Closed-Cell Spray Foam Insulation in Maine
R-6 to R-7 per inch, an air and moisture barrier in one pass, and it makes walls stronger. The premium option for Maine weather.
How Closed-Cell Spray Foam Insulation Works
Closed-cell spray foam is a two-part liquid insulation that we spray with a heated hose and a mixing nozzle. The moment the two components meet on your wall or roof deck, the foam expands to about 30 times its liquid volume, fills every crack and cavity, and cures into a rigid cellular plastic. It is not a batt that gets cut around an electrical box — it grows around the box, the wire penetrations, the baseboards, and the spot where the wall meets the window frame. Those are exactly the gaps traditional insulation always misses.
R-value is where closed cell earns its price: generally R-6 to R-7 per inch, varying slightly by manufacturer. Two to three inches in a wall assembly gets you R-13 to R-20 while also sealing air movement, and four to five inches in a roof assembly is typical. Because the cured foam is rigid, it also stiffens the assembly — on walls, ceilings, and floors it acts as an air and moisture barrier solution that windproofs the building in a single application.
The chemistry is a job-site discipline. Before we spray we check that the surface is at least 40°F and under 18% moisture content — before every job and at the start of every day. We shave any excess flush so the site is ready for the next phase of construction, and we leave it broom clean. That is stated in the contract, not just promised.
Where Closed-Cell Foam Makes Sense in a Maine Home
Some parts of a house punish insulation, and closed cell is the right answer there. Rim joists and sill plates, where the house sits on the foundation, take cold wind straight off the ground — a couple of inches of closed cell seals and insulates them in one pass. Foundation walls and crawlspace walls benefit from as little as two inches because the foam is hydrophobic and does not care about ground moisture. Rooms over garages, cathedral ceilings, and low-slope rooflines where there is not much cavity depth get full R-value from limited thickness.
It is also what we spray on metal buildings, post-frame barns, and workshops across Maine, where batts sag and collect condensation against steel. Closed cell is non-corrosive — neutral, neither acidic nor alkaline — so it is ideal for metal construction. And for camps and cottages that are being upgraded from three-season to year-round, closed cell is usually the difference between a space that is merely warmer and one that is actually comfortable in February.
New construction and siding-off renovations are the cleanest applications, since we can see and spray every cavity before it is covered. But closed cell is not only for new builds. Retrofits happen all the time — rim joists, crawlspaces, and accessible rooflines are all sprayable in an existing home without opening walls.
Why Heat and Moisture Escape a Typical Maine Home
Warm air is constantly trying to leave your house, and it leaves through the cracks you cannot see. Heated indoor air rises and escapes high in the house, which pulls cold outside air in low through the basement and rim joist. Fiberglass and cellulose slow heat passing through the center of a wall, but they do almost nothing to stop that air movement — air moves right through them, carrying your heat and the moisture riding along with it.
That moisture is the quiet destroyer. When warm, humid indoor air reaches a cold surface inside a wall or a cold piece of roof sheathing, water condenses there. Over a Maine winter, that is wet insulation, stained sheetrock, mold food, and rot — in a cavity you will never see until the damage is done. In the attic it is worse: heat leaking up the Roof melts snow, meltwater refreezes at the eave, and you get the ice dams that back water under shingles.
Closed cell attacks both problems at once because it is an air barrier and a moisture barrier in the same layer. Air does not move through it, so moisture does not move through it either. UN-conditioned air cannot seep in from the outside carrying moisture, spores, pollen, or other pollution, and you get to actually control your indoor air quality — possibly for the first time in the life of the house.
What Affects the Cost of Closed-Cell Spray Foam
Spray foam is sold by the board foot, and the math is simple: one board foot is one square foot of coverage one inch thick. If you spray three inches thick you have 3 board feet per square foot. Five inches thick is 5 board feet per square foot, and so on. Price per board foot varies with the amount to be sprayed, the location, and the degree of difficulty, so we quote each job individually.
