Wood Insulation Guide - Pros, Cons, and Cost

What Companies Make Wood Insulation?

Several brands make insulation from wood fibers. These include Gutex, SONOclimat, and STEICO. These products' applications include above-grade walls, cathedral ceilings, open attic spaces, dry finished basements, and floors. All three of the above manufacturers also make other wood fiber insulating products, including loose fiber for blow-in applications, external thermal insulation composite systems, rigid wood fiberboards, grooved systems for in-floor heating, and tongue-and-groove roofing installations.

What Are The Pros of Wood Insulation?

Wood insulation has the same benefits that wood has always had: it is safe, natural, high performing, and renewable. Each of the above products is made from wood harvested from sustainable forests and is recyclable. STEICO reports that because their wood fiber products are manufactured without artificial additives. They "are easily recycled or may even be composted to provide a valuable soil conditioner." Moreover, wood is a natural carbon sink: i.e., forests store more carbon dioxide than they release into the atmosphere. STEICO calculated that the insulation used to insulate an average single-family home binds "as much CO2 as a small car emits over 50,000km."

Good Thermal Insulation

Wood batt insulation is also an excellent thermal insulator. It has a high capacity to absorb and release moisture, is easy to install, and may even have soundproofing benefits. Let's look at each of these in turn.

An excellent thermal insulator resists the conductive flow of heat, keeping interior spaces warm in winter and cool in summer. The R-value measures the resistance to heat flow through a given thickness of the material, with a higher R-value indicating greater thermal resistance and better insulating properties. The R-value per inch of Gutex Thermoflex is 4.0. By contrast, the R-value per inch of fiberglass batt insulation ranges from 2.9-3.8, and cotton batting is about 3.5.

Moisture Control

The topic of moisture control in insulation is a complicated one. It starts with an understanding of dewpoint, which refers to the conditions under which condensation (the change of water vapor to water) occurs. Practically speaking, water vapor is most likely to condense when the home's internal temperature and humidity are high, and the outside weather is freezing. If a home is not adequately insulated, this condensation can occur on any surface and make that surface wet. Specifically, when moist (indoor) air passes through an interior wall and then batt insulation, its temperature drops as it gets closer to the cold outside air. If dewpoint is reached, water vapor will condense to water in the wall itself, becoming an unseen breeding ground for mold.

When fiberglass batting gets wet, an additional negative is that the R-value falls. Sharing the "cotton is rotten" mantra of outdoor sports enthusiasts, reports are that cotton batt also has less than optimal moisture control. When wet, it gets heavy, packs down, and takes a long time to dry out.

By contrast, wood batt insulation has a natural "vapor-permeable" quality, which means that while water vapor can get in, it can just as easily get out. In a landmark paper, "Understanding Vapor Barriers," by the Building Science Corporation, author Joseph Stiburek tells us that the central principle of water vapor control is to keep it outside and let it exit if it gets in. GUTEX wood fiberboards can absorb up to fifteen percent of their weight in moisture without losing their insulation capacity. They say that later when the air is dry, the moisture diffuses out of the product. This ability for water to escape and pass through the assembly creates a safer, more resilient wall assembly that is much less susceptible to mold formation.

Easy and Safe Installation

Installing wood batt insulation is particularly easy due to its high density and friction. Wood batts don't need support and won't fall out or sag, and they can be cut to shape with a sharp blade without producing any irritating fibers.

In contrast, common hazards encountered when installing fiberglass insulation are skin, eye, and lung irritation; OSHA requires a cancer warning on all fiberglass products. Complaints about installing cotton batt insulation include ill-sizing of the pieces requiring compression into place, reducing R-value.

Soundproofing

Finally, while not rated for soundproofing, SONOclimat Eco4 boasts that its product has "impressive sound attenuation properties."

What Are The Cons of Wood Insulation?

Cost

The biggest "con" might be that wood batt insulation is not widely available and is more expensive than other batt insulation materials. Wood fiber insulation is often sold by the pallet, so you have to buy a large quantity. In contrast, you'll pay between $0.80 to $1.00/square foot for fiberglass and between $1.20 and $1.40/square foot for cotton and can buy these materials from a wide variety of retailers.

Availability

Another negative for the purchase of wood batt insulation is that it simply does not seem readily available, perhaps because of its newness. STEICO Flex Wood Fibre Insulation Batts are currently available from Ecomerchant in the UK. Gutex Thermoflex is available to ship but with significant lead times. In other cases, you'll need to contact the manufacturer directly and get a quote.