Tiny house design is all fun and games at first: watching inspiring tiny house build videos, sketching up your dream floor plans, and daydreaming of that perfect garden or solar array or loft.
But there comes a moment when you realize, "oh wait, I'm designing a house...this is hard."
That is why it is important to think about all of the components of your tiny house in tandem. Fortunately, this is more straightforward than a traditional large home. Unfortunately, there are common pitfalls too many people still make now.
The Components Everyone Thinks About Already
Just to cover some of the basics, here are some elements of your tiny house that you're probably already thinking about. I won't belabor the point on these but must mention that these all relate to each other, and that you should think of your house less as a collection of parts and more as a cohesive home that must work in unison. Almost like an organism, if we want to get a little bit carried away with it.
Electrical
Electricity is a common component that steals lots of attention from people. In some ways, it is not as difficult as it seems: designing where to place fixtures and outlets and roughing in the electrical wiring, for example, are not particularly challenging.
In other ways, electricity is rightfully daunting. For one, doing it wrong can have flame-filled consequences. Installing a subpanel and solar array (if you choose) are not small tasks, and most would recommend hiring an electrician for those components.
In fact, hire an electrician to check any work you do. If the point of the tiny house is some form of freedom, don’t put it or yourself at risk.
Water and plumbing
The systems here come right in there with electricity on the “this is a lot I’m scared” scale…Luckily, it is not particularly expensive and can be done on your own if you choose.
The main things to focus on are the drinking water system, greywater system (dirty water from sinks/showers/appliances), and blackwater system (sewage).
For many tiny houses, especially those that are on wheels or off-grid, the drinking water system and greywater system are one fully functioning system, with clean water flowing in and dirty water flowing out, while the blackwater system is a separate system that comes in the form of a composting toilet or macerating toilet.
For tiny houses designed like traditional houses, the plumbing and water system isn’t much different.
The key is: focus on this ahead of time. Don’t assume you can figure out the water and plumbing once the walls are built. A plan is key.
The structure and the space itself
Well, this one is probably the most fun and most obvious design element. We all love thinking about the design of the space, the natural light we’ll get through our windows, the shape of the roof, and the function of a loft or deck.
Just keep in mind that these choices affect other systems and vice versa. Certainly, enjoy this more creative aspect of design, but don’t forget that it is just brushing the surface.
The Forgotten System That Causes Lots of Issues
To get straight to it—the forgotten system is…THE AIR.
…yes, the air itself is a system, and it plays more than one role in the tiny house. It also has multiple sub-components.
Let’s break it down.
Role 1: Breathing
We all know that we breathe air, but the air challenge in a tiny house is distinct.
Let’s say you have a tiny house that is 240 sq ft x 10 ft tall (22 sq meters x 3 meters). This is a pretty standard-sized tiny house.
This gives you 2400 cubic feet (66 cubic meters) of space to breathe.
To give you an idea, the average home in the US is about 10 times that. Even the average hotel room size is slightly larger in volume.
Imagine spending all day in a hotel room…might get kind of stuffy don’t you think?
Now imagine that the hotel room doesn’t have any ventilation, and no windows you can open. The air would get super stale.
Beyond the stale nature of the air being uncomfortable, the small space can also cause issues with polluted air staying inside the tiny house, and humidity from showers and cooking lingering in the air. Dirty and humid air can cause space to be not only uncomfortable but also unhealthy or even dangerous depending on the level.
When humidity gets above 50%, it can cause interior mold and bacteria to grow on the walls. When it gets below 30%, it can ruin furniture and make your nose, throat, eyes, and skin itchy or irritated.
So you might be wondering: why not just open the windows? Shouldn’t that do the trick?
That leads to the second role that air plays in your tiny house.
Role 2: Structural Integrity
The issue with solely relying on windows is that windows, even in clean and naturally moderate climates, do not protect the structure of the building itself.
Many folks don’t realize what the role of a wall actually is. Walls of course separate the tiny house residents from the outside and hold up the roof, but they also are there to protect the tiny house wall frame and roof from the elements.
