Where spray foam earns its price in a southern Maine house, how open-cell and closed-cell differ under Efficiency Maine's rules, what the fire protection is for, and how long the household stays out while it cures.
Spray foam is the most expensive way to insulate most of a house and the best way to insulate a few parts of it. The parts are the ones blown fiber cannot seal: the rim joist and sill where the house sits on the foundation, a basement wall, a sloped ceiling with no attic above it, and the odd closed bays of an old Cape.
In a heating climate like this one, with 6,795 heating degree days a year at the Portland Jetport, those spots matter because they are where cold air gets in. This page covers where foam fits, the open-cell and closed-cell choice, the fire protection the code expects, the cure and re-entry question, and how Efficiency Maine treats foamed zones.
Efficiency Maine's description of a leaky house is cold air coming in low, warming up, and leaving through the upper floor and the attic. The low end of that loop is the framing that rests on the foundation: the sill and the rim joist. It is full of seams, nails and wire holes, and a batt pushed into it does nothing about the air. Foam sprayed against it seals and insulates in one pass, and Efficiency Maine's basement requirements name the sill and band joist as part of the wall to be insulated.
The other places foam earns its cost:
On an open attic floor, blown cellulose or fiberglass usually does the same work for less. The attic page covers that case.
The two foams are sold for different jobs, and Efficiency Maine's Weatherization Requirements Checklist shows the difference in the thickness it accepts for each:
| Where | Closed-cell foam | Open-cell foam |
|---|---|---|
| Every surface of an attic | 5 inches or more | Not listed for this use |
| Attic cavities later closed in | Within 1.5 inches of full depth | Full depth of the cavity |
| Wall cavities | 2 inches or more | Filled to capacity |
| Foundation walls | 2 inches or more | Not listed |
| Floor cavities over a basement | 2 inches or more | 2 inches or more |
In practice closed-cell goes where a thin layer has to do a lot, such as a rim joist or the inside face of a foundation, and open-cell goes where there is room to fill a cavity full. That follows from the program's own thickness rules above.
Ask any installer which product they are spraying, its thickness, and the R-value they are building to, and expect all three in writing.
Spray foam is a plastic, and the residential code Maine enforces, the 2021 International Residential Code, has its own rules for foam plastic insulation. Efficiency Maine puts the practical version in its checklist for rebated jobs: code-approved fire protection has to be added over foam installed as part of the work.
The checklist has a second fire row that applies to every material, foam included: anything flammable put in during the upgrade has to be kept away from chimneys, flue pipes and recessed lights that are not rated for contact with insulation, with non-flammable material between them. That is why a chimney chase is sealed with metal and high-temperature sealant rather than foam.
What that means for your job: in a basement used for storage or a finished room, exposed foam on the walls usually gets a covering, and the type depends on the product and where it is. Ask how the foam will be protected before the job is priced, because the covering is part of the cost. Your town's code office can tell you what it will look for.
EPA's guidance on spray polyurethane foam is plain about the installation itself: only workers wearing the right protective equipment should be present, and the household and other trades should be out. Re-entry should wait until the foam has finished curing and the building has been ventilated and cleaned.
How long that takes is the part EPA will not put a single number on, because it depends on the product. It reports that some manufacturers recommend 24 hours after application for the two-part, high-pressure foam professionals spray, and that one-part foam from a can is estimated to take about 8 to 24 hours to cure. It asks people to get specific re-entry guidance from the contractor before the work, and to think about children and anyone with asthma.
Efficiency Maine builds the same step into its checklist: the customer has to be told about the foam's off-gassing and occupancy limits. On a basement job that can mean a day out of the house; plan pets and a place to sleep before the date is set, not the morning of.
Foam on a foundation wall seals out air, but it does not stop water coming through the wall. Efficiency Maine wants damp handled ahead of air sealing or alongside it, and on a rebated job the installer must flag bare earth or standing water anywhere outside the sump pit before the spraying begins.
On a stone, block or poured wall that weeps in spring, the order is water first: gutters and grading outside, drainage or a sump inside, and then insulation. Foam sprayed over a wall that is still wet hides the problem rather than fixing it.
Radon is the other basement question. Under the 2021 codes every new one- or two-family house in Maine gets a radon mitigation system, the state's code office says, and a rebated job needs either a working radon system already in place or a recommendation to test. Sealing a basement changes how air moves through the house, so a test before and after is worth the small cost. The basement page goes further.
We publish no per-square-foot price, because foam jobs vary more than any other insulation work: thickness, product, access, how much prep the surface needs and whether a covering goes over it all move the number. You get the measured area, the thickness, the product and the fire protection on one line-itemed proposal.
Efficiency Maine does not pay by material. It pays by zone, so foam on the foundation walls counts toward the basement zone, and foam in a sloped ceiling toward the attic zone, at the same amounts as any other insulation. For a zone of 500 square feet or more that is $2,000 for any household, rising to $3,000 for a verified moderate-income one and $4,000 for a low-income one; the program's registered vendors do the work, and the table applies from October 1, 2026. Each zone also has a ceiling on what it may start with: R-5 for a wall or a basement.
A foam job over $3,000 needs a written contract under Maine's Home Construction Contracts Act, with no more than one-third down.
Not everywhere. On an open attic floor, blown cellulose or fiberglass usually reaches the same R-value for less. Foam is worth it where air has to be stopped and the space is tight: rim joists, sills, foundation walls, sloped ceilings and knee-wall bays.
EPA's advice is to be out while it is sprayed and to come back only once curing is finished and the house has been ventilated and cleaned. It notes that some makers of the high-pressure foam installers use suggest a full day; get your product's figure in writing first.
Usually, yes. The residential code has rules for foam plastic, and Efficiency Maine requires code-approved fire protection over foam installed in a rebated job. The right covering depends on the product and how the space is used.
No. It pays per zone, not per material: a basement done in foam earns what one done in rigid board earns, so long as the zone began no better than R-5 and the job follows its checklist.
Not until the water is handled. Foam over a weeping wall hides the problem rather than solving it, so drainage, grading and gutters come first, and the foam goes on once the wall stays dry.
Spray foam insulation across greater Portland and southern Maine, from the Casco Bay islands to the York County coast and the Sebago Lake towns. Each city has its own page with the permit rule and code edition that apply there:
Sources: Closed-cell and open-cell thicknesses, fire protection, occupancy notice, flammable separation · Cold air enters low and leaves through the attic · Moisture before air sealing; high-temperature sealing materials · Vacating during installation, re-entry times · Radon systems in new one- and two-family homes · Per-zone rebates and conditions · Rebate table for upgrades completed on or after 10/1/2026 · Home construction contracts over $3,000 · Portland Jetport heating degree days. Codes, programs and prices change; confirm the current rule with your city before you rely on it.
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