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This publication was developed and printed through support of the Alaska Housing Finance Corporation (AHFC). The opinions, findings, and conclusions expressed in this publication are those of the author(s) and not necessarily those held by AHFC.

The Alaska Building Science News is a joint publication of the Alaska Building Science Network and Cooperative Extension Service, Office of the Energy Specialist. It is edited by Richard D. Seifert. Any letters, opinions and responses to the articles should be directed to Seifert either by e-mail [email protected], phone (907) 474-7201, or fax at (907) 474-5139.

The purpose of Alaska Building Science News is to bring timely building science information to Alaskans in order to improve the quality and durability of the housing stock in Alaska as well as save energy and maintenance expenses for homeowners.

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Alaska Building Science News

A quarterly publication of the Alaska Building Science Network and Cooperative Extension Service

Spring 2011 Vol. 16, Issue 3

America’s Arctic UniversityThe University of Alaska Fairbanks Cooperative Extension Service programs are available to all, without regard to race, color, age, sex, creed, national origin, or disability and in accordance with all applicable federal laws. Provided in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Fred Schlutt, Director, Cooperative Extension Service, Uni-versity of Alaska Fairbanks. The University of Alaska Fairbanks is an affirmative action/equal opportunity employer and educational institution.

I N S I D E T H I S I S S U E

To Shovel or Not To Shovel .................3

Carbon Monoxide: A Silent Killer ........4

Safe & Effective Exterior Insulation Retrofits: Phase I .............................8

LET’S START A DIALOG ABOUT ALASKA’S FUTURE

by Rich Seifert

Things are changing and it is hard not to notice. The unravel-ing of political situations in the Middle East are only some of

the huge world events that will have an effect on Alaska as an oil resource and production state. The governor is asking to change the oil tax basis, which will affect our economic future. There is a proposal for the Susitna hydroelectric dam to be built in the rail belt; it will cost billions and deserves full discussion. There are several natural gas options vying for attention and investment from our businesses and the state. There is a history now and a few years experience with a very wonderful energy rebate and weatheriza-tion program, which can be exceptionally helpful in decreasing our vulnerability to fossil fuel price fluctuations. There is pressure to use the Strategic Petroleum Reserve mounting in the nation at the federal level. The trans-Alaska oil pipeline is nearing the end of its economic life, and the production of oil is declining along with the temperature of the crude oil in the line. And, of course, fossil fuel prices are going up, pres-suring life in all regions of Alaska and, perhaps, affect-ing food prices as well.

Continued next page

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A l a s k a B u i l d i n g S c i e n c e N e w s

Energy use and policy are at the center of all these issues, and that can only mean that energy use and demand are crucial factors determining our Alaska future. Right now Alaska has an envi-able position among all the states of the country. It has no budget deficit and very little debt, and, of course, it has the Alaska Permanent Fund. We are unique in this respect, and how we protect our po-sition is going to be a very important factor in the future. It is time we start to openly discuss this and inform our friends and neighbors about the reali-ties and opportunities that the future holds for us.

To give a powerful indication of just how nec-essary it is to begin this discussion, let me pose a hypothetical “What if?” What would happen, as was subtly threatened even this past winter, if we had to shut down the trans-Alaska oil pipeline for an emergency leak stoppage and couldn’t get it turned back on with oil flowing in a reasonable amount of time? A shutdown did actually occur this winter and fortunately the pipeline did start up again. But as production levels decline and the flow is slower and the oil thicker and colder, it could “sludge up” and be unable to flow as it

could when oil was flowing at peak and the tem-perature was somewhere around 160°F in the line. Oil flow is now one-third or less of the peak flow and the oil in the line is about 60°F — a BIG dif-ference! If such a stoppage occurred in midwinter and oil stopped flowing and coagulated to a thick, waxy sludge, it would be virtually impossible to get it flowing again, if ever. That would mean the end of oil production, and the impact of such an event would be huge.

