Faced or Unfaced Insulation: Which Do You Need?
What the facing is
The kraft paper on a faced batt is asphalt-coated and works as a vapor retarder: it slows water vapour migrating from humid indoor air into the cold parts of the wall or roof, where it would condense. The flanges also staple to framing, which holds batts in ceilings and makes spacing consistent. That is all it is — paper, tar and a job description. The insulation value is identical to the unfaced batt behind it.
Which to buy, by location
| Location | Batt | Facing orientation |
|---|---|---|
| Exterior walls, first insulation | Faced | Toward the interior (drywall side) in most of the US |
| Attic floor, first layer | Faced | Down, against the ceiling drywall |
| Attic, topping up over old insulation | Unfaced only | Laid across the joists, no facing anywhere in the stack's middle |
| Cathedral ceiling / rafters | Faced | Toward the interior; mind the ventilation baffle above |
| Floor over crawlspace | Faced | Up, against the subfloor (the warm side) |
| Interior walls for sound | Unfaced | No vapour issue between heated rooms |
| Basement walls | Neither by default | Below-grade moisture runs inward — foam-based systems, a different design problem |
The one real rule: never two retarders
A wall can dry toward whichever side has no vapour barrier. Put retarders on both sides — a faced batt against poly sheeting, or a new faced batt stacked on an old faced batt — and moisture that gets in (it always does) has no way out. That is the recipe for damp insulation, mould and rot discovered years later. Hence:
- Topping up an attic: unfaced, always. If you only have faced stock on hand, slash the facing liberally so it cannot act as a barrier.
- Walls that already have poly sheeting under the drywall (common in cold-climate builds): use unfaced batts behind it.
- One retarder per assembly, on the side that is warm in winter for most of the US.
"Warm side" depends on where you live
The retarder faces the side the moisture comes from — the humid side. In heating-dominated and mixed climates that is the interior, so kraft faces the drywall. In hot-humid Gulf climates where air conditioning makes the interior the cold side, outdoor humidity drives inward and interior vapour barriers can trap it against cold drywall — practice there leans to unfaced batts and letting the wall dry inward. If you are in that zone, follow local practice and code rather than a national rule of thumb.
Working notes
- Facing goes toward you as you install from inside — visible kraft, then drywall over it. The paper is flammable and must not be left exposed in living space.
- Staple flanges to the stud face or inset, keeping the batt loft — do not compress edges into the cavity.
- Fill, do not pack. Split batts around wiring rather than stuffing them behind it; a batt compressed to half depth delivers well under half its R.
- Same quantity either way: faced and unfaced cover identically, so the insulation calculator's bag count stands — just buy the right one for the layer.
Work out how many bags of batt insulation a wall or attic needs. The tool deducts the framing — batts go between the studs, not over them — and divides by the coverage printed on your bag.
Frequently asked questions
Which way does faced insulation go?
Facing toward the warm-in-winter side, which in most of the United States means toward the interior: against the drywall in walls, down against the ceiling in an attic floor, up against the subfloor over a crawlspace. Hot-humid Gulf climates are the exception — follow local practice there.
Can I put faced insulation over existing insulation?
No. A facing buried in the middle of the stack traps moisture between layers. Top up attics with unfaced batts laid across the joists, or slash the facing thoroughly if faced stock is all you have.
Do interior walls need faced insulation?
No — there is no meaningful vapour drive between two heated rooms. Interior walls are insulated for sound, and unfaced batts (or mineral wool) are the right product.
Is faced insulation warmer than unfaced?
No. The R-value of the batt is identical; the facing is a vapour retarder and a stapling flange, not insulation. The choice is entirely about where the assembly needs a retarder — and about never having two.