Attic Insulation for Snohomish County and North King County Homes
Most homes built before the 1990s in our area have R-11 to R-19 in the attic, often compressed to less. Current Washington energy code calls for R-49 above a ceiling. We seal the attic floor first, then blow cellulose or fiberglass to full depth, with baffles at the eaves so the insulation never blocks ventilation.
Signs the attic needs more insulation
- You can see the tops of the ceiling joists. Joists in most houses here are 2×6 or 2×8; if insulation is level with or below them, you have roughly R-19 or less.
- Upstairs rooms are noticeably warmer in July and colder in January than the main floor.
- Snow melts off your roof in patches days before the neighbors' roofs.
- The insulation looks gray, flattened, or has tunnels through it — usually rodent travel paths.
- The heating bill jumped after a cold month and nothing else changed.
Which insulation we use and why
| Material | R-value per inch (approx.) | Best for | Notes |
|---|---|---|---|
| Blown cellulose | 3.5 | Most open attics | Dense, fills around wiring and framing, borate-treated |
| Blown fiberglass | 2.5 – 2.9 | Attics where weight on old ceilings is a concern | Lighter, needs more depth for the same R-value |
| Fiberglass batts | 3.0 – 3.5 | Knee walls, sloped sections, small areas | Must be cut tight with no gaps or compression |
| Spray foam (closed-cell) | 6.0 – 7.0 | Rim joists, cathedral ceilings, conditioned attics | Higher cost, used selectively |
For an ordinary vented attic, we usually recommend cellulose. It costs less per R-value, settles less around obstructions than batts and slows air movement better than loose fiberglass. In older homes with plaster ceilings that already sag, we use fiberglass to keep the load down.
What is included
- Air sealing first. Top plates, plumbing and wiring penetrations, chimney chases and recessed lights get sealed. Insulation stops heat; it does not stop air. See air sealing.
- Baffles at every eave bay. Rigid vent chutes keep a clear air path from the soffit vents to the attic.
- Hatch dam and insulated hatch cover. A rigid frame around the access so insulation does not spill when you open it, and a weatherstripped, insulated lid.
- Clearance around heat sources. Chimneys, flues and non-IC-rated light fixtures get metal or mineral wool dams at the distances the manufacturer and code require.
- Depth markers. Rulers stapled to framing every few hundred square feet, so you or a future inspector can confirm the installed depth.
- Certificate. A posted insulation certificate showing material, installed thickness, R-value and date.
When old insulation has to come out first
Topping up over existing insulation is fine when it is dry, clean and free of droppings. It is not fine when the old material is soiled by rodents, water-stained, smoke-damaged, or when it is vermiculite. In those cases we remove it before adding new. See insulation removal and our guide to vermiculite and asbestos in attics.
Knob-and-tube wiring
Many pre-1940s homes in Everett, Edmonds and North Seattle still have live knob-and-tube wiring in the attic. The national electrical code does not allow loose or blown insulation to envelop it, and Washington sets its own conditions for existing installations. Before we insulate, a licensed electrician confirms whether the wiring is live and either decommissions it or replaces those runs. Read more in knob-and-tube wiring and insulation.
What attic insulation costs
| Attic size | Top-up to R-49 (air sealing included) |
|---|---|
| Under 900 sq ft | $2,300 – $3,600 |
| 900 – 1,400 sq ft | $3,000 – $4,800 |
| 1,400 – 2,000 sq ft | $3,900 – $6,500 |
Utilities in our area — Snohomish County PUD, Puget Sound Energy and Seattle City Light — run weatherization rebate programs at various times. We will tell you which program applies to your address and provide the paperwork the utility asks for; amounts and eligibility are set by the utility.
Attic insulation questions
How long does the job take?
One day for most houses, including air sealing. If old insulation comes out first, plan on two.
Do I need to be home?
Someone needs to let us in and show us the attic access. After that you can leave. We cover the path from the door to the hatch with drop cloths and plastic.
Will blown insulation make dust in the house?
The hose runs from a truck-mounted or trailer machine through a door or window to the attic. Dust stays in the attic. We seal the hatch opening with plastic while blowing.
Is R-49 worth it over R-38?
Each step adds less than the one before. The jump from R-11 to R-38 does most of the work; R-38 to R-49 adds a few inches and a modest cost. Because the labor and setup are the same, we usually recommend finishing at R-49.