Unfaced vs. Faced Insulation: Which to Use
Both unfaced and faced insulation serve the same purpose–providing thermal resistance to heat conduction and ensuring that buildings remain warm or cool as required. The differences between them involve where and how they are used.
What is Unfaced Insulation?
Unfaced fiberglass batts or rolls don’t have a vapor barrier and are the most popular type of insulation for all applications. Many jurisdictions don’t mandate faced insulation but may require a vapor barrier. Unfaced batts are less expensive than faced products and easy to obtain.
Unfaced insulation is non-combustible – it can help slow flame spread and prevent fire.
Where to use unfaced insulation
You can use unfaced insulation anywhere that requires a barrier between warm and cold areas, such as exterior walls, crawl spaces, vaulted roofs, and attic floors. You can add it to existing insulation for more R-value as long as it’s not compressed – compressed fiberglass loses its insulation value. For soundproofing, you can add unfaced insulation to interior walls.
In colder climates, you’ll need a vapor barrier over unfaced insulation on the warm side of walls to prevent moisture penetration.
What is Faced Insulation?
Faced insulation is the same fiberglass batts or rolls with kraft paper applied to one side. The kraft paper–sometimes vinyl or light aluminum foil–provides a vapor barrier. Faced insulation prevents moisture from entering wall cavities, which helps reduce mold and mildew and protects framing from moisture damage and rot.
Where to use faced insulation
Use faced insulation in places you need moisture and thermal protection, such as exterior walls or vaulted roofs. It’s also beneficial to use faced insulation in the interior walls of kitchens and bathrooms to prevent moisture from passing from room to room. Install the faced side towards the humid room.
You can also layer faced insulation over unfaced insulation to add a vapor barrier and increase the R-value, provided the cavity is deep enough to accept it without compression.
Layering Unfaced and Faced Insulation: Dos and Don’ts
You can layer unfaced insulation can over the top of unfaced insulation without any problem, such as double batts in wall cavities or double layers on attic floors. A layer of faced insulation can go over unfaced insulation, provided that the kraft paper is on the warm side of the wall, floor, or roof.
Never install multiple layers of faced insulation. Doing so creates a double vapor barrier that can trap moisture between the layers leading to rot, mold, and mildew. The fiberglass insulation may also absorb the moisture, making the r-value next to zero.
Installing Unfaced vs Faced Insulation
Unfaced insulation relies on friction between studs, rafters, or joists to stay in place. It’s light enough that it should not sag–especially after the drywall is installed to create a tight sandwich. If you’re not adding drywall in places like rafters, you may need strapping to keep the batts in place.
Faced insulation is easier to install than unfaced since the kraft paper provides stability to the batt. The paper side tabs are folded out and stapled to the sides or faces of studs, rafters, or joists. Some local building codes specify which method. Non-standard-sized wall cavities require cutting the insulation to size and manufacturing a tab. You can also cover them with poly to keep the vapor barrier intact.
In hot climates installing faced insulation with kraft paper on the outside may help keep moisture outside. Some hot, humid climate jurisdictions ban the use of faced insulation altogether.
Take care installing either type of insulation so that the fiberglass fits snuggly against all framing members. Even small gaps and holes compromise the wall’s insulation integrity.
Difference in Unfaced vs. Faced Insulation Costs
Unfaced insulation costs $0.10 – $0.25 per square foot of installed area less than faced insulation–depending on thickness and R-value. For locations requiring a vapor barrier on the warm side of the exterior walls, 6 mil poly is usually acceptable. Add $0.05 – $0.20 per square foot for the poly, plus the time to install it.