Ventilation Strategy for an Air Quality Condition: Filtered MVHR, Rear Intakes and Why a Generic Report Gets Sent Back

A ventilation strategy for an air quality condition is the report a council asks for before work starts. It shows how the new homes will get clean air when the air outside them is polluted. The council checks three things. First, whether the condition is triggered, using real monitoring and modelled data. Second, whether the air intake sits where the air is cleanest. Third, whether the strategy names a real ventilation unit and filters, with each filter's published test figure. This guide sets out what goes in each part, using two Air & Flood Consultants (AFC) strategies in Hammersmith. In October 2026 the council's air quality officers did not recommend signing off one of them. It met every other part of the condition but named no filtration system.

Got a ventilation strategy condition on your permission? Send us the decision notice and your approved drawings through our fee proposal form for a fixed fee proposal. Our ventilation strategy service page has an example report.

What goes into a ventilation strategy for an air quality condition

Councils in London attach these conditions to new homes in polluted places: flats over shops on main roads, conversions of commercial floors, and homes inside an Air Quality Management Area. The wording varies from borough to borough. Hammersmith and Fulham uses one of the most detailed versions. It is worth reading in full, because each part becomes a section of the report.

Condition 6 of permission 2025/00356/FUL, granted on 10 September 2025 for a lower ground floor flat on Shepherd's Bush Road, Hammersmith, is a pre-commencement condition. It applies "to all residential floors where Council 2030 World Health Organisation (WHO) aligned Annual Mean Air Quality Targets for Nitrogen Dioxide (NO2) - 10ug/m-3, Particulate (PM10) - 15 ug/m-3 and Particulate (PM2.5) - 5 ug/m-3 are exceeded and where current and future predicted pollutant concentrations are within 5% of these limits." It then asks for four sets of details:

1. intakes "at rear roof level or on the rear elevations of all residential floors";

2. extracts "located a minimum of 2 metres away from the air ventilation intakes", citing paragraph 8.9 part C of the Scottish Government's Domestic Ventilation guidance (2nd edition, 2017);

3. "the independently tested mechanical ventilation system with Nitrogen Dioxide (NO2) and Particulate Matter (PM2.5, PM10) filtration", with "a minimum efficiency of 90% in the removal of Nitrogen Oxides/Dioxides, Particulate Matter (PM2.5, PM10) in accordance with BS EN ISO 10121-1:2014 and BS EN ISO 16890:2016";

4. "restricted opening windows (maximum 200mm for emergency purge ventilation only) for all habitable rooms".

A closing paragraph adds that "The whole system shall be designed to prevent summer overheating and minimise energy usage". It puts maintenance on "the primary owner of the property". A second condition, condition 7, then asks for a compliance report after installation from an MRICS chartered building surveyor.

Other councils word it differently. In Barking and Dagenham, AFC's 2026 strategy for a five-flat roof extension on Longbridge Road answered a condition that the architect summarised as mechanical ventilation that takes air from a clean location or treats it. No removal percentage appeared in that summary (Longbridge Road case study). Read your own decision notice line by line. Whatever it lists is what the officer will tick off.

Figure 1: The parts of the condition, the evidence each needs, and where strategies go wrong. Part 3 drew the council's comment on 23 October 2026.

Is the condition triggered? National objectives against the borough's targets

The first paragraph of the condition is a test. Two sets of numbers go into it.

The national air quality objectives are set in the Air Quality (England) Regulations 2000: 40 µg/m³ as an annual mean for nitrogen dioxide (NO₂) and 40 µg/m³ for PM₁₀, with short-term objectives for each. PM₂.₅ has no numeric objective in England. The Environmental Targets (Fine Particulate Matter) (England) Regulations 2023 set a target of 10 µg/m³ by the end of 2040, and the government has an interim target of 12 µg/m³ by January 2028.

The council's 2030 targets are far lower. Hammersmith and Fulham's Air Quality Action Plan 2025-2030, adopted by Cabinet on 16 December 2024, adopts the WHO 2021 global air quality guidelines as its 2030 targets: annual means of 10 µg/m³ NO₂, 15 µg/m³ PM₁₀ and 5 µg/m³ PM₂.₅. As AFC's reports read the plan, it requires mitigation at new homes where those targets are exceeded, or where concentrations are within 5% of them. The condition repeats that test.

