Spray Foam Insulation in Williston, ND

Closed-cell foam is a dense, rigid two-part polyurethane that expands to roughly 30 times its liquid volume and cures hard. It runs about R-6 to R-7 per inch, so two inches on a rim joist delivers roughly R-12 to R-14 and three inches on a steel wall approaches R-20. It bonds to wood, concrete, and steel, and it adds stiffness to whatever it touches.

The property that matters most here is vapor behavior. At around two inches, closed-cell foam becomes a vapor retarder. In a Zone 7 winter, warm indoor air carries moisture outward through the wall toward the cold side. If that moisture reaches a surface that is below the dew point, it condenses. Closed-cell foam stops the air movement and slows the vapor before it gets there. That is why it is the right answer against concrete, against steel, and in any assembly that cannot be vented.

Closed-cell also does not absorb water. A crawl space wall that gets damp in spring, a rim joist that sees a little ice dam backup, or a shop floor edge that gets splashed will not hold moisture in the foam. For most of the work we do around Williston, closed-cell is the default.

Open-cell foam is a softer, lower-density foam that expands much more than closed-cell and cures spongy. It runs roughly R-3.5 to R-3.8 per inch, so it takes nearly twice the thickness to match closed-cell for R-value. It is an excellent air barrier and it is quieter to live with because it absorbs sound.

Open-cell is not a vapor retarder at any practical thickness. Moisture vapor passes through it. In a mild climate that is a feature, because the assembly can dry in both directions. In Climate Zone 7 it is a risk unless the assembly is designed for it. Open-cell sprayed directly against cold roof sheathing in a Williston winter can let vapor reach that sheathing and condense. If we use open-cell in a roof deck, it is paired with a separate interior vapor retarder or a layer of closed-cell on the cold side.

Where open-cell makes sense here: interior partition walls for sound, deep wall cavities in a conditioned space where a vapor retarder will be installed separately, and budget-driven attic floor work where the goal is air sealing and the thickness is available. We quote it when it fits. We do not push it because it is cheaper per inch.

Foam costs more per R than batts or blown-in. It pays for itself in the assemblies where nothing else works well.

Rim joists are first on the list. The band of framing where the floor system sits on the foundation is the leakiest part of almost every house in Williston built before the 2010s. Fiberglass stuffed in there does nothing against air movement. Two inches of closed-cell seals it and insulates it in one pass.

Crawl spaces come next. A vented crawl with batts hanging from the floor joists gives you cold floors and damp insulation. Closed-cell on the foundation walls and rim, with a ground vapor barrier, turns it into a conditioned space.

Metal buildings and shops have steel skin on steel purlins. Fiberglass blanket against steel gets wet from condensation and sags. Closed-cell sprayed direct to the metal stops the condensation because the steel never sees interior air.

Cathedral ceilings and unvented roof decks have no room for R-60 of loose fill and no way to vent properly. Closed-cell against the underside of the sheathing makes the assembly work.

Heated shops and garages with a concrete stem wall and a wood or steel wall above are a hybrid. Foam at the stem wall, the sill, and the rim, then batts or blanket above, is often the right mix.

• Rim joists and sill plates on any house with a basement or crawl
• Crawl space walls and encapsulation
• Steel shops, pole barns, and oilfield service buildings
• Cathedral ceilings and unvented roof assemblies
• Bonus rooms over garages and knee walls
• Heated garages and shop additions

Prep comes first and takes longer than most people expect. We clear the work area, remove any old fiberglass that would trap moisture behind the foam, and vacuum out debris. Electrical boxes, windows, floor drains, and anything that must stay clean gets masked with plastic and tape. In a house, we isolate the work area from the living space.

Spray passes are done in lifts. Closed-cell is applied in layers of roughly one to two inches and allowed to set between passes. Spraying too thick in one lift traps heat from the reaction and can shrink or crack. We build to the specified thickness and check it with a depth gauge, not by eye.

Cure and ventilation matter. The foam is tack-free within minutes, but it continues to off-gas as it cures. We run ventilation during the spray and for a period after, and we ask the homeowner to stay out of the sprayed area during that window. We will give you the re-entry timing for the product we used.

Trimming is the last step. Any foam that expanded past the face of the framing gets cut flush so drywall or sheathing can go on. On a rim joist or a shop wall that stays exposed, we leave the surface as sprayed unless a thermal barrier or ignition barrier is required by code, in which case we talk through the coating or covering options before we start.

Williams County builds under IECC Climate Zone 7. The 2021 IECC residential minimums call for R-60 in the ceiling, R-20 cavity plus R-5 continuous in above-grade walls, R-15 on basement walls, and R-10 at the crawl space wall or slab edge.

Spray foam meets these numbers differently than batts. Closed-cell in a 2x6 wall at three inches delivers roughly R-18 to R-21 in the cavity with the rest of the bay left for wiring or filled with batt (the flash-and-batt approach). The continuous R-5 still has to come from foam board or another layer outside the framing, because foam in the cavity is interrupted by every stud.

Rim joists and basement walls are where foam most directly satisfies the code. Two to three inches of closed-cell on a basement wall hits R-15 and acts as the vapor retarder in one material. Code also requires a thermal barrier (typically half-inch drywall) between foam and living space, or an approved ignition barrier in crawl spaces and attics. We build those requirements into the quote so there is no surprise at inspection.

On new construction, we coordinate with the builder and the inspector on blower door targets, which foam makes much easier to hit. MDU serves gas and electric in Williston; ask about current utility rebate programs when you plan a project.

We quote foam by the assembly, not by a flat rate, because the same square footage can be an easy job or a hard one. The factors that move the number are listed below. Send a quote request with the building type, the surfaces you want sprayed, and a few photos, and we will come out and measure.

• Square footage of surface to be sprayed
• Thickness in inches, which sets how much material goes on the wall
• Closed-cell versus open-cell (closed-cell costs more per inch but needs fewer inches)
• Access: a rim joist you can stand at versus one behind ductwork, or a roof deck that needs a lift
• Whether old insulation has to be removed and hauled first
• Whether the building is heated, which affects cure conditions in winter
• Thermal or ignition barrier coatings where code requires them