Indoor Air Quality - Part 2, Humidity & Mold

We primarily build in wetter climates, the West Coast being the primary area. The climate mostly ranges from very damp and humid to extraordinarily wet and humid (although there are dry and arid areas). Still, excess humidity and mold are a concern in all locations and can be introduced through cooking/showering and breathing.

Mold needs moisture (humidity) and a nice warm temperature to grow. Our homes will always provide the right temperature for mold to grow because mold likes similar temperatures as we do. So, we can control the humidity inside the house and where the condensation in the wall/roof assemblies occurs (see our previous posts on condensation points in different wall assemblies). If you look at our earlier posts on condensation locations, it is typically inside the wall and roof cavities, so you won’t see the mold growing visually, and often, the smell will be so minor that it will masked by other house smells. Great news, right? Mold can grow inside your wall, roof, or floor, and you won’t notice it (outside of the health impacts).

Mold is typically more damaging to children and the elderly but can still cause serious health problems in everyone. More and more studies are coming out linking mold to serious health issues in children, up to and including brain swelling (and many associated conditions like anxiety, cognitive problems, and short attention span).

I often hear people say things like, “How can mold be a problem now? It never was before.” Well, a few things; the first is that we have changed how we build and heat homes. Homes used to be barely insulated and heated with a tremendous amount of wood heat, which is very drying (I will write a separate post on wood stoves, but the health impacts from wood stoves are also significant). Now, homes are built with more insulation and are heated more efficiently with less drying heat, so they do not dry out as much. It is also difficult to dry out the wall assemblies used now because drywall and paint are nearly airtight (all electrical boxes and areas like the bottom of the wall are not sealed), so water gets into the wall, and the moisture condenses, but it is very difficult to dry the wall back out (with the standard walls you see built).

Most contractors who have remodeled homes, even homes built in the last 15 years, have probably encountered water inside the wall cavity. As an extreme example, we looked at a home for a client that was almost 10 years old and already had such significant water and mold damage that it would have required reframing a large portion. That home was built how most builders build homes; they didn’t make any serious mistakes that are different from what is considered the standard building practice.

What are some easy solutions to help control mold? The first is to control the humidity inside your home. One easy solution we implemented for an existing home was installing an in-wall dehumidifier (we used the Santa Fe UltraMD33) near the HVAC return. That took the home’s relative humidity from 55 to 70% down to approximately 45%. Below 55% relative humidity is considered safe to prevent mold growth, but I would like to be at 50% or slightly below so that the spikes that occur from showering and cooking do not raise the relative humidity above 55%. This was proven effective by watching the air quality monitor placed in the kitchen; the relative humidity stays below 55% even when cooking. That was a perfect, easy solution because there was a central HVAC system, but similar approaches can be taken with mini-split systems. You can also try out different locations in your home to see how well it works to control the overall humidity by using portable dehumidifiers, which we often do first. Place one where you think it is needed, run it for a week, and see how well it works.

Another point that cannot be stressed enough is to make sure the exterior of your home is properly maintained, and there are no water leaks. If water is actively leaking into your roof or walls, a dehumidifier isn’t going to fix the problem. Even small items like cleaning out your gutters are important.

If you have any questions, please let me know. We also consult on projects in many different capacities, from reviewing details to providing owner’s representative services, and can help ensure your project achieves long-term success.

Indoor Air Quality - Part 1

Indoor Air Quality (IAQ) is an in-depth topic that touches on many different systems within a building. This will be the first post in a series covering this topic. Please note that this will not cover everything, and if you want to take a really deep dive, the EPA has some fantastic information to start with: https://www.epa.gov/indoor-air-quality-iaq.

The first order of business is what IAQ (indoor air quality) means and why we care. In the most straightforward definition, IAQ is the quality of the air in and around buildings (for our purposes, I will be focusing on homes). Now, the why do we care part? I can already hear many people saying ‘I’ve never checked the air inside my home, and I’ve always been fine,” or “A little mold never hurt anybody.” There are studies linking poor IAQ, and mold in particular, to developmental/brain problems in children. Maybe you don’t have kids. Did you know that Radon is one of the leading causes of lung cancer in the US? If you are curious about Radon, look at the EPA risk maps, https://www.epa.gov/radon/epa-map-radon-zones, for a starting point. Just for reference, all homes should be tested for Radon regardless of the zone in which they fall. The test is extremely inexpensive, and many IAQ monitors will even monitor Radon.

