Crawl Space R-21


Note: Installation instructions and illustrated drawings are recommendations only, while proper local construction methods are the responsibility of the installer.

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. It comes in convenient roll sizes that install cleanly and quickly. The product is dust and fiber-free, and does not require any protective garments or respirators to work with.

Recommended Products

Double Reflective Insulation

Reflective/Bubble/Bubble/Reflective – Roll

  • BP24025 (24” x 25’)
  • BP48025 (48″ x 25′)

Staple Tab, Reflective/Bubble/Bubble/Reflective – Roll

  • ST16025 (16” x 25’)
  • ST24025 (24” x 25’)

Note: Click here for information on our larger rolls which are available by Special Order at the Contractor or Customer Service Desks.


  • R-21 and fiber free
  • Installs quickly because of its easy-to-handle characteristics and convenient roll sizes
  • No need to insulate ducts or pipes between the product and the sub-floor
  • Does not require protective garments or respirators when installing
  • Resists growth of fungi, mold and mildew
  • Does not support insects or rodents
  • Vapor / radon retarder
  • When properly installed, prevents ground moisture from causing dry rot

Installation Instructions

Installation Instruction pdf: DIY Crawl Space R-21 Revised 012021

This application meets the thermal performance requirements for new construction in the 2012, 2015 and 2018 International Energy Conservation Codes for Climate Zones 1, 2, 3 and 4.

Note: This product is reflective on both sides and the direction of product installation is not pertinent to thermal performance.

Note: For this application it is recommended to use at least 3/8 inch staples that are Heavy Duty or Galvanized.

  • Inspect the crawl space and make any needed repairs before installing Reflectix® Reflective/Bubble product.
  • For floor joists that are 16” on-center, the installation is easiest with the Reflectix® Staple Tab (ST) product.
  • Determine if there are water pipes and heating ducts which hang below the floor joists. They will need to be insulated. There is no need to wrap water pipes or duct work that fall between floor joists. Reflectix® will provide adequate insulating without extra wrapping.
  • Begin at one end of the house and staple the first course of product to the top of the band board or the subfloor (also terminating this course in this fashion). Insert the Reflectix® half way up into the joist cavity and staple (at approximately 3” to 4” intervals) the edge of the product to the side of the joist. The resulting product installation will split the cavity into two approximately equal air spaces. It is easiest to utilize the Reflectix® Reflective/Bubble/Bubble/Reflective, Staple Tab product for this step.
  • For cross bracing, refer to the type of bracing directly below for installation techniques:

Solid Wood: Terminate the product at the brace. End staple to the middle of the brace. Continue with the installation on the opposite side, stapling the product to the brace at the approximate mid-point in the cavity.

Metal or Wooden Slats – Cross Braced: Extend the product 5 inches beyond the brace. Cut the product perpendicular to the joist direction at this point. Cut a slit down the middle of the product 3 inches beyond the middle of the cross. Run each flap of product through the cross (one flap on each side), stapling the product to the side of the joist. Continue the product run on the opposite side of the cross brace as before. Tape all seams (horizontal and parallel) with Reflectix® Foil Tape.

  • Continue with the second course of product at one end of a joist cavity (after the first course has been installed) and secure the product “end” with staples to the band board. Proceed down the joists by stapling each edge (or middle of the Reflective/Bubble/Bubble/Reflective 48” wide product) to the face (bottom surface) of each joist. Staple the product at intervals of approximately 3” to 4”. At the end of the product run, staple the Reflectix® to the band board.
  • Seal the seams with Reflectix® Foil Tape. This product is a vapor barrier with the seams sealed, no additional vapor barrier products are necessary.
  • Any penetrations, openings, rips or tears shall be sealed with Reflectix® Foil Tape or an equivalent.

Installation Video


Review These Important Safety Guidelines Prior to Installation:

  • ALWAYS check local building codes before installing Reflectix®.
  • ALWAYS check the area you are insulating and make any needed repairs. Any worn wiring should be replaced before you begin installing Reflectix®.
  • ALWAYS make sure work areas are well ventilated and well lighted.
  • ALWAYS use eye protection when operating a staple gun.
  • ALWAYS use caution and common sense when using a staple gun. Be aware of electrical wiring locations. Stapling into a wire can cause severe shock or death. NEVER staple into electrical wiring.
  • ALWAYS be careful when working with large pieces of Reflectix® on windy days.
  • When installing Reflectix® on bright sunny days, it is best to wear sun glasses.
  • Do not work in areas such as attics when temperatures are too hot.
  • Please Note: The intention of these Installation Instructions and 3-D renderings are for the sole purpose of illustrating the correct location and relative position of the Reflectix® products in specific building assemblies. The correct construction methods and techniques are the responsibility of the installer or contractor. The methods outlined are recommendations on location of the Reflectix® products as a guideline. There are no claims on the part of Reflectix, Inc. that these building assemblies are finite standards or meet building code requirements (as they can vary by region).

Reflectix Fact Sheet per FTC

Testing and Certification

Reflectix® products are thoroughly tested at either nationally approved, independent laboratories or leading universities. Tests are performed to current American Society of Testing and Materials (ASTM) standards when a standard exists. To obtain a copy of our Product Testing Specifications, please refer to the “Additional Resources” tab. The documents are also available by e-mail at or call (800) 879-3645.


Pictured: 1. Double Reflective Insulation, 2. Double Reflective Insulation with Staple Tab, 3. Tools for Installation, 4. Product Installation

Damon CS to Btm of Joist 72 RGB