That is the answer to the question almost nobody writes about: if there is no leak, no flood and no burst pipe, why is there mold on the vents and the ceiling? In this climate the water does not have to come from a pipe. It is already in the air, and the house is what decides whether it condenses on something.
This page is the record: what was measured, what was not, and what the counts came out to. I have not found another remediation contractor publishing anything like it, and the articles that assert what I am about to show you do not have data behind them.
How this was collected
- Source: my own quote records, June 2025 through August 2026.
- Selection: five quotes opened at random from each month, 75 in all. I quote a good deal more than five houses a month, so this is a sample of the work, not all of it. Not the best five and not the worst — choosing by how interesting the notes are selects for the worst houses and pushes every number in this page up.
- Recorded at the visit: date, city, indoor relative humidity, what the customer called about, filter MERV, condition of the HVAC system, attic airflow, whether a leak was present, and my notes.
- Stripped before publishing: addresses, names, health details, prices. City only.
- Indoor RH is what my meter read while I was in the house. Where a dehumidifier was already running, the row says so — that number is what the equipment is holding, not what the house does on its own.
- Not recorded: outdoor conditions at the house. Anything about the weather that day comes from station history by date and city, not from a reading I took.
Some of these people had already gone to work on it. They read up, put in a dehumidifier, moved to a better filter, sealed something, corrected the thermostat — and then called me when the growth kept coming back anyway. Where that happened the numbers in this page are what the house reads after the homeowner's own efforts, not what it does left alone. That cuts both ways: it pulls some of the humidity readings down, and it means several of the houses here had already ruled out the easy answer before I walked in.
What this sample is: one climate zone. South Louisiana is IECC zone 2A — hot and humid — which also covers Houston, Mobile, Pensacola, Tampa and Charleston. The northern parishes are 3A and I do not work them. Seventy-five houses supports "most of the houses I see." It does not support slicing by city or by cause — each of those needs a sample of its own.
The counts
Leak or no leak
| Houses | |
|---|---|
| No leak found | 58 |
| Leak present | 12 |
| Not recorded | 5 |
Indoor relative humidity — 72 of 75 had a reading.
| Indoor RH | Houses |
|---|---|
| 65% or above | 38 |
| 60–64% | 11 |
| Below 60% | 23 |
Twenty-three houses read under 60%, and they are worth looking at rather than averaging away. Eight of them had a dehumidifier running (seven noted at the reading, one in the notes) when I arrived. Several were vacant with the thermostat left at 80–82°F, which means the system almost never ran — the reading was low at the moment I took it, and the growth on the walls is what the house did over the months before. The rest are the small under-sink leaks, where humidity was never the problem.
Attic airflow
| Houses | |
|---|---|
| None | 26 |
| Weak | 25 |
| Adequate | 13 |
| Not recorded | 11 |
Filter — 58 houses had a MERV recorded.
| Houses | |
|---|---|
| MERV 8 or below | 34 |
| MERV 11 or 13 | 24 |
HVAC system
| Houses | |
|---|---|
| Recorded as needing service, repair or sealing | 23 |
| Recorded as working correctly | 23 |
| Not assessed | 29 |
The part nobody publishes: these houses do not have one cause
Every article on this subject names a cause. One thing went wrong, fix it, done. That is not what is in the houses.
Counting the contributing problems present at each house — indoor RH at 60% or above, a filter restricting airflow, an HVAC system needing work, impaired attic airflow, an active leak, an unsealed attic access, missing insulation, and how the house was being run — this is what 75 homes came out to:
| Contributing problems | Houses |
|---|---|
| Four or more | 26 |
| Three | 22 |
| Two | 18 |
| One | 6 |
| None identified | 3 |
Sixty-six of the 75 houses had two or more. The average was three.
That is the finding, and it is the reason a single fix so often does not hold. A house with a weak attic, a restrictive filter, a system that short-cycles and a bathroom fan nobody turns on is not going to stop growing anything because one of those four got corrected. Whoever treats the growth and leaves the other three has sold that customer a repeat visit.
It is also why I will not quote a treatment before the moisture is addressed. Fifteen months of quote records showing this is the evidence for the thing every page on this site says. What removal costs once the moisture is handled is on the mold removal cost page.
What those problems actually were
Reading back through the notes, the same handful keep coming up.
