Building Science Information for Builders
Building Science Information for Builders
A review of Jacob Deva Racusin’s book, Essential Building Science
Jacob Deva Racusin, a Vermont builder and educator, has just written a book called Essential Building Science. The book aims to provide builders — especially so-called “natural builders” — with a basic understanding of the ways that heat and moisture flows affect residential buildings. (The book is available from New Society Publishers for $34.95.)
Racusin is one of three partners who founded a company in Burlington, Vermont, called New Frameworks Natural Building. Racusin, a member of the Northeast Sustainable Energy Association (NESEANorth East Sustainable Energy Association. A regional membership organization promoting sustainable energy solutions. NESEA is committed to advancing three core elements: sustainable solutions, proven results and cutting-edge development in the field. States included in this region stretch from Maine to Maryland. www.nesea.org), is a builder who “gets it.” He is well versed in house-as-a-system thinking. Among the mentors he credits are GBAGreenBuildingAdvisor.com contributors John Straube and Marc Rosenbaum.
Racusin’s construction company takes an admirable approach to air sealing — an approach that more builders should emulate. In his book, he writes, “We use the blower door frequently during the building process. During new construction, we use the tool at least once, if not multiple times, to make sure we are on target with our air-sealing goals; this allows us to correct the installation of all of the various materials and components prior to finishing.”
Racusin has posted at least one comment on the GBA site, and he’s familiar with the Pretty Good House idea. In fact, a table in his book listing residential standards and certification programs includes a line for the “pretty good house.”
Racusin's book aims to accomplish two goals. His first goal is to introduce building science concepts to builders. Racusin describes the various ways that heat and moisture flow into and out of a building: for example, he explains the stack effectAlso referred to as the chimney effect, this is one of three primary forces that drives air leakage in buildings. When warm air is in a column (such as a building), its buoyancy pulls colder air in low in buildings as the buoyant air exerts pressure to escape out the top. The pressure of stack effect is proportional to the height of the column of air and the temperature difference between the air in the column and ambient air. Stack effect is much stronger in cold climates during the heating season than in hot climates during the cooling season. and discusses vapor permeance. After these introductory chapters, Racusin focuses on his second goal: providing advice on building assemblies (foundations, walls, and roofs), mechanical ventilation systems, and heating systems.
The book is an important introduction to topics that residential builders need to understand. If every builder in North America followed the principles outlined in Racusin’s book, the quality of newly built homes would increase dramatically.
Unfortunately, though, Racusin’s book has several flaws, so it’s hard to recommend the book without stating a few important reservations.
Worries over toxins
Racusin often praises older homes. When discussing homes built in North America over the last two hundred years, he writes, “Homes built of solid wood (i.e., logs, planks) and earth were very durable and quite comfortable.” Well, maybe — depending on your definition of “comfortable.”
Here’s another example: “In the days before insulation was common, our old buildings in cold climates did not have condensation problems — despite the fact that they were incredibly drafty.” Really? Then how should we describe the water dribbling down the single-pane windows of my youth?
In contrast, Racusin sometimes disparages more recently built homes. For example, he refers to “the preponderance of newly constructed homes with terrible indoor air quality.” (Needless to say, Racusin doesn't disparage all recently built homes. He favors highly insulated, relatively tight homes built with mostly natural materials.)
Racusin spends a lot of time worrying about toxins. Is he worried about the lead paint and asbestosMineral fiber once commonly used in many building materials, including insulation, fireproof siding, and resilient flooring. Inhalation of invisible asbestos fibers can lead to chest and abdominal cancers as well as scarring of the lungs. The use of asbestos in some products has been banned by the EPA and the U.S. Consumer Products Safety Commission; manufacturers also have adopted voluntary limitations on its use. When found in older buildings (most commonly in floor tiles, pipe and furnace insulation, or asbestos shingles), the product's friability is a major determinant in how it must be handled during renovations. More information: http://www.epa.gov/iaq/asbestos.html that contaminated the homes I grew up in (and that still contaminate millions of American homes)? No — for Racusin, modern homes without any lead paint or asbestos are apparently more worrisome. He’s worried about vinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate). windows and homes insulated with EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest..
In fact, he flags EPS and polyisocyanurate for “high toxicity.” He recommends avoiding vinyl windows, because “PVC [used for window frames] is a particularly toxic plastic…”
What’s the solution? The book recommends straw bales: “Straw bales provide good thermal insulation as part of a plastered assembly, while helping sequester carbon and reduce toxicity in the home compared to other insulation choices.”
Racusin fails to mention research showing that vinyl windows and EPS have no role in low indoor air quality. Far more worrisome than vinyl windows and EPS are the gases given off by cooking food.
