What kind of insulation should I use under my house?

Insulate Under Floor: Fiberglass insulation batts or rolls are the most economical and easiest DIY choice for insulating between the floor joist in a crawl space. The U.S. Department of Energy recommends R-11 (3½”) insulation under floors in warm climates and an R-25 (6” to 8”) in cold climates.
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What kind of insulation should I use in my crawl space?

The Building Science Corporation recommends a foam based insulation as the best insulation for crawl spaces because it creates an air barrier. This means spray foam is the best floor insulation so you won't need to wear extra pairs of socks.
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Should a house be insulated underneath?

Crawl space insulation, as a part of overall home air sealing and insulation, helps maintain your entire home's energy efficiency. Without insulation, heat and cool air are easily lost through the floor. Insulation also helps to preserve the air quality and reduce energy costs.
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What is the best way to insulate a crawl space with a dirt floor?

If you would like to keep your crawl space vented because you live in a low humidity environment we recommend insulating the crawl space floor with fiberglass or rock-wool mixed with spray foam for air sealing.
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Should you insulate crawlspace under house?

Crawl Space Insulation is Key to Energy Efficiency

The short answer is YES you should insulate your crawl space IF you want to make your home MORE energy efficient.
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How to Choose and Use Insulation | This Old House



Is a vapor barrier necessary in a crawl space?

Yes. You need a vapor barrier in your crawl space. What's more, a moisture barrier is the minimum amount of protection that you should have in your crawl space. A vapor barrier helps you to avoid expensive repairs.
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Should I use faced or unfaced insulation in crawl space?

It is recommended that you use faced insulation in a crawl space since it has a moisture barrier that keeps the moisture from seeping into the air beneath your home. However, if you are adding another layer of insulation to meet the stipulated R-value, it is advisable to use unfaced insulation.
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Is spray foam good for crawl space?

Because closed-cell foam is resistant to moisture and rodent activity, many well-intentioned handymen and homeowners have started to use it as an insulation material in basements and crawl spaces. Don't get me wrong, spray foam, when used in moderation to seal gaps, can be effective.
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Can underfloor insulation cause problems?

What Can Go Wrong With Underfloor Insulation? Worst case scenario you trap moisture from spills or interstitial condensation up against the timbers within hydrophobic insulation and in turn risk rotting the floor joists.
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Does underfloor insulation really work?

Underfloor insulation is effective in the winter… and the summer. Insulation doesn't just keep you warm in the winter. Your home stays cool in the summer. Insulation doesn't trap heat in, instead it reduces heat loss.
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Is R 19 insulation Good for crawl space?

Six-inch R-19 fiberglass batts installed with the paper moisture guard facing the living area (and hung securely without compressing) will effectively insulate your crawl space.
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What R-value do I need for crawl space?

The U.S. Department of Energy recommends R-11 (3½”) insulation under floors in warm climates and an R-25 (6” to 8”) in cold climates. Install the insulation with the paper vapor barrier facing up toward the heated living space, and make sure the insulation fits tightly between the joists.
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What is the best R-value for crawl spaces?

They vary a little in R-value and cost. Polyisocyanurate, also called Polyiso and Iso by contractors, has the best R-value of about R-6 depending on the specific product. However, it loses effectiveness below about 50F. If your crawl space is below grade, this likely won't be a problem.
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Can mold grow behind spray foam insulation?

Adding spray foam insulation in potential problem areas is a great way to insulate your home and goes a long way towards mold prevention. It is mold-resistant because it expands when it gets wet, meaning there's no room for mold or mildew!
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Where should you not use spray foam insulation?

When NOT to Use Spray Foam Insulation
  1. For areas that are too close to electrical boxes:
  2. For areas too close to ceiling light boxes:
  3. Open-cell spray foam on your roof:
  4. For closed-cavity spaces:
  5. If you have a history of skin, respiratory, or asthma problems:
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Can spray foam insulation be used under floors?

Spray foam was applied between the floor joists. Spray foam insulation expands as it is applied, filling every gap around joints, plumbing, wiring, ducts and fixtures. Spray foam not only insulates but air seals the floor as well.
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Should floor joists in crawl space be insulated?

The U.S. Dept. of Energy currently suggests insulation with an R-value of at least R-9 in floors. So the answer to the question should a crawl space be insulated is yes, they most certainly should be.
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Is Rockwool good for crawl spaces?

The inherent air-permeance of mineral wool insulation makes it inappropriate for this application, writes GBA senior editor Martin Holladay. “The mineral wool can't prevent humid interior air from contacting the cold crawl space walls,” he says. “The likely result will be moisture accumulation and mold.”
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How do you insulate under a subfloor?

Fiberglass insulation batts are installed in the cavities between floor joists and held snug to the subfloor with twine or lathe. When possible, R30 should be used for proper subfloor insulation. If the joist cavities are too shallow, we will use the highest R-value that will fit.
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Should a crawl space be sealed or vented?

Because much of the air you breathe in your home comes directly from your crawl space, most contractors today agree that the crawl space should be treated as part of your living area—in other words, it should be sealed, insulated and kept free of moisture.
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Does mold grow under crawl space vapor barrier?

Moisture from the ground and from crawl space vents combine to create all sorts of problems under your home. This moisture can create mold, mildew, dry rot and allows insects and other pests to thrive. A vapor barrier is key step to reducing this moisture.
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Is R 13 insulation Good for basements?

TBF closed cell foam insulation and concrete board basement wall products offer industry-leading R-13 insulation value that will reflect back 99.987% of heat back and lead to the optimal insulating of a basement area.
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Is foam board a vapor barrier?

Rigid foam board, especially foil-faced polyisocyanurate, creates a vapor-impermeable barrier, so the wall would have limited drying potential. Even more permeable types of insulation, such as expanded polystyrene, are vapor barriers when the installation is thick enough.
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