What It Means To Dry

Where does water go when it dries? This sounds like a replacement line for Nirvana’s cover-song “Lake of Fire,” originally written by the Meat Puppets (who knew…). But seriously, where does it go?

As home inspectors, building consultants, homeowners, trades professionals, we all have this magical understanding related to things drying. But, what really happens when something dries and how might it be important to our understandings of our modern-day huts? Strap on the old thinking cap because we’re on a reading rainbow journey!

Let’s take drying clothes as an achievable example: We pull the clothes from the washing machine and hang the delicates to dry. How is this happening? We feel the clothes wet when they come out of the washing machine drum, so we tangibly know the water is there. But, then we hang them and poof, the water isn’t there…but also isn’t anywhere else we can see. Evaporation.

Okay, so maybe you’re thinking I’m new to this world. But, no. You can’t just say, “It evaporated.” What does that mean? Can you say? Most can’t. So let’s: Evaporation would be the process where a tiny mouse wizard comes behind us when we leave the room and waves a wand around, chants some very indiscernible words, and creates just enough energy (think megajoules per kilogram) to disperse the bonds of the water molecules near the surface. These molecules are henceforth not a liquid, but a gas and then, like all well-meaning gases, leave to play pickleball, go see an over-priced movie, or get their hair blown out. Eventually, they will get lonely and re-congregate into a nefarious fluffy cloud and phase change back into a liquid. They could also re-appear as condensation…depending on several variables.

This is Fred. He’s pretty busy drying all our clothes.

As a side bar, as those water molecules nearest the surface change phase and evaporate, water molecules left behind take their place (more on this below) at the surface, and then, they too evaporate and disperse if conditions are proper. And thus, eventually, we get “dry.”

So, maybe ditch the magical mouse and wand, but the energy part is true. The thing is, the required amount of energy to “dry” depends on several factors we shan’t be including herein. Now, the key for us in the built environment is what often gets phrased as “the drying potential.” This is not the same as “college potential,” though both could prove to be unexpectedly expensive. While we may not need to worry about how our plasticized briefs and bras air dry (there’ a reason many of our undergarments come with warnings to avoid excessive heat), we should be concerned with the drying potential for moisture in the materials that make our fancy huts.

Seriously, if your undergarments aren’t cotton, look at the packaging and/or labeling. Most have a warning to stay away from heat sources…

You see, in my glorious 1940 home, any water that adsorbs onto or absorbs into the board sheathing will diffuse readily along the grains (wood in particular) and eventually evaporate/dry out with minimal effect because my home has great drying potential due to being poorly air sealed and insulated (please, send me money in lieu of medals for this amazing accomplishment…it can help me pay my utility bills). But, in some homes of various vintages, inclusive of modern builds and commercial applications, there is LESS drying potential due to modern configurations of our wall assemblies and building materials (that is, those areas that get wet don’t necessarily have access to the energy needed for evaporation because energy is being properly sequestered within the home’s interior habitable enclosure). This is not a bad thing, if you care about the status of the environment or your bank account. It IS a bad thing, however, if you want your walls to not be a terrarium of mush that can’t stand up to wind and pests AND you build without paying heed to moisture movement.

You know all those local news stories, social media posts, and leaflets dropped from above that focus on toxic mold in homes (side bar: such mycological toxicity is real and really, really bad where it actually occurs…that’s not every time, however)? Those highly credible news sources should be focused on how those fun guys (get it…) showed up to party in the first place. If we managed our assemblies better with a mind toward drying potential (read, evaporation), then it would be less frequent for these spores to rudely take over. I digress.

Yep, imagine these spores just waiting to party in your home’s walls, or ceiling, or crawlspace, or basement, or ductwork…well, anywhere where variables are conducive to their partying..

