Blown-in vs. batt insulation for attics
Both can get your attic to the recommended R-value. The better choice depends on the attic's shape, what's already there and whether you're doing it yourself.
On this page
At a glance
| Blown-in fiberglass | Blown-in cellulose | Fiberglass batts | |
|---|---|---|---|
| R-value per inch (DOE range) | 2.2–2.7 | 3.2–3.8 | 2.9–3.8 |
| Depth for R-49 (approx.) | 18–22 in | 13–15 in | 13–17 in |
| Fills around obstructions | Very well | Very well | Needs careful cutting |
| DIY | Rented blower; two people | Rented blower; two people, dusty | No special tools |
| Settling | Little | Some — installed a little deeper to allow for it | None |
R-value ranges from the U.S. Department of Energy. Follow the coverage chart on the bag for installed depth.
Blown-in (loose-fill) insulation
Loose fill flows around wiring, pipes, framing irregularities and into tight corners, forming a continuous blanket without the gaps that batts can leave. That makes it the usual choice for topping up an existing attic floor and for attics with lots of obstructions. Many home centers lend or rent a blowing machine with a bag purchase.
- Cellulose (recycled paper treated with fire retardant) has a higher R-value per inch and is dense, which also reduces air movement through the layer. It settles somewhat, so bag charts specify an initial installed thickness.
- Fiberglass loose fill is lighter and settles less, but needs more depth for the same R-value.
Batts
Batts are pre-cut blankets sized for standard joist spacing. They're easy to handle without equipment and work well in open, regular framing — new construction, knee walls, or a second layer laid perpendicular across the joists. Their weakness is gaps: every space around a wire, a pipe or an uneven joist lets heat bypass the insulation, so they need careful fitting.
- Use unfaced batts when adding a layer over existing insulation — faced batts would trap moisture between layers.
- Don't compress batts; squashed insulation loses R-value.
Whichever you choose
- Air-seal first. Seal gaps around plumbing and wiring penetrations, chimneys (with fire-rated materials) and the attic hatch.
- Keep vents open. Install baffles at the eaves so insulation doesn't block soffit ventilation.
- Respect clearances around chimneys, flues and recessed lights not rated for insulation contact.
- Mark the depth with rulers stapled to joists so you blow an even layer.
Use the insulation calculator to find the recommended R-value for your climate zone and the depth each material needs.
Frequently asked questions
Can I put blown-in insulation over batts?
Yes — it's a common way to top up an attic, as long as the existing batts are dry and not moldy.
Which is cheaper?
It depends on local prices, but loose fill is often cheaper per square foot for thick attic layers, especially DIY with a borrowed blower.
Does insulation need a vapor barrier in the attic?
It depends on your climate and local code; many attics rely on air sealing and ventilation rather than a separate vapor barrier. Check local requirements.
Sources
- U.S. Department of Energy, Insulation materials — R-value per inch ranges.
- ENERGY STAR, Recommended home insulation R-values.