Approximately 28 million U.S. homes have a crawl space, which is an area under the house that’s hollow and usually vented to the outside. Its purposes are many, and so are its potential problems. One of the crawl space’s biggest drawbacks is that it exposes the home to moisture, which can cause mold, wood rot, bad indoor air quality, and pest infestations. Another is that it leaves the house more vulnerable to both cold and hot air, causing discomfort, excessive wear and tear on HVAC systems and high energy bills.
If keeping your house comfortable without breaking the bank is a challenge, making sure your crawl space is properly insulated will help. If your home was built before 1990, when energy-saving building codes were standardized, it’s possible your crawl space has no insulation at all. There’s also a chance it does, but the insulation has deteriorated or fallen down. And, of course, there’s the possibility that it was insulated incorrectly.
If any of these are the case, insulating or reinsulating the right parts of your crawl space — with the right materials — is one of the best things you can do for your home, the quality of life inside it, and your wallet. Not only will a properly insulated crawl space help keep your home at a comfortable temperature and reduce your energy bills; it will help preserve your home, including your pipes and other fixtures.
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Where to Begin
The first thing you must determine is which parts of your crawl space should be insulated. You can begin this process by answering a couple of key questions:
- What kind of climate do you live in?
- Is your crawl space vented or closed?
Climate is ultimately the most important factor in determining the best way to manage your crawl space in general — not just in terms of insulation, but also with regard to venting and air conditioning. As you will discover, insulation, venting, and air conditioning are all related. The decisions you make on each front will help determine what the best choices are on the others. Venting is also critically important. The best insulation strategy for space with outside air flowing into and out of it is different from the best approach to insulating a closed space. In short, you have two choices for managing temperature inside your crawl space and its effect on the temperature inside your home:
- Make your crawl space warm. Seal it off. Close vents, insulate foundation walls and heat it. That way, it won’t steal hot air from your house because it’s got its own.
- Make your crawl space cold. Ensure it is properly vented and insulate the subfloor above it. If you do this, you will also need to properly insulate your pipes and ductwork, so they don’t freeze in the winter when temperatures hit their lowest points.
Depending on the climate you live in and which of these two approaches you decide to take, the best way to insulate your crawl space is going to vary. If you live in a dry and moderate climate, and your crawl space is vented and unconditioned (in other words, unheated and uncooled), only the subfloor of the room above the space should be insulated. If you live in a moderate, dry climate and your crawl space is unvented, only the walls should be insulated. However, in areas where winter temperatures dip below freezing, it’s a good idea to insulate both the subfloor and the walls of your crawl space, and completely seal off the area as well.
If you’re in a moist climate and your crawl space is vented, the recommended solution is closing and sealing the space, and insulating just the walls. Keep in mind that climate varies a lot throughout the U.S. In addition to moderate and dry, and very cold in the winter, there are marine climates and ones with different degrees of dryness and humidity. (The U.S. Department of Energy’s Building America program’s insulation best practices guide contains a handy map that will help you figure out where your area falls on the spectrum.)
To make matters even more complicated, if you’re in an area where closing and sealing your crawl space is recommended, levels of radon gas in the soil surrounding your home must be evaluated and considered before you undertake that project. Additional detail on the implications of climate and radon levels for crawl space insulation projects can also be found in the Building America guide.
The Best Type of Insulation for the Job
Unless you’re an expert, selecting the right materials for any home improvement project can be difficult. Even if you start out thinking you know what you need, the more options you realize there are, the harder it becomes to know you’re making the right choice. Insulation projects are no exception. On Home Depot’s website, when you enter “insulation” in the search bar, 409 products come up.
There’s fiberglass, mineral wool, cellulose, cotton, sheep’s wool, polystyrene, polyisocyanurate, polyurethane, vermiculite, and perlite. There are foams: urea-formaldehyde, phenolic and cementitious. There are rolls and batts in every imaginable size, rigid planks, blown-in insulation, reflective insulation, soundproofing acoustic insulation, and more. Clearly, before you begin an insulation project of any kind, it makes sense to do some research to determine exactly what kind of insulation you need!
One question that often arises when considering insulation types is whether your insulation should be “faced” or “unfaced.”
What is Faced Insulation?
Faced insulation has a sheet of material attached to one side. This material may be kraft paper, foil, plastic or vinyl. Kraft paper facing is by far the most common type of vapor barrier you can find “pre-attached” to blanket insulation intended for installation in homes. Vinyl-faced insulation is generally only used in commercial and industrial buildings. The purpose of this facing is to provide a vapor barrier, which stops excess moisture from leaching into the wood in your home.
Another (less important but still handy) benefit of facing is that it offers small flanges around the edges of the insulation, which can be used to staple the insulation to joists or studs. Faced insulation is a little (but not a lot) more expensive than unfaced, simply because of the extra material it includes. The upside is you save money by not having to pay to add your own vapor barrier. The protection the facing provides against the disastrous effects of moisture on your home also saves you money — lots of it — in the long run.
The most frequently asked question about-faced insulation is, which way should the facing go? (Imagine insulating your entire crawl space, only to discover all your insulation is upside down!) The general rule is to lay the faced side of your insulation against the surface closest to your living space. For example, when insulating the sub-floor above an unconditioned crawl space, in most climates, you will want the facing to lie against the subfloor. However — and here is another example of how climate considerations can complicate your decision-making process — in some Gulf states, or other areas with hot summers and mild winters, you will want to orient the facing down toward the crawl space.
What is Unfaced Insulation?
Unfaced insulation is just insulation without an attached moisture barrier. If you’re using unfaced insulation in an area where a vapor barrier is required or recommended, you may be able to add your own barrier using plastic sheeting. In crawl spaces, unfaced insulation is generally only used when adding to existing insulation. It’s important not to lay faced insulation on top of faced insulation. Doing so can create a moisture trap.
Faced or Unfaced Insulation in Crawl Space
Homes with crawlspaces are more susceptible to cold than those that rest on concrete foundations. They are also more vulnerable to moisture and its potentially disastrous effects — namely, mold and rot. As such, it’s critical that your crawl space has a moisture barrier. Insulation facing is a moisture or vapor barrier, so it only makes sense to use faced insulation in your crawl space. However, when adding multiple layers of insulation, you want to make sure that only one layer has faced, and that the facing does not lie against the second insulation layer. This will allow moisture to seep into the insulation, which will damage it and create a breeding ground for mold, mildew and other nasty stuff like bugs and rodents.
When insulating subfloors above crawl spaces, faced insulation is almost always the right choice. The only time this isn’t the case is when you are adding to existing insulation in order to increase the total R-value. As for which type of facing is best for crawl spaces, radiant facing is ideal for subfloors because it reflects heat that might otherwise be lost back toward the living space within your home.
For insulating the walls of your crawl space, most experts recommend a rigid foam board. Like blanket or batt insulation, foam board comes in faced and unfaced varieties. If a moisture barrier is required or recommended in your climate zone, you will want to use the faced board (again, reflective facing is a good choice) to insulate your walls. If you don’t, you’ll need to use additional material, such as spray foam, to repel moisture.