Attic Insulation Services | Pacific Northwest Spray Foam LLC

There are two common ways to insulate your attic space and enhance your home's energy efficiency by protecting it from weather-related moisture damage using spray foam insulation.

Building Science (The Traditional Way)

Attic Floor Spray Foam Insulation Application (Through a Vented Attic)

Building science and design principles that your builder or architect subscribes to often dictate the method of spray foam used in the attic. Insulation applied on the attic floor serves to insulate the ceiling from seasonal temperature fluctuations in a traditional vented attic setting. Between the floor joists, where cellulose and fiberglass insulation is typically used, spray foam is also utilized. However, no insulation is applied to the rest of the attic, which remains highly vented through soffit, ridge, and gable vents. While this may not be the most effective system, it is the most commonly engineered system found throughout the U.S.

In contrast, many professionals in the spray foam insulation industry consider a different method to be more effective, as it effectively seals and insulates the entire attic space, preventing air infiltration. The air barrier is created by applying foam directly between the joists, on the gable wall ends, and around the rim and soffits of the roof's underside.

The traditional practice of insulating under the roof in the attic has raised significant debate within the building industry because standard roofing and design techniques call for attic ventilation to prevent moisture problems and minimize heat buildup during hot summer months.

However, inside a vented attic, temperatures can soar to approximately 130 degrees in the summer, forcing air-conditioning and ductwork to operate in severe conditions. Furthermore, there's a chance for moisture to accumulate due to condensation on these appliances.

To effectively insulate the attic space from the scorching heat that radiates through the roof, sheathing, and shingles, spray foam insulation needs to be applied directly to the underside of the roof deck. This method provides the attic with insulation that blocks out extreme temperatures, making it as comfortable as any other room in the house, as it becomes a “conditioned” space.

Critics argue that this application can cause roof shingles to overheat and curl. According to designers and builders, this occurs because wood requires ventilation to “breathe.”

However, the “breathing wood” issue is largely overstated. Extensive research has shown that most furniture manufacturers kiln-dry wood before use. They claim that wood can deteriorate faster if left to “breathe,” as kiln-dried wood contains minimal moisture and is used in all furniture. Over time, this moisture can generate cracks and splits. Manufacturers take great care to ensure that wood is properly sealed. Conversely, if properly finished and maintained, wood would not experience these issues, which further supports the rationale behind painting our fences and homes. Consider the wood fence you installed a few years ago that is now falling apart because it was left to deteriorate—did “breathing wood” really turn out to be the better option?

GAF Building Products, one of the leading shingle manufacturers, asserts that they have no issues with unvented roof decks and the performance of their shingles. To this, we might ask: “Are curling shingles really that concerning?”

Spray foam insulation contributes to energy efficiency in several ways, particularly when applied on a roof. It can significantly eliminate energy loss from ducts in the attic, and with reduced infiltration and exfiltration, excess moisture is kept out of the attic, resulting in a much tighter top of the building. Furthermore, spray foam minimizes infiltration through the ceiling, thus enhancing overall energy efficiency by maintaining a lower attic temperature.

During summer months, standard ceiling insulation helps mitigate heat transfer from the attic to the living space, where temperatures can reach 140F. Heat enters the attic through a multi-step process, starting with the shingles and sheathing absorbing solar energy, followed by convection and conduction from the hot sheathing.

Applying spray foam insulation to the roof surface can result in an approximate 40F reduction in the temperature responsible for this heat transfer. This is because heat transfer through convection and conduction is directly proportional to temperature differences.

Including the attic in the insulated space can yield multiple benefits:

- The reduction of heat gain/loss from ducts and the likelihood of duct leakage.

- Sealing the roof against air infiltration is generally more effective than sealing the ceiling.

- The living space remains free of loose insulation and dust.

- A sealed attic leads to lower energy costs, as shown in various tests.