Attic airflow. More than any other single item. No ridge venting, blocked venting, a second roof built over the first with one small opening cut for air, a spray-foamed attic reading 82% RH of its own. When attic air is hot and wet and the ceiling below it is cooled, the vents and the sheetrock around them are the first place it shows.
The attic access nobody sealed. An unsealed hatch, a pull-down stair, an old attic fan left in place — each one an open channel between attic air and the conditioned house. This turns up over and over and costs almost nothing to fix.
The thermostat left high in an empty house. Vacant while the owner traveled, set at 80 or 82, the system barely running. Every one of those came back to growth on belongings and furniture. The house was never dehumidified, because that is what a running AC does.
The filter. Thirty-four of 58 were MERV 8 or below. On several of these the airflow problem and the filter were the same problem.
How the house gets used. Long showers with the exhaust fan broken or never switched on and the door shut after. Rooms closed off with the vents shut. Window units in a house with central systems that no longer work.
The system itself. Ductwork leaking into the attic, a plenum open to attic air, an AC sitting in a closet open to the attic, systems needing repairs that had been deferred for years.
Each one of these on its own is survivable. Two or three together in August is what puts growth on a ceiling.
Honest limits
- One climate zone, 2A. Named above so a reader in a different zone can decide for themselves how much of it carries.
- Fifteen months is long enough to say the picture does not change much with the season — the houses I walk into in January look like the ones in July. It is not a large enough sample to publish a season-by-season table off, so I have not built one.
- Some houses had already been worked on by the owner before I arrived. Noted above.
- These are houses that called a mold remediation contractor. Houses with the same problems and no visible growth are not in here, so this cannot say how common any of it is across all homes.
- Indoor RH is a single reading at one moment, not a logged average.
- The contributing-problem count uses the categories listed above. A different set of categories gives a different average. The raw rows are published below so anyone can count them their own way.
The record
All 75, in date order. The notes are mine from the visit, tidied for spelling only.
Local pages for the areas with the most homes in this record: mold removal in Baton Rouge · mold removal in Denham Springs · mold removal in Hammond.
| Date | City | Indoor RH | What they called about | MERV | HVAC | Attic airflow | Leak | Notes |
|---|---|---|---|---|---|---|---|---|
| 2025-06-11 | Baton Rouge | 65 inside main room 75 inside closet | Attic stairway in a closet. Heavy growth in the closet, no airflow, high humidity | 8 | OK | None to weak | No | — |
| 2025-06-16 | Gulfport | 50 when measured | Customer was out of state for months and left the HVAC system set at 82, so it almost never ran | — | — | — | — | — |
| 2025-06-20 | Baton Rouge | 75 | Growth on the bathroom ceiling and HVAC vents | 11 | OK | Adequate | No | No faults found. The HVAC system had been checked by an HVAC company and called fine. Two teenagers taking long showers, but something was keeping the house wet — some houses are just wetter than others. Dehumidification needed to control it. |
| 2025-06-26 | Prairieville | 69 | Growth around grilles; health concerns | 8 | OK | Weak | No | — |
| 2025-06-30 | Walker | 73 | Growth on vents and around the crown molding; visible condensation on the vents | 11 | Needs check | — | No | — |
| 2025-07-01 | Hammond | 67 | Growth on walls and ceiling | unknown | Service advised | Adequate | No | — |
| 2025-07-15 | Denham Springs | 68 | Growth on vents and the sheetrock around them | 5 | Needs check | — | No | — |
| 2025-07-18 | Baton Rouge | 62 | Growth on vents and on the sheetrock around them | 13 | OK | Weak | No | Not running the AC enough; thermostat kept too high |
| 2025-07-23 | Prairieville | 72 | Visible condensation on vents; growth on vents and inside the ductwork | 11 | Needs check | — | No | — |