An unsophisticated approach
Racusin’s description of rigid foam and vinyl windows as “toxic,” along with his decision to ignore toxins (like lead and asbestos) that are known to threaten the health of homeowners, is highly problematic. Racusin hasn’t backed up his “toxic” label with any evidence. Meanwhile, readers are left with vague worries and unanswered questions: Will a home insulated with rigid foam injure the health of the occupants? Will these windows poison my children?
Although Racusin’s book has “science” in its title, his discussion of toxins isn’t particularly scientific. His vocabulary is sloppy; consider, for example, his use of the word “chemicals” in this discussion of insulation. “Mineral board (also known as mineral wool…) is often used as a replacement for foam,” Racusin writes. “Made from spun blast furnace slag, these boards … contain far fewer chemicals [than foam insulation]…”
Some of Racusin’s statements, while technically defensible, are misleading. He wrote, “Plastic foams have a high global warming potential and are the source of ecologically persistent toxins.” This broad-brush statement fails to note the significant differences between polyisocyanurate (which is relatively benign) and XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation. (which is manufactured with a blowing agent that has a high global warming potential). Nor does Racusin explain that some types of rigid foam, properly specified, will, by saving energy, reduce enough CO2 emissions during the lifetime of the insulation to more than make up for the CO2 emissions associated with the manufacture of the rigid foam.
Of course, such a discussion would require Racusin to distinguish between rigid foam that is properly specified and rigid foam that isn't. (Examples of bad specifications include very thick layers of rigid foam and the use of XPS when EPS or polyiso would work.) It would also require a much clearer distinction than Racusin provides between CO2 emissions associated with the manufacture of rigid foam and the damage to the atmosphere caused by blowing agents with a high global warming potential.
Instead of such a discussion, all we get are broad-brush condemnations focusing on the word "toxic."
Racusin’s writing can be unclear
In his section on windows, Racusin writes, “Optimizing U-value [of windows] is worthwhile in any climate…” But choosing the U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. of a window isn’t really a matter of “optimization” — a process that involves trade-offs. Rather, it’s simple: the lower the U-factor, the better. There isn’t any “optimization” involved.
Near the end of the book, Racusin introduces the abbreviation “MEP” without explanation. Engineers involved with commercial projects probably know that MEP stands for “mechanical, electrical, and plumbing,” but for residential builders, the abbreviation is confusing if not explained.
A few muddled passages are excusable. More troublesome are the book’s technical errors:
- Racusin writes that ductless heat pumps and electric resistance heaters are “potentially less resilient in the face of storms or power disruptions, depending on grid reliability, unless backup power provisions are made…” Less resilient than what? Almost all central heating systems, including gas-fired furnaces and boilers, stop working during power outages.
- Racusin writes that exhaust-only ventilationMechanical ventilation system in which one or more fans are used to exhaust air from a house and make-up air is supplied passively. Exhaust-only ventilation creates slight depressurization of the home; its impact on vented gas appliances should be considered. systems “can increase risk of pollutant infiltration (such as … radon…).” Moreover, the book includes a table that explains that exhaust-only ventilation systems are “especially problematic for buildings with radon…” These statements aren’t true. (For more information, see Exhaust-Only Ventilation Systems and Radon.)
- For some applications, Racusin recommends “open-cell spray foam with a vapor barrier paint.” There are two problems with this statement: (a) there is no such thing as vapor barrier paint — only vapor retarder paint; (b) when applied to open-cell spray foam, vapor retarder paint won’t retard vapor transfer, because the surface of the foam is too porous for the paint to work.
- Racusin writes, “This is a very important thing to understand: R-values are dynamic [emphasis in original], constantly changing in response to different conditions.” That’s not true. While the thermal performance of a layer of insulation can change with temperature, its R-value is fixed. In fact, this attribute of R-value — its fixedness — is enshrined by a federal law called the R-value Rule.
- Racusin writes that when pultruded fiberglass is used for window frames, it is “susceptible to UV damage if not protected/treated.” As anyone who has left a pultruded fiberglass stepladder or a fiberglass canoe exposed to the weather knows, this isn’t true. For more information on this issue, see “Debunked: 3 Myths About Fiberglass Windows.”
- Racusin writes, “Fiberglass [has] … moderate toxicity (formaldehydeChemical found in many building products; most binders used for manufactured wood products are formaldehyde compounds. Reclassified by the United Nations International Agency for Research on Cancer (IARC) in 2004 as a “known human carcinogen." in some products…).” This information is out of date. As I noted in my article, All About Indoor Air Quality, manufacturers of fiberglass batts in North America no longer use formaldehyde binders.
