Mould in Dubai buildings.
The rules, the numbers, the evidence.

TL;DR

• Dubai Municipality issued DM-HSD-GU142-MRC2 on 12 May 2025 — the Technical Guideline for Mold Remediation and Control. It is a first issue: before this, Dubai had no dedicated mould guideline.
• Its moisture-control section instructs: keep indoor relative humidity below 60%, ideally between 30 and 50% — a stricter framing than the general comfort ranges in other DM documents.
• It calls for bi-annual visual inspections of risk zones — basements, crawl spaces, HVAC ducts — and names the tools: moisture meters, thermal imaging cameras, and smart sensors that send real-time alerts on moisture changes.
• The laboratory limit for airborne mould sits in a different document: DM-HSD-GU119 V4 caps total fungal count at 500 CFU/m³ — a lab air-sampling number, not something a sensor reads.
• Dubai Law 5/2025, Article 33, places built-environment health obligations on the Owner — including keeping indoor air quality within approved limits and providing devices for measuring water and indoor air quality.

1. Why Dubai buildings grow mould at all

Mould needs two things a Dubai building supplies generously for half the year: moisture and warm surfaces. Coastal humidity runs high through summer. Air-conditioning keeps interiors cool — and every surface an AC system chills below the dew point of the surrounding air becomes a condensation plate: supply-air grilles, duct boots, the wall cavity behind a poorly insulated line set, window frames at dawn.

The typical failure patterns are mundane, not exotic:

• Set-and-forget thermostats. A villa left at 18–20 °C while the family travels turns interior surfaces into condensers running 24/7.
• Concealed leaks. A weeping connection inside a riser or behind a kitchen cabinet raises local humidity for weeks before anything is visible.
• Oversized or short-cycling AC. Units that cool fast without running long enough to dehumidify leave the air cold and damp — the worst combination.
• Closed, unventilated rooms. Bathrooms and maids' rooms without functioning extract fans accumulate moisture with nowhere to go.

None of these announce themselves. All of them show up in a humidity trace days or weeks before they show up on a wall — which is the entire case for measuring continuously rather than inspecting occasionally.

2. What GU142 actually says

The guideline's moisture-control section (10-1) sets the operating target:

"Maintain indoor relative humidity levels below 60%, ideally between 30-50%"

Around that number it prescribes the discipline you would expect: regular checks of plumbing, roofs and windows for leaks with immediate repair, dehumidifiers and ventilation in wet zones such as bathrooms and kitchens, HVAC cleaning and inspection to prevent condensation, high-MERV filtration per ASHRAE 62.1, and sealing of building-envelope cracks with moisture-resistant materials in wet areas.

Section 10-2 is the part that matters for monitoring. It calls for bi-annual visual inspections of the zones where mould starts — basements, crawl spaces, HVAC ductwork — and then names the instruments:

"Utilize tools like moisture meters and thermal imaging cameras for non-invasive monitoring" … "Use smart sensors that send alerts regarding moisture changes in real time"

That is unusually specific for a DM guideline. Thermal imaging finds damp that is already hidden behind finishes — we run those as scheduled robot-assisted inspection jobs on commercial sites. Smart humidity sensors with real-time alerts are precisely what a continuous monitoring subscription is. The regulator's own recommended toolkit, in one sentence each.

For confirming mould once suspected, GU142 recognises three sampling routes: air sampling, surface sampling and bulk sampling — all laboratory work, not sensor work.

3. Which number applies where

Dubai Municipality documents give several humidity and mould-related figures. They answer different questions, and a report should say which one its verdict rests on:

The practical reading: 60% is the line. Below it, comfort documents argue about preference; above it, sustained, you are running a mould incubator regardless of which document you prefer.

4. Where the law sits

GU142 itself is a technical guideline. The legal weight comes from above it. Dubai Law No. (5) of 2025 on Public Health — in force since late July 2025 — devotes Article 33 to the health of the built environment and places its obligations on the Owner: conducting water analysis and indoor air quality measurements to the standards of the responsible entity, keeping indoor air quality within approved limits, ensuring ventilation to approved standards, and — in clause 9 — providing:

"the necessary tools, equipment, systems, and modern technologies to ensure the Built Environment Health, including devices for measuring water quality and indoor air quality"

Article 49 of the same law sets the penalty range for violations at AED 500 to 1,000,000, doubling on repeat within a year up to AED 2,000,000. The itemised violation-by-violation amounts await Executive Council resolutions that, as of this page's publication date, have not been published — so any vendor quoting you a specific "mould fine" is inventing it. The obligation structure, however, is already in force.

5. The dispute problem — and what a record changes

Every mould argument in a rented villa or apartment runs the same script. The tenant says the building leaked or the AC was inadequate. The landlord says the tenant kept the place shut, dried laundry indoors, never ran the extract fan. The contractor who painted over it last year says it was fine when they left. By the time anyone measures anything, the only fact available is the stain — and the stain is silent about its cause.

A continuous humidity record changes the shape of that conversation. It shows whether relative humidity was held below the GU142 ceiling or spent June-to-September above 70%. It shows the step-change on the day a leak started, weeks before the wall showed it. It is timestamped, and — on our platform — tamper-evident: entries cannot be rewritten after the fact by whichever party the record ends up inconveniencing. That does not decide who pays; it decides what happened, which is the part disputes otherwise spend months on. Nothing here is legal advice — it is measurement.

6. What monitoring does and does not do

In keeping with how we write about scope elsewhere on this site, the honest boundaries:

• Sensors do not detect mould. They measure the conditions that permit it: sustained RH above 60%, temperature, dew-point margin at the sensor location. Confirming a colony takes visual inspection and lab sampling per GU142.
• A monitoring subscription does not replace GU142's bi-annual inspections — it tells you where to point them, and it covers the 180 days between them.
• The 500 CFU/m³ fungal count is a laboratory number, produced by accredited air sampling. We can schedule and log those tests; we do not perform them.
• Remediation is a separate, specialised trade. If monitoring and inspection find an established problem, removal is remediation contractors' work, done to GU142's protocols. We monitor before, during and after — we do not remove mould.

What continuous monitoring is for: weeks of warning before conditions become a colony, an alert the day a leak moves the humidity baseline, and a defensible record of the conditions your building actually maintained.

7. Practical checklist for an owner or property manager

1. Know your summer humidity profile — not the thermostat reading, the actual RH in the rooms that historically stain: bathrooms, north-facing bedrooms, anything backing onto a wet wall.
2. Hold the GU142 target — below 60% RH, ideally 30–50%, in occupied spaces, year-round.
3. Instrument the risk zones, not the hallway — the guideline's inspection list (basements, crawl spaces, ducts) is also the sensor-placement list.
4. Set real-time alerts on change, not just level — a 15-point RH jump overnight is a leak announcement, whatever the absolute number.
5. Do the bi-annual visual inspections GU142 asks for — with thermal imaging where finishes hide the risk.
6. Keep the record somewhere it cannot be edited — the day a dispute starts, an editable spreadsheet is worth exactly nothing.