Saturn Home Energy Saving Blog
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Information and Opinion about Home Energy for Buildings
Welcome to the Saturn Home Energy Saving Blog. We hope you find our posts useful and entertaining. Our goal is to mix valuable energy saving information with our opinions. We value your opinions too, so please please comment! These are some of the main topics for this blog.
- Energy auditing and energy retrofit.
- Heating, cooling and ventilation.
- Home Insulation and air-sealing.
- Energy policy and energy programs.
- Energy training and certification.
- Technical communication.
We have more specific and less opinionated energy-saving information in our Energy Saving Tips.
Latest Blog Posts
Humid Climates and the Danger of CondensationI estimate that there are at least 100 cities and towns on the eastern seaboard, Gulf Coast, and coastal Pacific Northwest that have average annual relative humidities between 78% and 82%. We should suggest caution in installing cellulose wall insulation in these areas. Various laboratory studies report cellulose insulation EMCs of up to 140% water by weight at RHs of up to 95%. At 80% average Rh, aged OSB has 30% moisture content and wood has around 17%, according to research. I would estimate that cellulose insulation has 30% to 60% moisture content under these same conditions. That means that dense-packed cellulose at 4 pounds per cubic foot actually weighs 5.2 to 6.4 pounds per cubic foot including the water and water vapor.
Mechanisms of WettingI agree that cellulose insulation won't get wet during most normal conditions. However buildings last a long time and there's ample opportunity for unusual humidity and temperature conditions that could cause the cellulose insulation to become wet and suffer permanent damage. No designer or computer software can control the outdoor relative humidity. If outdoor RH remains high for a long time, the building materials absorb moisture. The whole building absorbs moisture depending on the relative humidity, temperature, and rainfall. Many building designers focus only on controlling indoor relative humidity and minimizing airflow between the indoors and outdoors. Air leakage through the wall isn't the only way that the wall can absorb moisture. High outdoor relative humidity will absolutely affect the EMC of cellulose insulation.
Possible Wetting Conditions
- Consider a wet fall where snow or heavy rain has saturated the ground. October is very humid and rain has dampened the cladding. The sun pushes the moisture through the cladding into the cellulose. Then the temperature drops below freezing saturating the cellulose insulation with condensation and even ice.
- And then there's fog. Consider relative humidity of between 75% and 100% with millions of water droplets per cubic foot. Consider a ventilated roof cavity insulated with cellulose insulation. The ventilating foggy air could be 90% RH with fog that deposits water droplets in the cool roof cavity.
- Or consider a damp location. Ketchikan Alaska has over 100 inches of rainfall and a very high relative humidity. Mold grows on Tyvek during construction and most builders use plywood instead of the more vulnerable OSB for sheathing. Builders in Ketchikan know better than to use cellulose insulation.
Old and new water barriersOnce upon a time, builders stapled 15-pound asphalt felt to wall and roof structural sheathing as a water-resistive barrier (WRB). The 2012 International Residential Code (IRC) still specifies: “one layer of No. 15 felt… or other approved water-resistive barrier.” Most builders used perforated felt to allow water vapor to escape the wall cavity years age. [caption id="attachment_5333" align="alignright" width="300"] Poor installation and mold on house wrap.[/caption] Then came house wrap, various types of vapor-transmitting spun-bond or perforated plastic sheeting that hopefully also shed water. These WRB products became the building assembly’s last resort to prevent wetting of wood sheathing. Somehow, house wrap got the reputation of also being the building’s air barrier. As a material, most house wraps are air barriers, however as installed they leak air at joints and fasteners.
Canadian air-barrier researchInvestigators Lawson, Quirouette, and McDonald from Morrison Hersfield Limited, working for the Canada Mortgage Housing Corporation (CMHC), reported that house wrap fails as an air barrier some time after construction in windy areas unless sandwiched between two layers of fiberboard. In their experiments they had to use fiberboard to protect the house wrap from failing from air pressure due to wind, building mechanical systems, and stack effect. This air barrier research, conducted in the early 1990s, should have squelched the hope that house wraps could function as air barriers when stapled and taped to the surface of structural sheathing. Even if the house wrap was perfect air barrier when workers applied the cladding, high winds and other pressures can pull the house wrap through its staples and separate its seams. A few times, I’ve heard house wrap rustling and squealing behind the cladding of a wall during high winds here in Montana, particularly during construction before drywall application. House wrap, as well as any other flexible material that isn’t continuously bonded to the structural sheathing, won’t last the life of a building as an air barrier in most buildings. [caption id="attachment_5334" align="alignright" width="204"] WRB bonded to sheathing by the manufacturer.[/caption]
Air barrier, water barrier, or both?Nevertheless builders and others remain confused about the function of house wrap. Many people refer to house wrap as the air barrier. First and foremost house wrap is the building’s code-required WRB. We assume it is watertight.. Joe Lstiburek and others have done empirical tests, finding that most WRB products are watertight but that some aren’t. In year-2000 empirical testing by Paul Fisette at UMass Amherst, he observed leakage through the perforated house wraps and at nail penetrations in all house wraps. In very humid climates, house wrap may grow black mold while waiting for its cladding. Many in wet climates still use 15-pound felt, which is no longer 15 pounds per hundred square feet and no longer as waterproof as used to be. If we want to material to be the air barrier along with the WRB, we need to use a liquid applied system, or a factory bonded WRB-to-sheathing system (such as: ZIP sheathing) along with joint sealing and penetration sealing for permanent air-barrier solution. And also, let’s make sure that the house wrap or other WRB really does shed water and that the joints and fasteners don't leak.
