) at 50 Pa not more airtight (< 3 m3/(h.m2) at 50 Pa); or dwellings with basements
c) Alternative ventilation system provided it can be demonstrated to the Building Control Body that they satisfy the Requirement,

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 below.

Select the ventilation system to be used

System 1: Background ventilators and intermittent extract fans.
Minimum provisions for extract and whole dwelling ventilation is set out in the table above.

System 2: Passive stack ventilation (PSV)
Guidance on minimum provisions for extract and whole dwelling ventilation is given below.

System 3: Continuous mechanical extract (MEV)
Guidance on minimum provisions for extract and whole dwelling ventilation is given below.

System 4: Continuous mechanical supply and extract with heat recovery (MVHR).
Guidance on minimum provisions for extract and whole dwelling ventilation is given below.

System 1 – Background ventilators and intermittent extract fans

Background ventilators (follow these steps)
Step 1: Determine the total equivalent ventilator area
Step 2: Follow as appropriate depending on the number of storeys:.

Multi-storey dwellings, and single-storey dwellings more than four storeys above ground level. Use the total equivalent ventilator area from Step 1.

Single-storey dwellings up to and including the fourth storey above ground level. Add a 10000 mm2 to the total equivalent ventilator area from Step 1, shared between rooms.

Step 3: Dwellings with single exposed façade, or at least 70% of the EQA is designed to be on the same façade, cross-ventilation is not possible, additional ventilation provisions are recommended.

In this case background ventilators should be located at both high and low positions in the façade to provide enhanced single-sided ventilation. The total EQA as described in Steps 1 and 2 above should be provided at the high position (typically 1.7 m above floor level) for all dwelling types and all storey heights.

In addition, ventilators having the same total EQA should be provided at least 1.0 m below the high ventilators.

Minimum requirements

 

System 2 – Passive stack ventilation (PSV)

Background ventilators (follow steps below)
Step 1: Determine the total equivalent ventilator area –
Step 2: Make an allowance for the total air flow through all PSV units.
Step 3: Actual equivalent ventilator area required for the dwelling is the value found in Steps 1 and 2.

 

Location of background ventilators
Background ventilators should be located in all rooms with external walls except the rooms where a PSV is located, At least 5000 mm2 EQA in each habitable room and 2500 mm2 EQA in each wet room not containing a PSV.

Background ventilators should be located to avoid draughts, e.g. 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 EQA of 2500 mm2 should be fitted in each room, except wet rooms, from which air is extracted.

Where the designed air permeability is > 5 m3/(h.m2) at 50 Pa background ventilators are not necessary, but see the cautionary advice in paragraph 5.10. Where this approach causes difficulties (e.g. on a noisy site) seek expert advice.

Fans and background ventilators fitted in the same room should be a minimum of 0.5m apart

System 4 – Continuous mechanical supply and extract with heat recovery (MVHR)
Background ventilators are not required

Ventilation of a habitable room through another room or a conservatory
Background ventilators of at least 8000 mm2 EQA should be supplied.

Where the original windows were fitted with trickle ventilators the replacement windows should include them and they should be sized as below,

Where the original windows were not fitted with trickle ventilators and the room is not ventilated adequately by other installed provisions, it would be good practice to fit trickle ventilators.

In all cases where controllable trickle ventilators are to be fitted, the new ventilation opening should not be smaller than was originally provided.

Where there was no ventilation opening, or where the size of the original ventilation opening is not known, use these minimum sizes.

Dwellings
habitable rooms – 5000 mm2 EQA
kitchen, utility room and bathroom (with or without WC) – 2500 mm2
EQA.

Buildings other than dwellings
Occupiable rooms: for floor areas up to 10 m2 – 2500 mm2 EQA; greater than 10 m2 – at the rate of 250 mm2 EQA per m2 of floor area

Kitchens (domestic type) – 2500 mm2 EQA
Bathrooms and shower rooms – 2500 mm2 EQA per bath or shower
Sanitary accommodation– 2500 mm2 EQA per WC.

Adding a habitable room to an existing dwelling
The adjoining rooms could be ventilated by one of the following options.

Background ventilators could be used.

The additional room is connected to an existing habitable room which now has no windows opening to outside, follow the new dwelling guidance. If the new room is connected to an existing habitable room which still has windows opening to outside but with a total background ventilator EQA less than 5000 mm2, follow the new dwelling guidance.

If the new room is connected to an existing habitable room which has windows opening to outside and with a total background ventilator EQA of at least 5000 mm2, background ventilators of at least 8000 mm2 EQA between the two rooms and background ventilators of at least 8000 mm2
EQA between the new room and outside.

Addition of a wet room to an existing dwelling
Whole building and extract ventilation can be provided by an intermittent extract and a background ventilator of at least 2500 mm2 EQA

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