A Prequel To Evaporation

Let me preface this by saying most professionals in the trades (inclusive of home inspectors, building inspectors, consultants) are not chemists, physicists, or molecular specialists. If you don’t get the concepts herein, or I fail to enumerate their conditions properly, that’s okay. There’s a world of chemistry out there that needs and requires specialists – we don’t need to be them; I just want to expose more of us to very basic premises that can and should help decision making when designing, building, or inspecting structures.

In the physical world, where materials are felt and cut and manipulated, it’s hard to pay attention to what is right there but not readily visible – namely, gases and chemistry. So, this is a walk-through (for me, as well) to create awareness of how a solid, liquid, or gas responds to another solid, liquid, or gas related to material performance.

Perhaps the most accessible and best starting example would be liquid and tape flashings. In modern construction, we have become very reliant on liquid and tape flashing for helping to limit air and moisture (and pest) infiltration into our structures (because, don’t forget, our aim is to control the inside and keep the outside out when it comes to building a structure). Well, not all builders/trades professionals are on this bus yet; but, each year the ranks do appear to be increasing.

These are not the tapes with which you seal…wall, floor, and roof assemblies

When a liquid or flashing tape is used, it relies on a chemical bonding of materials – adsorption; this is one of our key terms. Adsorption is the accrual of atoms, ions, and molecules on another surface in a bonding method. When liquid flashing is applied, the chemical concoction adheres to the surface of the other material. The liquid flashing does not fully penetrate or incorporate into the other material, but bonds at the surfaces. This is adsorption for building materials. The other really important take-away relates to too much of the adsorbate – the liquid flashing – being applied to the absorbent – the other material to which it is adhering: There is a finite layering that can be productive before the liquid flashing stops its intended adhering. Basically, you don’t have to apply (nor would it perform properly) three inches of liquid flashing along the sill/sheathing joint of a wall/foundation assembly.

Think of it like holding hands…but much, much stronger and “wetter”

If we look at flashing tape and adsorption, the same premise applies but a bit differently. You know how you may have heard, “You have to roll the tape,” by flashing tape manufacturers? Well, that’s because the rolling of the tape creates a sorption process whereby the chemicals of the adhesives in the tape “wet” into the tiny pores of the material to which it is adhering. In other words, the mechanical process of physically (think energy usage) wetting the tape by rolling helps to induce the adsorption of the adhesive onto the material at hand – wood, concrete, etc. The tape’s adhesive does not penetrate into the surface, but bonds at the teeny-tiny level to create the “long-term sticking.” This is the same thing that happens when activated charcoal filters your water.

Now, perhaps you do a lot of reading and listening and have heard the on-going rumblings of those nay-sayers that are afeared of failure when relying on liquid or tape flashing. Chemically speaking, this would be desorption; for adsorption and surface bonding, it is the premise that what adheres can also come loose (with an investment of energy). Technically, this is an accurate fear; on-going testing of tapes and liquid flashings continue to help determine long-term chemical bonds and what sort of stressors (think energies) can break those bonds and cause failure in flashing-related protections which could lead to water infiltration and unhealthy issues developing in a structure. This is why the manufacturer’s literature is so vital – the manufacturer literally tells you what you can use their product with and how it must be used and when it will fail. If you don’t follow the recipe, don’t be surprised when your crepe eats like a pancake. As both a home performance consultant, and a licensed home inspector, I cannot begin to extol the merits of reading all that tiny print. That’s my soap box.

Seriously, read the fine print from the manufacturers. It’s good stuff!

The other key term I intended to confuse and befuddle you regarding is absorption. If adsorption is surface adherence, then absorption is full-on “I’m going to gobble you up and put you in my belly.” Think, alligator and a doe at the water’s edge. The doe goes in the alligator, not onto the alligator. A very crude metaphor, yes, but one that helps to express the point – the deer doesn’t adsorb to the alligator’s skin, although that would be interesting. Absorption is the process by which one material is fully incorporated within another, sometimes temporarily and sometimes permanently.

For building science and trades, think of moisture in a wall assembly, or in a floor assembly for those of us accustomed to wet crawlspaces. Unlike caulk, which only adheres (adsorption) to a surface, water can absorb into a material – wood or concrete, for example. Ever seen composite cement fiber board improperly installed and exposed to water? The rate is not fast, but absorption eventually reaches a point of equilibrium/saturation (a max concentration of sorts) that the material was never intended to manage and the related energies and stressors exert so much antagonism on the material that it starts to flake apart in these thin layers. That process starts with absorption and is one of the reasons why wood and cement-based composites are intended to be primed and sealed and separated from ground and roof surfaces (well, we have to introduce capillary action in here to really explain it properly…we haven’t enough word space remaining in this article).

Another ready example would be manufactured adhered stone veneer (a cement product) or brick veneer – both claddings (unless painted/sealed) readily absorb moisture from their exposed surfaces. The veneers will continue to absorb moisture until they reach an equilibrium. Then, either it stays (if it is raining) in the material, or it may begin to exit the material in the direction of less water. If the wind is driving the rain to the brick from the exterior, water may leave the brick on the interior side that faces away from the rain (more to less). And what’s on this side of the brick? The wall assembly. If this assembly lacks proper configurations to manage bulk water, the water may then begin both the adsorption (weather resistive barrier) and absorption (wall sheathing) processes all over again. We all know what water does in wall assemblies, right? Right.

If you guessed you’d find a mocktail therein, well…you are a cheery bloke, ain’t ya?

To further convolute, solar drive is an energetic process whereby the sun’s radiant heat physically forces the water onward/inward, which can have detrimental consequences for a wall’s performance. But, solar drive is not absorption. I am no chemist, but I suspect it is a variant of desorption since energy and heat are involved in altering the chemical relationships and driving one material out from within the other.

