Faced or unfaced insulation in the attic: which one and where
The facing is not decoration. Put it on the wrong side, or in the wrong layer, and it can hold moisture where you do not want it.
If you are adding insulation on top of insulation that is already in the attic, buy unfaced. If you are laying the first layer between the joists, faced batts can be right, with the facing toward the warm side. That is the short answer. The reasoning matters, because the mistake that gets people into trouble is a second layer with its own paper facing.
What the facing actually is
The paper or foil on faced batts is a vapor retarder. It slows water vapor moving through the insulation. It is not an air barrier and it is not waterproof. Unfaced insulation has no such layer and lets vapor pass freely.
Why would you want to slow vapor at all? In a cold climate, warm indoor air carries moisture upward in winter. If that moisture reaches the cold underside of the roof deck, it can condense. A retarder near the ceiling cuts down how much arrives. We cover the mechanism in attic condensation.
Facing goes toward the warm side
In heating climates, the facing sits on the side that faces the living space. In an attic floor, that means face down, toward the ceiling below. Facing up puts the retarder on the cold side, where moisture that does get in can be trapped under it.
Warm, humid climates reverse some of this thinking, and mixed climates sit in between. Check your local building code and your area's guidance before you choose. This site cannot tell you your climate zone's rule, and a wrong guess is easy to make.
Never stack two facings
A second layer of faced insulation laid across the first creates a sandwich with a retarder in the middle. Vapor gets in and cannot leave. That is a recipe for damp insulation, and the same pattern is described in wet attic insulation.
Use unfaced for any layer added on top, or for blown-in loose fill. Lay batts perpendicular to the joists so they cover the framing too.
Air sealing matters more than the facing
Here is the opinion worth taking away: the facing is the minor player. The big moisture mover is air leaking through gaps around the hatch, recessed lights, wiring holes and plumbing stacks. Vapor diffusing through paper is slow. Warm air rushing through a hole is not.
Seal those gaps first. A faced batt over an unsealed ceiling does very little. An unfaced layer over a sealed ceiling works fine.
Keep the eaves clear
Whichever you pick, do not let insulation crowd the soffit vents at the eaves. Blocked intake leaves the attic damp and stale. Baffles hold the channel open.
All of this happens from the attic floor with a flashlight. You do not need to be on the roof for any of it, and you should stay off it. If you are unsure which layer you have, a qualified insulation or energy auditor can tell you before you buy anything.
Frequently asked questions
Should attic insulation be faced or unfaced?
It depends on the layer. A first layer between joists in a cold climate can be faced, with the facing toward the warm living space. Any layer added on top of existing insulation should be unfaced.
Which way does faced insulation go in the attic?
In a heating climate, the facing goes toward the warm side, which means face down toward the ceiling below. Check your local building code for your climate zone.
Can I put faced insulation over existing insulation?
It is not a good idea. A second facing creates a vapor retarder in the middle of the stack and can trap moisture. Use unfaced for the added layer.
Does the facing stop air leaks?
No. The facing slows vapor, but it is not an air barrier. Seal gaps around the hatch, lights and wiring holes separately.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- US EPA. A Brief Guide to Mold, Moisture and Your Home
- US EPA. Mold Cleanup in Your Home
- US EPA. Introduction to Indoor Air Quality