If you care about your health and the health of your loved ones, you should care deeply about the air quality in your home.

What are some of the significant things that can impact the IAQ? Household cleaning products, cooking, excess moisture, fuel-burning combustion appliances (I will likely make an entire post about wood-burning fireplaces, but they can be exceptionally terrible), some building materials (especially newly installed materials), and sources from outside like pesticides and outdoor air pollution (two great examples are wildfires in the West and living in/near a city with the associated pollution). These are not a complete list of items that can impact IAQ, but they are some of the significant items.

Do you monitor your IAQ? I recommend monitoring it for no other reason than to understand what is happening inside your home. I am amazed to see our particulate matter count spike every time we cook on our stovetop. We run multiple air filters in our home, one specifically next to the kitchen, separate from the other filters to help contain the particulates, but I also have a monitor in our kitchen.

Get curious about your home and what you are breathing in. The long-term health benefits are amazing, and the short-term health benefits can be incredibly significant. Please let me know if you get an IAQ monitor and have questions. I’d be happy to provide recommendations for checking and improving the IAQ in your home.

If you are still with me this far, the next post on this topic will examine humidity and mold, which are typically the most pressing issues where we build. It will be followed by a post on particulates, Radon, and carbon dioxide. I will also cover the easiest (in most cases) ways to improve indoor air quality.

If you have any questions, please let me know. We also consult on projects in many different capacities, from reviewing details to providing owner’s representative services, and can help ensure your project achieves long-term success.

Thermal Performance of Walls - Final Thoughts

We have walked through different thermal models for different wall types, but so far, we have mostly focused on the condensation potential of the different walls. First, I will provide a few final thoughts on how to help wood frame walls with condensation potential. Then, I will go through other considerations, like heating/cooling, associated with the different walls.

So, how can we mitigate the condensation issue in wood-frame walls? I will only touch on the two broad methods I see commonly used. The first method is to put a significant amount of the wall insulation outside of the wall cavity, ideally in the form of continuous insulation. What does that mean? It depends (doesn’t it always??) on the climate, but it can easily be 60% or more of the wall insulation value placed outside of the wall cavity; this also requires special attention to providing a well-detailed vapor barrier. The second method, typically employed along with the first, is actively managing the humidity inside the home. Actively managing the humidity inside the house moves the point in the wall cavity where condensation will occur. For example, with an air temperature of 70 degrees and a relative humidity of 65%, the dewpoint temperature is 57.7 degrees (that means that if the air comes into contact with a surface lower than 57.7 degrees, it will start to condense). But reducing the relative humidity to 45% moves the dewpoint temperature to 47.7 degrees! Why is moving the dewpoint to a lower temperature good? It moves the place in the wall where condensation will occur, and the goal in a wood frame wall is to move the condensation location out of the wall cavity (ideally to outside of a rain screen where there is excellent drying potential for the assembly). It should be noted that simply controlling humidity is a great help in all buildings and can make otherwise deficient wall assemblies function for much longer.

One thing to note is that humidity in a home should be actively controlled regardless of the type of building system used.

How do wood frame walls compare to ICF walls for heating and cooling loads? A “mass wall,” is a wall assembly like ICF; the code gives us a good indication of how much better it will perform than a traditional wood frame wall. Let's look at the 2024 IECC (International Energy Conservation Code). For climate zone marine 4, we see that a wood frame wall needs R30 cavity insulation or R20 cavity and R5ci (ci means continuous insulation) or R13 and R10ci, or R0 cavity and R20ci. Alternatively, a mass wall requires R13 (if half or more of the insulation is on the exterior of the mass wall, like ICF) or R17 if more than half of the insulation is on the interior of the mass wall (I have never seen a mass wall constructed in that way). So, if we look at the wood frame wall requirement of R0 cavity and R20ci vs the typical mass wall of R13, we can see that the code recognizes that the mass wall performs approximately 43% better than the wood frame assembly. THEN, we look at the typical R-value of an ICF wall, which is R22+ (most manufacturers are in the R22 to R24 range, but it can be increased); we can see that an ICF wall is over two times the performance of a wood frame wall. OR, put another way, to get comparable performance from a wood frame wall, it would need to have a continuous insulation value of R55 to perform similarly to the R24 ICF wall. Many studies show that ICF performs even better than what the code recognizes compared to wood frame. What does that translate to? Well, that 43% performance difference translates really well into heating and cooling costs, and many studies show that ICF uses 40% to 50% less energy (with some showing significantly more).

