The Issue With Modern Airtight Homes
Since the mid-1970s, homes have been built increasingly airtight. Older houses typically went through ~0.6 air changes per hour, while modern ones may be as low as 0.08, nearly 10x less leakage.
That’s great for energy efficiency: your carefully conditioned indoor air no longer mixes freely with the outdoors. But it also creates the perfect breeding ground for mold.
For mold to appear in your home, you need three things: a mold spore, an appropriate level of moisture for that spore, and some organic matter for the mold to eat (like wood).
Modern airtight homes have created the perfect storm on these three fronts: the airtightness lets incident mold spores bounce around until they find a place to grow; it traps moisture that the mold needs; and our increasing use of wood-sheathing and wood-framed walls creates plenty of “edible” landing ground.
It’s worth noting that this problem is increasingly recognized, and solutions are beginning to appear. Homes built since the 2010s often have better ventilation systems, and we’re seeing more use of mold-resistant building materials, like autoclaved aerated concrete.
The Problems With Most Mold Inspections
Most inspectors rely on air sampling to initially screen for mold, which is notorious for false negatives if not done in an unusually rigorous way with many wall cavity samples. It’s true that if the sample comes back positive, it usually means there’s a real issue. But if it comes back negative, that doesn’t mean the house is clean.
Mold is easily missed with air sampling because the results are highly dependent on airflow patterns at the specific moment of sampling. Two tests in the same location, just hours apart, could give completely different results.
Additionally, some molds species don’t travel well in the air or are hard to collect, meaning their presence is underestimated. And if there’s a lot of dust or pollen, it can lead to under-reporting.
That said, air sampling does have value when assessing localized issues in specific areas. We just don’t recommend it as an initial screening tool.
Why a Manual Inspection is the Gold Standard
The best way to uncover mold is a manual inspection by a highly skilled inspector: someone who truly believes in getting eyes on the problem, not just running lab samples.
A proper manual inspection means crawling through the home, checking hidden areas, and combining a thorough visual survey with tools like moisture meters, thermal cameras, and borescopes.
A good inspector will also evaluate findings in the context of the house’s history, materials, and design, and understand the air pathways in the home that could be allowing mold to spread throughout the space.
Why We Use MSQPCR Testing (but Differently)
If you already know or strongly suspect mold in your home (visible growth, musty odors, or a recent water event), we recommend going straight to a manual inspection from a top-tier mold inspector (unfortunately few and far between!).
But if you’re not sure whether mold is an issue, we recommend starting with MSQPCR tests, but you need to run them carefully. We use them in our home health assessments to evaluate mold likelihood and see if a full manual inspection is warranted.
For context, an MSQPCR test is a DNA-based method that analyzes dust for mold. It provides a snapshot of what mold has been present in the home over time. ERMI, the well-known “Environmental Relative Moldiness Index,” is built on this same MSQPCR technology.
The main strength of MSQPCR is that when you run the test rigorously and the results are very low, you can be fairly confident mold isn’t an issue, which is why we use it as a screening tool.
The limitation is that it only looks at 36-40 species and tends to lean toward false positives, flagging potential issues even when none are active. Elevated results therefore require careful review in context.
At Lightwork, we’ve developed our own process to turn MSQPCR data into a more advanced mold likelihood assessment, with support from our mold & building forensics advisor, Bill Weber, G.C., CR, CIEC, CMRS. This includes:
- Taking multiple samples across the home, not just a single composite, and prioritizing sample areas based on size and likely impact
- Including outdoor baseline tests to distinguish internal mold sources from natural outdoor molds.
- Evaluating the species detected in depth, including their ability to release mycotoxins, associated health effects, and moisture preferences.
- Accounting for possible inhibition that can suppress results.
- Interpreting results in the context of the home’s broader profile and history
We also ignore the ERMI score that often comes along with these tests, which adds another layer of confusion. It subtracts “common indoor molds” from “water-damage molds,” which means a home with high levels of everyday molds can receive an artificially low score, even if concerning species are present.