It is also important to note that the pipeline will most likely shut down in the future (I can’t and won’t predict precisely when) due to simple depletion of the North Slope oil reserves some-time over the next 10 years. That is NOT a long time from now! The pipeline changed Alaska for-ever, and the end of the pipeline and oil revenue will again change Alaska forever. It is time to start thinking and talking about what this means and how we are going to manage a transition. Banking on luck or another “boom” from resource devel-opment is a huge gamble, one that we don’t need to take. We have other very promising options, and those we very much need to discuss.

Figure 1 is one of the latest charts on the history and predicted future of oil production on

Figure 1. Historic and predict-ed North Slope oil production (after Alaska Division of Oil and Gas, 2009). Everything to the left of the vertical line is historical production (fact) and everything to the right is prediction (an estimate).

Alaska’s Future, continued from page 1

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Alaska’s North Slope. Note that the peak of pro-duction occurred a long time ago, in 1988. It has declined to about one-third of that production rate since then and is due to decline further with time.

Figure 2 shows Cook Inlet gas production, past and future. It clearly demonstrates that production will be at about half the 2007 levels by 2014. This is hardly good news. After all, it is 2011!

These two graphic pieces of information are only part of what needs to be discussed, but they are perhaps two of the most pressing. It would serve us and our children well to begin to discuss these important factors and to build awareness of how they will affect our future. I welcome your interest and support in helping to bring us together to do just that.

Figure 2. A plot of Cook Inlet historical and projected gas production from 1958 through 2026.

TO SHOVEL OR NOT TO SHOVEL: SNOW ROOF LOADS IN ALASKA

by Rich Seifert

Recently, Fairbanks had the heaviest snowfall in more than 20 years, and heavy snowfall

always causes concern about the roof snow load as the snow gets deeper on the roofs. This is an important question and it is not well understood. Many people don’t know when snow load should be a cause for concern or if it is within the range of standard roof design loads.

First, let’s just clear the air about roof failures under snow loads. Most residential construction is very well designed for the average snowfall loads

in the communities in which we live. The uniform building code has, in the past, recommended that roofs be designed to handle a dead load of about 40 pounds per square foot. This is typical for most towns and cities in Alaska, but NOT ALL. Coastal communities such as Valdez may have snow de-sign loads of 100 pounds per square foot because very high precipitation in some years can lead to very deep snows and, thus, heavy snow loads. But generally roofs are capable of handling the local snow loads and they perform very well.

So, how much snow does it take to reach a snow load of 40 pounds per square foot? It’s hard to say exactly how many inches of snow that is because the snow density changes with time. The important thing to measure is the weight of the snow pack, which can be calculated in inches of water equivalent. It turns out that about 10 inches

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CARBON MONOXIDE: A SILENT KILLER

by Rich Seifert

You can’t see it. You can’t smell it. But you can be warned. This guide focuses on promoting

awareness of carbon monoxide poisoning. Since most cases of carbon monoxide (CO) poisoning occur in the home, most information is geared to-wards homeowners, renters and landlords. Even at low concentrations, CO can build up in the blood over time. Prolonged exposure to low levels of CO can be just as dangerous as short-term exposure to higher levels.

Carbon monoxide is the leading cause of poi-soning in the United States, and during the 1990s Alaska had the highest death rate from CO in the

of snow is typically equivalent to 1 inch of water content. However, since the snow compacts with time, it is necessary to take a cylindrical core sample to determine the weight of the snow on the roof.

Since the calculation is based on pounds per square feet, it is a simple matter of mathematics to determine how much weight there is on the square foot of roof by calculating how much a cubic foot of water weighs. A cubic foot of water weighs 62.4 pounds, so every inch of water (equivalent weight of snow) on a square foot of roof weighs about 5.2 pounds. It would take almost 8 inches of water equivalent on a roof to reach the standard roof design load of 40 pounds per square foot. (A little less than 8 inches is really the case since 5.2 pounds per inch times 8 inches of water equiva-lent means the snow would weigh 41.6 pounds.) A homeowner would be ensuring a safe roof load if he or she shoveled the roof when the load got to 40 pounds per square foot.

Of course, the problem here is determining just how much the snow weighs on your roof and what the weight is.