Figuring your own rough number works like this. Take the total square footage of the walls, ceilings, or other areas to be insulated, subtract the square footage of the doors and windows, multiply what is left by the thickness of insulation you want, and multiply that total board footage by the price per board foot. Call us for current pricing — the number moves with the market and we would rather give you a real quote than a ballpark that goes stale.
A few honest warnings. Closed cell costs more up front than fiberglass — that is real, and anyone telling you otherwise is selling something. What you are buying is double the R-value per inch, a structure that seals itself, and lower energy costs day after day for the life of the building. Also know that if you are outside our home base we still come to you — we provide statewide service with a minimum charge that depends on your location, so a job in far Down East or the county carries a little more to get us there.
Closed-Cell vs. Open-Cell Spray Foam
Both are spray foams and both seal air, but they are different tools. Closed cell is dense and rigid, runs R-6 to R-7 per inch, and refuses water — it is hydrophobic, so it does not absorb moisture and it doubles as a vapor barrier. It also adds structural strength to whatever it is sprayed on. Open cell is softer and lighter, runs roughly R-3.4 to R-3.9 per inch, fills cavities with less material cost per board foot, and absorbs sound better than almost anything you can put in a wall.
The practical answer for most Maine projects: choose closed cell anywhere water, soil gas, or structural value is in play — rim joists, foundation and crawlspace walls, metal buildings, thinner cavities where you need maximum R-value in minimum depth — and anywhere you want the vapor barrier built in. Choose open cell when you have full-depth wall or roof cavities, want sound control, and are watching the budget on a large square-footage job.
It is not either-or for the whole house, either. Plenty of our jobs are closed cell at the rim joist and crawlspace with open cell up in the walls or roof deck, each material where it does its best work. Tell us the building and the budget, and we will tell you straight where each belongs.
Ready to Talk About Closed-Cell Spray Foam Insulation?
Call 207-223-6332 or fill out the form — the owner reads every request personally, calls you back, and quotes the job upfront.
207-223-6332Other Services We Offer
Open-Cell Spray Foam Insulation
Costs less per board foot, fills wall and roof cavities completely, and quiets a house down. The smart choice for framing with full cavity depth.
Learn More →Attic & Rim-Joist Air Sealing
Stop the cold at the two places Maine houses actually leak — the rim joist and the attic. The highest comfort-per-dollar job in the house.
Learn More →Closed-Cell Spray Foam Insulation FAQs
What is the R-value of closed-cell spray foam per inch?
Generally R-6 to R-7 per inch, varying slightly with the manufacturer. Two inches in a wall is around R-13, and three inches is around R-19 to R-21 — and that is before you count the air sealing, which adds real-world performance no R-value printed on a batt can match.
Is closed-cell spray foam waterproof?
It is hydrophobic — it does not absorb water. The classic demonstration: weight a chunk of closed cell foam down in a bucket of water for weeks and it floats to the top when you remove the weight, dry. Since it does not retain water, it gives bacteria and fungal growth nothing to live on.
Does closed-cell spray foam need a thermal barrier?
Like fiberglass, spray foam will not sustain flame once you remove the flame source, but it will be consumed by fire — so building codes require a thermal barrier in occupied spaces, typically sheetrock. Where sheetrock is not suitable, we paint the foam with a thermal barrier paint approved by the Maine State Fire Marshal.
How thick should closed-cell spray foam be?
It depends on the application. Most wall assemblies run two to three inches, roof assemblies four to five, and rock foundations or crawlspaces get real benefit at as little as two. We size the thickness to the assembly during the free estimate, so you get the performance you need without paying for inches that do nothing.
How long does closed-cell spray foam last?
Indefinitely, in practical terms. Once the foam reaction is complete you are left with an inert, cellular plastic — it never sags, shrinks, or settles. It is non-corrosive to metals, tested with no electrical wiring overheating concerns, and it does not change physically over time. You install it once.
Book Your Closed-Cell Spray Foam Insulation Today
Call 207-223-6332 or send us a message. Free quotes, upfront pricing, and owner-operated spray foam service across Maine.