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Building Science Information for Builders

A review of Jacob Deva Racusin’s book, Essential Building Science

Posted on Jan 13 2017 by Martin Holladay

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., is a builder who “gets it.” He is well versed in house-as-a-system thinking. Among the mentors he credits are 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: 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.

Technical errors

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.

Questionable advice

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.”

Click here to follow Martin Holladay on Twitter.

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Image Credits:

  1. New Society Publishers

Jan 16, 2017 12:11 AM ET

Response to Review
by Jacob Deva Racusin


Thank you for taking the time to publish a review of my book, I appreciate your consideration! I am responding to some of the critiques that you brought up.

It seems that you missed an important point I made in the first chapter regarding the concept of toxicity. In our green building community, toxicity frequently only extends as far as indoor air quality (IAQ) and direct risk exposure to occupants or builders - a myopic perspective. I believe it is critical we acknowledge more openly the toxicity impacts of our materials prior to and post use in building situation. In critiquing my cautions concerning the toxicity of modern building materials – such as vinyl and foam, as you reference – you evaluate these solely in the context of occupant exposure. My references to toxicity are not only in regards to IAQ but in a more comprehensive, cradle-to-cradle impact perspective, as I explain in identifying criteria for evaluation - the toxicity is certainly there for others to experience. From your review, it sounds like straw bales were the only alternative I suggest – in fact, I reference many alternatives for less-toxic materials, such as fiberglass frames for windows, and fiberboard or mineral board for insulation, among others. I included references regarding nuances of different foam impact profiles for further exploration – including a breakdown of embodied carbon between different insulation materials.

The “optimization” reference in selecting U-values is an appropriate term – certainly as it relates to the occasional need to sacrifice a bit of U-value for the sake of enhanced SHGC or VT, let alone as it relates to cost. Of course lower U-value is better than higher, I state that clearly – but the “optimization” is in the context of evaluating different characteristics. Simply stating “lower U-value is better”, as you suggest, does a disservice to the point of balancing competing priorities in window performance and cost, which was the intention of that section.

To speak to some of the technical errors you cite, the resilience of all-electric heating systems is a relevant concern, and not an error to note. Leaving aside non-electric options such as wood stoves, there is a big difference between the small infrastructure required to provide backup power to the fan and ignition system of an oil boiler and that for two or three mini-split compressors. I took my radon recommendations from state and private radon remediation experts – your article is very interesting to note, and I’m glad my error was on the side of caution!

As for the “debate” around air-tightness – I trust that the rest of the page I devote to discussion of the issue to be accurate and appropriately presented (such as confirming that the majority of professionals agree with your position), and that you simply take issue with whether or not it is settled debate as “technical error”? I do regret some of the errors that slipped through editing, such as the term “vapor barrier” rather than “retarder” as I intended (and reaffirmed in thorough discussion of vapor control), and the Icynene misspelling and classification. I would hope that these errors would not seriously cast doubt in the readers’ ability to trust in the credibility of the book writ large, as you suggest, given the degree of rigor, reference, and accuracy that I have demonstrated throughout in the presentation of this complex subject matter.

Regarding the examples of different building systems, again it seems you missed a couple of important points. I start the conversation around wall assemblies stating clearly “….framed walls, which are the most common style in residential construction in North America.” There is no confusion about my intention here, the leading sentence for an entire section. I regret that this confused you to the extent that it did. All of the examples I used are sourced from a broad survey of both widespread and relevant emerging practices within our building community, many of which I referenced from this publication. As I describe in the introduction, the intention of these examples is to illustrate the function of the different parts of a building enclosure as described in the preceding chapters, including various hydrothermal dynamics of different strategies, to help develop critical thinking skills for builders to evaluate, select, and design their own systems.

This book is intended to be a concise guide, and not a comprehensive manual, as I state in the Introduction. The goals of this book are primarily to unpack the underlying building science of our homes, and to create a framework for decision-making to establish a strategy, based on stated goals. The intention was not to comprehensively evaluate building energy/energy efficiency. I do, in fact, discuss a range of cooling options, including heat pumps, night flushing, and ducted A/C (which are nested within the six pages of mechanical system evaluation you describe), as well as the vapor management implications of air conditioned buildings in hot-humid climates. Heating systems have more to discuss regarding combustion and fuel choice.

