Insulation is one of the most important aspects of any school bus conversion build. There are many different types of insulation that can be used to insulate a skoolie and there are pros and cons associated with each of them.
To quickly answer the question – “How do you insulate a school bus conversion?” There are 4 basic steps:
Step 1: Demo and strip down the interior of your school bus to the bare framing.
Step 2: Clean, repair and prep/frame out walls, ceiling and floor surfaces for installation of insulation.
Step 3: Apply closed cell spray foam insulation to the ceiling and wall surfaces.
Step 4: Apply foam board to the sub-floor.
Keep in mind that the above steps are the basics of how we insulate a school bus conversion, and there can be many variations in terms of types of material used and their location.
Ultimately, the main factors to consider when determining how to insulate your skoolie conversion are the costs of insulating, the effectiveness of the insulation, the availability of the products, and the ease of installing the insulation.
Why You Need to Insulate a Bus Conversion
You may be wondering if a stock school bus comes insulated in any way. In short, yes. Most school buses come with insulation. However, the effectiveness (and the cleanliness) of that insulation is subpar at best. Typically, the insulation is a fiberglass type insulation that is not equipped to handle extreme weather.
Since the primary purpose of a school bus is to shuttle students a short distance from home to school and back, proper insulation is not a main concern for the original school bus design. The stock insulation does vary from state to state, of course.
For example, the State of Minnesota says there needs to be insulation installed with a minimum R-value of 5.5, while Texas says that there needs to be insulation installed with a minimum R-value of 5.75. Which brings me to my next point.
What R Value Does a Skoolie Need?
This is entirely up to the skoolie owner, and their plans for travel. If they choose to chase the nicer weather, stock insulation may work for them, R-value wise. The skoolie owner may still, more than likely, have to deal with dirty (and potentially moldy) insulation.
For more reasons as to why you should remove the old insulation (and the ceiling!) be sure to check out Trail and Summits article on 10 Most Common Skoolie Conversion Mistakes.
Back to the R-value. There is no standard R-value required for a skoolie. NOAH, the certifying company that Phoenix Skool Buses works with, requires that the insulation be installed in accordance with the RVIA, which specifies a minimum of R-7 in the floors, walls, and the roof.
However, the higher the R-value, the better the insulation. If you can afford to, and if it will fit, we always recommend as high of an R-value as possible.
How do you Insulate a Skoolie Ceiling?
The easiest (and, in my opinion) the best way to insulate a skoolie’s ceiling is by using closed cell spray foam. Closed cell spray foam is a noise reducer, mold/mildew resistant, and has an R-value of 7 per inch. That means that you can fit a lot more of the insulation in a smaller space, and it’s easier to fill the smaller gaps that a school bus ceiling tends to have.
We like to build the framing first, as it can be difficult to go back later and add the framing, but you can add it later. Just be sure to tape off the parts of the ceiling that you don’t want covered with spray foam or you’ll have to trim it back at a later date, which can be time-consuming to do. Your other options are to use foam board or sheep’s wool. More on those options later.
Should you Insulate a Skoolie Subfloor?
Yes, absolutely you should insulate a skoolie sub-floor. First of all, direct metal contacting a wooden sub-floor can create condensation. Secondly, metal can get very cold! If you’ve ever walked on a concrete floor, it’s a little like that, but colder.
That temperature will transfer to the wood and will create a very chilly floor. This can be mitigated with rugs in a pinch, but the condensation cannot be prevented. As such, the easiest way to insulate the floor is by using foam board.
Foam board is a cheaper option than spray foam, and can easily be DIYed, but it has a smaller R-value per inch. You’ll also need to cut each individual piece to fit perfectly and ensure that there are no gaps in between the foam board to prevent condensation from forming.
Also, to complete the vapor barrier, you’ll need to tape all of the seams together. You can spray foam the floor, as well, but it can take a decent amount of time to trim the spray foam back to be completely flat.
How To Insulate School Bus Windows
The best way to insulate a school bus window is to not have a school bus window. That is to say, while the light is beautiful, the windows are one of the biggest sources of heat and cooling loss. We recommend removing as many of your windows as possible. This article provides some great information on how to easily remove school bus windows.
The best way to insulate a school bus window is to not have a school bus window.
If, for whatever reason, you choose not to remove your windows, you should insulate them as much as possible. One option is to create foam board cut outs that you can easily stow away when not in use.
While this may not be the prettiest option, it is one of the most effective ways to insulate your skoolie windows. Your other option is to either create curtains for each window, or to use Reflectix for the windows.
Should you use Sheep’s Wool to Insulate a Skoolie?
Sheep’s wool is a great, eco-friendly and one that we have used in the past. It is chemical free and manages moisture well. It is also said to absorb chemicals, which helps improve the air quality of your home. It accomplishes this by heating up when wet, which allows it to dry quickly and maintain its R-value.
However, shipping times vary but usually take at least a few weeks to get to you. One of the popular wool options available to you offers loose fill (blown-in) and batt insulation available in many different R-values. Additionally, due to being chemical-free, the installation process does not require protective clothing to install.
Spray Foam Insulation for a Skoolie
In our opinion, spray foam is the best bang for your buck insulation wise. It provides the greatest R-value while taking up the least amount of space. It is mold and mildew resistant, a sound deadener, and can help seal leaks. There are two different types of spray foam: open cell spray foam and closed cell spray foam.
Open cell spray foam is like it sounds, the cells are purposefully left open, making the material softer and more flexible. Likewise, closed cell spray foam is like it sounds, the cells are closed, so moisture and air aren’t able to get inside the foam. This is what makes contributes to its great qualities. We always recommend using closed cell spray foam and here is why.