| 2025-07-30 | Gonzales | 65 | Growth on vents and the sheetrock around them | 8 | Needs check | Weak | No | — |
| 2025-08-02 | Hammond | 46 | Mold from a leak | 5 | OK | Adequate | Yes | — |
| 2025-08-10 | Watson | 80 | Growth on vents and ceilings | 11 | Needs check | — | No | AC system not set correctly — fan left on, cooling temperature set at 82 |
| 2025-08-20 | Zachary | 70-76 | Visible growth on vents and significant growth in a closet on clothing and personal items | 4 inch high merv filter | Needs check | None | No | — |
| 2025-08-26 | Metairie | 67 | Growth on vents | 8 | Needs check | Adequate | No | — |
| 2025-08-27 | Baton Rouge | 50 | Growth throughout the home on furniture and belongings | 5 | Needs check | Adequate | No | Customer left the AC set at 80 and was away from the property for months |
| 2025-09-04 | Pride | 67 | Growth in various rooms and on vents | 8 | Needs check | Adequate | No | Owner keeps all the rooms closed up and some vents shut off. Circulation problems throughout the home. |
| 2025-09-18 | Central | 65 | Growth on vents | 8 | OK | — | No | Attic access leaking hot air into the conditioned space |
| 2025-09-22 | Osyka | 71 | Growth on vents; health concerns | 13 | OK | — | No | Customer built a second roof over the existing one and cut a two-square-foot hole in the old roof for airflow. No circulation in the attic space. |
| 2025-09-23 | Addis | 65-72 | Growth on vents, around the fireplace and on the crown molding | 11 | Needs check | — | No | This house had close to every problem we see: no attic airflow, wrong filter, no insulation in places, an AC system malfunctioning, an off-the-ground house with water pooling underneath, and exterior water seeping in around the fireplace and several other spots. |
| 2025-09-29 | Baton Rouge | 62 | Growth on vents | 8 | Needs check | Weak | No | — |
| 2025-10-02 | Baton Rouge | 65 | Growth on vents and the bathroom ceiling | 6 | — | Weak | No | — |
| 2025-10-05 | Baton Rouge | 53 | Growth on vents | 8 | — | Weak | No | — |
| 2025-10-15 | Denham Springs | 50 | Leak caused the mold | 11 | OK | Weak | Yes | Using a dehumidifier to hold the humidity down |
| 2025-10-17 | New Orleans | 73 | Growth on belongings and a vent | 13 | — | Weak | No | Little airflow in the attic, doors kept closed, and not running the AC system or the dehumidifier enough |
| 2025-10-28 | Zachary | 68 | Growth on vents | 11 | — | — | No | — |
| 2025-11-03 | Clinton | 71 | Growth throughout the property | 13 | — | — | No | No insulation over most of the attic, the HVAC system not used regularly, no humidity control at all, and an old attic fan left unsealed, leaking air into the conditioned space |
| 2025-11-17 | Prairieville | 63 | Growth on vents | 8 | — | Weak | No | — |
| 2025-11-17 | Hammond | 67 with dehu running | Growth in cabinets and window units | — | Window units | — | No | Off-the-ground house with water pooling underneath. Running window units and a dehumidifier and still cannot hold RH under 60%. Lacks proper insulation. |
| 2025-11-21 | Geismar | 65 | Growth on vents and the sheetrock around them | 11 | — | — | No | — |
| 2025-11-29 | Denham Springs | 44 | Growth in a bathroom cabinet | 5 | — | Weak | Yes | Small leak under the sink caused minor growth |
| 2025-12-07 | Denham Springs | 67 | Growth on vents and the surrounding area | — | Needs check | — | No | Metal building. Some AC systems not working, high RH sustained over long periods. |
| 2025-12-07 | Denham Springs | 72 | Growth throughout the property | 8 | Needs check | Weak | No | Airflow problems, some HVAC systems not working, and water penetration from outside after rain bounced off an exterior object back onto the side of the property |
| 2025-12-17 | Prairieville | 65 | Growth on vents and the surrounding area | 11 | Needs check | — | No | — |
| 2025-12-18 | Hammond | 60 | Past customer, different property — wanted it checked just in case | 5 | — | Adequate | No | — |
| 2025-12-20 | Greensburg | 72 | Growth on walls and vents | 11 | Needs check | Impaired | No | Uncontrolled attic space, heat rolling down from upstairs through an opening into the attic, and no insulation |
