The most common time I am asked the question of how to identify moisture issues is when someone buys an existing straw bale house. Moisture is not often a problem in straw bale homes as long as the house was built well. That said, there may be issues that show up over time. Here are some basic things to consider when wondering about moisture issues in the home.
Take a look around the lower corners of the windows for signs of moisture damage. This is the most common area that moisture damage occurs. Check inside and out in this area. You’ll see staining on the plaster, or worse, buckling and peeling plaster.
Anywhere there is a penetration (electrical plugs are the most obvious), take a strong smell and see if you get a hint of damp. In most cases you won’t.
If you believe there is moisture damage, the best thing to do is drill some small holes in the plaster in the suspect areas and insert the probe of a moisture meter. Any readings over 20% are bad and can sustain mold growth. I would want to see readings around 12%. If you do have moisture problems, you’ll need to push some dry heat through the wall while it’s hot and dry outside as well, if possible. The key will be finding the source for the moisture and that will dictate how hard of a fix it will be.
About the Author
Andrew Morison is a specialist in straw bale and green construction. He has shown thousands of people how to build their own straw bale projects through his comprehensive series of instructional straw bale, concrete foundation, and plastering DVDs, as well as his hands on workshops. You can check these out at www.StrawBale.com/store.
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January 15th, 2010 at 11:36 am
Hi Andrew,
I’ve paid the $200 dollar fee for registration for your next workshop but I’m starting to have some doubts about straw bale homes. I read the info. that you sent in your straw bale success tips about moisture in straw bale homes and mold. This is a really big issue for me and one I had not read about before. I have a lot of allergies, am very sensitive to mold and the thought of having a home that could get these mold issues is very troubling to me. I live in Washington state an,d it’s pretty wet in this part of the state. I am starting to have second thoughts about the whole straw bale process.
What info. do you have to alleviate my concerns?
January 15th, 2010 at 9:52 pm
Hi Andrew
In response to the moisture aspect, would it not be wise to include damp sealing around door and window apertures, much the same way you would damp seal at the base of the walls, or would the plastering around these areas be compromised?
I am considering a straw bale home and, in contrast to Allen Robertson, I live in South Africa, a much drier part of the world, but the area I am considering is one of the high rainfall areas of our country. I am considering a double damp course layer at the base of the walls, broad roof overhangs, the lowest level of the plinth to be at least 6 inches above ground level (gradient considering)at its lowest point. As I am considering thatch for the roof, I intend installing ground gutters to drain rainwater away (to storage tanks)as quickly as possible…. are these all sensible ways to deviate possible damp away from walls and foundations?
Comment please…
January 15th, 2010 at 10:32 pm
As someone wanting a “healthy” dwelling who has been considering and excited about building with strawbale, I too am concerned about the mold issue in the wet Northwest. Beyond building correctly, do you recommend that the design include overhangs/porches/raised foundation? Would that help protect the walls from potential water/ dampness infiltration and potential mold?
Concerned.
January 17th, 2010 at 1:05 pm
Don’t worry Allen, if it is built well there is no chance for moisture trouble.
I have strawbale walls in quarter of my newly renovated home, and there has been no sign of moisture or mold for almost year and a half, and weather was rainy, snowy and temperatures went bellow -15 celsius.
It’s all about good roof that has to be extended as much as it can, so less rain would fall on wall and windows.
And lime plaster does miracles to moisture control in house and on outside surface.
All the best, and don’t give up!
January 21st, 2010 at 11:22 am
I found this article about the difference between straw bale home and clay straw homes. In it talks about the ability of the clay straw home to regulate humidity. Does the straw bale home have this ability? This is the quote from the other site:Straw bale and clay/straw construction are actually quite different in many ways. Clay/straw construction combines loose straw with clay soils and water to form a 12″ thick monolithic wall that contains both the insulating properties of straw and the mass storage capacity of earth. In the mixing process each straw fiber is coated with clay making it fireproof, vermin proof and resistant to decay. The clay/straw walls have sufficient texture to receive natural plasters directly without the need for additional netting. Due to the high clay content clay/straw walls are hygroscopic which means that they have the ability to moderate and balance indoor humidity, an important health promoting factor.
January 22nd, 2010 at 12:53 pm
If you use clay plaster or lime plaster, there is an ability to manage indoor humidity; however, this is not the same as handling exterior humidity. Again, your area is not a problem for bale construction and would, in my opinion, be served well by it. Clay/straw walls are very cool, yet are different than straw bale walls and not as insulative. They’re better suited for areas that get really cool at night and hot during the day as they release their stored cool into the room throughout the day. They are best used in desert climates.