Evaporation. Okay. So, evaporation happens when water molecules near the surface gain enough energy (heat energy, temperature) to free their oppressive bonds. Then, diffusion (think about perfume being sprayed in the air) via physics disperses these from high to low concentration and hence they “disappear.” Again, remember that diffusion also is the reason one concentrated wet area spreads to less-concentrated dry areas during the stage of what we’ll call “water wetting” (this is named thusly because there’s another chemical process referred to “wetting” that I don’t want to confuse with our current topic). Without diffusion in the product/material, evaporation would not be possible – but, we’re talking about diffusion in a liquid phase first, then in a gas phase post-evaporation. Meanwhile, back at the farm, if your environment is really wet, or cold, the moisture in our proverbial materials, be they clothes or building supplies, will not evaporate as quickly because there isn’t enough potential energy and there may not be enough dry air for diffusing from wet to dry/more to less.

Very simplistically, diffusion is one of the things occurring in this photo…along with a jean vested bartender in the background…

There’s also osmosis. This technically isn’t the same as water drying, but it plays a role in the exchange of water from Point A to Point B. We won’t get into osmosis because it technically reverses the always high-to-low principle, but then it doesn’t because it isn’t about the water for osmosis – it’s about the sketchy people water hangs out with (solutes) and the need to dilute those 1980s Seattle-based punks. As an aside, osmosis can be the force behind the death of your brick and other masonry materials; the force is strong with this one. So, the next time you see spalling brick and efflorescence, you can thank me (again, send money).

Why does this truly matter for us as inspectors, builders, and consumers? Well, if you have a failure in a wall, roof, or floor assembly (use the same mental image of a rectangle, just rotate for each position), whether that failure results in catastrophic damage and fungal growth partially depends on the drying potential which happens via diffusion, evaporation, and diffusion. The longer organic-based materials (and non-plasticized composites) stay wet, the greater potential for degradation. And, in many of our regions, most trades professionals remain ignorant (in the truest sense of the word) related to building with a mind’s eye toward the physics of drying and so moisture gets “trapped” in the assembly components (assume Liam Neeson [heat energy/potential] can’t get to his daughters [moisture] to free them from the bad guys [the building materials]). If you read the fine print by many manufacturers who make these building materials, you will see they assume their products will get wet. After all, they are exposed on the exterior, which is outside. They provide instructions, configurations, and videos explicitly showing how to make sure said product(s) can be protected and/or can dry by not trapping water.

Seriously, the literature that accompanies materials can be very informative and valuable.

So, if you find evidence of something wet, it has at least one source and that source may or may not be readily obvious. Try to find it or hire someone who can. Remember – water, heat, energy, and pressure move from high to low, more to less. If you see something deteriorated from being wet, you can assume it doesn’t have the potential (energy) to dry via evaporation and diffusion because there are nearby variables askew for healthy conditions (or, it was exposed to moisture in a way that it was never designed to be…like composite cement cladding in direct contact with a roof/ground surface). Find them (the askew variables). When you can name “it” and “them,” you can put the puzzle pieces together, inform your client, and help the right people answer, “so what now?”

No Flashing Where It Counts

Case Study – Flashing at Dissimilar Materials Joints

In roof framing, it is widely understood that those areas of most interruption, or planar differences, pose the greatest risk for leaking (think valley, or greedy dormer). Ergo, the more complicated a home’s roof line, the greater risk for leaking. How do professionals (not you, Grandpa – real, actual professionals industry trained with real world experience) manage this? Flashing.

Now, let’s move that concept down from the roof to the wall assembly. If you have a wall made of wood, that wooden wall will inevitably end. In our middle Tennessee region, it usually ends on the foundation (concrete blocks aka CMUs), but slabs are becoming more prevalent and we do have old housing stock (stone and brick foundations).

Where that wooden wall ends (you have to picture the wall naked – of siding/cladding here) the materials are dissimilar (usually wood and concrete or masonry). Dissimilarity, in home performance, is the ideal location for issues to develop – usually via air, moisture, and pest. The solution would be, like roofing, flashing. The problem is flashing of wall assemblies and components is not a highly regulated area of home production in our region and, based on what I see often, there is a wide spectrum of understanding and skill by those performing the work.

Where a wall meets a foundation, or any transition, merits your attention — where is it here?!?

Often times, wall flashing is overlooked, or under executed. In some of our housing stock, the home survives with deficient wall flashing purely because the interior enclosure is so very much perforated (read, not air-tight) and the walls can dry. But what happens in our younger homes? Let’s see.

