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What are the Causes of Mold in Tiny Houses?

November 25, 2019 by Corinne 8 Comments

 

common areas that go moldy in tiny homes


This post contains affiliate links, upon purchase I earn a small commission at no extra cost to you.

1. Built by Non-Experts

Highly skilled builders are rare. They tend to focus on upscale houses because that extra work and time they spend to build something right does translate to more expensive homes.

Most tiny house companies I have seen were started by contractors who don’t have much experience, they certainly don’t have the expertise in building science (which is mold prevention), and high craftsmanship.

Most small companies I have looked at started with someone who had not even managed a whole house build before! That was the case with my builder.

Even if a company is well established, it’s rare that an architect or other building science expert is recruited as a designer and consultant on a tiny house build. It is necessary to have that building science expertise to building anything that will hold up to mold, no matter the size.

My resource page contains links to architects, builders, and building science experts who I think are good.

I certainly wished I had chosen an experienced builder who really cared about details, and hired an architect to design and manage the project.

2. Building Codes not Followed 

Building codes are not perfect, they are only the bare minimum requirements and even though they are just the absolute bare minimum of what needs to be done on a house, they are not usually followed.

To build a truly mold-resistant (regular) building you have to hit many of those codes right on and in many other areas go above and beyond those codes if you want the house to hold up to moisture and mold.

Tiny houses don’t even meet those codes on some of the most basic building standards. If you are having trouble finding a regular house that does not have mold, I don’t have good news, tiny houses are built even more poorly.

For some areas of the build, RVIA certification could help ensure things are done better. But some RVIA codes are not mold preventative (like the requirement a vapor barrier), that could make things even worse!

Look at RVIA codes and see if that will work with your moisture management system. You may have to forgo that certification. There may be important guidelines to follow there for general quality (plumbing, electrical, fire safety), but not necessarily for mold prevention.

You can build a mold preventative build (like this one) and also meet the International Residential Code (IRC) (which would be a good idea).

 3. The Trailer is Tricky to Insulate

All Tiny Homes on Wheels are built on a metal trailer – that’s a tricky interface for condensation in most climates. Building the house by using that trailer as a floor cavity is a bad idea.

The house should be built up on top of the trailer, and even then there are many very detailed decisions and details to consider and execute. See this post on a Mold Preventative Tiny House for details on the trailer base.

4. Metals Frames 

Many THOWs are also made with metal framing. That is really tricky too! Now you have a whole house with thermal bridging and the possibility of condensation in the wall. Even if you go with all foam for insulation, this has to be well thought out and designed well.

I have seen trailers with a metal frame and then an organic insulation! No!

The wheel wells, another metal area, are also particularly difficult to insulate and are usually done wrong. The wheel wells in my tiny house went moldy within the first 3 years. They need to be thought out and detailed right.

Hire a building science expert to design your building envelope.

5. Which Climate is it Built for?! 

Tiny homes are often moved throughout many different climates in the US and Canada. Which climate was it designed and built for?

Even if some thought was given to design the building envelope and HVAC for that climate, will it now be moved to many different climate zones? How will the house perform in those?

If the house is made for multiple climates that has to be factored into the design of the entire envelope and moisture management system as well as the HVAC right from the start.

WUFI is one program that you can use to model the moisture in the house and see how it will perform in various climates.

6. Movement is not Your Friend!

Taking a house and then jostling in on the highway does not lead to something very durable. All those little details that need to add up to have things perfectly sealed and flashed do not benefit from a lot of movement.

You can easily lose the integrity of your sealing or flashing here, you may even have trouble with your framing or siding. Problems with your framing could lead to problems with your doors and windows and more…

7. A One Year Warranty??

Many tiny houses are very expensive and only come with a one year warranty! What!

What other 60K item would you buy that only has a one year warranty? Builders can get away with a lot because major mold problems will take longer to show up than one year.

My house had a few problems in the first year, but there were other major problems that took more than a year to show up. Mold above the shower in the ceiling, mold on the framing, an insulation system in the floor that was not done right – I fixed these myself on my own dime.

Ben Garrett (Tiny Healthy Homes) who built my house only paid for things that went wrong in the first year. He then changed the name of his business (and so I could not sue him). That’s another reason these small companies are very risky. I lost 100k as a result of the building defects in that house.

Though I did learn a lot about building science when I took it apart! And this did lead me to become certified as Building Biologist to help others build low offgassing, mold-safe houses.

The most helpful course in mold prevention is Cheryl Ceicko’s Building a Healthy Home.

8. Siding is Prone to Mold

Siding is frequently done wrong on tiny houses. Mold preventative siding almost always has a rainscreen with very few exceptions.

Regular wood-framed houses almost always require a vented rainscreen siding system to prevent water damage and mold. This is rarely done on a tiny house.