The gap between the two sets of numbers matters. A site can meet every national objective with room to spare and still trigger the condition on all three pollutants. Both Hammersmith jobs show it.

Shepherd's Bush Road. The nearest monitoring is the council's roadside station HF4 Shepherds Bush Town Centre, 200 m from the site and 2 m from the kerb. In 2024 it recorded annual means of 34 µg/m³ NO₂, 20 µg/m³ PM₁₀ and 9 µg/m³ PM₂.₅. NO₂ there was 60 µg/m³ in 2019. The London Atmospheric Emissions Inventory (LAEI), interpolated to the 2027 opening year, gives a site maximum of 21.7 µg/m³ NO₂, 18.3 µg/m³ PM₁₀ and 10.3 µg/m³ PM₂.₅. AFC's strategy took the higher figure for each pollutant: 34, 20 and 10.3 µg/m³. On those figures the national objectives are met. The same values are 340%, 133% and 206% of the council's 2030 targets.

Dalling Road. This building on Dalling Road, Hammersmith, is being converted to a single house (permission 2025/02481/FUL, 10 November 2025, condition 9). The nearest monitoring is indicative monitoring at Brackenbury Primary School, 159 m north, which recorded 28.2 µg/m³ NO₂ in 2024 against the 40 µg/m³ objective. The LAEI for 2027 gives 19.6 µg/m³ NO₂, 15.7 µg/m³ PM₁₀ and 9.6 µg/m³ PM₂.₅. AFC's report found these at least 29% below the national objectives. All three borough targets were still exceeded, so the condition applies on every floor.

Figure 2: Below the national objectives, above the borough's targets: the condition still applies. Values from AFC's two strategies.

Two points follow for the report.

First, show the test in a table: each pollutant, the governing value and where it came from, the national objective and the margin, then the council target and the percentage. A report that stops at "the national objectives are met" has not answered the condition.

Second, use the monitoring the council itself relies on. Hammersmith and Fulham's diffusion tube network stopped in 2023, according to the council's 2024 Annual Status Report as read in AFC's strategy. The automatic stations and the LAEI are therefore the current evidence. Free online air quality maps do not replace them.

Figure 3: Monitoring around the Shepherd's Bush Road site (AFC strategy P03, Figure 2). HF4, 200 m away, gave the 2024 values used for NO₂ and PM₁₀.

The Air Quality Neutral test under London Plan policy SI 1 is a separate question: it covers the development's own emissions. A car-free, all-electric flat passes it easily, and both strategies said so in a paragraph. Policy SI 1 also says proposals should not "create unacceptable risk of high levels of exposure to poor air quality". The ventilation strategy is how a council secures that for the future occupants. To check whether a site sits in an Air Quality Focus Area or an AQMA before the application goes in, use our London AQFA checker and AQMA screening tool.

Where the intake goes

Approved Document F Volume 1, paragraphs 2.2 and 2.3, asks for ventilation intakes away from the direct impact of local pollution sources, as high as possible and on the less polluted side of the building. The condition makes that specific: rear roof level or the rear elevation.

At Shepherd's Bush Road the flat has a bedroom at the front, behind a sunken front yard about 5 m from the kerb, and a living room in a new rear extension. The LAEI shows NO₂ falling from 36.3 µg/m³ at the kerb to a site mean of 21.0 µg/m³ in 2027. The rear faces an enclosed garden with no road on that side. A grille low on the rear wall would sit in a sunken, enclosed yard where air moves slowly and dust is re-suspended. The strategy therefore takes the intake to a cowl 450 mm above the flat roof of the new extension, about 3.45 m above the flat's floor. A riser up the main building was ruled out: it would cross three storeys in other ownership in the Shepherd's Bush Conservation Area.

Figure 4: Intake at rear roof level, away from the road. The two neighbouring restaurant extracts are marked R1 and R2 (AFC mark-up, August 2026, P02).

The 2 m rule applies to every extract, not only the MVHR exhaust. The Shepherd's Bush strategy dimensions the MVHR exhaust at 2.4 m from the intake and the ducted cooker hood terminal at 3.2 m. The two restaurant kitchen extracts on the neighbouring buildings are more than 10 m and at least 5 m away. The separations were scaled from the approved roof plan, and the elevation is marked "not to be scaled". A case officer can check a dimension on a plan. A separation shown only on an elevation cannot be checked.

