What are the differences between open-cell vs. closed-cell Spray Polyurethane Foam (SPF) insulation?

There are two general categories of SPF insulation materials; open-cell, low-density (a.k.a. ‘half-pound foam’) and closed-cell, medium-density (a.k.a. ‘two-pound foam’). Both foam categories provide excellent insulation and air sealing. Although both are made using almost identical chemical reactions, there are some inherent physical property differences that often determine which product is chosen for a particular project.

Open-cell spray foam (ocSPF) has an open cell structure where the cells are filled with air. The open-cell structure renders soft, flexible foam, with a density of about 0.5-0.8 pounds per cubic foot (pcf). Still air is the primary insulation medium in ocSPF, fiberglass and cellulose. These insulations work by reducing the natural air movement within these materials thereby reducing the ability of the material to conduct heat. The R-value per inch of open-cell foam typically ranges from R3.6 to R4.5 per inch. Unlike fiberglass and cellulose, the fine cell structure of ocSPF makes it air-impermeable at certain thicknesses. The air-impermeability of ocSPF qualifies it as an air-barrier material, dramatically reducing air leakage through the building envelope, significantly lowering the building’s heating and cooling costs. ocSPF, like fiberglass and cellulose insulations, is moisture-permeable, and may require the installation of a vapor retarder in colder climates.

Closed-cell spray foam (ccSPF) has a closed cell structure which yields a rigid, hard foam, with a density of 1.8-2.3 pound per cubic foot (pcf), and has been demonstrated to provide structural enhancement in certain framed buildings. These smaller cells trap an insulating gas, called a blowing agent. This blowing agent has a lower thermal conductivity than still air, and increases the R-value. Typical R-value per inch of closed-cell foam ranges from R5.8 to R6.9* per inch, making it a great choice in applications where clearance is limited. Like ocSPF, ccSPF is also air impermeable at certain thicknesses and and can qualify as an air-barrier material. The closed-cell structure of ccSPF makes it water-resistant, and is the only spray foam that can be used where contact with water is likely (e.g., below-grade concrete walls, in contact with the ground, or on exterior side of the building envelope). At a thickness of 1.5 inches, ccSPF has a moisture permeance typically less than1.0 perms and no additional vapor retarder is required for most applications.

What does R-value really mean?

R-value is the measure of resistance a material has to heat flow. The higher the Rvalue, the greater the resistance. Resisting heat flow is the primary purpose of insulation which in turn lowers energy costs.

Should access to the work area be restricted during and immediately after spray foam installation?

During and immediately following spray foam applications, fumes and mists are generated that can be hazardous to your health. Access to the work area during this time should be restricted to personnel wearing appropriate personal protective equipment (PPE), including respirators, and whose job responsibilities require them to be in the area.

How soon can buildings be re-occupied after SPF installation?

The application of SPF can produce hazardous levels of airborne chemicals during and just after installation. These chemicals, most notably MDI, will degrade into nonhazardous compounds in a few hours when combined with moisture in the air. Because of these short-term airborne levels, re-occupancy of the work area by other trades or building occupants is typically 24 hours. However, specific re-occupancy time may vary depending on type of material, volume of mists and fumes generated, building size and rate of ventilation.

Is SPF more expensive than traditional fibrous insulation? Will using it drive up the price of a building?

When only the initial costs are taken into consideration, SPF is more expensive than traditional insulation products. However, when the energy savings and the reduction in other building component costs (e.g., heating, ventilation and air conditioning (HVAC) equipment) are considered, SPF is a worthwhile investment. Various studies have shown home or building owners recover their initial costs within 1 to 5 years.

Stabilized Cellulose vs. Conventional Fiberglass. Aren’t all insulations the same?

No, absolutely not. The R-value listed on insulation products is a standard that comes from laboratory testing. Real world tests demonstrate just how vastly superior Stabilized Cellulose Insulation is in comparison to conventional fiberglass.

Is cellulose insulation fire resistant?

Thermospray’s cellulose provides up to 50% more fire resistance than fiberglass –
working so well that in some jurisdictions it’s actually approved as fireblock. Our unique liquid-injected fire retardants penetrate deep into cellulose fibers for added safety and very low dust.

I don’t want to use cellulose in my attics and walls because it will settle, is this true?

It will settle in attics until it reaches a stable density, as will other types of blown
insulation. Coverage charts have already taken this into account, so it’s nothing to worry about. In Sidewalls, Thermospray insulation will not settle when properly installed.

What is Cellulose insulation made from?

Our cellulose insulation consists of at least 85% post-consumer paper fiber. It also contains additives for fire resistance, and has been treated with boric acid for protection from pest infestation and moisture. What it doesn’t contain is also important: There’s no formaldehyde, asbestos or fibers from textiles, fiberglass or mineral wool.

Should I remove the old insulation on the attic floor when insulating the roof deck with spray foam in an existing home?

Yes, there are 3 reasons, in increasing order of importance.

  1. To prevent moisture problems. If you leave the insulation on the attic floor after insulating the roofline, the attic will be cooler in the winter than if you remove the insulation. The air in the attic is connected to the air in the house. That means it’s more humid than outdoor air and more humid than vented attic air.
  2. To get a better air seal. A properly done spray foam job not only insulates but also greatly reduces the air leakage of a home. But that only works if the installer can get it into the places where most of the air leakage happens. In an attic, the eaves are one of the most critical places to get good coverage with the foam. If you leave the existing insulation in the attic, it interferes with the foam installation.
  3. To reduce odors and improve indoor air quality. The old insulation is full of dust, debris, leaves used by that mouse that had a nest up there, rat poop, bat guano, the remains of a dead squirrel, or remnants of rat poison that someone put up there ten years ago to kill that squirrel. These are just a few things that we find in attics. When the attic was vented to the outdoors, all that nasty stuff wasn’t so connected with the living space in your home. By encapsulating the attic and leaving the old insulation up there, that filth is in your conditioned space. You may have odor problems. Your indoor air quality may get worse.

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