Attic insulation types, compared on one sheet
Short answer
The main attic insulation types are loose-fill fiberglass, loose-fill cellulose, batts (fiberglass or mineral wool), spray foam and radiant barrier. Most Bay Area attics get fiberglass or cellulose blown across the floor. Batts suit open framing, spray foam suits vaulted ceilings and sealed attics, and a radiant barrier adds to insulation, mostly inland.
Material against material
When two options both fit your attic.
1 page
Fiberglass vs cellulose
Two loose fills, one code target. The real differences are narrower than the online arguments suggest, and one wiring situation settles it outright.
Who does the work
Doing it yourself, or handing it over.
1 page
DIY vs a pro
Renting the blower is the easy part. What decides whether a weekend job pays off happens before the first bag is opened.
Insulation advice online tends to crown a winner. This page doesn't, because the material matters less than where it's going: an open attic floor in Daly City, a vaulted ceiling in the Oakland hills and a hot attic full of ductwork in Pleasanton each want something different. The tables below put the common attic insulation types side by side, using the Department of Energy's homeowner guide and its Building America data, and each row points to the page where we go into that material properly.
The attic insulation types, and where each one fits
| Type | What it is | Where it fits in a Bay Area house | Fog side (zone 3) vs inland (zones 4, 12) | More |
|---|---|---|---|---|
| Loose-fill fiberglass | Spun glass in small tufts, blown through a hose | Open attic floors, topping up what's there | Works in every zone. Light, and not permanently damaged by a soaking | Blown-in insulation |
| Loose-fill cellulose | Recycled paper treated with fire retardant, blown in | Open attic floors, closed walls (dense-packed) | Works in every zone. Keep it dry: water costs it R-value and retardant | Blown-in insulation |
| Fiberglass batts | Pre-cut blankets laid between framing | Open walls, knee walls, floors over crawl spaces and garages, easy attic bays | Zone doesn't change much; fit does | Batt insulation |
| Mineral wool | Rock or slag spun into fiber; batts or loose fill | Where noncombustible insulation or sound control matters | Same as fiberglass; heavier, and loses R-value when compressed | Batt insulation |
| Open-cell spray foam | Soft foam that expands in place; lets vapor through | Vaulted ceilings, kneewalls, open walls in a remodel | Most useful where an attic is being brought inside the insulated house, more often inland | Spray foam |
| Closed-cell spray foam | Dense, rigid foam; slows vapor | Rim joists, shallow rafters, tight spots | Same as open-cell; picks up where space is tight or moisture is a concern | Spray foam |
| Radiant barrier | Reflective foil (or spray-on coating) under the roof deck | Attics with ducts, a dark roof or a big west-facing slope | An add-on for hot inland attics; a low priority on the fog side | Radiant barrier |
Fire, moisture, dust and cost
| Type | Fire | Moisture | Dust and installing | Cost tier |
|---|---|---|---|---|
| Loose-fill fiberglass | The glass doesn't burn; DOE notes its binders do | Not permanently damaged when saturated (DOE/PNNL) | Needs a blowing machine; protect skin, eyes and lungs | Low to middle, see /cost |
| Loose-fill cellulose | Treated; must meet the federal cellulose standard, and kept away from flues | Absorbs water; DOE says wetting can drain its fire retardant | Needs a blowing machine; DOE calls loose fill dusty | Low to middle, see /cost |
| Fiberglass batts | Glass doesn't burn; kraft-paper facing is flammable | Gaps let air and moisture through | Hand-cut; quality depends on fit | Lowest, see /cost |
| Mineral wool | Noncombustible (DOE) | Absorbs water; vapor permeable | Hand-cut or blown | Above fiberglass in DOE's relative costs; no separate Bay Area range |
| Open-cell spray foam | Burns; must be covered by a fire barrier | Lets vapor through | Trained crew and special equipment; re-entry wait | Middle, see /cost |
| Closed-cell spray foam | Burns; must be covered by a fire barrier | Very resistant to moisture; a vapor retarder | Trained crew and special equipment; re-entry wait | Highest, see /cost |
| Radiant barrier | Not rated in the DOE guide's fire notes; it adds no R-value of its own | DOE warns it may create moisture problems | Stapled under rafters or sprayed on; DOE says not for use in an unvented attic | Low to middle, see /cost |
How to read the columns
Cost tier is the order of the Bay Area market ranges on our cost page, per square foot installed. They are ranges collected from published Bay Area sources, not our prices, and the tier is only a rough order: a radiant barrier is priced per square foot of attic, foam per square foot sprayed. Fiberglass and cellulose share one blown-in range, because the sources we found don't price them apart reliably. Prep work, such as removal, air sealing and rodent work, can move a quote more than the choice of material does.
Zone fit uses the California Energy Commission's climate zones. Zone 3 covers the fog-side cities from San Francisco down the Peninsula and along the East Bay flats; zone 4 is the Santa Clara Valley; zone 12 is the inland East Bay from Concord to Livermore. Napa, San Rafael and Santa Rosa are zone 2. The code asks for the same kind of upgrade whatever material you pick; what changes by zone is how hot the attic gets and which add-ons pay their way.