In short, we use the MSQPCR test as a screening tool. A low result is a strong sign that mold is not a problem. An elevated result gives a clear reason to dig deeper with a manual inspection.
How to Prevent Mold
- Watch for leaks, musty odors, and signs of water accumulation.
- Maintain indoor humidity levels between 30-50% using a dehumidifier or humidifier as needed. Avoid ultrasonic humidifiers, as they release a significant number of particles into the air. Opt for evaporative or steam humidifiers instead.
- Fix any water leaks promptly.
- Use a HEPA air purifier and deep-clean your HVAC system regularly.
- Consider adding mechanical ventilation (e.g., ERVs or HRVs).
- Possibly seal ingress points from interior walls into the home (e.g., outlet boxes, door hardware).
How to Find a Good Mold Inspector / Remediator
Indoor mold is a very common issue, with estimates suggesting that 47% of homes in America have some form of mold or dampness (we suspect it may be even more!). It can impact health through allergic responses, infections, and toxic effects from byproducts like mycotoxins.
But unfortunately, despite it being a big problem with serious health effects, it can be very hard to find a good inspector or remediator.
How to Find a Good Mold Inspector
- Holds recognized inspector credentials (e.g., ACAC, NORMI, or advanced credentials like CIH) and follows standards such as ANSI/IICRC S530 and/or AIHA guidelines
- Conducts a thorough visual and manual inspection, not just lab sampling
- Uses the right tools, including moisture meters, infrared cameras, borescopes, and hygrometers
- Specializes primarily in mold inspection rather than general home services
- Delivers detailed, photo-based reports with clear findings and next steps
- Interprets results in the context of the home’s history, materials, and air movement patterns
How to Find a Good Mold Remediator
- Follows recognized protocols such as ANSI/IICRC S520 or Medically Important Remediation guidelines, with certification from bodies like the IICRC, ACAC, or NORMI
- Uses proper containment methods, including sealed barriers, negative air pressure, and HEPA filtration
- Physically removes contaminated materials instead of relying on fogging, surface sprays, or killing the mold
- Works with non-toxic cleaning agents rather than harsh biocides
- Provides detailed, photo-based documentation of the entire process
- Has no conflict of interest; inspection and remediation should always be performed by separate companies
The ISEAI’s Indoor Environmental Professional Directory is a great resource for finding experienced inspectors and remediators.
What Good Mold Remediation Looks Like: The IICRC S520 Standard
Once you know you have a problem, you need a remediator to fix it. Unfortunately, it can be very hard to find a good one.
Here’s exactly how to find a good one
To start, look for a remediation company that follows the IICRC S520 standard. This is a very effective industry remediation standard published by the Institute of Inspection, Cleaning, and Restoration Certification.
Here’s a high-level summary of what it involves:
- Physically removing contaminated materials, not “killing” the mold. Alternative solutions like dry fogging and biocidal approaches claim to kill the mold, but they don’t address the underlying problem. Additionally, dead mold is still allergenic and can continue to cause problems, so it’s important to fully remove it.
- Addressing moisture at the source. Without fixing any underlying water issues, the mold can return after the remediation work is done.
- Using proper containment strategies. During remediation, the affected area should be fully contained using physical sealing, negative air pressure, and HEPA filtration to prevent spores from spreading into other parts of the home.
- Using non-toxic cleaning agents. Harsh biocides are commonly used, which are very toxic and are not required to effectively remediate the mold issue.
Note: If a remediator won’t put it in writing that they are following IICRC S520, be skeptical. The protocol is difficult to do correctly and is most effective when all steps are followed precisely.
After the remediation work is done, always get a post-remediation verification inspection by an independent inspector (not the same company that did the remediation work!) to ensure there is no conflict of interest.
There is another protocol for mold remediation called “Medically Important Remediation” (MIR). This is a more rigorous process and goes beyond the IICRC S520 with some additional steps. The decision to go with MIR depends on the occupant’s health (typically recommended for those with CIRS) and the extent of the issue and remediation work. It is harder to find MIR-trained remediators, but even better if you can.
If you have any questions, we’re always happy to support!