Damp-sprayed Cellulose: Insulation Improvements for Multifamily and Light Commercial Projects

Wednesday, August 6th, 2008

Cellulose insulation has been used for more than 50 years in residential housing stock, multi-family projects, and light commercial structures. It is a high-density and dust-free material and can be installed via dry or wet applications. In the case of the former, a fill tube is inserted into a cavity and blown-in, dense-pack cellulose is compactly spread by pneumatic means. Upon completion, the holes in the walls are covered.

What was once known as the ‘wet’ spray application process is now more properly called a ‘damp’ spray process. Equipment improvements have more than halved the original moisture content, dropping it to the current 20 to 30 percent. Insulation is applied through nozzles on spray machines, and pump pressure controls the fiber-to-water ratios. This technique is far superior to its wet ancestor because the cellulose adheres more easily to surfaces, takes less time to apply, and minimizes the amount of drying necessary before drywalling. The wait time previously required for wall preparation has been virtually eliminated. Damp-spraying must be performed by certified contractors with specialized equipment. No other activity can be performed on the floor while cellulose is being applied, necessitating careful scheduling by the project manager. Though the required extra time and expertise raises well-considered questions about the complications of cellulose application, a close look at material properties and performance illustrates the benefits of using this product.

Understanding Cellulose

A comprehensive body of federal, government, and private procurement specifications and standards cover cellulose insulation and its processes. Consequently, the material has been exposed to myriad construction, environmental, and various other code requirements defining its physical properties. Particularly pertinent is 16 Code of Federal Regulations (CFR) Part 1209, a Consumer Product Safety Commission (CPSC) standard that covers:

settled density
corrosiveness
critical radiant flux (a measure of surface burning)
smoldering combustion

It is illegal to market cellulose insulation that does not conform to this section of the CFR.

Also important is 16 CFR Part 460, perhaps better known as the Federal Trade Commission’s (FTC’s) R-value Rule on Labeling and Advertising of Home Insulation. This legislation is intended to eliminate dishonest or misleading marketing claims about insulation, ensuring the publication of accurate R-value and coverage data.

Other critical standards include:

ASTM International C 739, Standard Specification for Wood-base Cellulose Fiber for Loose-fill Cellulose Insulation
ASTM C 1149, Standard Specification for Self-supported Spray-applied Cellulosic Thermal Insulation
Federal HH-1-515E (i.e. General Services Administration [GSA] purchasing specification for loose-fill cellulose insulation; it requires ASTM C 739 conformance and stipulates insulation assemblies of no less than 42 Pa [0.88 psf])

Cellulose can be efficiently applied into wall cavities as a low-moisture spray application at a minimum 52 kg/m³ (3.25 pcf), which limits the material’s settling. One setup involves a double-hopper blower arrangement, with one hopper blowing dry insulation and the other recovering overspray, recycling spent cellulose for continuous application.¹

All pipes, ducts, wiring, and outlets should be in place prior to spraying, which occurs before drywall installation. After spraying, the cellulose is trimmed with a stud scrubber for a uniform surface flush with stud facings. The insulation material must be allowed to dry for 24 to 48 hours (depending on climate conditions) until it attains a papier mâché quality, ensuring its impermeability and thermal barrier attributes.

For remodeling work, the dry application method is recommended-since walls are already drywalled, drilling holes is appropriate. The damp-sprayed technique, however, is more applicable to new or ‘gut rehab’ work in which walls are open. As stated, all electrical and plumbing work should be installed first so as not to disturb any sprayed insulation. Due to the limited water content in damp spray and cellulose insulation’s hygroscopic nature (i.e. it allows moisture to slowly diffuse through without accumulation), the possibility of metal fittings corroding is not an issue.

The application is made with stabilized cellulose material that incorporates adhesive for bonding and contains a total borate fire retardant derived from borax. The material carries the U.S. Environmental Protection Agency (EPA) designation, ‘Board Defense,’ as a product repelling rodents and insects, and protecting against the growth of fungi. Due to cellulose’s hygroscopic property, borate will not leach out in concentrated quantities that could pose hazardous conditions. (Borate is not a carcinogenic material; in fact, it is found naturally in some salt lakes and alkaline soils.) When properly treated, cellulose can be considered environmentally neutral; it emits neither formaldehyde nor any other indoor pollutant.

Conventional stabilized (or ‘refined’) cellulose products commonly have settled densities of 24 to 27 kg/m³ (1.5 to 1.7 pcf), with some types as low as 21 kg/m³ (1.3 pcf). This material achieves a particularly good seal-38 percent tighter than fiberglass, according to a 1990 study by the University of Colorado at Denver.² The Cellulose Industry Manufacturers Association (CIMA) claims this tight building envelope does not deteriorate with time, which is consistent with CEC’s own observations in the field.

A very important point to consider when specifying damp-sprayed cellulose is the use or non-use of vapor retarders. As mentioned, the insulation’s hygroscopic properties cause moisture to slowly diffuse through the material without accumulations or water damage, unlike other traditional products that lack moisture storage capacity. CEC has never felt the need for a vapor retarder, a position supported by the insulation manufacturer/supplier. However, it is important to note no claims are being made with regard to the use or non-use of vapor retarders in other areas of the country-the design team should consult its manufacturer/supplier and/or a building science consultant.

