Tiny House Insulation: What I Wish I Knew When I Built My Tiny Home

tiny house insulationFall is here and, with it, colder weather, so let’s talk about the best insulation options for your tiny house. Having lived in my tiny house for seven winters now, I know a little bit about how to stay warm in a cold climate. Insulation is critical to a comfortable tiny home. I’ll break down R values, costs, options, and the pros and cons for each of the top tiny house insulation options for when you build your own tiny home.

You can review all the options for tiny house insulation below or choose what is most important to you:

highest r value insulation
lowest cost insulation
best value insulation
sustainable insulation
spray foam insulation
ryans recommendation

Tiny House Insulation Basics

Tiny House Insulation Basics

Insulation is an important choice and you want to make sure you choose the best insulation for your tiny home. Let’s start with some basics before we dig into the details. Most of the info in this post is from living in my own tiny house for close to a decade now and from helping build hundreds of tiny homes.

NAVIGATION

tiny house insulation basicsInsulation Basicshow to insulate a tiny houseHow To Insulateinsulating different parts of a tiny houseInsulate Wall/Rooftiny house insulation optionsInsulation Optionsclosed cell spray foamClosed Cell Spray
open cell spray foamOpen Cell SprayFiberglass batts for a tiny houseFiberglassrock wool insulationRock Woolfoam board insulation optionsFoam Boarddenim or cotton insulationDenim Cotton

What Does R Value Mean For Insulation

What Does R Value Mean For Insulation

R value is a measurement of how well an insulation resists heat being transferred. One thing that confuses first-time builders is that insulation doesn’t keep the heat of your heater in or the cold of your air conditioning in. All insulation does is slow heat from transferring to where you don’t want it.

In the case of air conditioning, cold isn’t actually a thing — it’s just air that has much less heat. So in the summer, the coolness of your house warms up as heat seeps inside. In the winter, you house will cool off as heat seeps outside.

R value is just a measure of how well something insulates from heat transferring. You’ll see it referred to as R-30 or R-7 the higher the number, the better job it does. But one thing to consider is how well something insulates per inch of thickness. This lets you compare insulations apples to apples. Keep in mind that most framed houses have 3.5 inches of space to insulate, unless you frame with 2×6’s, which have 5.5 inches of space to insulate.

Another important thing to remember is that heat rises, and for this reason, code requires your attics to be well insulated — often two to three times as much as the walls and floors. It’s pretty common to see walls that are rated at R-13, but the ceiling be rated at R-30.

highest r value per inch of insulation

Insulate Your Tiny Home For Your Climate – Climate Regions For US With R Values

Insulate Your Tiny Home For Your Climate

How much insulation do you need for your tiny house? Well that depends on your climate and how efficient you want your tiny house to be. The best guide is first determining your climate region with the Department of Energy’s climate zone map, which you can see here. Then use the chart below to see what the general guidelines are. From there you’ll need to get specific guidance from your local codes, which can often be found on Municode.

regional r-values of insulation
insulation r-value for wall thickness

How To Insulate Your Tiny House

How To Insulate Your Tiny House

It seems simple: choose your insulation, put it between your studs, move on. The problem with that approach is that the devil is in the details. If you get them wrong, your home will be hot, cold, moldy and uncomfortable.

Insulation does more than keep you warm. It also helps manage air flow through your wall systems and manages moisture in some very important ways. Nothing about insulating is difficult to do, but it requires you to understand some of the basics which I get into below.

Step 1: Air Seal Your Tiny Home

Air Seal Your Tiny Home

Air sealing will do wonders for your home’s comfortability and how well your insulation will work. A leaky house with excellent insulation will actually perform worse than a house that’s sealed well and has average insulation.

The best thing to do is seal your house the best you can, then perform a blower door test. This creates a lower pressure inside the house and lets you see where air is being pulled in. You can use a smoke pen or a thermal camera to see where air leaks are.