Please, don’t take my word on any of this. Check with your local, friendly, neighborhood professional chemist. We all have those, right? Remember, you don’t have to be a chemist and you don’t need to be able to write a dissertation on any of this. What you should be able to do is have an inkling of an idea how this stuff works so you can make informed choices as a professional, so you can properly cite deficiencies or discovered issues, and so you can proficiently communicate to the client/consumer thereby being respectful of their time and money.

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?”

Unvented Conditioned Attics, Take II

A wrinkle to consider, if you read the last post.

I’m in an attic that has been sealed with our foamy plastic stuff that is both amazing and potentially torturous for the planet. I’m staring at the far gable wall of the attic over the garage and it’s spray foamed. So is the roof framing. This garage is shaped like a rectangle until it turns 90 degrees and opens into a giant square which is the main structure living space (so, think an “L” shape). My brain is screaming at me and I can’t interpret fast enough. So, I stand there.

The garage attic is spray foamed. The garage attic attaches to the main attic. The main attic is spray foamed. There is no partition between the two spaces. Okay. Thank you brain.

The garage is an exterior enclosure. This means every time the overhead doors are opened, or left open, untreated humid air (summer) and cold air (winter) will enter into the garage.

The main home, and now attic, are an interior enclosure. The main home, and now attic, are conditioned via the HVAC systems and commercial grade dehumidifier. The garage is conditioned via the outside. Ah-ha!

My brain is screaming at me because our garage is going to introduce an entirely different moisture load into the attic space than the main structure. This moisture load, particularly in more humid times of the year (so, like 6-8 months per year), is going to stress the unvented conditioned attic. Couple with this the inefficiencies of foam installation we chatted about last time, and we have all the variables we need for potential moisture issues developing over time to the roof framing (likely, near the ridge if my educated brain recalls properly — see people smarter than me).

Where Do We Land?

The fix for this interesting configuration is to insulate and air seal the ceiling of the garage. Basically, block off the garage from being able to mix with the unvented conditioned crawlspace. If done properly, ta-da! No additional stress or strain to the home’s attic space. Now, the attic likely merits monitoring to make sure the size of the attic does not present issues with relative humidity over time (the volume of the total unvented conditioned attic space will be greater than the perimeter footprint of the interior enclosure’s main floor). If RH is found to be consistently elevated (say, greater than 55%), then perhaps a balanced moisture management system would be beneficial, or a vapor diffusion port as written in Green Building Advisor by Martin Holladay back in 2018 (yeah, we’re not reinventing the wheel here — other peeps have done that for us — we just have to seek it out and read and digest). All we need do is think as a system. If that fails, reach out to these industry giants that came before us and everyday make this stuff look more like paint drying on a wall than performing complicated physics equations.

G.

A Moment With Unvented Conditioned Attics

Our eyes are amazing organs. They filter something we can’t otherwise perceive and allow us to perceive the worlds which we see. But, what happens when we pay for a service that addresses what we can’t see with our eyes? How do we know we are getting what we pay for? Or, if we’re the contractor, how do we really know what we’re doing is effective?

We test.

In our middle TN region, we don’t have many homes that are built with unvented conditioned attics, or are converted to unvented conditioned attics. To my knowledge, we also don’t have a hardy education for trades professionals regarding the building science behind vented unconditioned attics vs. unvented conditioned attics. So, our line of ignorance places us in a precarious position as home owners and builders.

In our region, what I see mostly is low density open cell spray foam installed along the roof line and eaves. In theory, this closes off the attic from the exterior environment extending the interior enclosure from the finished ceiling to the now-foam-filled roof framing. In theory.

In actuality, because our trades professionals aren’t regulated in relation to the depth of the installed low density open cell spray foam, often there are irregularities, voids, and gaps. These, individually, are no big deal. But taken as one larger whole (get it…?), they are a very big deal. Thermal imaging helps us see this clearly.

Further Complication

In addition to no real standardization of installation and resulting thermal intrusion and potentially moisture issues (for our immediate market), we would naturally need to worry about moisture issues anyhow. The biggest potential issue for unvented conditioned attics is moisture. Per this article by Joseph Lstiburek and Building Science Corporation, moisture is the most pernicious concern for unvented conditioned attics. Why is this so complicated?

Low density open cell spray foam in an unvented conditioned attic

Installation is key — the bright yellow indicates thermal inefficiencies which indicate questionable installation

Well, if it’s a new home, then there is moisture from the building materials. If it is an existing home, there is moisture (in our market) from deficiencies related to poor water management and indoor air quality. And then there’s our subtropical environment that tends to be hot, wet, and humid. This is why some building science folks argue for use of high density closed cell spray foam only — it blocks moisture getting to the roof sheathing/decking a bit better (when properly installed). But, it carries it’s own pitfalls.

So What’s To Say

In the end, I put my money where Lstiburek puts his decades of experience and knowledge — the man is a compendium of building science experience and testing. So, if you ask me I will tell you low density open cell spray foam is acceptable when properly installed. The problem, as this photo from a recent new build shows, is installation. Now, this particular home has an in-line dehumidifier in the basement which should help. I recommended further monitoring via hygrometer installation in the attic as close to the ridge line as possible. If the moisture loads are noted to be beyond ideal percentages, then the client can manage the unvented conditioned attic space in one of several ways. Lstiburek’s recommendation for balanced ventilation would be sweet to see, but in our region I suspect it might be too complicated for many professionals to get right without causing more harm. FYI, that article also has great information on walling and basement configurations, too. If that kind of thing tickles your fancy.