If you opt to simply rely on windows for ventilation, you’re basically removing this protection and making the inside of your tiny house part of the elements. In very specific climates, this may work, but for the vast majority of people that don’t live in year-round room temperature climates, this approach will not suffice.
So how does it work?
When air gets into the walls, it carries with it moisture, since air is up to 5% water vapor. When that air gets trapped in the walls, and then reduces temperature, either from the wall or the air itself changing its temperature, the water vapor then condenses into liquid water.
As the liquid water is absorbed by the walls, it can create dangerous mold. It can also rot away the structure itself.
For this reason, it is very important that you frame your walls well, without openings and seems that let air seep into the walls from outside or inside. You’ll also need to make sure you are properly using a vapor barrier, and using the right insulation for your climate(s).
What You Need to Do to Prevent Air Issues
Once your structure is built and you are ready to address air and insulation, here are the steps that must be taken.
This is not a robust how-to guide, but a general checklist. If you’re interested in getting deeper into this, I cover it in my tiny house construction book.
Step 1: Seal Your Tiny House on Wheels
Sealing your tiny house is forgotten all the time by DIY-ers. First of all, the better your construction of the frames, the less sealing you’ll need, as sealing is basically the filling of gaps in your tiny house. It is the prevention of a draft before the draft is a problem.
You can do this by conducting a blower door test, where you turn on all the exhaust fans in the tiny house, and then light an incense stick at critical seams (intersections of roof and wall or wall and floor, electrical outlets, exterior penetrations, doors, and windows), and then using spray foam to seal and leaks.
Step 2: Determine and Install Your Insulation
Determining the right insulation is a big undertaking and is its own topic entirely. However, know that there is no answer to the question, “what insulation is best?”…because the insulation is highly dependent upon where you live.
All in all, you must select insulation based on three things: climate and R-value for that climate, cost, installation method.
The wrong insulation makes air control measures–mostly those related to moisture in the walls–a significant issue a year or so after you move in.
Don’t forget to insulate the wheel well, floor, and roof.
Step 3: Install the Vapor Barriers
The vapor barrier is a specific plastic sheet within the wall that is used to prevent moisture from condensing within the walls and is super important. In the event you use closed-cell spray foam insulation, the vapor barrier is already accounted for, but for all others, you’ll need a designated vapor barrier.
This step may come before step 1, but it may not. It depends where you live because the vapor barrier will go on the side of the wall that is warmer. That means for warmer climates, the vapor barrier is exterior to the frame, whereas in colder climates the vapor barrier is interior to the frame.
Do your homework on the vapor barrier by researching your specific region.
Step 4: Finish Your Tiny House Walls & Ceiling
Once the bones of the wall and insulation are finished, you can finish the interior wall and ceiling (and floor if you have one above the subfloor).
Step 5: Install Passive Air Vents and Exhaust Ventilation
Now, it is time to account for the movement of air. As previously mentioned, you need to be able to have air flow through the house and have humidity dealt with properly.
The more obvious ventilation we’re all used to is exhaust ventilation. These are the fans we install above a stovetop and within the bathroom. Install these. Again, it is not recommended to purely rely on windows.
The less obvious but equally important ventilation is the passive air vent. The passive air vent is basically a hole cut through your walls that allows air to passively flow in and out of the house.
Do your research for your climate on the passive air vent, especially if you live in a climate with poor air quality outside.
Step 6: Select and Install Heating and Cooling Systems
From the mini-split to the propane heater to the woodstove to the window unit, you have several options. You could even go with a floor heater or heat pump.
Consider cost, comfort, installation, and humidity when selecting the type and size of your system.
Step 7: Consider Further Air Quality Control Measures
Don’t assume good air quality even if you followed all the steps. Test it out. Get yourself a smoke detector, carbon monoxide detector, propane detector, and radon detector where applicable.
You may even consider a humidity sensor and oxygen monitor.
All said and done, air quality makes a massive difference to your health and the health of your tiny house. Take these measures and understand how it all works, and you’ll avoid this terribly common pitfall. If you do, you’ll not just have a safe tiny house, you’ll have a pleasant and durable one.
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