February 8th, 2010 at 12:20 pm
I live in a straw bale in Bend Oregon. A roof leak caused some mold in the insulation at the attic area. It was found during home inspection and had a professional remediation performed. 4 years later no problems and my son is highly allergic to mold. Mold isn’t the end of the world, just needs to be dealt with correctly. Many homes, straw bale or not will have this issue.
March 21st, 2011 at 8:55 am
We live in Louisville, KY where the humidity is high here and local farmers have a problem with mold growing in their hay bales. We have 50 acres in Breckinridge County, KY and are making plans to build. We were intrigued with the straw bale construction and ordered DVD’s to watch but haven’t had the time yet. My husband was convinced building a straw bale house was the way to go until we started researching a little further and realized that mold could cause a problem. We keep reading if the house is constructed right, we SHOULD not have a problem, however how do you ensure it will be built correctly? We really want to believe we should not worry, but are afraid to take any risks even in the rare chance we could get moisture. It seems with the high humidity levels, moisture would develop in the walls even if the house was built well.
March 21st, 2011 at 10:59 am
Hi Rebecca. You are so right when you talk about the “should be fine” aspect of building in humid climates. There is not a lot of research data to show how bale structures fair in humid climates. There is some out there, but often the research is done in a sterile setting that does not really reflect what the conditions are like in the real world. I can say that there are several houses in the South, Northwest, and other humid climates that are doing fine after years of use. Does this mean that yours would do just as well? It should! Sorry, I couldn’t help but say it.
I believe, based mostly on the experience of those who live in bale homes in humid areas and my experience building in Tennessee last year, that a bale house can do very well in humid climates if certain details are accounted for.
I think it is vitally important to have some type of moisture removing system within the home. I know that mechanical systems are just one more thing that can fail (power loss, broken parts, etc…) but I do see them offering a great assistance to the overall longevity of the home. A heat recovery ventilator (HRV) in areas that are more cool than they are hot or a energy recovery ventilator (ERV) in areas that are more hot than they are cool is a great idea. These machines provide a constant exchange of fresh air into the home without the loss of conditioned air, allowing things to remain in flow, i.e. no stagnant air. They also remove a large percentage of “excess” moisture from the air and dump it through a drain line outside the home. This helps keep the interior air condition, flowing, and balanced in moisture. It is that excess moisture that can cause damage in the walls if it is pushed out through the natural pressure of the home into the straw as an attempt to leave the structure.
Of course, quality construction is of utmost importance as well. Keeping moisture from entering the walls as vapor is very important. Clay or lime plasters do a great job of absorbing moisture and holding onto it until it can be released back into the air. They have a higher capillary action rate than straw and so will actually draw moisture out of the bales. Cement plaster will not do this as well. Keeping the moisture out of the wall is also necessary in penetrations and joints. Be sure to seal the wall/floor and wall/ceiling junctions in a way that eliminates the direct path for moisture. The same is true around electrical fixtures or any other wall penetrations. Gaskets around electrical plates are a really good idea as is sealing the back of the box to the bales. Using a short shot of expansion foam in the back of the box to seal the openings is a good idea.
Hope this all helps you decide what to do. In the end, you will need to be comfortable with your decision or your house will never be a place in which you can fully relax. There’s no point in building a house you can’t relax into.
June 26th, 2011 at 6:16 pm
Rebecca..I also live in Ky & have worried about the humidity that we experience here ..Would love to have a straw bale house but am worried about anyone having enough experience to assist with building a straw bale in Ky, We don’t seem to be too much into sustainable living around here!!! If you decide to build and would like assistance…let me know, would love to be in on working on it. ( sweetdesignsky.blogspot.com)
September 27th, 2011 at 7:23 pm
We want to convert a cinder block barn into our home. Since we live in a hot, humid region of North Carolina, we are concerned that the cinder blocks will have too much thermal mass. So, we want to massively insulate it on the inside, thinking that straw bails might work nicely. What we’re wondering is if the cinder blocks or the paint on the outside of the cinder blocks will prevent the bails from breathing and cause them to mold in this very humid climate? Do you have any other suggestions as to a better way to go about insulating our barn/house?
September 29th, 2011 at 5:09 am
You can certainly do that; however, I suggest you put the bales on the outside of the block. This will improve the efficiency of your home by placing the added thermal mass inside the insulation (bales) and better regulating the heating and cooling cycles of the house. This will also reduce the risk of trapping humidity in the bales which I would worry about if you place the bales inside the block wall, especially since the block is painted. This will mean more work: extendin foundation, roof, etc, but. Is a far safer way to go. If you cannot do it this way, I would not suggest you ace the bales inside the block. Good luck