In the Seattle area, closed-cell spray foam runs roughly $1.00 to $2.00 per board foot installed, and open-cell runs roughly $0.50 to $0.70 per board foot. A typical project, call it 1,000 square feet of surface at three inches thick, commonly lands somewhere around $2,200 to $5,400.
Those are the real numbers we work from. The rest of this page is the part most cost pages leave out: what a board foot actually is, how to run the math yourself, what moves your number up and down, and the situations where we will tell you to spend a lot less than that.
The honest headline
Spray foam is priced by volume, not by square footage, so two houses with the same floor area can be thousands of dollars apart. Anybody who quotes your house over the phone is guessing, and that includes us. We will give you ranges here so you can sanity-check every bid you get.
First, what a board foot is
A board foot is one square foot of surface, sprayed one inch thick. That is the unit spray foam is sold and installed in, because the cost is driven by how much foam comes out of the rig, not by how much floor you walked across.
The math is one line:
square feet of surface × inches of thickness = board feet
board feet × the per board foot rate = the installed price
So 500 square feet of crawl space wall at 2 inches is 1,000 board feet. The same 500 square feet at 4 inches is 2,000 board feet, and it costs about twice as much. This is why “how much per square foot” is an incomplete question and why one contractor can look cheaper than another while quoting less foam.
Run the typical project both ways
Take that typical job, 1,000 square feet at three inches. That is 3,000 board feet. Derived straight from the rates above:
| Product | Board feet | Rate | Arithmetic range |
|---|---|---|---|
| Closed-cell | 3,000 | $1.00 to $2.00 | $3,000 to $6,000 |
| Open-cell | 3,000 | $0.50 to $0.70 | $1,500 to $2,100 |
Real projects in this market tend to land in that $2,200 to $5,400 band rather than at either arithmetic extreme, because almost nobody buys exactly three uniform inches of one product over a clean 1,000 square feet. Jobs mix thicknesses, mix products, include prep, and include areas the sprayer can barely reach. Both the arithmetic and the observed range are useful: use the arithmetic to check a quote line by line, and use the observed range to know whether you are in the right neighbourhood at all.
What actually moves your number
Which product, and why
Closed-cell costs two to three times what open-cell costs per board foot, so this is the single biggest lever on the price. It is also the one you should not decide on price alone. Closed-cell earns its money where moisture is part of the problem: crawl space walls, rim joists, roof decks, shallow cavities. Open-cell is a fine buy where you have depth to fill and no moisture concern. The full comparison is on open-cell vs closed-cell spray foam, and the case for the premium product is on closed-cell spray foam insulation.
How many inches the assembly needs
Thickness is a multiplier, straight through to your invoice. Two inches at a rim joist and five inches on a roof deck are different jobs on the same house. We spec the depth the assembly actually needs in our climate zone, then show you the board feet so you can see what you are buying.
The size and shape of the area
A big open rectangle sprays fast. The same square footage chopped up by ductwork, plumbing, joist bays, knee walls, and a chimney chase takes much longer for the same volume of foam. Complexity costs time, and time is billed at Seattle trade rates, roughly $95 to $175 per hour.
Access
This one surprises people more than any other. An open basement wall you can stand in front of and a 20 inch crawl space with a 16 by 24 hatch are not the same job, even at identical board feet. In the tight crawl space the hose has to be dragged in, the crew works on their back, containment is harder, and everything comes out through that same small opening. Expect the per board foot number to sit at the top of the range on a difficult crawl space, and to sit lower in an open basement or a walk-up attic.
Whether old insulation has to come out first
Foam only works against a clean substrate. Wet batts, settled blown-in, or anything rodents have been living in has to come out before we spray, and that is a separate line item with its own labour, bagging, and disposal. On a Seattle crawl space with soaked fiberglass and rodent contamination, removal can be a meaningful share of the total. See insulation removal for what that involves.
Containment, prep, and protection
Masking, poly, sealing off the rest of the house, and mechanical ventilation are not optional extras, they are part of doing the job correctly. They take hours before a drop of foam is sprayed and more hours to break down afterwards.
Setup time versus spray time
Here is the part that explains most of the “why is the small job so expensive” confusion. A spray rig has a fixed startup: get the truck there, run and warm the hose, bring the chemical up to temperature, mask, contain, suit up. That is often half a day regardless of whether you are spraying 400 board feet or 4,000. The spraying itself can be the shortest part of the day.
So the effective price per board foot on a very small job is high, not because anybody is gouging you, but because you are paying for a setup that a larger job spreads over more foam. If you have a small job, the cheapest thing you can do is bundle it with the other work you already know you need.
Rough ranges for the jobs we actually do here
These are worked from the verified rates above, using surface areas typical of Puget Sound homes. They are ranges to orient you, not quotes. Your house will have its own numbers.
| Job | Typical surface and depth | Board feet | Derived range |
|---|---|---|---|
| Crawl space walls and rim joist | About 350 to 550 sq ft of perimeter wall and band at 2 in, closed-cell | 700 to 1,100 | About $700 to $2,200, plus removal and prep if needed |
| Attic floor | About 1,000 sq ft at 5 in, open-cell | 5,000 | About $2,500 to $3,500 |
| Roof deck, conditioned attic | About 1,200 sq ft of sloped deck at 4 in, closed-cell | 4,800 | About $4,800 to $9,600 |
| Bonus room over a garage | About 400 to 600 sq ft of ceiling, knee walls, and slopes at 3 in, closed-cell | 1,200 to 1,800 | About $1,200 to $3,600, usually the upper half because of setup |
Two honest notes on that table. The roof deck row is the expensive one and it is the one people underestimate, so if a conditioned attic is what you want, budget accordingly. And the attic floor row is the one where we most often talk people out of foam entirely, which brings us to the next section. More on those two assemblies specifically on attic insulation and crawl space insulation.
