Hey, it is AJ, the DIY Specialist here with Crawl Space Ninja Supply.

If you're insulating crawl space walls and don’t want to fight rigid foam board, our Crawl Space Insul-Barrier is one of the most practical solutions we offer in the Crawl Space Ninja Supply DIY Store. This product was introduced to simplify crawl space wall insulation while also providing moisture control in one step.

Instead of installing foam board insulation and then adding a separate vapor barrier, this combines insulation and vapor protection into a single multi-layer system. It’s built using cross-woven polyethylene, closed-cell foam, high-density bubble insulation, and a reflective layer. Together, those layers provide thermal resistance and function as a Class A vapor barrier for crawl space encapsulation systems.

Each roll measures 4’ x 25’ and covers 100 square feet of crawl space wall. It weighs about 10 pounds per roll, making it far easier to handle and ship than foam board insulation. The material itself provides approximately R-8.73. If you install it with a ¾-inch furring strip to create an air gap between the foundation wall and the insulation, the system can reach roughly R-12. That air space improves thermal performance and helps reduce condensation on crawl space foundation walls.

We install this directly to crawl space foundation walls as part of a full crawl space encapsulation system. It pairs with our Crawl Space Ninja® 12-mil Crawl Space Solid Vapor Barrier

on the floor, sealed with Crawl Space Ninja® Seam Tape (Single Roll) and supported with Crawl Space Ninja® Double Sided Foundation Butyl Tape. When combined with proper drainage and a crawl space dehumidifier, it becomes part of a complete moisture control system.

One thing we consistently recommend at Crawl Space Ninja Supply is insulating the perimeter crawl space walls rather than spray foaming the subfloor. By insulating the foundation walls, you keep the thermal break at the boundary of the crawl space. That stabilizes the entire environment. If wall insulation ever gets damp, it’s far less problematic than spray foam applied directly to the underside of the subfloor. Besides it is much more effect for home inspections as well. Spray foam can be a mess.

Installation is straightforward and much faster than foam board. The Crawl Space Insulation Vapor Barrier installs just below the sill plate and drapes down the wall. If you’re adding the ¾-inch furring strips for the higher R-value, install those first to create the air gap. 

To fasten it, we typically use a Hilti GX-3 (gas-operated) or Hilti BX-4 (battery-operated). Both fastening tools work the same way. The tool has a magnetic tip that holds the fastener in place. You load the nail, place a metal washer onto it, then shoot the fastener through the washer, through the insulation vapor barrier, and into the concrete or block wall. We fasten approximately every 16 inches along the top and down the wall as needed. Between fasteners, we apply Crawl Space Ninja® Double Sided Foundation Butyl Tape to help seal and support the material against the foundation wall. This keeps the insulation barrier tight and properly integrated into your crawl space encapsulation system.

If you trim the insulation vapor barrier to match your wall height, simply seal the cut edge with Crawl Space Seam Tape to maintain the vapor barrier integrity. The product arrives ready to install.

From a moisture standpoint, this crawl space wall insulation does not support mold growth because it is constructed from plastic and foam layers. It has extremely low vapor permeance and performs well across a wide temperature range. It can also be used in basements or other foundation-wall applications where insulation and moisture control are required.

Over the past few years, crawl space insulation vapor barrier systems have gained popularity as a replacement for foam board insulation because they install faster, ship easier, and create a cleaner finished look on crawl space foundation walls. For DIY crawl space encapsulation projects, it simplifies the wall insulation process while integrating directly with the rest of the Crawl Space Ninja Supply system.

If you're building out a full crawl space encapsulation using our 12 Mil Vapor Barrier, Crawl Space Seam Tape, and drainage components, this insulation vapor barrier completes the wall portion of the system.

If you’re unsure how much insulation vapor barrier you need for your crawl space walls or how to fasten it properly, reach out to us at Crawl Space Ninja Supply. I’m always happy to help you plan it out so you can install it once and do it right.

— AJ
Crawl Space Ninja Supply