Quick answer
For most existing Seattle attics, blown-in wins: loose-fill fiberglass or cellulose flows around the irregular joists, wiring, and framing quirks of 1920s–1980s housing stock, and it typically costs less per R-value installed. Batts belong in open, accessible, regular framing — new walls, some crawlspace floors, DIY-friendly jobs — but a compressed or gapped batt underperforms its label badly. Coverage quality decides this comparison more than the material does.
- R-value on the bag assumes perfect installation — batts compressed around wiring or cut short at the edges can lose a large share of rated performance.
- Blown-in fills the odd-width bays, blocking, and diagonal bracing that fill a 1926 Wallingford Craftsman attic; batts fight all of it.
- Batts win where framing is open, regular, and reachable — and they're the realistic DIY option, since blown-in wants a machine and a crew.
- Settling is real but manageable: cellulose settles more than loose-fill fiberglass, and good installers over-blow to the settled depth on purpose.
- Whichever material you choose, air-seal the attic plane first — insulation of any kind over open chases and can lights underdelivers.
What does each option cost installed in the Seattle area?
Representative Seattle-area ranges for professional attic work; Eco doesn't perform insulation installs, but material choice affects the envelope result we plan around. Per R-value delivered, blown-in usually comes out ahead in retrofit attics because the machine does the fitting that batt installers do by hand.
| Option | Typical installed range | What that covers |
|---|---|---|
| Blown-in attic job (loose-fill fiberglass or cellulose, to R-49+) | $2,500–$6,000 | Machine-blown over a sealed plane; typically the cheaper route per R-value and the better one over irregular framing. |
| Batt installation (fiberglass or mineral wool) | Comparable installed; lowest as DIY | Professional batt work in an attic prices similarly but demands meticulous fitting; DIY batts save labor and quietly cost performance when gapped or compressed. |
| Air sealing the plane first (either material) | $1,500–$4,000 | The prerequisite step that makes either material perform at its rated value. |
What changes the price
- Access difficulty: low-slope rooflines and hip corners are miserable batt territory but easy hose reach for a blowing crew.
- Home era: 1920s–1940s houses rarely have consistent joist spacing — every bay becomes a custom batt cut, and every imperfect cut is a gap.
- Moisture exposure: damp Northwest crawlspaces are hard on fiberglass batts underfloor; ground vapor-barrier condition matters more than material brand.
- Rebate documentation: insulation depth and coverage feed the measured-savings math behind WA HOMES whole-home rebates (up to $20,000, income-eligible) and PSE weatherization rebates.
- HVAC downsizing offset: a well-covered R-49 attic lowers the Manual J heating load — sometimes enough to step down a heat pump size when Eco specs the system.
Ranges are representative Seattle / Puget Sound installed prices, not a quote — your home's specifics set the real number. Eco gives you an upfront price before any work begins.
How do they work differently?
How blown-in gets its coverage advantage
Loose-fill is thousands of small tufts blown through a hose, and it behaves like a liquid: it flows around cross-bracing, plumbing vents, odd-width bays, and electrical runs, then levels into a continuous blanket with no seams. That conformity is the whole advantage — heat can't find an uninsulated shortcut, because there are no edges. The trade-off is that depth can settle over time, which competent installers pre-compensate for by blowing past the target depth.
Why batts live and die by the fit
A batt is a pre-cut block of insulation whose rated R-value assumes it sits at full loft, touching all six sides of its cavity. Compress it around a cable and the trapped-air structure that does the insulating collapses; cut it an inch short and the gap becomes a thermal highway. In regular, open framing a careful installer can hit near-rated performance — which is exactly why batts suit new walls and accessible floors, and struggle in the improvised framing of older Seattle attics.