Spray foam versus the cheaper options
On up-front cost, spray foam is the expensive choice. That is not a criticism of it, it is just true, and you should hear it from us rather than find it out after three bids.
- Fiberglass batts are the cheapest material per square foot by a wide margin. They do not air seal, they perform badly if they are compressed or installed sloppily, and they are miserable in a damp crawl space. In a clean, square, accessible cavity they are still a reasonable buy.
- Blown-in fiberglass or cellulose in an open, vented attic floor costs a fraction of what foam costs for the same coverage, and it is genuinely the right answer in a lot of Seattle attics. If your attic is vented and staying vented, this is usually the better buy.
- Spray foam costs the most up front and is the only one of the three that insulates and air seals in a single step, holds its shape and performance over time, and can be specified to handle moisture.
And the thing we will say out loud
For a lot of houses, air sealing alone, at a fraction of the price of a foam job, delivers most of the comfort improvement. Sealing the top plates, the chimney chase, the can lights, the attic hatch, and the rim joist penetrations is what stops the draught you actually feel. If that is what your house needs, we will tell you that, quote it, and leave the foam conversation for another year or for never.
We are not going to talk about payback periods or savings percentages on this page, because honest numbers there depend entirely on your house, your fuel, and how you heat. That conversation lives on how much spray foam can actually cut your energy bill.
How we price a job
Get in the space
Crawl space, attic, wherever the work is. We measure the real surfaces and find out what is already in there.
Spec the assembly
Product and depth for each area, with the reasoning written down, including any area where a cheaper material is the right call.
Show the board feet
Square feet, inches, board feet, rate. Removal, prep, and access called out as their own lines rather than buried.
Give you the number
In writing, with no expiry date on it, and no pressure to sign anything while we are standing there.
Why nobody should price your house over the phone
We get asked for a phone number every week, and we understand why. Here is the problem. Over the phone we do not know your crawl space height, your hatch size, whether the existing insulation is dry, whether there is rodent damage, how many joist bays are blocked by ductwork, or whether the assembly needs two inches or five. Every one of those changes the price by hundreds or thousands of dollars.
A contractor who gives you a firm figure without looking is doing one of two things: padding it high enough to be safe, or lowballing to get in the door and revising it once you are committed. Neither one is good for you. What we will do on the phone is talk you through the ranges on this page, tell you which scenario yours sounds like, and book a look at the house. The estimate is free and nobody will try to close you in your kitchen.
Common questions about spray foam cost in Seattle
Why is spray foam quoted per board foot instead of per square foot?
Because the cost is driven by the volume of foam, not the area it covers. A board foot is one square foot at one inch thick, so 500 square feet at 2 inches is 1,000 board feet. Quoting per square foot hides the thickness, which is exactly where two quotes can differ without either one being obviously cheaper. If a bid you are comparing is written per square foot, ask what thickness it assumes and multiply it out yourself.
Why does my small job cost so much per square foot?
A spray rig has a fixed setup: travel, hose run, bringing the chemical up to temperature, masking, containment, and PPE, which is often half a day whether the job is 400 board feet or 4,000. On a small job that setup is spread over very little foam, so the effective rate per board foot goes up. It is not a penalty, it is arithmetic. If you have several small areas, doing them in one visit is the cheapest way to buy them.
Does removing the old insulation cost extra?
Yes, and it should be a separate line on the quote rather than folded into the foam price. Removal has its own labour, bagging, and disposal cost, and it goes up when the material is wet or rodent contaminated, because containment and cleanup get more involved. We quote removal separately so you can see what you are paying for each part of the job.
Is open-cell always the cheaper choice?
Per board foot, yes, roughly $0.50 to $0.70 against $1.00 to $2.00 for closed-cell. Per completed assembly, not always. Open-cell delivers less R-value per inch, so hitting the same performance takes more inches, which takes more board feet. In a shallow cavity you may not have the depth to get there at all. And in a damp crawl space, open-cell is the wrong product at any price.
How can I check whether a quote I already have is reasonable?
Ask for the square footage, the thickness, and the product for each area. Multiply square feet by inches to get board feet, then divide the quoted price by the board feet. If the result is far below about $1.00 for closed-cell, ask what product is actually going in and at what thickness, because something has to give. If it is far above $2.00, ask what about the access or the prep is driving it. A contractor who will not show you those three inputs is the real warning sign.
Do you charge for the estimate?
No. We come out, get into the crawl space or attic, measure the actual surfaces, and give you a written number with the board feet shown. There is no fee, no obligation, and no expiring discount attached to it. If the honest answer is that you need air sealing rather than foam, or nothing at all this year, that is what the estimate will say.