In the ancient days of the art of constructing buildings, say the 1980s, builders looked at their structures, particularly homes, apartments and townhomes, not as a complete entity, but as a structure with different parts. Take the attic, for instance. Builders didn’t really consider that as part of the building environment. And a crawl space, prevalent in Colorado and other parts of the country, was not even considered an integral part of the building envelope.

Because the building industry gave short-shrift to these all-but-forgotten parts of the homes, they created problems the industry is just now starting to fully understand.

A leading voice in the area of Building Science is Joseph Lstiburek with the Building Science Corporation. Lstiburek has this advice for builders as reported on

“Wall assembly design and construction need to consider rain, temperature, humidity as defined by the hygro-thermal regions, annual rainfall and the interior climate classes as environmental loads that affect mold, decay and corrosion as well as other degradation mechanisms,” he said. “Design and construction need to consider the exterior and interior environmental loads, the nature of the materials that comprise the environmental separation and the energy flow across the environmental separation.”

According to Lstiburek, wall assemblies should be designed and constructed “for specific hygro-thermal regions, rain exposure zones and interior climate classes.”

Lstiburek said all wall assemblies should have four principal control layers.

  • A water control layer or water control approach for rainwater
  • An air control layer or air control approach for air transported moisture
  • A vapor control layer or vapor control approach for vapor transported moisture.
  • A thermal control layer or thermal control approach for thermal transfer

“Joe taught me one thing that was really important when it came to water damage,” said Dan Travers, Emergency Services Manager of Restoration Logistics, “that every wall has two sides to it. That means the conditions on either side of the wall may be vastly different. Because you may have water damage on one side and nothing on the other.”

All day long and everyday water vapor is transferring through our structures. And, depending on where you live, the conditions could be quite severe bringing hidden damage even as you sit at the breakfast table. The conditions are different in different parts of the country and for different times of the year.

So what would be some of the differences between a building in Florida and a building in Colorado? Well, according to Travers, a building in Florida might not even use a foundation. The builders will use footers, and they just pour that part of the concrete straight on the ground.

For the most part, homes in Florida don’t have crawl spaces or basements. In Colorado, basements and crawl spaces are prevalent.

“There’s no such thing as a basement in Florida,” Travers said. “The water tables are too high.”

Water can get into a home in a variety of ways. If the water table rises, as it does in Florida, water can seep in through the foundation. Rain can seep in through basement window casings or around windowsills. So, understanding the dynamics of how water moves through the structure is paramount for a successful build.

“A good structural drying contractor understands the dynamics of the building and how water vapor migrates through those assemblies,” Travers said. “They also know how to take those water out of those assemblies and what is an impedance to those assemblies?”

A quarter-way through the 21st Century buildings are built to the specific environment they’re in. But during the early 2000s, for instance, there was a lot of home builders that built structural floors with significant water issues in the interstitial space below those structural floors. 

“They didn’t allow those spaces to breathe. So what happened?” Travers asked. “You get mold. So, allowing building assemblies to breathe and let that water vapor transfer is essential.”

What many builders failed to realize, getting back to the “wall has two sides” concept, is that the exterior of a wall and the interior wall have totally different dynamics in the summer and the winter, depending on the climate. Water vapor is transferring through our structures all day long, every day, and the conditions are different in different parts of the country and different times of the year. So a good structural drying contractor needs to understand the dynamics of the building and how water vapor migrates through those assemblies. And how to take those water vapors out of those assemblies and how to deal with any impedance to those assemblies?

“There are certain building techniques that they used in the past and I’ve seen in Colorado. For instance, I don’t know how many times I have gotten into a crawl space and found the HVAC system in the in the crawl space,” Travers said. “That’s OK, right? Well, what’s down there? The HVAC system is sucking up mold, dust and who knows what else. And it’s outside the conditioned space. That’s why you don’t see that much anymore.”

When builders now look at a structure, they try to consider the entire structure, crawlspaces, basements and attics. The goal is to find those impedances to water vapor and take them out, essentially letting the structure “breathe.”

“If a control layer approach is selected the best place for the control layers is to locate them on the outside of the structure in order to protect the structure,” Lstiburek said.  “However, many configurations are possible. In many assemblies a combination of control layers and control approaches are typical.” 

What builders are trying to do is keep any impedance to water vapor transfer. In other words, take areas where water can potentially get trapped inside the building — condensation from HVAC systems, showers where water gets into an area and is unable to dry out, etc. — and make sure it has a way to get mitigated. They do this with control barriers.

“We want assemblies to breathe and dry out,” Travers said. “If they can’t breathe and dry out, we’ll have a problem due to a number of reasons, such as the materials themselves.”

Think of how many different materials you might have in your own home. There are wooden studs. If you have a basement there are concrete floors and if not, probably a concrete foundation. There are plaster walls. Most basements have a steel beam. There may be wallpaper. All of these need to be considered when trying to control water vapor.

“We need to let the materials dry out and all the materials in our structures are different,” Travers said. “Natural wood absorbs water differently than laminate. Concrete is a great absorber of water. Concrete and plaster, these products are called anhydrous, meaning they get water chemically bonded to them. And a lot of times, if they get saturated, we just have to let nature take its course and try to get it dried.”

Travers said plaster is one of the most difficult materials to dry.

“So, we need to understand the materials in the building as well as the dynamics of that water and how it transfers in between.” Travers said. “Different areas of the country, different types of climate, exterior, interior, all that plays a role. So, understanding those wet areas and how to keep them and allow them to dry out is paramount to building a successful structure.”