The Home

This home was built in the mid-2000s and likely was intended to be a moderate-to-high-end home based on materials used and aesthetic finishes. Composite cement fiber product was used for siding. Concrete cast stone veneer (lick and stick as it is so lovingly referred to here) was used for both foundation veneer AND some areas of siding. Where the cement boarding terminated and adjoined the stone veneer, there sat a shelf. A very flat, flat, shelf (see photo above).

As best I could tell, there was no flashing beyond a typical weather resistive barrier installed along this common joint line (which ran around the entire perimeter). And, this is for yet another article, the concrete cast stone veneer appeared to be adhered via thin-set directly to the wall assembly over the WRB with no adequate separation and this negates any water management ability…but, I digress.

Our flat joint had no special flashing installed. Flat surfaces hold water, or at least don’t let it drain away and off. When water is held flat, it will follow capillarity (think trees) and find other points by which to travel – up, down, sideways. At our dissimilar joint with no special flashing, the water readily accessed a percentage of the walling assembly over time. Time and moisture vs. OSB. Which do you think wins? Hint: pick moisture.

This is NOT how the rim joist should be looking — if only there had been flashing…

This home that was less than 20 years old, was set up for disaster from the onset of construction. With no attention to flashing detail, and no apparent understanding of needing to protect engineered laminated products (OSB, manufactured I-joists which were the substructure framing), this home started rotting very soon after construction. And unlike old housing stock that was more drafty, this home was less drafty (still drafty, just less drafty). Less drafty means less drying or longer drying time. Prolonged exposure to the moisture delaminated the resins/adhesives in the engineered materials, primed the wooden fibers for pest snacking, and degraded the general strength of the framing.

ENTER ME

By the time I came on the scene, the murder had already occurred. The un-flashed joint work at the exterior was my first clue. My knowledge of the abhorrent installation practices of concrete cast stone veneer in my Tennessee market was my second clue. A very pervasive and present musty odor in the garage was my third clue (have we talked about garages not being air tight and communicating air with crawlspace and interior space?!?). My fourth clue was degrading or already deteriorated rim joist, I-joist ends, and sill plates around the perimeter of the structure. Only along the perimeter of the structure in these areas.

If you had a probe, and lightly poked, you would find this wood readily gave

Some Science

Wood is comprised of polymers (like most things, glucose is king at the molecular level for form and energy). Some of those polymers form cellulose and lignin, the two components that help wood in its natural form withstand biodegradation for an extended period in the natural world. However, we’re talking processed wood here and wood that has had moisture removed (and likely some of the lignin) as part of the engineering process. If you take out the water in the wood fibers, then the degradation slows down even more. Guess what happens if/when you reintroduce continued cycling of wetting to those same wooden fibers that were mechanically dried out? If you said it speeds up the microbes that “eat” the wood, you are correct. Additionally, we get oxidation of the wood fibers which lends to the very darkening of wood coloring. Oxidation also is a decay process. **See this 2011 MIT paper for a brief explanation of wood and moisture.

Does Your Brain Hurt?

Okay. Okay. Let’s jump ship from chemistry. I usually don’t bring up chemistry with clients or in field reports because it’s confusing and usually unnecessary. And in truth, I usually have to “refresh” my own understanding routinely. The simple explanation fits well – you can’t take a material that was intended to be dry post-processing and allow it to repeatedly get wet. It degrades and anything it was supporting no longer is supported as well. Ergo, you must protect this dry product and keep it dry. Dry from the exterior wet world and dry from the interior (crawlspace) wet world. When you fail at this, the material(s) fail and you get unhappy homeowners, or shocked buyers who no longer want the otherwise pretty home.

All of this – and I mean all of it – could be avoided by well-executed flashing. But, then again, you can’t execute flashing installation well IF the installer doesn’t understand the basic principles of building science and why they should flash, where they should flash, and how the flashing should be designed (ahem, to shed water…).

I’m not the best artist, but you can “see” the idea here — if the home had this flashing, there wouldn’t be this problem so early in it’s life.