| 2026-01-12 | Denham Springs | 75 | Growth on the ceiling upstairs and on vents and belongings | — | — | — | Yes | Active leak upstairs, no attic airflow, three HVAC systems and none of them work, running window units, no dehumidifier. The leak is still active. |
| 2026-01-13 | Prairieville | 75- 50 when heater was on | Growth on belongings | — | — | — | No | Central system used for heating, window units for cooling. Big swings when the heater ran. Not using the HVAC system properly; it needs work. |
| 2026-01-17 | Baton Rouge | 66 | Growth | 8 | Needs check | — | No | Attic has no exterior air access |
| 2026-01-28 | Saint Martinville | 50 dehu running | Growth on vents | 11 | OK | Weak | No | Apartment. Tenant was not running the HVAC correctly. |
| 2026-01-30 | Baton Rouge | 63 | Growth on vents | 8 | — | Weak | No | — |
| 2026-02-07 | Baton Rouge | 64 | Growth on vents and under the kitchen sink | 13 | OK | Weak | Yes | Small leak under the sink with some growth |
| 2026-02-16 | Maurepas | 49 | Shower leak; mold on the sheetrock | — | — | Adequate | Yes | — |
| 2026-02-17 | Franklinton | 68 | Growth on ceilings, walls and vents | — | — | — | No | Long-term with no working HVAC system — one window unit in one bedroom and the doors kept wide open. Growth all over. |
| 2026-02-21 | Lutcher | — | Massive growth; full demolition needed | — | — | — | Yes | Long-term abandoned property. Roof leaks, no climate control. The whole property will need to be gutted to the studs and then treated. |
| 2026-02-28 | Covington | 67 | Growth throughout on vents and the surrounding area | — | — | Weak | No | HVAC system needs major repairs. Ductwork leaking everywhere. The plenum needs to be completely rebuilt — broken and open to attic air. |
| 2026-03-02 | Denham Springs | 64 | Mold on vents | 11 | OK | — | No | Zero airflow in the attic |
| 2026-03-05 | Angie | 68 | Wanted treatment to make demolition work safer; growth all over | — | — | — | — | — |
| 2026-03-06 | Saint Francisville | 47 | Failed test; visible growth in the HVAC system and at the cathedral peak | 5 | OK | None | No | Past customer who buys houses. Saw mold, had it tested, came to me for treatment. Seller left the house with the AC turned way up for an extended period. Very tall cathedral ceiling with minimal airflow at the top. |
| 2026-03-09 | Zachary | 50 dehu in use | Mold on bathroom ceilings | 11 | — | Weak | No | Long showers with the exhaust vent unused or broken depending on the bathroom. Growth noted on every vent in the home. |
| 2026-03-16 | New Orleans | 65 | Mold in the AC closet | 8 | Needs sealing | Weak | No | AC system sitting in a closet open to attic air |
| 2026-04-12 | Baton Rouge | 67 | Growth throughout | — | — | — | — | Power and water turned off for an extended period |
| 2026-04-14 | New Roads | 50 set dehu | Growth on the second floor around the crown molding and on vents on both floors | 5 | OK | Weak | No | Friend of a past customer, so they had already taken steps to address the moisture before I got there. Attic door needs a better seal. |
| 2026-04-17 | Denham Springs | 47 | Small spot of mold under a sink | — | — | — | Yes | — |
| 2026-04-20 | Slidell | — | Leak behind a sink; customer had already demoed and repaired it | 8 | OK | Weak | Yes | — |
| 2026-04-23 | Baton Rouge | 62 | Growth on vents | 8 | OK | Adequate | No | — |
| 2026-05-04 | Walker | 66 downstairs 73 up | Growth at the leak; heavy growth on the ceiling upstairs and on vents throughout | 5 | OK | — | Yes | Several problems at once: a leaking toilet, high RH, not using the AC system properly, no attic airflow, and long showers in the affected bathroom with the door closed after and the exhaust vent unused |
| 2026-05-05 | Hammond | 65-73 | Growth on vents; failed test with a high airborne count | 8 | OK | Adequate | Yes | Started as a bathroom leak. Flooded the floors in half the house, and it was dried but never addressed properly. After months wet the flooring started to buckle and the homeowner contacted their insurance company to start remediation. The floor still read 40 — maxed out — four months later before demolition started. All flooring and baseboards came out and sheetrock was cut around the affected areas. The customer had turned the HVAC system off to keep spores from moving through the house, which made it worse. |