Why no R-value per inch here. It's easy to compare materials inch for inch, but the code sets a target R-value for the whole ceiling, so a material with less per inch simply goes in deeper. The per-inch figures and the depth for R-38 and R-49 are on the guide to checking your attic insulation.
Why no rodent column. No primary source we found ranks these materials by how well they keep rats or mice out. The DOE guide notes that batts can become nesting material. That's a reason to close entry points before insulating, not a reason to choose one fill over another.
Head-to-heads, and where each one lives
Some comparisons get searched often enough that they have their own home on this site:
- Fiberglass vs cellulose, the decision most Bay Area attic owners actually face, has its own page: fiberglass vs cellulose. It covers settling, weight, moisture on the fog side, fire treatment and the knob-and-tube rule that takes cellulose off the table.
- Blown-in vs batt insulation is on the batt insulation page, with labor hours and where each one fits.
- Spray foam vs blown-in is on the spray foam page, including where foam is and isn't worth its price.
- Radiant barrier vs insulation is on the radiant barrier page, with the fog-side vs sun-side breakdown and the reroof rule.
The one rule that overrides the table
If live knob-and-tube wiring is staying in the attic, the California Electrical Code exception that allows insulation around it requires, in the words of Berkeley's Form 146, that "the insulation shall be noncombustible as defined in the California Building Code." That takes cellulose and foam off the table, whatever the other columns say, and it needs an electrician's survey first. We don't handle that part ourselves; we refer you to an electrician.
Doing it yourself, or hiring it out
The other comparison people make isn't between materials at all. If you're weighing a rented blower against a crew, DIY vs professional covers when doing it yourself makes sense, the air sealing that decides the result, and the stop signs that mean leave it alone.
When you'd like a recommendation for your own attic, book a free inspection or send photos, and the written quote will name the material, the R-value and the depth.
Questions people ask
Which type of attic insulation is best for a Bay Area home?
There isn't one winner. For an open attic floor, blown-in fiberglass or cellulose is the usual fit in every Bay Area climate zone. Vaulted ceilings and sealed-attic projects point to spray foam, open framing to batts, and a radiant barrier earns its place mostly in hot inland attics, on top of the insulation rather than instead of it.
What is the most common attic insulation in the Bay Area?
On an open, vented attic floor, which describes most Bay Area attics, the usual choice is loose fill: fiberglass or cellulose blown in to an even depth. The Department of Energy's homeowner guide describes loose fill as well suited to retrofits because it fills around wiring, plumbing and framing. Batts, foam and radiant barriers each have narrower jobs.
Is spray foam better than blown-in for an attic floor?
Not for an ordinary vented attic floor. Foam's strength is sealing and insulating in one pass where space is tight or the attic is being brought inside the insulated house. On an open floor, blown-in reaches the code's R-value for less, with air sealing done underneath it first. Our spray foam page covers where foam earns its price.
Why is there no rodent column in the table?
Because we found no primary source that ranks insulation materials by how well they resist rats or mice. The Department of Energy notes that batts can become nesting material, but rodents nest in loose fill and chew foam too. What keeps them out is closing the entry points, not the choice of material.
Does the Bay Area need a radiant barrier and insulation?
A radiant barrier reflects heat from the roof deck; it doesn't replace the R-value on the attic floor. The Department of Energy's guide calls it cost-effective in hot climates, which in the Bay Area means the inland valleys more than the fog side. Insulation comes first everywhere; the barrier is an add-on.
Where are the R-value per inch numbers?
On our guide to checking attic insulation yourself, next to the depth for R-38 and R-49 by material. This page compares how materials behave; that guide turns a ruler reading into an R-value.
Sources
- Insulation: A Guide for Contractors to Share with Homeowners (Building America, May 2012), U.S. Department of Energy (opens in a new tab)
- Loose-Fill Insulation, Building America Solution Center (Pacific Northwest National Laboratory for DOE) (opens in a new tab)
- Attic Insulation Project, ENERGY STAR (opens in a new tab)
- 16 CFR 1209.9, Labeling (Interim Safety Standard for Cellulose Insulation), Cornell LII (opens in a new tab)
- Knob and Tube Wiring Safety Report (Form 146), City of Berkeley (opens in a new tab)
Published by: Attic WISEUpdated:
Let's go look at your attic.
Start with your ZIP code. A few questions later you'll have a Bay Area market range, and you can pick a time for a free inspection.
What happens next
- 1
Price range online. The estimator gives you a Bay Area market range in a couple of minutes.
- 2
Free inspection. In your home, or from photos or video you send if you'd rather skip the visit.
- 3
Written quote. What comes out, what gets sealed, what goes in.
- 4
Install day. Done by our own crews.
- 5
Cleanup. Old material bagged and hauled away, the work area cleaned.
- No deposit until you sign, and never more than 10% of the contract or $1,000, whichever is less.
- Every customer gets five business days to cancel after signing.
- Materials carry the manufacturer warranty.
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