7.3 Individual Thermal Control (T04) & Humidity Control (T07)

7.3 Individual Thermal Control (T04) & Humidity Control (T07)

Core Exam Takeaway: T04 Individual Thermal Control (3 pt / WELL Core 1.5 pt) has three parts worth 1 point each — personal cooling, personal heating, and a flexible dress code policy. Its performance catch-all is a PMV change of ±0.5 within 15 minutes of activation, without changing PMV for other occupants. T07 Humidity Control (1 pt / Core 2 pt) is the 30%–60% relative humidity feature, and its modelling and data options both demand that band for at least 98% of all business hours of the year.

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Feature T04: Individual Thermal Control — Optimization (3 pt / WELL Core 1.5 pt)

Intent: maximize and personalize thermal comfort among all individuals, through personal thermal comfort devices and flexible dress codes.

Why individual control is the only real answer

Recall that PPD never falls to zero: even a perfectly tuned space at PMV = 0 leaves roughly 5% of occupants dissatisfied, and the two personal variables in the ASHRAE 55 model — metabolic rate and clothing insulation — vary between individuals sitting three feet apart. No central setpoint can resolve that. T04 therefore attacks both personal variables directly: devices change the individual's local environment, and a flexible dress code lets the individual change their own clo value.

T04 Part 1 — Provide Personal Cooling Options (1 pt / Core 0.5 pt)

For all spaces except dwelling units. All regular occupants can cool their individual environment through one or more of:

• (a) A user-adjustable thermostat connected to the building's mechanical cooling system or to an air conditioning unit. The room or thermal zone controlled by the thermostat may not be regularly occupied by more than one person.
• (b) Desk fan or ceiling fan that does not increase air speed for other occupants.
• (c) Chair with mechanical cooling system.
• (d) Any other solution capable of affecting a PMV change of −0.5 within 15 minutes from activation, without changing the PMV for other occupants.

T04 Part 2 — Provide Personal Heating Options (1 pt / Core 0.5 pt)

For all spaces except commercial kitchen spaces and dwelling units. All regular occupants can warm their individual environment through one or more of:

• (a) A user-adjustable thermostat connected to the building's mechanical heating system, with the same one-person zone restriction.
• (b) Electric parabolic space heater
• (c) Electric heated chair or footwarmers
• (d) Blankets, which are washed at least weekly
• (e) Any other solution capable of affecting a PMV change of +0.5 within 15 minutes from activation, without changing PMV for other occupants

T04 Part 3 — Allow Flexible Dress Code (1 pt / Core 0.5 pt)

For all spaces except commercial kitchen spaces and dwelling units. A flexible dress code policy is in place that allows regular occupants to dress for individual thermal preferences.

WELL Core guidance: Parts 1 and 2 in non-leased spaces, with an additional point for the whole building; Part 3 for direct staff.

+-----------------------------------------------------------------------------+
|         T04's PERFORMANCE CATCH-ALL: THE THREE-CONDITION TEST               |
|                                                                             |
|   Any device qualifies if it can:                                           |
|                                                                             |
|     1. Shift PMV by  -0.5 (cooling, Part 1) or +0.5 (heating, Part 2)        |
|     2. Do so WITHIN 15 MINUTES of activation                                 |
|     3. WITHOUT changing PMV for other occupants                              |
|                                                                             |
|   Condition 3 is why an open-plan pedestal fan pointed at a neighbour        |
|   fails, and why the single-occupant restriction attaches to the             |
|   thermostat options: one person's relief cannot become another's            |
|   discomfort.                                                               |
+-----------------------------------------------------------------------------+

[!IMPORTANT] The one-person zone restriction is the most counter-intuitive rule in the concept. A thermostat only counts as individual control if the room or thermal zone it governs is not regularly occupied by more than one person. A shared office with one wall thermostat is zoning (T03), not individual control (T04) — which is exactly why the two features are separate and why T01's ±1.0 PMV band accepts two points from either or a combination of both.

[!TIP] Blankets, washed at least weekly is the standard's most quotable low-tech provision — and the washing frequency is a real requirement, because shared textiles are a hygiene vector. Note also that Part 2 excludes commercial kitchen spaces: kitchens run hot, so personal heating is irrelevant there, while Part 1 cooling still applies to them.

[!TIP] Part 3 costs nothing but a policy document. A written flexible dress code earns a full point, and it is the single cheapest point in the Thermal Comfort concept. It also directly enables the adaptive comfort logic in T01 Option 1(b): occupants who can add or remove layers tolerate a much wider operative temperature range.

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Feature T07: Humidity Control — Optimization (1 pt / WELL Core 2 pt)

Intent: limit the growth of pathogens, reduce off-gassing and maintain thermal comfort by providing the appropriate level of humidity.

T07 Part 1 — Manage Relative Humidity

All options apply to all regularly occupied areas, except high-humidity areas:

Option 1: Mechanical humidity control. The mechanical system has the capability of maintaining relative humidity between 30% and 60% at all times by adding or removing moisture from the air.

Option 2: Humidity modeling. The modelled relative humidity levels in the space are between 30% and 60% for at least 98% of all business hours of the year.

Option 3: Long-term humidity data — both:

• (a) The project meets Feature T06: Thermal Comfort Monitoring.
• (b) Humidity data covering at least the previous six months are between 30% and 60% for at least 98% of all business hours of the year.

Recertification note: projects previously awarded T06 must consider all data collected since the previous (re)certification. WELL Core guidance: whole building; projects pursuing Option 1 must have access to at least 10% of leased space for testing.

Why 30% and 60% specifically

The band is bounded by three distinct failure modes, one below and two above:

[!IMPORTANT] Note the difference between Option 1 and Options 2 and 3. Option 1 asks only for capability — the mechanical system must be able to hold 30–60% at all times, which is a design and equipment-selection demonstration. Options 2 and 3 ask for outcome — modelled or measured performance inside the band for at least 98% of all business hours of the year. The capability route is far easier to document for a new build; the data route suits an existing building with T06 sensors already installed.

How T07 knits the standard together

T07 is one of WELL's most cross-connected features:

• With A14 Microbe and Mold Control and W07 Moisture Management, it closes the mold triad — air-side equipment, building assemblies, and ambient air respectively.
• With T05 Radiant Thermal Comfort, it is effectively mandatory: radiant cooling surfaces below the dew point condense, so humidity control is the engineering precondition for radiant cooling.
• With T06 Thermal Comfort Monitoring, it shares the sensing infrastructure — T06 already measures relative humidity, which is why Option 3 simply points at it.
• With A01 and X06, it moderates off-gassing: emission rates from materials rise with humidity, so holding the band lowers measured VOC concentrations at no additional filtration cost.