Barring a blower door test, you can just make sure all the critical junctions are sealed:

  • Doors
  • Windows
  • Outlets
  • Exterior penetrations
  • Intersection of wall to floor
  • Intersection of wall to roof

The two biggest pieces of advice I have are to use Zip Panels tapped properly and use Great Stuff expanding foam to seal around cracks. These two things will let you seal up all the major areas of your home.

Step 2: Consider Thermal Bridges

Consider Thermal Bridges

This is a little advanced, but we’re now getting a lot of data showing this can be a big problem in the efficiency of tiny homes. To put it simply, thermal bridging is where a material that transmits heat crosses into or out of your conditioned space.

A practical tiny house example is wheel well fenders when building on a trailer,. If you build your walls partially over the wheel wells, you won’t be able to insulate around them as much as the rest of your walls. The metal of the trailer will take the heat from inside your tiny home and provide a pathway for it to more easily bleed out into the outside climate.

The studs of our walls act as a thermal bridge too, which is why we see more and more homes being build with an outer layer of insulation or a product called Zip-R which is sheathing with a layer of insulation built in.

Step 3: Check Your Codes

Check Building Codes for your area

Another important step is learning what code requires for your floor, ceiling, and walls. This is largely based on the climate you live in, so it will be different for each city/town. For moderate climates, you typically need an R factor of 15 in your walls and 30 in your ceiling. Colder climates will require higher R values.

Here is a great resource for finding your local insulation requirements.

Step 4: Choose Your Insulation For Your Tiny Home

Choose Your Insulation For Your Tiny Home

Later on in this post, I’ll get into the pro and cons of different insulation options for your tiny houses, but more broadly speaking I wanted to talk about choosing your insulation. The main considerations when choosing are:

  • Can you do it yourself or do you have to hire someone?
  • How much do you have to spend?

I’ll make this really simple: there are options that stand out clearly, but people don’t choose them because of cost or the need to hire someone to install it, which is essentially also cost. It comes down to how much money you can spend on your insulation.

The important thing to know is that insulation pays for itself in the long term. This is a widely understood and agreed upon fact, but people trying to get the most out of their budgets look for ways to cut costs and thus cut corners on insulation.

The difference between average insulation and the best insulation is around $2000, but remember that your power bill will be about 30% less each month for the rest of your life. This means that after about 3.5 years, you should be saving money.
Depending how long you live in your tiny house, it could save you thousands of dollars over the life span. Between my solar panels and insulation, I have not had to pay a power bill for the last eight years, so trust me when I say it’s game changing.

My advice is to buy the best option, even if that means delaying your build a few months for you to work and save extra. This isn’t an area you should skimp on, and if you do, it will cost you big!

Step 5: Understand Vapor Barriers

Understand Vapor Barriers

Vapor barriers are one of the most controversial topics among the building community. There is a lot of “that’s how we’ve always done it” thrown around, but most building hasn’t benefited from a lot of the data coming from actual building science.

The trick is that this can vary based on your location and your material choices. Take some time to read up on the basics of vapor barriers.

The quick summary is that we want to control where water vapor can enter and exit a wall, roof, or floor. Controlling this in the right place is all about where the moisture is coming from and which side warm moist air can come into contact with. When warm moisture comes into contact with a cool surface, it results in water condensing onto that surface. This can lead to mold, which obviously, we don’t want.

In general, you want to put your vapor barrier on the warm side of the insulation, but that’s where it can be complicated. For very cold climates or very hot climates, it’s pretty straight forward. If you live in a place like I do (North Carolina), it can be very hot in the summers and pretty cold in the winters, and we have a lot of humidity.

Step 6: Install Based On Manufacturer’s Directions

Install Based On Manufacturer’s Directions

There is a lot of science that goes into today’s insulation, so getting the details are critical to it performing they way it was designed to work. Luckily, many manufacturers have realized the better job they do of teaching people on correct installation, the happier customers are. Happier customers will buy more of their product.