The same point is missed in your critique of the purpose of the selection tables, which is to provide information to help enable critical thinking to make decisions based on one’s own goals and values. Your choice to reject sheep’s wool and favor foam expresses your values, and I would consider myself presumptuous to impose my own set of priorities in this regard, particularly over a very wide climate range for the book’s audience. It is interesting that you call out two of the least common materials in your critique of the approach – do you find no value in contrasting advantages and disadvantages of spray foam and cellulose insulation? I appreciate that you don’t hold some of the more alternative materials as worthy of consideration and would prefer a more directive approach to use preferred systems or materials – to this end, I strongly recommend readers read your blog, and the many other resources that are regularly updated with market-specific, research-relevant information that I consistently list in my references. I fear you confuse the intention of the book in that regard, as this is meant to accompany, and not replace, these other resources.

You have done a terrific job of highlighting criticisms of the content, some appropriate (which I appreciate your bringing to light) and some I believe are taken out of context, or are simply inaccurate. I would have hoped to have seen more in the review that actually describes the contents of the book to the readers in more detail, as there are significant sections of the book that are entirely absent from the review; I greatly appreciate your recognition and support of the work of our company, and validation of the principles of the book in the first section. I beg the reader’s understanding for the handful of errors that may be present, and trust that there is far more to offer of value to the interested builder, designer, or homeowner for having used this book as a resource.

Jan 16, 2017 10:22 PM ET

Jacob, That was an
by Stephen DeMetrick

That was an excellent, respectable response to a book review that was basically a compliment sandwich from a reviewer that forgot that two slices of bread are required to make a sandwich.


Jan 17, 2017 10:16 PM ET

Thank you, Steve. If anyone
by Jacob Deva Racusin

Thank you, Steve. If anyone who has read this far would like a more complete description of the book's contents and approach, I would be happy to provide excerpts. In fact, mention this review, and I'll give you a discount ;)

Jan 18, 2017 2:40 PM ET

Edited Jan 18, 2017 2:44 PM ET.

Dubious about some fiberglass claims
by Derek Roff

I'm a fan of fiberglass reinforced window frames, and so I was embarrassed to read the almost content-free claims in the linked article, "Debunked: 3 Myths About Fiberglass Windows", which, among others, offers this curious assertion: "Even if additional coating is applied, ensuring that your finish materials were made with care and quality will guarantee an unfading and fresh look for your painted windows. As a result, the paint does not peel easily". No supporting evidence is offered for this logically-challenged statement, and the links in the other myth descriptions are very superficial.

Unlike Martin's experience, all the weather-exposed fiberglass ladders that I see in my sun-drenched region show some sun damage, and as do perhaps half of the fiberglass boats that I see. Fiberglass composite materials are not inherently UV resistant. The most common resins used in fiberglass products deteriorate in the sun, so manufacturers add various UV stabilizers. Some work better than others. I hope that all manufacturers of fiberglass window frames have formulations with sufficient UV protection. Jacob Deva Racusin expresses skepticism. I couldn't find any testing to confirm or deny my hope. Does reliable documentation exist, comparing long-term exposure for fiberglass windows from various manufacturers?

Jan 23, 2017 1:14 PM ET

Edited Jan 23, 2017 1:16 PM ET.

Response to Jacob Deva Racusin
by Martin Holladay

Thanks for providing an author's perspective. Interested GBA readers should, of course, read your book and judge for themselves whether my perspective reflects actual flaws in the book or my misunderstandings. (It should come as no surprise that authors and reviewers often have a different perspective.)

Concerning just one of the materials that your book calls "toxic" -- PVC, otherwise known as vinyl -- interested readers may want to read my article, “Vinyl Windows and Vinyl Siding.” Suffice it to say that many green building experts who have taken a life cycle analysis approach to the vinyl question have concluded (as did the USGBC) that “The evidence indicates that a credit that rewards avoidance of PVC could steer decision makers toward using materials that are worse on most environmental impacts, except for the case of resilient flooring, in which sheet vinyl and VCT are worse than the alternative materials studied for most environmental impacts.”

Jan 23, 2017 1:20 PM ET

Response to Derek Roff
by Martin Holladay

I'm willing to admit that I may not have chosen the best link to reinforce my point about the durability of pultruded fiberglass. That said, my own direct experience with fiberglass window frames, fiberglass ladders, and a fiberglass canoe are the direct opposite of yours. None of these objects show the slightest deterioration in spite of years of exposure to the weather.

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