2.3 Construction Pollution Management (A04), Pollution Infiltration (A09) & Air Filtration (A12)

2.3 Construction Pollution Management (A04), Pollution Infiltration (A09) & Air Filtration (A12)

Core Exam Takeaway: A04 Construction Pollution Management is a precondition, and it is far shorter than candidates expect — duct protection, MERV 8 return-air filtration if the permanent system runs, filter replacement before occupancy, and four moisture-and-dust measures. A04 contains no building flush-out requirement and no SMACNA reference — those belong to LEED, not WELL. The 10 ft (3 m) entryway system lives in A09 Part 1, and the filtration levels live in A12, keyed to outdoor $PM_{2.5}$.

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Feature A04: Construction Pollution Management — Precondition

Construction and demolition are dominated by coarse particulate matter but also generate ultrafine particles. WELL's approach is duct protection, moisture and dust management, filter replacement and proper equipment selection — limiting exposure during an intense contamination period.

A04 Part 1 — Mitigate Construction Pollution

Applies to construction occurring after project registration. All three requirement groups must be met:

(a) Duct protection — choose one:

1. Ducts are sealed and protected from possible contamination during construction; or
2. Ducts are cleaned prior to installing registers, grills and diffusers.

(b) Temporary filtration — if the permanently installed ventilation system operates during construction:

1. Media filters with a PM10 removal rating of at least 70% (e.g., MERV 8) are used to filter return air; and
2. All filters are replaced prior to occupancy.

(c) Moisture and dust management — all four:

1. Carpets, acoustical ceiling panels, fabric wall coverings, insulation, upholstery, furnishings and other absorptive materials are stored separately in a designated area protected from moisture damage.
2. All active areas of work are isolated from other spaces by sealed doorways or windows, or through temporary barriers.
3. Walk-off mats are used at entryways to reduce transfer of dirt and pollutants.
4. Saws and similar tools use dust guards or collectors to capture generated dust.

WELL Core guidance: meet A04 for the extent of developer buildout.

[!WARNING] Three things people wrongly attribute to A04.

1. A 14,000 cf/sf building flush-out (with 3,500 cf/sf phased occupancy and 0.30 cfm/sf continuous delivery) is the LEED v4 Indoor Air Quality Assessment credit. WELL v2's A04 has no flush-out pathway at all.
2. The five SMACNA IAQ control measures are a LEED construction-IAQ framework. WELL v2 A04 does not reference SMACNA.
3. The 10 ft (3 m) walk-off system length is A09 Part 1. A04 requires only that walk-off mats be used at entryways — no dimension.

The underlying construction practices — HVAC shutdown, poly barriers, HEPA vacuums, wet cutting, sequencing wet trades before porous finishes — remain excellent means of achieving A04's four dust-and-moisture requirements. Know them as good practice; do not recite them as WELL requirements.

Why the sequencing practice still matters

Porous materials act as chemical sinks: carpets, fabric-covered dividers, drapery and acoustic wall treatments absorb VOCs while paints and adhesives cure, then re-emit them slowly for months. Storing absorptive materials separately and protected from moisture (requirement c1) is WELL's codified expression of exactly this concern, and it is why teams schedule wet trades before dry, absorbent installations even though WELL does not mandate the sequence.

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Feature A09: Pollution Infiltration Management — Optimization (2 pt / WELL Core 4 pt)

WELL notes that approximately 65% of outdoor air particle inhalation occurs while indoors, and that occupants themselves track particulate matter — including coliforms and E. coli — indoors on clothes and shoes.

A09 Part 1 — Design Healthy Entryways (1 pt / Core 2 pt)

Option 1: Building entry design — both requirements:

• (a) All regularly used entrances that open to a pedestrian network include an entryway system of grilles, grates, slots, rollout mats or removable carpet tiles that is at least the width of the entrance and 10 ft (3 m) long in the primary direction of travel, where the length is the sum of indoor and outdoor length.
• (b) One of: a building entry vestibule with two typically closed doorways, or revolving entrance doors — to slow outdoor-to-indoor air movement.

Option 2: Building entry maintenance — entryway systems are wet-cleaned at least once a week and vacuumed at least once a day, or as the manufacturer instructs.

Option 3: Outdoor sport areas — all facilities adjacent to an outdoor sports field have a staging area separating the playing field from other internal areas to capture moisture and debris.

[!TIP] Option 1's "sum of indoor and outdoor length" is a favourite exam detail: a 4 ft exterior grate plus a 6 ft interior mat satisfies the 10 ft requirement. Option 2 is a maintenance-only alternative — a project with existing entryway systems can earn the point without changing the architecture.

A09 Part 2 — Perform Envelope Commissioning (1 pt / Core 2 pt)

For projects undergoing design and construction, all five:

• (a) The project uses a façade engineer responsible for defining building envelope performance metrics — materials, components, assemblies and systems — at the concept design stage.
• (b) Envelope performance requirements are included in the Basis of Design and reflect the Owner's Project Requirements.
• (c) The commissioning process includes envelope commissioning for air infiltration and leakage, reflected in the specification and commissioning plan.
• (d) The envelope commissioning process is executed as outlined in the plan.
• (e) The envelope commissioning plan is included in the project Operation & Maintenance (O&M) Manual.

Note that WELL sets no numeric building pressurization target (there is no "+10 to +25 Pa" requirement); envelope performance is governed by the commissioning process, and A11 Source Separation — not A09 — is where negative pressurization of specific rooms appears.

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Feature A12: Air Filtration — Optimization (1 pt / WELL Core 2 pt)

Standard commercial filters rated MERV 6–8 exist mainly to protect coils and fans, offering little protection against respirable $PM_{2.5}$. A12 raises filtration — but the required level scales with the project's outdoor particulate burden, which is the structural insight the exam tests.

A12 Part 1 — Implement Particle Filtration

Option 1: Filtration levels. Media filters are used in the ventilation system to filter outdoor air supplied to the space, per this table:

Option 2: Filter maintenance. Evidence that the filter has been replaced according to the manufacturer's recommendation is submitted annually through the WELL digital platform.

WELL Core guidance: meet A12 in the whole building; up to 10% of the total tenant-occupied area may be excluded from feature scope.

ASHRAE 52.2 MERV EFFICIENCY SPECTRUM (context for the A12 tiers)

Filter Rating   0.3 - 1.0 um     1.0 - 3.0 um     3.0 - 10.0 um
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MERV 8          < 20%            < 20%            >= 70%    <-- A04 temporary filter
MERV 11         20% - 34%        65% - 79%        >= 85%
MERV 12         ~35% - 49%       >= 80%           >= 90%    <-- A12 tier 1
MERV 14         >= 75%           >= 90%           >= 90%    <-- A12 tier 2, A13
MERV 16         >= 95%           >= 95%           >= 95%    <-- A12 tier 3
HEPA            >= 99.97%        >= 99.97%        >= 99.97%

[!WARNING] MERV 13 is not a WELL v2 threshold. It is the ASHRAE 62.1-2019 / LEED figure. WELL v2's A12 tiers are MERV 12, MERV 14 and MERV 16, selected by outdoor $PM_{2.5}$, and A13 Enhanced Supply Air separately calls for MERV 14 (≥90% PM2.5 removal) where recirculated air is treated.

Why filter frame integrity still matters

A12 specifies removal efficiency, not installation detail — but bypass leakage defeats the specification. Gaps of even a millimetre around a filter frame let air take the path of least resistance, so a nominally MERV 14 bank can behave like MERV 8 in service. Airtight gaskets and positive latching are how the specified efficiency survives contact with a real air handler.