Why not to install cellulose insulation in deep wall cavities[caption id="attachment_5312" align="alignright" width="300"] Slumped cellulose in a deep wall cavity in Vermont.[/caption] Cellulose shrinks, slumps, and dries very slowly after wetting. Deep wall cavities are have more risk because the outdoor side of the wall is colder than shallower cavities. Voids left by the shrinking and slumping insulation create more room for humid air in the wall cavity. A vapor retarder can't ensure that cellulose wall insulation won't get wet. Of course, fiberglass and rock wool insulation also get wet. However they don't adsorb much water vapor. When the water vapor condenses in rock wool or fiberglass insulation, the water falls out by gravity, leaving the insulation undamaged. However, mold can grow in fiberglass batts, but hardly ever in cellulose, in my experience.
What is hygric buffering?My first exposure to hygric buffering was reading research papers that discussed the possibility that hygric buffering could control indoor relative humidity. These papers hypothesized that hygric buffering could substitute for some of the electricity-consuming dehumidification provided by mechanical ventilation or dehumidifiers. Builders eliminated vapor barrier in the ceilings of some buildings here in Montana 30 years ago to substitute for ventilation. That hygric buffering didn't work so well. Cellulose attic insulation got wet, shrunk, and hardened throughout these attics. Many building professionals still believe that cellulose insulation provides humidity control and condensation protection. Hygric buffering adsorbs and distributes moisture, they claim, protecting both the cellulose insulation and building materials around it from condensation. Although I believe this can happen, I also believe that cellulose will get wet at a particular and unknown equilibrium moisture content (EMC).
WUFI and hygric buffering[caption id="attachment_5314" align="alignright" width="196"] Vapor diffusion: small compared to air leakage, but not negligible.[/caption] WUFI is a software program distributed by the Fraunhofer Institute in Germany. Passive House builders swear by WUFI nd seem to think that WUFI analysis has miraculous powers to protect buildings from condensation. When I ask questions about cellulose insulation and the possibility of wetting, the WUFI users assure me that WUFI proves it won't happen. Realistically, WUFI can't stop cellulose from getting wet. High-performance builders and building scientists do mention wetting and drying in walls. However, they don't often acknowledge that wetting damages cellulose insulation. Almost all of the research on wall wetting focuses on the wall sheathing and not the insulation.
Air leakage & water-vapor diffusionJoe Lstiburek created a famous illustration showing that air leakage is usually a more important factor in wall moisture compared to vapor diffusion. That illustration made many building professionals think that vapor diffusion was a negligible factor. Joe didn't mean that. Maybe WUFI now perpetuates that belief that water-vapor diffusion is a negligible factor in wetting. Can someone answer the following questions about hygric buffering with reference to cellulose insulation?
- What is the benefit of hygric buffering?
- Is hygric buffering an important design consideration?
- How do we achieve optimal hygric buffering without condensation?
- Are the benefits of hygric buffering why builders choose cellulose insulation for walls?
Introducing 29 New RESNET CEU CoursesAttention raters, rater trainers, and RESNET training organizations: Saturn Resource Management now offers 29 new short courses that qualify for RESNET CEUs. These short e-learning courses mix media such as slides, slide narrations, videos, illustrated text, exercises, and quizzes. Our e-learning lessons contain between 15 and 25 slides. We narrate each slide with between one minute and three minutes of scripted instruction. A lesson might also contain a couple of short videos. A multiple-choice quiz follows each short course. The average short course requires 1.7 hours of student effort and counts as 1.7 RESNET CEUs.
Benefit from Online LearningContinuing education can be expensive and time-consuming. But you don't have to travel to collect your continuing education units (CEUs). There is a better way to learn: Saturn's eLearning short courses. Here are some advantages of eLearning over traditional classroom instruction.
- You study your lessons whenever you like on your computer, tablet or phone.
- You use marginally useful time to study and avoid the possible lost-opportunity cost of a scheduled seminar.
- You stop when you want and return to your place in the lesson later, regardless of which of your devices you're using.
- You don't need to travel, sleep in a motel, or eat in mediocre restaurants.
- You don't have to listen to your instructor's jokes and personal stories.
- You avoid eating awful seminar food.
- You don't feel inadequate because other students are showing off their knowledge.
- You pay a fraction of what a college or technical school would charge for continuing education.