Most houses I have seen have siding right up against the sheathing. Sometimes it’s permeable siding, meaning solar vapor drive can drive moisture in, but even if it’s not, it prevents drying from the inside out. And you are losing your layer of protection from water entering behind the siding.

A rainscreen helps water that will get behind your siding drain out.

I highly recommend Cheryl Ciecko’s course on building a mold preventative house which is now evergreen, you can start the course at any time.

To hear about future course you can sign up for my email list:

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9. Roofing Prone to Mold 

Regular sized houses have a fairly complex roof system that often has venting. An unvented roof (like tiny house roofs) would have to be done really carefully.

In a small space, your roof cavity can start to mold fast. Mine did over the shower as the builder had no interior vapor barrier and the breathable roof sheathing membrane was enough to trap moisture there.

Many tiny houses also have roofs that are flat or don’t have the right material for the slope.

Here is an example of a highly detailed mold preventative roof.

10. Details not Done Right 

The devil and mold prevention are in the details. Window flashing, house wrap installation, house wrap taping, metal head flashing, the detail below the rainscreen, flashing on any permeations going through the wall, details around the door- all of these are super crucial.

It’s especially important to get right due to the lack of overhangs over windows and doors on most tiny houses. This means everything has to be done perfectly. The overhang on a regular house is insurance against too much rain hitting these vulnerable areas.

Filed Under: Mold-Free Building, Tiny Homes and Trailers Tagged With: mold free building, tiny home

Reader Interactions

Comments

  1. Sarah says

    October 15, 2022 at 10:05 am

    This is an amazing blog (as are so many of Corrine’s). So grateful to all that you do and share with the public, including how active your page is and how you maintain your data base with updates on various topic. Simply amazing.

    Reply
  2. Mortgage Broker Australia says

    October 5, 2022 at 8:03 pm

    Great tips provided. Thanks a lot.

    Reply
  3. PF says

    January 27, 2022 at 11:14 am

    Hi Corinne,

    Thanks for all of your work on this website, we have been learning from it for several years.

    We just now for the first time realized that Ben Garratt built your tiny house. We bought a tiny house from Ben early last year, and are starting to have serious mold problems as well. We had assumed that because he specializes in building homes for sensitive folks, and charges a premium for them, he would know how to avoid these problems. However we are also now in the position of being about to lose our investment in the house due to mold and other issues.

    We are still within the 1-year warranty window. We were hoping we could ask you about your experience in issuing the warranty claims, and ask for any advice you have about discovering all possible problems before the warranty period is up. So far Ben has been unwilling to respond to our emails & phone calls. We would gladly book a consultation, but there don’t seem to be any slots open at the moment and the question is somewhat time-sensitive.

    Thanks very much

    Reply
    • Corinne says

      January 27, 2022 at 5:41 pm

      Please get some legal advice for that. Be sure to identify the issues before the 1 year mark. You might need to do an appointment with Cheryl Ciecko to make sure you properly identify the errors with an architect. That’s what I wish I did. I would bet a million dollars he is not detailing the base correctly.

      Reply
      • PF says

        January 29, 2022 at 5:45 pm

        Hi Corinne,

        Thanks for this information; we appreciate your prompt response.

        The mold that we’ve observed so far has been on the windows and door threshold since the weather turned cold. We’ve been taking steps to address it immediately when we notice it, but we have been very concerned about non-visible mold, especially after reading about your experience.

        We also finally got a hold of Ben, and talked to him about the steps he took against more serious mold problems in this house, and feel reassured that the vapor barrier, HRV and other preventative measures were correctly installed (In Ben’s response he told us that your tiny home had neither an HRV nor vapor barrier installed– would you be willing to confirm whether that information is true?). In any case we are grateful to be better informed now about how the house is built. We are still planning to have a professional come do mold and air quality testing as well.

        Thanks again.

        Reply
        • Heather says

          February 25, 2022 at 5:15 pm

          Hello, Corrine and Paige.
          I’m planning to purchase a tiny home soon and mold has been a concern of mine. Do you mind telling me if you live in a damp climate? Or any other tips of things to look out for? Thanks!

          Reply
          • Corinne says

            February 25, 2022 at 7:58 pm

            Climate was not related to the problems in my house or most tiny house problems. Check out the post on building a mold preventative tiny house that is prob the most important article on my site written by someone who built one right.

  4. Miriam says

    January 6, 2020 at 3:42 pm

    Hiya! I know this is kinda off topic however , I’d figured I’d ask.
    Would you be interested in exchanging links or maybe guest authoring
    a blog post or vice-versa? My blog discusses
    a lot of the same subjects as yours and I believe we could greatly
    benefit from each other. If you might be interested feel
    free to shoot me an email. I look forward to hearing from you!

    Superb blog by the way!

    Reply

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Hi, I’m Corinne Segura, I hold a certificate in Building Biology, and a certificate in Healthier Materials and Sustainable Buildings, among other credentials below. I have 8 years of experience helping people create healthy homes.

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