Another critical component of the wall assembly is how airtight it is. A wood frame wall assembly requires special care for the entire wall area to ensure that every gap/joint/penetration is sealed, whereas an ICF wall simplifies the air sealing (the concrete core is essentially airtight). However, wood frame walls and ICF walls can both be relatively airtight if good detailing is followed, especially around all openings/penetrations. By having an airtight assembly, we can control the air in the home (great for having clean air inside the house), potential wall condensation (only of concern for wood frame walls), and minimize heating/cooling costs. ICF makes it much easier to achieve an airtight wall, but again, it is possible to achieve this with a wood frame wall.

One essential item I will not touch on in this post because it needs a dedicated post is windows and doors. They are a critical component in the wall assembly, but an entire post is required to cover the nuances adequately. Similarly, I will not be covering ERVs or HRVs and the need to bring in fresh air in this post, but I will cover that topic in a future post.

In summary, code minimum wood frame wall assemblies are less expensive upfront than ICF walls but are significantly more costly over the long term. I recommend slightly reducing the home’s size and switching to ICF, which is by far the best assembly right now. It is also worth noting that ICF is typically less expensive than a high-performance wood frame wall.

For information, we build ICF homes and wood-frame homes. Ultimately, it is the client’s choice, and it is possible to build either one well. I recommend ICF because it is far superior, but we build using both.

If you have any questions, please let me know. We also consult on projects in many different capacities, from reviewing details to providing owner’s representative services, and can help ensure your project achieves long-term success.

Thermal Performance of Walls - Additional Information

Following up on the last post regarding thermal performance of different wall assemblies. That post looked at a code minimum wall vs ICF because those are two common wall assemblies we see.

A quick reminder, I am sharing this thermal modeling we have had performed to compare different wall assemblies and in particular where condensation is predicted to occur. These models were done for a few projects in climate zone 4C, so a somewhat mild climate that sees typical temperature ranges from the 20’s overnight in the winter to 100 (ish) on peak summer days.

Of particular note, these models appear to be very accurate based on older homes we have remodeled for clients over the years and where we have found mold in wall systems. I will cover mold, indoor air quality and proper flashing in later posts. It is worth noting that the majority of the mold we have found in wall assemblies during remodeling is at least partially due to improper flashing and not controlling the relative moisture inside homes. But, the typical wall assembly is flawed from the start as you will see from the below thermal models.

This post will look at some other wall assemblies that are being proposed and will soon become code minimum.

The above two images are a typical 2x6 stud wall with cavity insulation WITH continuous R5 rigid insulation outboard of the wall framing and an insulated slab on grade with exterior insulation at the edge of the slab. This is the 2024 IECC (international energy conservation code) minimum for climate zone 4C (there are a couple of other wall assemblies (R30 cavity insulation, R13 cavity insulation with R10 continuous outboard, and R0 cavity with R20 continuous outboard are the other options for 4C) . The 2024 IECC is not yet adopted in Oregon but it likely will be in the coming years. This model is shown with a 23 degree outside temperature and a 72 degree inside temperature. Condensation (depending on the relative humidity) is expected to occur in the green band, near the yellow band which is on the interior third of the cavity insulation. That is a major problem, how will it dry out? Along with other problems, for example wet insulation loses it’s insulation ability (reduced R-value) and will have a tendency to sag over time (typical cavity insulation is fiberglass batts).

The one benefit this wall has to the current code minimum wall is that it pushes the point of freezing in the wall further outboard.

The next point I often hear is, “but no water will get into the wall.” But this is not true, was every electrical penetration sealed perfectly? Was every HVAC and plumbing penetration sealed perfectly? On a code minimum wall I can guarantee that the answer is no. If air can get into the wall then water WILL get into the wall as well, carried by the air. So what is a better wall assembly?

So, in summary this updated code minimum wall will have essentially all of the same problems the current code minimum wall has. Is there a better wood framed wall?

The above two images are a typical 2x6 stud wall with cavity insulation WITH continuous R13 rigid insulation outboard of the wall framing and an insulated slab on grade with exterior insulation at the edge of the slab.

To spare repeating myself, this wall assembly has essentially all of the same problems we saw with the other two wood frame wall assemblies.