That means that most insulation manufacturers are willing to help you with questions and often have a lot of good resources about installation for free. Follow them closely and ask a lot of questions!

Insulating Different Parts Of Your Tiny House

Insulating Different Parts Of Your Tiny House

By and large, insulating your roof, walls, and floors is a pretty similar process. We frame out each of these in 16 inch on center framing (or 24 inch on center if you’re doing advanced framing). There are also some special notes about how to do each that I wanted to include as well.

Tiny House Roof Insulation

Tiny House Roof Insulation

The insulation in your roof is a big deal because heat rises, so it’s a major location for heat loss. That’s why code typically stipulates a much higher requirement for insulation, usually around R-30. The height of a tiny house is a critical dimension because we can only build so tall.

My recommendation is to frame your roof with 2×6 trusses which will give you 5.5 inches of space to insulate. Fill that with spray foam and you’ll have an R-30+ roof.

Tiny House Wall Insulation

Tiny House Wall Insulation
Your walls are pretty straight forward, with one major exception: slumping of insulation. Because the stud bays are vertical, your insulation is going to want to slide down to the bottom of the wall cavity. This is bad because insulation needs to completely fill the void and keep its loft to be effective.

Manufacturers know this can be a major point of failure for batt insulation, so they’ve devised several ways to prevent this. Typically they add in fibers or chemicals to maintain insulation loft, and include backings that can be affixed to the studs to hold up the insulation. The installation instructions include details to help prevent this, too.

Whatever your insulation option, pay special attention to installation instructions and choose options that are known to keep their loft for a long time to prevent insulation slump down the road.

Tiny House Floor Insulation

Tiny House Floor Insulation

Insulating the floor of your tiny house is a critical area, as I find that tiny houses often have cold floors. The trailer of your tiny house on wheels will allow for cold air to flow beneath it. Add to that that there is a ton of thermal bridging happening in a tiny house through the floor, and you can see why this is an area that needs a lot of attention when it comes to insulating.

Because it’s so close to the ground, my suggestion is to frame this with treated lumber and choose an insulation that handles moisture very well. Foam board is a good option here, with any gaps sealed by Great Stuff foam.

Insulated Skirting For Your Tiny House

Insulated Skirting For Your Tiny House

As I mentioned above, a lot of tiny houses have cold floors. To help with this, you might want to consider installing insulated skirting for your tiny house on wheels. This creates a warm pocket of air underneath your tiny house trailer and reduces wind from flowing underneath, which carries your heat away.

The downside to this is that you’re making an ideal place for bugs, animals and mold to make a home. You’ll want to make sure it’s vented in such a way that air can flow through, but animals can’t get in.

I’d also suggest clearing the ground down to dirt and laying out a plastic sheet directly on top of the dirt to keep moisture from rising from it. Clearing the space of leaves and other organic matter will keep the bugs at bay. And if you have some gravel laid out with plastic sheeting on top, you’ll have even fewer issues with bugs and animals. Keeping it totally clear also allows you to inspect the space easily and easily spot any nests being built.

The skirting you build can be a good-looking façade that matches your walls or a nice contrasting color. I’d build this with a treated exterior grade plywood, seal it with a waterproof coating, and then apply a foam board insulation to the back of it. I’d also apply a flashing to the bottom edge of the plywood and insulation because it will be in contact with the ground.

It’s best to have the point where it touches the ground to be a few inches of gravel to allow for water drainage away from the materials. Be sure to grade your ground around your house to have water flow away from the house, too.

Tiny House Insulation Options

Tiny House Insulation Options

There are several types of insulation out there, and most are pretty good, but a few really stand out. Choosing the best insulation option for you typically comes down to cost.

I’ve seen it time and time again, people will be penny pinching so much that they actually cost themselves money in the long term. There is rarely a circumstance in life that has such a clear return on your investment, but insulation is one of them.

If you cannot afford the more expensive insulation options, delay your build just long enough to afford it, and you’ll thank yourself later.

There are a few exceptions to this.

