In a crawl space, the best choice between faced and unfaced insulation depends on how the space is managed. For encapsulated (sealed and conditioned) crawl spaces, use unfaced insulation. For vented or unsealed crawl spaces, use faced insulation to protect the subfloor from moisture.
In a vented crawl space, the paper or foil facing (the vapor barrier) should always face upward toward the warm subfloor. This keeps moisture from the damp crawl space from passing through the insulation and condensing on your wood floorboards.
The best overall floor insulation for a closed (encapsulated) crawl space is rigid foam board because it resists moisture, prevents mold, and offers excellent air-sealing. For an open (vented) crawl space, traditional fiberglass batts are typically installed under the subfloor.
Faced or unfaced insulation in basement walls is a common question we get. Use faced insulation in basement walls when insulating between studs, with the facing toward the interior. However, if you're adding insulation over existing insulation, choose unfaced to avoid creating a double vapor barrier.
Average crawl space insulation costs
Rigid foam board costs range from $1.50 to $3.00 per square foot, while spray foam insulation may vary from $1.75 to $4.50 per square foot, with closed-cell foam being at the higher end.
What time of year is Insulation cheapest?
The absolute cheapest way to insulate a crawl space is to DIY with unfaced fiberglass batts installed between the floor joists ($0.30–$1.00 per sq. ft.). However, because fiberglass absorbs moisture and sags, a more durable DIY budget option is installing rigid foam board directly against the foundation walls ($0.25–$0.50 per sq. ft.).
Installing insulation without a vapor barrier in an exterior wall can cause condensation inside the wall cavity. In cold climates, this moisture buildup leads to mold, mildew, and wood rot. Use faced insulation or vapor control to prevent structural and health issues.
Mice are curious and always searching for safe, snug, and warm nesting sites. Attics filled with blown-in insulation provide an excellent option–from the mice's point of view. As long as there is a ready food source. Mice are omnivorous and will eat and chew on almost anything including wood and electrical wires.
Continuous insulation on the exterior side of wall framing is increasingly required in colder climate zones. This addresses thermal bridging through wood or steel studs, which can reduce the effective R-value of a wall assembly by 20% or more.
The choice between faced and unfaced insulation depends on your crawl space's moisture management. Use unfaced insulation if your crawl space is encapsulated with a sealed vapor barrier. Use faced (kraft-faced) insulation for vented crawl spaces to prevent moisture from moving up into the subfloor.
Because spray foam can trap moisture, hide the condition of the roof, make it difficult for surveyors to inspect, which means risks like timber decay, dry rot, and not forgetting increased fire risk. If you've got it or you're buying a property that does, this is something you need to know upfront.
Foam insulation is a common target because it's easy for them to chew through. The material offers little resistance, allowing mice to create tunnels or nests within the insulation. But mice aren't just interested in chewing for the sake of it—they're also drawn to the warmth and shelter insulation provides.
For a crawl space with a dirt floor, rigid foam board and closed-cell spray foam are the best insulation choices, as they resist moisture and prevent mold. Never use fiberglass, which acts like a sponge and breeds mold. For ultimate protection, install a heavy-duty vapor barrier (10-20 mil) completely sealing the dirt.
Insulate Your Crawl Space
At this point, you may ask, “Which way should insulation face in a crawl space?” Install faced insulation with the paper backing against the subfloor and the material side facing into the crawl space.
Don't Skip Sealing Seams, Edges, and Penetrations
A vapor barrier with unsealed seams fails at every gap. Moisture and soil gases enter through even small openings. Overlap panels by at least 12 inches and tape every seam.
The Amish rely on natural, low-tech, and self-sufficient methods to manage mice. Because they generally avoid chemical poisons, they focus on three core pillars: prevention, natural deterrents, and mechanical traps.
Potential problems with spray foam insulation
reduce air circulation and ventilation within a roof space. lead to dampness and condensation on the underside of a roof because it forms an air barrier and stops moisture from escaping. place timber-framed roofs at risk of decay.
Closed-cell spray foam and rigid foam board are hard, unattractive to rodents, and double as air barriers. Mineral wool is dense enough to discourage nesting. Fiberglass batts, especially in crawl spaces and attics, are essentially an open invitation.
No, standard Tyvek cannot be used as a traditional vapor barrier. Tyvek is a housewrap designed as an air and moisture barrier. It keeps bulk water out but is highly vapor-permeable, allowing moisture to escape the wall to prevent rot and mold.
Use faced insulation for exterior walls, attics, and basements where moisture control is vital. The facing (paper or foil) acts as a vapor barrier.
You should avoid using a traditional, impermeable vapor barrier (like polyethylene plastic sheet) when it traps moisture instead of letting the wall system dry. If moisture gets into a wall, the barrier prevents it from escaping, leading to mold, mildew, and wood rot.
The choice between faced and unfaced insulation depends on your crawl space's moisture management. Use unfaced insulation if your crawl space is encapsulated with a sealed vapor barrier. Use faced (kraft-faced) insulation for vented crawl spaces to prevent moisture from moving up into the subfloor.
10 Signs Your Home Needs Better Insulation