Is there a way to make a wood frame wall assembly work as well as an ICF wall? Some wood frame wall assemblies can and have been shown to work, but they are significantly more complex than an ICF wall and typically also more expensive. AND wood is always more prone to water damage than concrete.

I will cover other topics that make wood frame wall assemblies less prone to problems, such as actively controlling the humidity inside the entire home in future posts. Again, wood frame walls can be made to function but if you have the option to build better, why not? Code minimum wood frame wall assemblies are less expensive upfront than ICF walls but are more costly over the long term. If upfront costs are the main, or only, concern, then we can look at ways of making wood frame perform and be durable. I recommend slightly reducing the home’s size and switching to ICF, which is by far the best assembly right now.

If you have any questions please let me know. We also consult on projects in many different capacities, from reviewing details to providing owner’s representative services and can help ensure your project achieves long term success.

Thermal Performance of Walls

Hi everyone,

I am sharing some thermal modeling we have had performed to compare different wall assemblies and in particular where condensation is predicted to occur. These models were done for a few projects in climate zone 4C, so a somewhat mild climate that sees typical temperature ranges from the 20’s overnight in the winter to 100 (ish) on peak summer days.

Of particular note, these models appear to be very accurate based on older homes we have remodeled for clients over the years and where we have found mold in wall systems. I will cover mold, indoor air quality and proper flashing in later posts. It is worth noting that the majority of the mold we have found in wall assemblies during remodeling is at least partially due to improper flashing and not controlling the relative moisture inside homes. But, the typical wall assembly is flawed from the start as you will see from the below thermal models.

The above two images are a typical 2x6 stud wall with cavity insulation and an insulated slab on grade with exterior insulation at the edge of the slab. This is currently the code minimum wall assembly in 2024 in Oregon. This model is shown with a 23 degree outside temperature and a 72 degree inside temperature. Condensation (depending on the relative humidity) is expected to occur at the green/yellow interface which is on the interior third of the cavity insulation. That is a major problem, how will it dry out? Along with other problems, for example wet insulation loses it’s insulation ability (reduced r-value) and will have a tendency to sag over time (typical insulation in a code minimum wall is fiberglass batts).

The next point I often hear is, “but no water will get into the wall.” But this is not true, was every electrical penetration sealed perfectly? Was every HVAC and plumbing penetration sealed perfectly? On a code minimum wall I can guarantee that the answer is no. If air can get into the wall then water WILL get into the wall as well, carried by the air. So what is a better wall assembly?

The above two images are a typical ICF (insulated concrete form) wall and an insulated slab on grade with exterior insulation at the edge of the slab. This model is shown with a 13 degree outside temperature and a 72 degree inside temperature. Why did we model the ICF wall at a colder outside temperature? We know ICF will perform significantly better than a typical stud frame wall so we wanted to check colder climates at the same time. Condensation (depending on the relative humidity) is expected to occur in the green band, towards the yellow side which is in the solid concrete core of the wall system.

A well placed concrete wall will allow nearly zero air through it. If no air is able to pass into the concrete where the condensation is predicted to occur then also no water will get to that point in the wall assembly. AND even if a very small amount of water did get into the concrete core where it would condense there is no concern because concrete does not mind water.

We have been starting to switch entirely to ICF walls because the thermal performance of the wall is significantly better than a traditional wall (I will cover thermal performance in a separate post), an ICF wall is significantly more durable (will last much longer) and an ICF wall will help maintain much better indoor air quality.

The above modeling is just a few snapshots of what we do for clients and projects to ensure that the entire project will perform as expected. We also model the different components in wall and roof assemblies, for example the framing around the openings in an ICF wall and the roof/wall interface. In a future post I will go through some of our modeling we have done for different options to frame out window and door openings in ICF.

If you have any questions please let me know. We also consult on projects in many different capacities, from reviewing details to providing owner’s representative services and can help ensure your project achieves long term success.

Starting a Blog

Hi everyone,

I will be starting to add monthly content and particularly deep dives into current topics. From waterproofing to thermal performance to specific products. Please ask any questions you have as they come up, even if a blog post is years old I will circle back and respond.

I’m excited for you to join me on this journey. I am not a writer so please have patience with my generally short and to the point posts, I am an engineer and incredibly detailed though. I have the privilege of working with amazing architects, other builders and specialists around the world and am excited to share my knowledge (and theirs) with you.

A quick note, I will always disclose at the beginning of a post if a manufacturer is a sponsor.