Is r21 good for crawl space?

Author: Jared Lynch  |  Last update: Wednesday, July 2, 2025

Reflectix is now offering a dramatically improved performance application for the crawl space. This R-21 application includes a double layer of the Reflectix® Reflective/Bubble product. Its ease of handling and installation makes it the obvious choice when looking at crawl space insulation options.

What R-value is best for crawl space?

Basement or Crawlspace Wall Insulation:
  • Zone 3: Add R5 insulative wall sheathing or R13 batt.
  • Zones 4A and 4B: Add R10 insulative wall sheathing or R13 batt.
  • Zones 4C and 5–8: Add R15 insulative wall sheathing or R19 batt.

What size insulation for a crawl space?

Homeowners who live in warmer areas need R-11 (3 ½”) insulation. Colder areas require R-25 (6” to 8”) insulation. Here, R represents the resistance of the insulating material to conductive heat flow. The greater insulating effectiveness corresponds to a higher R-value.

Is R-19 insulation good for crawl space?

A Common Place to Use R19 Insulation

The most common application of R19 Insulation is in a vertical wall framed by 2×6 studs. As mentioned above this is a common code requirement in some parts of the United States. R19 Insulation can also be used in other areas around the home, including floors and crawl spaces.

What is the best way to insulate ductwork in a crawl space?

What is the best insulation for air ducts in the crawl space? Mineral wool wraps are the most affordable and effective insulation for crawl space ducts. They are easy to cut, last for a long time, and healthier for humans. Meanwhile, fiberglass wraps are cheaper but more hazardous and difficult to handle.

Crawl Space R-21

Why not to insulate crawl space?

Condensation in the crawl space causes fiberglass insulation to sag, making it ineffective at keeping cold air from reaching the floor above. Most crawl spaces have dirt floors, open vents, and porous, uninsulated walls that allow moisture and outside air to enter under the home.

How do I stop my ducts from sweating in my crawl space?

Seal – Sealing gaps and cracks in the walls surrounding your ductwork will help keep indoor humidity levels manageable. The lower the moisture in the air passing through the ductwork, the lower the chances of condensation forming.

What is R21 insulation used for?

Excellent Thermal Performance Owens Corning™ R-21 EcoTouch® insulation is specifically engineered to solve the efficiency problems of exterior 2x6 walls. “High density” means more fibers per square inch. It delivers a higher R-value per square inch in less space than standard insulation products.

What is the code for crawl space insulation?

N1102. 2.11 (R402. 2.11) Crawl space walls. As an alternative to insulating floors over crawl spaces, crawl space walls shall be insulated provided that the crawl space is not vented to the outdoors.

What is the difference between R19 and r21?

Key Differences: Thermal Resistance: R-21 polyiso boards offer higher thermal resistance compared to R-19, which makes them more effective at reducing heat transfer in colder climates. Thickness: Both R-19 and R-21 polyiso boards are compact by offering high R-values per inch.

What is the cheapest way to insulate a crawl space?

Spray foam insulation costs between $1 and $2 per board foot on average or $1,000 to $2,000 for a 1,000-square-foot crawl space. Spray foam insulation comes in many different types, with polyurethane spray foam costing the least.

What are the negatives of encapsulation?

If not properly installed or maintained, encapsulation can lead to trapped moisture, creating an environment conducive to mold growth and wood rot. Moreover, initial costs to seal crawl space can be high, and incorrect installation may inadvertently seal in existing pests or moisture.

Should insulation face up or down in a crawl space?

Which direction does the paper go? A: The paper should always be placed towards the living space according to the manufacturers we are familiar with.

What type of insulation is used in a crawl space?

While fiberglass insulation is commonly installed in crawl space ceilings, foam board is best used on crawl space walls. Many homeowners who DIY crawl space encapsulation opt for foam board as their crawl space insulation.

Can you over insulate a house?

It is possible to over-insulate your house so much that it can't breathe. The whole point of home insulation is to tightly seal your home's interior. But if it becomes too tightly sealed with too many layers of insulation, moisture can get trapped inside those layers. That's when mold starts to grow.

Is R13 good for crawl space?

R13 insulation is a cost-effective R-value for use inside walls when you select fiberglass rolls with or without facing. It can also be used in floors or crawl spaces in warm climates in the southeastern and southwestern U.S., including most of Texas and California.

How thick should crawl space insulation be?

Standard Crawl space vapor barrier thicknesses range from 6 mil to 20 mil, with 6 mil being the bare minimum and 20 mil being the most heavy duty and puncture-resistant. There are thicker options available, but not required.

Is R21 better than R13?

When comparing R13 to R21 insulation, the variance represents a substantial difference in thermal resistance. Moving from an R13 to an R21 insulation means gaining a higher resistance to heat loss, contributing to a more energy-efficient and comfortable living space.

Can you put R21 in 2x4 wall?

Fiberglass and rock wool batts—2x4 walls can hold R-13 or R-15 batts; 2x6 walls can have R-19 or R-21 products.

What is the difference between R21 and R38 insulation?

For batt insulation, a R-38 batt is thicker than an R-21 batt because it has a higher R-value. For spray foam, total R-value can be calculated based on the depth installed. A closed cell foam may have an R-value of R-7, giving it the same R-value as a R-21 batt with only 3 inches of foam.

Does homeowners insurance cover crawl space encapsulation?

As the saying goes, “It's better to have it and not need it than to need it and not have it.” That said, coverage varies widely for things like crawl space repair and encapsulation. It depends on your provider and policy, but the general rule of thumb is that if it's preventable, it's not covered.

Will wet duct insulation dry out?

Wet duct insulation dries out when exposed to air for long periods of time. This is why it is important to install duct insulation during the winter months.

Why seal crawl space vents?

Vote: seal off crawl space vents

"Properly sealing the crawl space and removing the moisture from the ground and air is part of the solution that helps provide a mold-free and insect-free environment, which leads to a more energy-efficient and healthier home," says Waltz.

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