| 2026-05-06 | Covington | 50 dehu | Growth on a wall and on vents | — | — | — | — | Small strip-mall restaurant. The walk-in refrigeration unit was touching the wall with no air gap as required, making moisture. Power was killed between renters. High humidity plus a long-term moisture source. |
| 2026-05-22 | Baton Rouge | 54 | Growth on the bathroom ceiling | 8 | OK | Adequate | No | Not using the vent and closing the door after long showers |
| 2026-05-27 | Mandeville | — | Pre-demolition treatment to make working conditions safer | — | — | — | — | — |
| 2026-06-04 | Denham Springs | 53 | Growth on the bathroom vent | 8 | OK | Adequate | No | Not using the bathroom vent |
| 2026-06-11 | Baton Rouge | 62 | Growth around the attic door and in the bathroom | 8 | — | Weak | No | Attic door is not sealed. Bathroom has long showers with no venting and the door kept closed. |
| 2026-06-17 | Hammond | 50 dehu in use | Growth in a sunroom and on vents | 8 | Old | Weak | No | HVAC left on 82 long-term. No climate control. |
| 2026-06-26 | Baton Rouge | 50 dehu | Growth upstairs; failed airborne test | 11 | OK | — | No | Failed airborne test with no visible growth found. The problem is the attic running too hot. Recommended running a dehumidifier constantly, as they cannot fix the attic. |
| 2026-06-29 | Baton Rouge | 67 | Growth on a grille and the surrounding area | 8 | Needs repair | — | No | No attic airflow, HVAC system not working correctly, and no dehumidifier |
| 2026-07-02 | Livingston Parish | 63-68 | Growth on vents | 13 | — | — | No | Ridge vent blocked; wrong filter |
| 2026-07-12 | New Orleans | 53 | Growth on vents, condensation on the bathroom grilles, and growth on one closet ceiling | 13 | Needs work | — | No | No attic airflow. Ductwork run wrong — a 90-degree turn in a flex duct causing airflow problems. |
| 2026-07-21 | Belle Chasse | 53 up to 58 when ac ran for 15 minutes | — | 5 | Needs work | — | No | Spray-foam sealed attic reading 82% RH. HVAC system not working properly. |
| 2026-07-22 | Baton Rouge | 56 | Growth throughout the home — HVAC, bathroom ceiling and wall, and the HVAC return bordering a closet | 8 | Needs check | — | No | Older home. Long showers and baths with the door closed and a non-working exhaust vent. AC system is not working correctly. |
| 2026-07-28 | Addis | 64 with dehu | Repeat customer; unable to repair the home | 5 | OK | Adequate | No | Repeat visit. Water under the home fixed and attic airflow fixed, but no insulation, so still getting a hot-cold mix that makes moisture. Keeping conditions livable until their new home is built. |
| 2026-08-03 | Baton Rouge | 46 | Mold under a sink | — | — | — | Yes | Small leak under the sink |
| 2026-08-09 | Saint Francisville | 52 | Mold in the HVAC system | 8 | OK | Weak | No | — |
| 2026-08-15 | Baton Rouge | 71 | Failed test with a high spore count; nothing visible | 13 | OK | — | No | No airflow in the attic; wrong filter |
| 2026-08-22 | Walker | 50 dehu | Mold in the HVAC system | 11 | Repaired | Weak | No | — |
| 2026-08-25 | Denham Springs | 63 | Mold on vents and the surrounding area | 11 | — | Weak | No | — |
Common questions
If there is no leak, where is the water coming from?
Out of the air. In this climate the outdoor air carries enough moisture that any surface held below its dew point will collect water — the metal grille of a supply vent, the sheetrock around it, an exterior wall behind a closed closet door. No plumbing has to fail for that to happen.
What indoor humidity is safe?
Below 60% is the number to hold. Thirty-eight of the 75 houses were at 65% or above.
My AC is running. Why is the house still humid?
A system that is oversized, short-cycling, leaking duct air into the attic, or fighting a restrictive filter will cool the air without removing much water from it. Twenty-three of these houses had a system recorded as needing service or repair.
I fixed the one problem and it came back.
That is what the stacking count above is about. Two thirds of these houses had three or more contributing problems at once.
Can I use this data?
Yes. Cite the page.
Source: Mold Shield Restoration quote records, June 2025 through August 2026.
Current as of September 2026.