If you have a severe chemical sensitivity and you want to build chemical free, you’ll have limited options. If you’re deeply committed to a sustainable building approach, there are a few options that do have some real drawbacks but are definitely a compromise.

Finally, if you want to use SIPs, they are mostly all the same, even across brands.

Closed Cell Spray Foam – R Value: 6.0 per inch

Closed Cell Spray Foam

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spray foam insulation
Spray foam tops my list and, after years of working in tiny house building science, it’s the clear choice. Closed cell foam has the highest R value and is both a vapor barrier and an air sealer. The fact that it’s all three rolled into one is a big deal.

Initially, I considered it to be one of the better options, but over the years, I’ve come to realize that it is the BEST option. That kind of statement is one I don’t make lightly, as so much in building science is very dependent on a lot of other variables. Spray foam, however, is unique in being a clear winner.

Open Cell Spray Foam – R Value: 3.7 per inch

Open Cell Spray Foam

I’m going to make this pretty simple: Open cell spray foam lacks a lot of the benefits of closed cell foam, but only comes in at a slightly lower cost. For this reason, I suggest that people skip this option. The only reason people opt for open cell spray foam is for the cost savings, but If I couldn’t have closed cell, I’d opt for Rock Wool insulation.

Fiberglass Batt Insulation For Tiny Homes – R Value: 3.1 per inch

Fiberglass Bat Insulation For Tiny Homes

lowest cost insulation for a tiny houseFiberglass batts are one of the most common and economical insulations available. Because of their broad use, economy of scale has driven the price down to be very affordable. I insulated my tiny home for around $500 at the time I built.

They aren’t the greatest thermal insulators at an R value of 3.1 per inch, but the cost versus benefit here is pretty good. Most rolls are sold in an R-13 rating for your standard 2×4 walls. If you need more R value from your insulation, you’ll either need to jump up to 2×6 framing, use an outer layer of insulation (more on that later), or switch to a higher R value insulation.

Most of the rolls will come designed for the depth of your wall cavity: 3.5 inches for your 2×4 walls and 5.5 inches for your 2×6 walls. You can also find widths to be pre-sized for 16 inch on center framing or for your advanced framing which is 24 inch on center.

This makes it pretty easy to install because it trims down on having to cut things. Just unroll, cut the height of the framed bay, then staple into place.

Rock Wool / Roxul Insulation – R Value: 3.3 per inch

Rock Wool Roxul Insulation

ryans best insulation
best value insulation for a tiny house

Rock Wool, aka mineral wool or the brand name Roxul, is my second favorite option for many reasons. First off, it’s water resistant which is a big plus in my book. In the event that water does enter your insulation cavity, rock wool won’t break down and generally handles moisture pretty well.

Unlike other insulations that can slump over time or deflate if they get wet, rock wool is pretty rigid. While still being pretty easy to work with, you don’t have to worry about it slumping in your wall cavity in a decade or two. This isn’t always the case with other insulations and can lead to cold spots in your walls.

Another huge plus is the acoustical benefit, Roxul does a very good job at dampening sounds, which makes for a more comfortable living space. I like the fact that I can use a single product to insulate my exterior walls for thermal insulation and my interior walls for noise insulation. I put these batts in bedroom walls for a quieter night’s sleep and bathrooms for extra privacy.

Finally, rock wool is also a fire barrier. It can withstand a direct flame and not catch on fire. This is good peace of mind on top of an already well-performing insulation option for your tiny house.

There are of course some downsides, the big one being cost. Rock wool is about 35% more expensive than your standard fiberglass batts. Rock wool has a slightly higher R value, thought, so that does help. While mineral wool insulations come at a small premium, I feel the benefits outweigh the cost.

Since we are talking tiny here, you’re going to spend less than $200 extra dollars for this upgrade. It’s reasons like this why building tiny is great, as upgrades to nicer materials come at tiny cost increases.