Pros and cons, honestly
Blown-in (loose-fill)
Pros
- Seamless coverage over irregular framing — the norm in 1920s–1980s Seattle attics
- Usually the lowest installed cost per R-value in a retrofit
- Fast: a crew can bring most attics to R-49+ in a day
- Tops up over existing insulation without tearing anything out
- Cellulose option adds density and sound-deadening at similar cost
Cons
- Needs a machine and a crew — not a realistic weekend DIY project
- Settles over time (cellulose especially) if the installer doesn't over-blow to compensate
- Loose depth makes future attic work messier — walking boards and care required
Batts
Pros
- The accessible DIY route — no equipment beyond a knife, straightedge, and PPE
- Predictable, inspectable: you can see exactly what's installed where
- Well-suited to open, regular framing — new construction, remodel walls, accessible crawlspace bays
- Mineral-wool batts add fire resistance and handle incidental moisture better than fiberglass
Cons
- Performance collapses with compression and gaps — the most common real-world install flaws
- Slow, fussy work in irregular old-house framing; every odd bay is a custom cut
- Professional batt labor often erases the material-cost advantage in attics
- Underfloor batts in damp crawlspaces sag and fall without careful support and moisture control
Which one should you choose?
Choose blown-in when
You're topping up an existing attic, the framing is irregular or hard to reach, or you simply want the most R-value per dollar installed by a professional crew. It's the default answer for the classic Seattle retrofit — a Craftsman or mid-century attic with shallow existing insulation, wiring runs everywhere, and a target of R-49 or better. Have the plane air-sealed first, then let the hose do what hand-fitting can't.
Choose batts when
The framing is open, regular, and accessible — a Green Lake remodel with walls studded and waiting, a garage ceiling, or accessible crawlspace bays with dry conditions and proper support. Batts are also the honest choice when DIY is the only way the project happens this year: imperfect batts beat an empty cavity. Just fit them obsessively — full loft, full contact, no compression around wiring — because the label R-value is a ceiling, not a guarantee.
Material is the second question — sequence is the first
Either material over a leaky attic plane underdelivers, so air sealing comes first regardless of what gets installed on top. And whichever route you take, tell Eco before you replace heating equipment: an attic brought to R-49 changes the Manual J load, and buying the smaller heat pump the tighter house allows is where the envelope spend pays you back a second time.
Ready to compare for your home?
Get honest numbers for both options side by side — an upfront range, the considerations, and the rebates you qualify for, before any work begins.
Continue exploring
- Book: Plan your envelope-to-equipment sequence →
- Book: Ask Eco which upgrade comes first for your home →
- Compare: Air Sealing vs Adding Insulation: Which Comes First? →
- Compare: Attic vs Crawlspace Insulation: Where to Start →
- Compare: Home Energy Audit vs Guessing at Upgrades →
- Heat pump sizing and Manual J, explained →
- Washington rebates for home energy upgrades →
- All home energy & electrification comparisons →
Common questions
Is blown-in insulation better than batts, full stop?
In existing Northwest attics, usually — because coverage quality beats material choice, and blown-in delivers coverage that hand-fitted batts rarely match over irregular framing. In open, regular, accessible framing the two are much closer, and batts' inspectability and DIY accessibility become genuine advantages. The dishonest answer is any blanket 'X is better' that ignores where it's going.
Does blown-in insulation settle and lose R-value?
Some settling is normal — cellulose more than loose-fill fiberglass — and good installers plan for it by blowing past the target so the settled depth still meets spec. Ask the contractor for the coverage chart showing installed depth versus settled depth, and keep it: it's also useful documentation if you pursue WA HOMES rebate measurement later.
Can I DIY batts now and have blown-in added later?
Yes, and it's a legitimate staged plan: carefully fitted batts between the joists now, a professional blown-in cap over the top later to reach R-49+ and bury the seams. The order matters less than the prerequisite — get the attic plane air-sealed before either layer goes down, because sealing after the fact means excavating your own insulation.
Which insulation handles damp Puget Sound conditions better?
In the attic, either works if the roof and ventilation are sound. Underfloor in a crawlspace is where our climate bites: fiberglass batts sag and hold moisture when the ground vapor barrier is compromised, which is common here. Fix the vapor barrier first, support batts properly, and consider mineral wool where incidental moisture is likely — and treat any musty smell as a stop-and-investigate signal.
Does the material choice affect my heat pump plans?
Not the material — the result. What matters to your heating equipment is the finished, real-world R-value and airtightness of the envelope, which feed the Manual J load calculation Eco runs before specifying a heat pump. A well-executed attic at R-49, blown or batted, can shrink the required system size. That's why we ask homeowners to finish planned envelope work before we finalize equipment sizing.
Last updated: 2026-07-05