Mold is one of the most significant challenges for homeowners, and once it takes hold, it can be incredibly difficult to eliminate. Preventing mold is the best approach, and the cornerstone of mold prevention is managing humidity. Now, researchers from Oak Ridge National Laboratory (ORNL) have developed a method using microwave radar to monitor the moisture content in wood inside walls.

“We know microwave radar shows great promise for this, because it’s well known that it can measure the moisture in wood samples,” ORNL’s Philip Boudreaux said. “But can it measure moisture in wood that is inside a wall to detect high-moisture issues before they become a big problem? That’s the challenge.”

Wood-frame construction is common in homes, but if walls are damaged or poorly designed, water vapor can seep through, raising humidity levels. This moisture can be absorbed by the wood, creating ideal conditions for mold growth. Over time, building envelopes can degrade, further increasing susceptibility to mold.

The use of radar to assess materials isn’t new. Ground-penetrating radar, for instance, has long been used to locate buried utilities or archaeological sites. It works by emitting waves that generate reflections as they penetrate materials. In this case, those reflections are used to assess moisture levels.

“You can detect water within wood with microwave energy that reflects off of the material using radar,” Boudreaux said. “You can also measure moisture in more than one type of material within the wall.”

The team tested the technique on one-cm-thick wood samples, first drying them completely and then conditioning them to various moisture levels. Using microwave radar, they measured the moisture content with remarkable accuracy.

“The results proved that microwave radar technology can detect and measure moisture within the sheathing and can do so within 3% when compared to conventional handheld detection meters,” he said. For the technique to work in buildings, Boudreaux’s team had to first find out if the microwave radar could see the sheathing behind the drywall.

“So, we placed a piece of drywall in front of the sheathing at a three-and-a-half-inch distance and immediately saw that, yes, the radar was seeing the sheathing,” he said.

In this realistic scenario, the microwave radar also proved reliable.

A Portable Inspection Tool

The technology shows promise as a practical, widely accessible tool. In fact, the researchers considered this possibility when they started working on the radar.

“When developing the detector, we made a system specifically applicable to walls in residential homes, and for general public access,” Boudreaux said. “It’s small, portable, lightweight with easy setup and can be adapted to transmit within frequency regulations.”

The ORNL team is working to license the technology for manufacturing, aiming to make the system commercially available. Additionally, they’re testing the radar on various wall claddings, such as vinyl siding and brick. If this becomes commonly accessible, it can save homeowners a lot of effort — and a lot of money.

“With early detection, a small issue can be repaired before major damage occurs,” he said. “We’ve found what can help locate that moisture early, but we still have work to do and more materials to test and more boundaries to explore with microwave radar reflection.”

Stephen Killough et al, Measuring the Moisture Content of Wood Sheathing with Continuous Wave Radars, 2024 IEEE Radar Conference (RadarConf24) (2024). DOI: 10.1109/RadarConf2458775.2024.10548546