Rigid Foam Board Insulations

Rigid Foam Board Insulations

Rigid foam board comes in a couple of varieties and the R values depend on which type you choose. In general, I use these types of insulation in the sub-floors of my tiny houses because they have a higher R value and are very water resistant.

With the floor system being closest to the ground, it has a higher chance of moisture contact, so rigid foam board is a good choice. In a perfect world, I would use closed cell spray foam in the sub floor of a tiny house, but you have to insulate the sub floor long before you insulate the rest of the house. You often won’t be able to get a spray foam contractor to come out and do such a small area. Sometimes they’ll even turn down the main body spray because it’s too small of a job.

To do this, first I built my sub floor framing and then sealed the seams with Great Stuff foam in a can. You can see how I did it in this video here:

From there I will lay in my foam board, which you can see here:

There are a few types of foam board that you will want to consider.

Extruded Polystyrene Foam Insulation (XPS) – R Value: 5 per inch

Extruded Polystyrene Foam Insulation

This comes in two varieties: blue board and pink board, which really is identical, just from different manufacturers. These have a good R value for the cost and thickness.

The one downside they have over the other major types is they will be slower to absorb water, but also slower to release the water back out. Generally, it is accepted that the other option I talk about next will hold up better long-term.

Expanded Polystyrene Foam Insulation (EPS) – R Value: 3.8 per inch

Expanded Polystyrene Foam Insulation

Expanded Polystyrene is essentially fancy coffee cup foam, which expands to fit a mold at the factory, creating a sheet of the foam. While EPS foam is similar to XPS foam (the one above), there are some performance differences.

Expanded foam is a good option for wet environments and is often used under slabs to insulate places where water contact is very likely. I’ve heard anecdotally that bugs like this stuff less than your XPS foams, but I’ve heard from others that they can still burrow through EPS, too.

This is commonly used as the foam board of choice for insulating tiny houses because it’s pretty easy to use, lower cost for the R value and handles water very well.

Polyisocyanurate Foam Boards (Poly ISO) – R Value: 6.7 per inch

Polyisocyanurate Foam Boards

Poly ISO foam isn’t used too often in residential construction, but you’ll invariably run across it on the shelves at your local big box store, so I thought I’d mention it. The nice thing about this foam is its higher R value and that it’s pretty tough stuff. It’s great when you want to affix it to commercial roofs and exterior cladding systems, and can take fasteners pretty well.

The Achilles heel of this is that when this foam gets very cold, it’s R value actually drops by 30%, a curious dynamic that not everyone in the building trade know about. At that point, studies have shown it to not be much better than EPS foam. In general, I’d skip this.

Denim Insulation / Cotton Insulation – R Value: 3.5 per inch

Denim Insulation Cotton Insulation

sustainable insulation for a tiny houseMade of recycled cloth, denim insulation is a reasonably sustainable option that has come to the mass market. I frequently see it as an option at my local big box hardware store. While cotton from recycled sources is great, cotton is a pretty intensive crop that isn’t always farmed in a sustainable manner.

The cotton is easy to work with because it doesn’t put off any toxic gasses or itchy fibers. However, it can be difficult to work with, as moisture absorption can be a real problem leading to mold. I’ve also seen a lot of problems with it slumping inside the wall.

Some people have also reported that it will not always be a uniform size, making it hard to fill stud bays with. In principal it’s a nice idea, but for me the moisture absorption is a big red flag.

Natural Wool Batt Insulation – R Value: 3.8 per inch

Natural Wool Batt Insulation

sustainable insulation for a tiny houseNatural wool batts are an interesting concept and the industry that produces them have come a long way. When I first starting building tiny houses, you could get wool, but it was a loose fill product. Today they come in batts which is much more practical and easier to install.

I think this approach is the most practical for a truly sustainable option. Sheep are sheared and the wool processed. The wool is cleaned, combed and washed several times, then created into the batts you’ll install in your walls.

Wool has been a practical fiber for a long time. People still reach for wool blankets, clothing and other wool items because it performs so well. It holds up to moisture quite well and has decent loft and good structure that holds up over time.