R-Values

If properly installed by trained workers, an R-value of about 3.8 per 25.4 mm (1 in.) is achieved with damp-sprayed cellulose. (There is no need for constant monitoring of the installation process.) While this is usually adequate in itself, cellulose’s thermal characteristics are not being truly represented. CIMA argues R-value is a laboratory standard that does not take into account all the criteria adding up to real, in-the-field thermal performance-most notably, how a material blocks air infiltration. Damp-sprayed cellulose does not settle; it flows almost like a liquid to form a uniform blanket throughout the wall cavity. According to the American Society of Heating, Refrigerating, and Air-conditioning Engineers’ (ASHRAE’s) Handbook of Fundamentals, a four percent void in wall insulation increases heat loss by 15 percent. Further, since cellulose insulation is 51 to 76 mm (2 to 3 in.) thinner than fiberglass with the same R-value, more insulation can be packed into the available space, creating a superior thermal barrier not taken into account by the R-value system. For example, the University of Colorado’s School of Architecture and Planning compared the installed performance of fiberglass and cellulose on two ‘model’ buildings.³These buildings were identical in every regard except for their installation. One was insulated with 140 mm (5.5 in.) of wet-spray cellulose in the walls (and loose-fill cellulose in the ceiling), while the other was insulated with R-19 fiberglass batts (and R-30 in the ceiling).

The test revealed the wet-spray building consumed 26.4 percent less energy than its fiberglass counterpart over a three-week period, attributable to cellulose’s success at stopping air flow. An overnight heat loss test found the cellulose building was about 4 C (7 F) warmer than its competitor after nine hours.

Fire Resistance & Sustainability

Although cellulose is manufactured from recycled paper, it is still fire-retardant after a borate chemical treatment. According to a 1994 National Research Council of Canada Institute for Research in Construction (NRC-IRC) study, “Results of Fire Resistance Tests on Small-scale Insulated and Non-insulated Gypsum Board-protected Wall Assemblies,” chemically treated cellulose increases a building’s fire resistance by 22 to 55 percent in comparison to traditional fiberglass, as explained in the enclosed single-sheet marketing document. Further, the high density of damp-sprayed cellulose ensures the material stays in place to smother fire and hot gases.

In 2002, CIMA sponsored testing by Omega Point Laboratories on the firestopping abilities of spray-applied cellulose insulation on small-scale wood stud wall sections. The studies showed the material was so fire-resistant it was safe to install electrical boxes on the opposite sides of walls if they are separated by at least 89 mm (3.5 in.) of cellulose insulation.⁴ The International Code Council’s (ICC’s) I-Codes accept this, while stipulating the separation must be at least 610 mm (24 in.) for fiberglass insulation.

Specifically, CIMA reports “glass, mineral, and cellulose fiber insulations produced an increase in the fire resistance performance of 44 percent, 64 percent, and 104 percent.” CIMA also reported NRC-IRC found “the lowest failure point for a fiberglass-insulated floor/ceiling assembly was 64 minutes; the lowest failure point for an assembly insulated with cellulose was 92 minutes.⁵

Cellulose is a sustainable material produced locally from recycled waste that would otherwise continue flowing to landfills. Every 45.4 kg (100 lb) of cellulose insulation contains 36 to 38.5 kg (80 to 85 lb) of recycled newsprint, according to CIMA, as included in its second “Consumer Update Insulation Effectiveness Bulletin.”

Further, the production of cellulose is environmentally responsible because of the low embodied energy. The insulation is made by electrically driven mills-rather than gas-fired furnaces-that process recycled wood fibers and shut down easily when product quotas are met, instead of operating around-the-clock.

Damp-Sprayed Cellulose & Masonry

A great deal of construction activity across the country involves rehabilitating older buildings, often converting them to cooperative and condominium complexes. Damp-sprayed cellulose can play a part in these so-called ‘gut rehabs,’ provided that walls are dry and waterproofed and exposed bricks are in sturdy shape. Past concerns regarding damp-spray’s relation to brick porosity and moisture have been eliminated with the development of modern damp-sprayed installation technology, especially when applied to gut rehab of high-rise buildings, where insulation is best applied between the exterior wall and cladding.

For example, CEC is heavily involved with City of New York projects to rehabilitate old housing stock. Under a mandate of the city’s Department of Housing Preservation and Development (HPD) and with funding by the New York State Energy Research and Development Authority (NYSERDA), the technology was used in 202 apartments in 18 buildings designed and specified for damp-sprayed cellulose for the walls and blown-in dry material for roof insulation.⁶This pilot demonstration was primarily undertaken because of speculation as to whether the product would work with high-rise masonry structures that feature metal stud construction. Special consideration was given to all potential scenarios in regards to both moisture and mold issues, and the cellulose’s fireproofing qualities was the focus of one building. The buildings are now occupied and have reported no insulation-related problems.

Notes

¹ See Technical Bulletin #2, “Standard practice for installing cellulose building insulation,” offered by the Cellulose Industry Manufacturers Association.

² See Soontorn Boonyartikarn and Scott R. Spiezle’s “Fiber Glass vs. Cellulose Installed Performance,” University of Colorado Graduate School of Architecture, 1990.

³ See note 2.

⁴ Omega Point’s Project No. 16094-11638 (Aug. 28, 2002) has since been written up in a CIMA consumer bulletin, “Straight Talk About Building Insulation and Fire.”

⁵ See Special Report #1, “The Burning Question: the truth about cellulose insulation & fire,” offered by CIMA.

⁶ In 2001, NYSERDA contracted CEC to perform technical assistance services for HPD, providing the department with specifications that have since been made standard requirements for all its gut rehab projects. A current version can be seen at www.nyc.gov/html/architects/energy.shtml, under ‘architects/engineers energy efficient specifications.’

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