Attic insulation has no single price, and we do not publish a per square foot figure, because two attics of the same size can need very different work. The cost comes from six things: how big the attic is and how deep the new insulation must be, whether the old insulation stays or comes out, how much air sealing the ceiling needs, the material, how hard the attic is to reach, and whether the job is part of a larger remodel. The target depth is set by code: the Washington State Energy Code lists R-60 for an attic ceiling. Your written estimate prices each of these on its own line.
Washington's energy code sets the attic target at R-60.
The residential energy code table for Climate Zone 5 and Marine 4, which covers the Greater Seattle area, lists a ceiling R-value of 60 (WAC 51-11R-40213, Table R402.1.3). Two rules soften that:
- "Where Section R402.1.3 would require R-60 in the ceiling or attic, installing R-49 over 100 percent of the ceiling area requiring insulation shall satisfy the requirement for R-60 wherever the full height of uncompressed R-49 insulation extends over the wall top plate at the eaves" (R402.2.1, WAC 51-11R-40220).
- "For single rafter- or joist-vaulted ceilings, the insulation may be reduced to R-38 if the full insulation depth extends over the top plate of the exterior wall" (Table R402.1.3, footnote e).
Seattle's own energy code carries the same R-60 value and the same R-49 rule. When you top up an existing attic, these numbers are the level worth aiming for: insulation is cheapest to add while the attic is open and the crew is already there.
Six things set the cost of insulating an attic.
- Area and depth. The ceiling area times the depth needed to reach the target sets the amount of material. An attic with a few inches of old fill needs less new material than a bare one.
- What is already there. Dry insulation can often stay. Wet, moldy or rodent damaged insulation has to be bagged and removed first, which can take as long as the new install.
- Air sealing. Gaps around light fixtures, pipes, chimneys and the attic hatch leak warm air into the attic. Sealing them before insulating is detailed work, and it is where much of the comfort comes from.
- Eaves and the hatch. The code says that for air permeable insulation in vented attics, "a baffle shall be installed adjacent to soffit and eave vents" (R402.2.3), and an attic hatch must be insulated to the same R-value as the ceiling and weatherstripped (R402.2.4). Baffles and a hatch upgrade are small items that add up.
- Material. Blown cellulose or fiberglass, batts and spray foam differ in material and labor, as the next section explains.
- Access. A tall attic with a walk-up stair is quick to work in. A low attic reached through a closet hatch, with wiring and ducts to work around, is slow.
Blown-in, batts and spray foam each suit a different attic.
- Blown-in (loose fill) insulation covers an open attic floor quickly and fills around joists and wiring. The code limits where it can go: loose fill may be used where the ceiling slope "is not more than 3 feet in 12 and there is at least 30 inches of clear distance" from the top of the ceiling joist to the underside of the roof sheathing at the ridge (R402.2.1.1).
- Batts fit between rafters or joists where the framing is open and regular, such as an attic being finished as a room.
- Spray foam seals and insulates in one step and suits tight rafter bays, but it costs more and is installed by specialist crews.
Which one fits depends on the shape of your attic and whether it will stay unheated storage or become a room.
Insulation is often part of a bigger attic remodel.
When an attic becomes living space, the insulation moves from the attic floor to the roof and the walls. In our Attic Bonus Room Remodel, finished in the summer of 2021, the old pine paneling came down and the attic was stripped to the rafters. Insulation went into the roof between the rafters and into the walls, and the room was then finished with drywall, recessed lights and carpet. In a job like that, the insulation is one line in a larger estimate rather than a separate project.
Seattle does not require a permit to insulate an existing attic.
The 2021 Seattle Residential Code lists "insulating existing buildings" among minor work exempt from a building permit, "provided no changes are made to the building envelope" (R105.2). The same code reminds owners that "All work shall comply with this code, even where no permit is required" (R105.1). If the job adds a bathroom fan, moves wiring or changes the roof framing, those parts can need their own permits. Other cities set their own rules, so we check yours before we price the work.
Here is how we price attic insulation.
We go up into the attic, measure the area and the depth of what is there, look for wet spots, gaps and rodent signs, and check the eaves and the hatch. Then you get a written estimate with removal, air sealing, baffles, material and labor each on their own line. See Insulation Installation Services Across the Greater Seattle Area for the service, the Construction Services Portfolio Across the Greater Seattle Area for the attic job above, and the Remodeling Pricing Guide for the Greater Seattle Area for how we price remodeling work.
Attic insulation questions
How much insulation does an attic need in Washington?
The Washington State Energy Code lists R-60 for ceilings in its climate zone (Table R402.1.3, WAC 51-11R-40213). Where the attic has room for full height insulation over the wall top plate at the eaves, R-49 over the whole ceiling satisfies the R-60 requirement (R402.2.1). Single rafter vaulted ceilings may use R-38 when the full depth extends over the top plate.
Do I need a permit to add insulation to my attic in Seattle?
Usually not. The Seattle Residential Code exempts "insulating existing buildings" from a building permit, provided no changes are made to the building envelope (R105.2). Wiring, fans or roof framing changes that come with the job can need their own permits.
Should old attic insulation be removed first?
Not always. Dry, clean insulation can often stay with new material blown over it. Insulation that is wet, matted, moldy or full of rodent droppings comes out first, and that removal is its own line on the estimate.
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