That said, unless someone is very concerned with sustainability or has a severe chemical sensitivity, I’d still favor closed cell foam. While far from sustainable, the higher R value, air sealing and total moisture resistance all add up to costing fewer resources in the long run from power plants or heating fuel.

Final Thoughts

thoughts about insulation

Insulating your tiny house on wheels is an important step in making your home efficient and to control costs going forward. A dollar spent on insulation will pay for itself many times over in savings on your power bill for years to come. There are a lot of options and many things to think about, but hopefully I’ve been able to help you navigate the question of what insulation you should use for your tiny home.

Why Closed Cell Spray Foam Is The Best Tiny House Insulation Option

Why Closed Cell Spray Foam Is The Best Tiny House Insulation Option

The thing that really won me over was the fact that closed cell spray foam is a vapor barrier in and of itself. This means that you have a vapor barrier on both sides of the envelope and within the insulation itself. That’s a really big deal.
Because tiny houses can move, you ideally want to be setup so your vapor barrier location accommodates all types of climates. If you build and layer your tiny house for a cold climate, then move to a hot climate, your vapor barrier will actually hurt you, not help you. Mold inside your home and wall cavities is highly probable at that point.
For people like me who live in a climate that has large temperature swings (hot humid summers and cold wet winters), there isn’t a great answer to where you put your vapor barrier.

Closed cell spray foam solves all that.

I can’t overstate how much of an advantage being an inherent vapor barrier is. Add to that that closed cell foam is a decent air sealer and has the highest R value insulation per inch — it’s truly a winning combination.

The Downsides Of Spray Foam

The Downsides Of Spray Foam

Closed cell isn’t without some drawbacks, and to not discuss them would be disingenuous. The biggest of course is cost. Spray foam will run you an additional $2,000 above the other options out there. But I’ve already covered why I think this is a smart place to spend your money.

The next biggest downside is that finding a roof leak could be tricky with closed cell spray foam. But I also think the spray foam, because it adheres to the surface it’s applied on, is just as likely to hold the water where the leak is and prevent it from spreading. Add to this that your roof will be brand new and most likely standing seam, and know that this is a small risk to take.

The other downside is that if you have an installer that doesn’t know what they are doing, they can make a real mess of things. The foam might not set right, it may cure and pull away from the studs, etc. If done improperly, it can be very difficult to clean up. For this, I’d make sure you visit some previous job sites of the installer, talk with customers, and get a sense for how many jobs the installer does in a given year. You want someone who has a good track record and does hundreds of jobs per year.

Spray Foam Off Gassing Of VOCs

Spray Foam Off Gassing Of VOCs

The final downside that I hear about is toxic off gassing after installation. The off gassing actually occurs while it’s being installed, but the EPA says after about 24 hours of curing, the foam becomes inert.

If you’re concerned about this, I’d stay out of your tiny house after the foam has been sprayed for at least 24 hours to allow it to cure. I’d then give it several days to continue to off gas any residual VOCs. Though there is a lot of anecdotal “evidence” thrown around, I prefer to read studies from reputable sources which mostly have not found any evidence of off gassing, but they readily agree that that’s also not the same as no off gassing.

This is how I choose to approach it. Since you spray your tiny house after you’ve already dried in your tiny house, meaning it’s a fully built shell of the house, you can let it sit empty to off gas before you continue building. If you’re really concerned, give it a few weeks while you plan the rest of your build or take a break.

Off gassing typically has a steep curve downward, meaning each hour that passes, you’re exponentially reducing the VOCs. Setting up a heater after the foam has cured to raise the temperature to something akin to an attic in the summer will also accelerate reactions. Ventilating well, using heat to facilitate any off gassing (if there is even any to be had), and time will all help this.

Your Turn!

  • What Insulation option are you thinking about choosing?
1 Comment
  1. You did not mention 20#/cf foamed concrete @ R 8.35.

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