With the thermostat dropping into the low teens each night for us in the mountains of Southern Oregon, it seems like an appropriate time to talk about the top 8 insulation options for tiny houses. Nearly as many insulation options exist for tiny houses on wheels as they do for conventional construction. Which one you choose will depend on your climate, how mobile your tiny house will be, what your budget is, and how natural/green you want the product to be. In this article, we will list the most commonly available options out there and offer the pros and cons of each. And I do want to add that each option listed below has its cons. There is a LOT of room for improvement when it comes to insulation. There some new and exciting emerging technologies that are green; however, they still cost prohibitive so most stores won’t sell them.
COMMON BATT INSULATION OPTIONS
DENIM/COTTON INSULATION: R=3.5/inch
Cotton mill waste and low grade recycled cotton are formed into batts. Pros: uses renewable resource and some companies use 100% post consumer fibers, highest ASTM rating for fire, non toxic, well suited to DIY, high sound insulation. Cons: cotton farming very high in water and pesticide use (look for 100% post consumer), weighs twice what fiberglass insulation does, is sometimes bound with melted synthetic, noncellulosic polyolefin fibers (check with manufacturer)
FIBERGLASS INSULATION: R=3.1/inch
Fiberglass insulation is created by fusing natural sand and recycled glass together at high heat. Fibers are created by molting hot glass through miniscule hole, creating a thin fiber (think cotton candy). Pros: readily available and inexpensive, very lightweight, uses recycled glass in part, relatively easy to install, can find formaldehyde formulas commonly now. Cons: lowest R value per inch, grows mold easily if exposed to water leak, paper backing highly flammable, creates more air pollution than any other batt insulation, vapor barriers required, irritant and can become lodged in lungs, skin and eyes.
Rock Wool: R=3.3/inch
Rockwool is produced by heating natural basalt rocks or industrial steel-mill slag in a surface to extremely high temperatures. As the materials melts, it is drawn out into fibers and formed into batts. It is also known as stone wool, mineral wool insulation, or slag wool. PROS: high flame retardation, rodents not attracted to it, one of least expensive options out there, generally does not require use of moisture barrier before installation (check with you local codes), EPA mandates at least 70% recycled content. CONS: use has decreased over years, can hold large volumes of water if there is a water leak, fibers can lodge in the lungs, eyes, and skin if protective gear isn’t used, very high energy use to create, some manufacturers add 5% phenolformaldehyde.
RIGID FOAM INSULATION
EXTRUDED POLYSTYRENE INSULATION (XPS) R=5/inch
XPS, or blueboard is usually blue or pink with a smooth plastic surface. It falls in the middle of the 3 rigid foam insulations in both cost and R value. XPS is manufactured in low density and high density versions. Pros: easily found, lightweight, resists moisture and air filtration, strongest of rigid boards. Cons: typically uses HCFCs as blowing agents, which have high global warming potential and moderate ozone depletion, flammable and produces toxic fumes when burned, made from crude oil byproducts, all brands of XPS sold in US include HBCD which causes concern to EPA as well as others, protective gear is recommended to be worn during cutting and installation.
EXPANDED POLYSTYRENE (EPS) R=3.8/inch
Often called beadboard, manufactured in low and high density formulas. Pros: least expensive rigid foam, uses pentane rather than CFCs as blowing agents so less ozone depletion, lightweight, uses 1/7 of petroleum based products than XPS. Cons: Though pentane doesn’t damage the ozone layer, it does contribute to smog, all brands in the US contain HBCD, flammable and produces toxic fumes, made from crude petroleum byproducts, easier to damage than the other rigid foams, protective gear is recommended to be worn during cutting and installation..
POLYISOCYANURATE FOAM BOARDS (ISO) R=6.7/inch
Known as polysio, this rigid foam is a high density, closed cell structure rigid insulation board. All ISO panels are faced. Foil faced ISO panels should never be used with an interior vapor barrier. Pros: has highest R value per inch of any other rigid foam, lightweight, resists moisture, highly resistant to air filtration, most environmentally friendly of the rigid foam board options. Cons: expensive, R value decreases slightly in time due to off gassing, flammable and causes toxic gases when burned, made from crude oil byproducts, protective gear is recommended to be worn during cutting and installation.
SPRAY FOAM INSULATION
OPEN CELL INSULATION: R=3.7/inch
In an open cell foam system, the gas pockets connect with each other. A bath sponge is an example of an open cell foam structure. It is generally used for interior wall application and is not recommended on exterior wall applications (though some claim that it can be used on exterior wall applications). Pros: some brands are water based so there are no ozone depleting compounds in them, lowest cost of spray foams, very good sound insulation, doesn’t shrink, settle or sag, fills all voids, relatively lightweight at 0.5lb per cubic foot. Cons: the health risks are potentially very high, ALL spray foams contain toxic ingredient Isocyanate (even those that have a percentage of soy and claim to be ‘eco’), embodied energy is extremely high while R value is relatively low and equivalent to so many other cheaper and more eco products, soy or castor oil content is at most 10%, the potential for off gassing and making inhabitants ill are significant, must hire a professional to install.
CLOSED CELL INSULATION: R=6.0/inch
Closed cell foam is much more dense than open cell foam. It has a smaller, more compact cell structure. Pros: has one of highest R value ratings, adds structural rigidity to a frame, resistant to pests, most effective at reducing air leakage, a kit can be bought/rented to do installation as homeowner. Cons: the health risks are potentially very high, ALL spray foams contain toxic ingredient Isocyanate (even those that have a percentage of soy and claim to be ‘eco’), because the material is so rigid closed cell systems tend to develop cracks in the material compromising the insulative envelope, many people on RV blogs are opening their walls to remodel and finding a pile of pulverized insulation in the cavities, if the ratio of parts A and B aren’t mixed exactly right, the material can off gas toxic fumes perpetually, a code approved fire barrier must be installed over spray foam in living spaces (such as ½” drywall).
As you can see, each insulation option has its own sets of pros and cons. Many other types of insulation options exist such as wool and hemp batt insulation, cork rigid panels, Air-Krete, and more. If you are building your tiny house on a fixed foundation, other options open up as well such as straw bale insulation (our favorite!). Before making any decision, make sure to do extensive research on the potential health risks of the product. Making an informed final decision will ensure that you have no regrets in your own tiny house build.
How about you? Do you know of an insulation option out there that are healthy AND affordable? We would love to hear!