Figure 5: Separations dimensioned in plan: exhaust 2.4 m and cooker hood 3.2 m from the intake, against the 2 m minimum.

At Dalling Road the house has one intake and one exhaust, both in the rear roof valley and 2.60 m apart. An existing gas boiler flue on the rear wall, the only penetration in the building, is to be removed and the brickwork made good. A soil vent pipe head 3.40 m from the intake is also marked, against a 1.50 m minimum.

Figure 6: One intake at rear roof level, exhaust 2.60 m away; the old boiler flue to be removed (AFC mark-up, Dalling Road).

Which system: balanced MVHR, not extract fans

The condition asks for filtered supply air from a rear intake. In practice that means balanced mechanical ventilation with heat recovery (MVHR), or a supply unit with the same filters, run at a slight positive pressure. Supply then slightly exceeds extract. Leakage through the walls and windows on the road side runs outwards, and the air the occupants breathe comes in through the filters.

Size the system to Approved Document F. Both jobs were designed to the 2021 edition of Volume 1 (with the 2022 amendments). A 2026 edition now applies to buildings subject to the 2026 standards, so check which one governs your building control application.

For the one-bedroom flat at Shepherd's Bush Road, the whole-dwelling rate is the greater of 19 l/s (Table 1.3) and 0.3 l/s per m² of floor area. On 77.5 m² that is 23.3 l/s. The kitchen and bathroom high rates of 13 l/s and 8 l/s (Table 1.2) total 21 l/s. Supply at boost is set at 24.3 l/s, 1 l/s above extract. For the Dalling Road house, the strategy gives a supply of 37.6 l/s and a design supply of 38.6 l/s.

Contractors often offer something cheaper: continuous mechanical extract ventilation (MEV) or humidity-controlled extract fans. On the Shepherd's Bush job, an extract-only unit was offered after the council's comment. Extract-only systems supply no filtered air. They also lower the pressure in the flat, so make-up air is drawn in unfiltered through the front facade, the one facing the road. The strategy states that an extract-only system is not an equivalent. Ask your contractor for a supply-side filtered system from the start.

The filter train, and the evidence for each filter

Part 3 of the condition is where generic strategies fail. Describing the performance is not enough. The council wants a named, tested system, with each removal figure traced to a test.

The Shepherd's Bush strategy, revision P03 of 27 October 2026, names three things in the order the air passes through them:

1. An activated-carbon NO₂ stage on the outdoor-air duct, with its own coarse pre-filter. The manufacturer reports 97.6% NO₂ reduction at 29 l/s and 97.9% at 80.3 l/s, with about 200 µg/m³ upstream, from a third-party test at BRE.

2. The MVHR unit, listed on the Product Characteristics Database with a specific fan power of 0.42 W/(l/s) and 91% heat recovery in this flat's configuration. Its own coarse filters protect the heat exchanger and are not counted towards the 90%.

3. A fine particulate stage on the supply duct, before it splits to the rooms: a separate housing with an F9 filter classed ISO ePM1 >90% under BS EN ISO 16890.

The strategy names each product with its manufacturer's part numbers and appends the data sheets. It also sets out what counts as an equivalent, so the contractor is not tied to one model. An equivalent needs an MVHR unit tested and listed on the Product Characteristics Database, a fine stage of ISO ePM1 90% or higher, an independently tested NO₂ stage removing 90% or more, and every litre of supply air drawn through the rear intake and both stages.

Figure 7: The filter train. All supply air passes the carbon stage, the unit and the fine filter in turn, with a pressure switch on each added stage.

Check the fan can push air through the filters. The two added stages add about 40 Pa of clean resistance at 24 l/s. The unit develops about 210 Pa at its 53% speed setting. The specific fan power with every stage fitted is then measured at commissioning against the 1.0 W/(l/s) criterion. A strategy that adds filters without this check can leave a unit that cannot deliver the Approved Document F rate once the filters load.

Give each stage its own alarm. P03 fits a differential-pressure switch across each added stage. Each is set at twice that stage's clean resistance, measured at commissioning. A pressure alarm shows particulate loading. It does not show when the carbon is exhausted. The carbon is therefore changed every 3 years, the short end of the manufacturer's 3 to 5-year expected life, whatever the alarm shows. The fine filter is changed at least three times a year. The pre-filter is changed at least annually.