Closed cell spray foam is denser. It’s designed to expand about 1 inch, while open cell spray foam is designed to expand about 3 inches. Generally, this means you can make (at the most with skoolie walls) about one pass. With an R-value of 3.5, this is not helpful with extreme weather conditions.
Meanwhile, with closed cell spray foams expansion value, typically one or even two application passes can be made. With an R-value of 7 per inch, you can achieve a total R-value of 14. This is way more useful for extreme weather conditions. But what exactly does R-value mean?
It means the materials resistance to heat flow. A higher R-value means the material has a greater resistance to heat flow. Closed cell spray foam also acts as a vapor barrier, while open cell spray foam does not.
It is important to keep in mind that some benefits of open cell spray foam are that, since it expands greater than closed cell, it can do a better job of insulating nooks and crannies and it is also typically less expensive than closed cell spray foam.
Can you DIY Spray Foam a Skoolie?
The short answer is, yes. There are many DIY kits available on the market. That being said, the application of spray foam is not as simple as cutting foam board into squares or stuffing sheep’s wool into crevices. Spray foam application requires a lot of prep work. First, all areas that do not require spray foam should be taped off or covered. Depending on the layout, this can be a long process.
If you are applying the spray foam yourself, you’ll also want to make sure that you are wearing the proper PPE. The EPA recommends wearing skin, eye, and respiratory safety equipment to protect yourself from the hazardous vapors and aerosols. Be sure that the area that you are applying the spray foam in is properly ventilated, and follow all EPA guidelines listed here.
Additionally, spray foam requires curing time for it to harden and work effectively. Some companies estimate that this period can last anywhere from 8 to 24 hours. It’s important to read all of the manufacturer’s instructions prior to installing the spray foam, as well as the precautions. With spray foam, there is the potential for off-gassing. The EPA does state that this process is not fully understood and does require more research.
Lastly, while the spray foam is considered to be relatively inert after is has been applied and is cured, the EPA does caution against conducting work that may disturb the spray foam post application, such as, but not limited to, heating or griding away at the spray foam.
That begs the question, should you DIY spray foam installation for a skoolie?
While there is the possibility that you can save some money from DIYing spray foam yourself, there are plenty of perks having it installed for you. Firstly, you will not need to perform the prep work yourself, which can be quite time-consuming. Next, you won’t need to worry about the potentially harmful chemicals exposed to the installer during the installation process.
You also won’t have to worry about the effectiveness of your job. Again, spray foam does require curing time, and if it is not given this time to cure it can, effectively, be rendered useless. You’ll need to fully remove the spray foam and reinstall should you notice that the spray foam did not cure.
DIY spray foam kits can be found at Lowe’s and Home Depot
Lastly, after the spray foam is installed, you’ll want to make sure that the spray foam is trimmed back to a flat surface so that walls can easily be installed. This clean-up and trimming process can take quite a bit of time.
The cost of having a company install spray foam can vary on the products availability and the space that you’d like spray foamed. Our company does hire out our spray foam application process, and we’ve seen prices range from $1,500 to $2,800.
However, we are located in a smaller town. We have found that other DIYers located within larger cities receive quotes greater than this. However, it’s important to note that you should shop around for different spray foam companies. Not only to compare prices, but also to compare timelines. Additionally, some spray foam companies will give you a discount if you prep the area for spray foam yourself.
How Much Does it Cost to Fully Insulate a Skoolie?
Again, the cost to fully insulate the skoolie depends on the type of insulation that you use, the R-value of the insulation, and the amount of area that you’d like to insulate. Let’s assume foam board in the floor and spray foam in the ceiling and walls. We’ve found that most foam board comes in 4 Foot by 8 Foot pieces. For the sake of this example, we’ll use this product here.
To totally insulate the floor of a 40-foot skoolie, it would cost about $350 for 11 sheets, which gives us room for error. Spray foam typically costs our company around $2,000 for the walls and ceiling, for a total of $2,350 to fully insulate the floor, ceiling, and walls.
Should you choose to use a combination of wool and foam board for the walls and floor (i.e. wool in the walls and foam board in the floor), depending on the product that you work with, it should cost around $1,000 to insulate the walls and floor.
We recommend that, regardless of what path you choose, spray foam insulation should be used in the ceiling, as it’s easier to work with the curvature of the roof. One important thing to note, though, is that some spray foam companies may not take on smaller jobs.
Phoenix Skool Buses LLC Approach
Our company uses foam board insulation in the floor and closed cell spray foam in the walls and ceiling. The thickness of the foam board really depends on the customers total height. All of our customers in the past have wanted to be able to stand up straight while walking through their skoolie (which is understandable) so we use the thickest foam board we can use while still allowing for them to stand up straight.
As far as spray foam, we typically have 1.5-2 inches of spray foam applied. Essentially, we have the spray foam company spray the foam even with the ribs of the bus. This is our preferred practice, but our next preference would be a combination of sheep’s wool, foam board, and spray foam.
Should you wish to keep your bus chemical free, we believe that a combination of sheep’s wool batting for the ceiling/walls and foam board for the floors would be an acceptable practice as well.
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Sabrina Bosserman is a former mechanic in the Navy’s Nuclear Power Program. She is the co-owner and operator of Phoenix Skool Buses, a tiny home building company. She’s been to over 20 different countries, and uses those experiences to breathe life into the skoolies that Phoenix Skool Buses build; from the layout to the decor. She has been featured on multiple podcasts as well as tiny house platforms such as Tiny Living and Tiny Home Tours. She was also a guest speaker at the Great American Tiny House Show. She is currently obtaining her MBA and loves to spend her down-time with a good book.