- In a table in Racusin’s book, “Icyenene” — yes, the book spells the word with an extra “E” — is described as “Formaldehyde foam” with “high toxicity.” In fact, IcyneneOpen-cell, low-density spray foam insulation that can be used in wall, floor, and roof assemblies. It has an R-value of about 3.6 per inch and a vapor permeability of about 10 perms at 5 inches thick. is not manufactured with formaldehyde, nor does it contain any formaldehyde.
- In a discussion of envelope air leakage rates, Racusin writes, “How tight is too tight? This is a matter of great debate.” In fact, there is no debate over this issue. A house can’t be too tight.
The trouble with these technical errors is that they undermine readers’ faith in the author’s authority.
OK, so Racusin got a few facts wrong. How is his advice?
This illustration by Dale Brownson comes from Racusin's book. The legend for the circled number 3 reads, "Band-joist insulation (i.e., cellulose, batt, spray foam)." While spray foam would work here, rigid foam is usually a better choice from a green building perspective. Cellulose or batts in this location can lead to moisture accumulation in the rim joist, especially in cold climates.
It’s uneven. Although Racusin has a cold-climate perspective, his top two insulation recommendations for rim joist insulation are cellulose or “batt.” When used to insulate the interior of a basement rim joist, however, these air-permeable insulations can lead to moisture accumulation or rot. The third suggested insulation type in his list is spray foam. For some reason, he doesn’t suggest my number-one choice for insulating rim joists: rigid foam.
Mysteriously, Racusin writes that an “insulated stud wall with exterior vapor-permeable insulation [mineral wool]” is the “most standard style of residential construction in North America; inexpensive to build.” This is a head-scratcher. In fact, walls with exterior mineral wool are quite rare. At first I thought that he was referring to just one aspect of the wall — the fact that such a wall assembly includes a 2x4 or 2x6 stud wall as part of the assembly — but that theory was undermined by the evidence that other wall examples in his book that similarly include a 2x4 or 2x6 stud wall aren’t called the “most standard style of residential construction in North America.”
An illustration of a roof with insulation on the exterior side of the roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. recommends the use of “vapor-permeable rigid insulation (i.e., mineral board) to allow outward drying of the assembly into the vent space above.” Well, this will probably work, but it’s a fairly experimental approach. Few builders have tried it.
An illustration of an unvented cathedral ceiling show rigid foam on the exterior side of the roof sheathing, and “cavity insulation” between the rafters; the description calls for “rigid board insulation” above the roof sheathing. So far, so good. The problem is that Racusin doesn’t provide any guidance concerning the minimum R-value of the rigid foam layer. He fails to note that if the rigid foam doesn’t keep the roof sheathing above the dew point during the winter, the sheathing can accumulate moisture.
Benefits? What benefits?
Racusin praises the benefits of interior thermal massHeavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night. and insulation materials that can absorb and store moisture. For example, he notes that one of the disadvantages of interior basement insulation is that the “Thermal mass benefits of masonry wall are lost.”
According to Racusin, a disadvantage of blown-in fiberglass insulation is that “Loose fiberglass does not offer the same hygroscopic benefits as cellulose.”
In the past, I accepted the ideas that there were some benefits to interior thermal mass and moisture storage in insulation. After I looked into the issues in detail, however, I didn’t find many benefits. (For more information on these topics, see these two articles: All About Thermal Mass and Hygric Buffering and Hygric Redistribution.)
What the book needs
Racusin’s book assumes that homes don’t need air conditioners. The book has six pages on mechanical systems — without once mentioning the need for cooling equipment.
This book includes lots of tables: for example, a table for different types of batt insulationInsulation, usually of fiberglass or mineral wool and often faced with paper, typically installed between studs in walls and between joists in ceiling cavities. Correct installation is crucial to performance. ; one for spray-applied insulations; and one for cavity-fill insulations. It also includes tables with lists of different types of foundations and wall assemblies. Most of these tables provide lists of advantages and disadvantages for each item in the table.
For builders, these tables don’t add up to much. The reader is left with the impression that most of these listed alternatives are similar — each with a grab-bag of advantages and disadvantages. The result isn’t clarity; it’s clutter and confusion. For example, how many builders really need to consider whether hemp insulation or sheep’s wool insulation makes sense for their next house?
Builders would be better served by simple advice, given straight, without any discussion of rarely used materials. While Racusin studiously avoids any mention of brand names, builders I know are always asking each other: “What brand did you use? Why?” If you’re a builder with that kind of question, Racusin can’t help.
Martin Holladay’s previous blog: “Windwashing in Exterior Mineral Wool.”
- New Society Publishers
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