Leave space to change the filters. The unit and both housings need an accessible cupboard with access panels. Tell the architect early, because a one-bedroom flat has little spare space.

Purge ventilation, overheating and energy

The condition's closing paragraph is answered with numbers:

• summer overheating: a 100% automatic summer bypass, so heat is not recovered into the supply air in warm weather;

• energy: sensible heat recovery of at least 90% and a specific fan power of no more than 1.0 W/(l/s). Both jobs used the same criteria;

• windows: restrictors limiting the opening to 200 mm on every habitable room, for emergency purge only. Everyday ventilation and purge come from the MVHR. At Shepherd's Bush, trickle vents are left out, because one on the front elevation would admit unfiltered air and undo the positive pressure;

• overheating assessment: a new dwelling needs an Approved Document O assessment at building control stage, and it should use the restricted 200 mm opening, not the full window area. Complete it before the windows are ordered;

• escape: check the restrictor setting against the fire strategy. At Shepherd's Bush, escape is through the front door, not a window, subject to building control's confirmation.

Noise belongs here too. Approved Document F limits a continuously running system to 30 dB LAeq,T in noise-sensitive rooms at the low rate. The strategy specifies attenuators and a unit sound power level, and the compliance report records measured levels. If the permission also has an acoustic condition, agree one ventilation system with the acoustician. At Longbridge Road the acoustic report ruled out trickle vents and open windows on the road facade, which led to an MVHR unit per flat with rear intakes.

The compliance report after installation

Hammersmith and Fulham pairs the strategy condition with a compliance condition: condition 7 at Shepherd's Bush Road and condition 10 at Dalling Road. It needs a post-installation report with photographs, prepared by an accredited chartered building surveyor (MRICS). The surveyor is a different professional from the air quality consultant who writes the strategy, so line one up early. AFC does not provide this report.

Make it easy for the surveyor by keeping, from the contractor:

• photographs of the unit and each filter housing, open, showing the filter labels and part numbers;

• the data sheets for the filters actually fitted;

• the commissioning flow record showing supply above extract, by an engineer independent of the installer;

• each pressure switch setting with the measured clean resistance;

• the window restrictors and the measured separations between the intake and each extract.

Traps that get a strategy sent back

A strategy that names no tested unit or filters

AFC's first strategy for Shepherd's Bush Road (P02, 19 August 2026) set out the trigger, the intake, the separations, the restrictors and the system's performance criteria. For part 3 it specified two filter stages by class and standard: a particulate stage classified to BS EN ISO 16890 and an activated-carbon stage "tested to BS EN ISO 10121-1:2014", each removing at least 90%. Test certificates were to follow with the compliance report. It named no product.

On 23 October 2026, on discharge application P/2026/02259/DET, the council's air quality officers commented that P02 gave no details of the NOx and PM₂.₅ filtration system for part 3. They did not recommend signing it off without them. AFC's revision P03 names the unit and both filter stages with their published test figures, and drops the ISO 10121-1 wording, for the reason given under "Claiming a test standard that the filter does not have" below. The discharge was still under assessment at 2 November 2026, according to the council's register.

Offering extract-only ventilation

MEV and extract fans supply no filtered air. They also pull unfiltered make-up air through the polluted facade. They cannot meet a filtered-supply condition.

Claiming a test standard that the filter does not have

The condition cites BS EN ISO 10121-1 for the gas-phase (NO₂) filter and BS EN ISO 16890 for particulate filters. In October 2026 AFC found no residential NO₂ filter that publishes a BS EN ISO 10121-1 result. Carbon stages quote laboratory rig tests, such as the BRE test above. Quote each figure with its test body. Never write that a filter is "tested to BS EN ISO 10121-1" unless its test report says so. A case officer who asks for that report will find the claim unsupported.

Treating an F7 filter as a 90% filter

An ISO ePM1 80% (F7) filter removes at least 80% of particles from 0.3 to 1 µm in the standard's laboratory test. It is not a 90% PM₂.₅ filter. For a 90% condition, specify ISO ePM1 90% or higher (F9).

Few residential fine filters publish separate ePM2.5 and ePM10 figures. The Shepherd's Bush strategy reads the F9 filter's ePM1 >90% class as covering PM₂.₅ and PM₁₀. BS EN ISO 16890 rates those over 0.3 to 2.5 µm and 0.3 to 10 µm, so they contain the PM₁ range and add only larger particles, which a fibrous filter captures more readily. Whether Hammersmith and Fulham accepts that reading is not yet known. Where a manufacturer publishes ePM2.5 and ePM10 figures, quote them instead.

Concluding "the condition is met" before the evidence is in

Conclude part by part: which parts the design meets, and, for the filtration part, what is named, what is evidenced and what follows at installation. A single closing line that the whole condition is met invites the officer to find the part that is not.

Forgetting the compliance report

The compliance report is a separate condition with a separate professional. It is due before occupation, so occupying the flat before it is approved breaches the condition, even when the strategy itself has been approved.

Copying a template from another borough

A strategy written for one council's wording can miss another council's parts. The condition text, not a template, sets the contents.

What to send for a fee proposal

To price a ventilation strategy for an air quality condition, AFC needs:

• the decision notice, with the condition and any compliance condition;

• the approved floor plans, elevations, sections and roof plan;

• the ventilation unit, if the M&E designer or contractor has chosen one;

• any comment from the council, if a strategy has already been submitted.

Without a chosen unit, AFC selects a system that fits the flat and names it with an "or equivalent" clause. Say at the outset if you already have a contractor, so the filters can be coordinated with their supplier. The same approach applies to other conditions: our guide to discharging a surface water drainage condition covers a drainage condition.

What is a ventilation strategy for a planning condition?

It is a report submitted to discharge a planning condition. It shows how new homes in a polluted location will be ventilated with filtered air. It covers whether the condition is triggered, where the intake and extracts go, which unit and filters are used with their test figures, window restrictors, overheating, energy and maintenance. Our ventilation strategy service page has an example report.

Do I need NO2 filtration if my flat is at the back of the building?

If the condition applies to all residential floors and the council's targets are exceeded at the site, yes. At Dalling Road the condition applied on every floor even though the site was at least 29% below the national objectives. A rear position helps the intake, but it does not switch off the condition.

Can I use extract fans or MEV instead of MVHR to discharge an air quality condition?

Not where the condition asks for a filtered supply. Extract-only systems supply no filtered air. They also draw unfiltered air in through the facade facing the road. Use balanced MVHR, or a supply unit, with a fine particulate filter and an activated-carbon NO2 stage.

What filter removes nitrogen dioxide?

An activated-carbon (gas-phase) filter stage. Particulate filters, even F9, do not remove NO2. The carbon stage sits in the supply air path, often on the outdoor-air duct. It needs a coarse pre-filter and a fixed replacement interval, because a pressure alarm does not show when the carbon is spent.

What does "independently tested to BS EN ISO 10121-1" mean, and do residential filters have it?

BS EN ISO 10121-1 is a test method for the gas-phase filter media used against gases such as NO2. In October 2026 AFC found no residential NO2 filter publishing a result to it. Manufacturers quote laboratory tests, such as a third-party test at BRE. A strategy should quote the figure with the body that tested it, and not claim the standard unless a test report shows it.

Why is my site above the council's air quality targets when it meets the national objectives?

The national objective for NO2 is 40 µg/m³ as an annual mean. Hammersmith and Fulham's 2030 target, taken from the WHO 2021 guideline, is 10 µg/m³. Most of inner London sits between the two. Shepherd's Bush Road was at 85% of the national NO2 objective and 340% of the council's target.

Who writes the post-installation compliance report?

Where the condition says so, as in Hammersmith and Fulham, an accredited chartered building surveyor (MRICS). The air quality consultant writes the strategy. The surveyor checks the installed system against it, using photographs, data sheets and the commissioning record.

How long does it take to discharge a ventilation condition?

Under article 27 of the Development Management Procedure Order 2015, the council has 8 weeks from receipt to decide an application to discharge a condition, unless a longer period is agreed in writing. A comment from the air quality officers adds a revision round. The Shepherd's Bush Road application was received on 28 August 2026 and was still under assessment on 2 November 2026. Because the condition is pre-commencement, submit it well before the planned start date.

Get a fee proposal

Air & Flood Consultants writes ventilation strategies and air quality assessments for planning conditions across London. More examples are on our Projects page, including the Shepherd's Bush Road and Dalling Road case studies, and our air quality services page. Send us the decision notice and your approved drawings through our fee proposal form for a fixed fee proposal.