In the past, the Natural Resources Conser-vation Service (NRCS) of U.S. Department of Agriculture has measured the snow pack weight on a regular basis. If the snow has drifted and is irregularly distributed around your house or on your roof, then it is difficult to know how much is actually pressing in certain areas. On February 28, Ann Rippy at the NRCS in Fairbanks informed me that the snow weight had just been measured and they were confident from the measurements that there were only 18 pounds of snow on the ground — and probably the same amount on most sheltered roofs as well. So, we are still below the worry level for shoveling as March begins, and we have a way to go before concern for shoveling the snow off the roof is very high.

Of much greater concern are the roofs that don’t have adequate load capacity to hold up under serious snow loads. These include some greenhouse roof systems, the roofs of RVs and camper caps on stored trucks, and some boat cov-ers and sheds. If the roof of the building or vehicle

doesn’t have the requisite structural strength, you are always well advised to keep it cleared of heavy snow. Alaskans lose a lot of camper caps and sheds over the winter, not to mention some sunken boats on the coast.

If and when there is a danger for roofs, we will certainly attempt to make it known and publish the concerns in the papers. Most communities and newspapers are already aware of this issue and will follow up with information. Every year, to some degree, this comes up. But this year, with the heavy snow in the Interior and perhaps more to come, it’s good to keep snow load in mind and to inform everyone about when to watch the problem.

Again, to keep your calculations straight, 1 inch of water equivalent on the roof is 5.2 pounds. Make every effort to determine the water-equiva-lent snowpack weight on the roof and when it gets to 40 pounds, that’s a good time to start thinking about shoveling the roof off or removing the snow from the roof in some way that doesn’t hurt you or the roof.

If you’re in doubt, you can always call the Cooperative Extension Service at 474-7201 or 1-800-478-8324; we’ll try to help.

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country.1 Poisoning is the second leading cause of accidental death in the U.S. after motor ve-hicle crashes, making carbon monoxide the No. 1 source of preventable accidental death in the U.S.

Americans spend 90 percent of their time indoors, where CO poisoning is most likely. In urban areas, Alaska also has high outdoor winter CO concentrations that can increase the risk of poisoning. CO poisoning is especially dangerous in the home because that is where we sleep, so a problem may not be noticed until it’s too late. This guide will give you the tools you need to keep you and your family safe from the most common and insidious poison we encounter.

Recently a client related a story of a brush with carbon monoxide. The story she shared was a com-mon Alaska adventure gone wrong. The woman and her husband had driven to their weekend cab-in. Upon arriving late, they built a fire in the wood-stove and went to sleep. The husband woke up several hours later, dizzy with the worst headache he had ever had. Recognizing the symptoms of carbon monoxide poisoning, he woke up his wife and got her outdoors. Both were having severe symptoms of weakness and confusion. Alarmed at how ill they felt, they took turns driving back to Fairbanks and checked into the hospital.

Blood samples taken revealed high carboxy-hemoglobin blood levels. Both patients were put on oxygen and recovered. These two people were lucky to have awakened. The source of the carbon monoxide was an improperly drafting wood stove.Who is at risk?

Everyone is at risk, but some people are more sensitive. Pregnant women, infants, the elderly, smokers, and persons with heart and respiratory ailments or anemia are more susceptible. Smokers may have normal carboxyhemoglobin levels as high as 10 percent, making them more susceptible to poisoning. Most fatalities from CO are children. Since the blood absorption rate for CO increases with altitude, climbers and pilots are at a greater risks. CO detectors are sold at aviation stores and

1Paulozzi, L, MD et al. “Unintentional Poisoning Deaths--United States, 1999-2004.” J. Am. Med. Assn. 2007.

are commonly placed on airplane instrument pan-els. Individuals who work in enclosed areas, where CO-producing machinery is used, are at greater risk because ventilation may not be adequate and exercise increases the rate of poisoning.What is carbon monoxide and where does it come from?

Carbon monoxide is a colorless and odorless gas. Because we can’t see, smell or taste it, CO can affect you or your family before you even know it’s there. CO is classed as an inorganic compound and is deadly because the oxygen-carrying hemoglobin prefers CO 210 times more than oxygen. CO in the bloodstream causes loss of oxygen to the body but also results in subcellular damage, which is much more catastrophic than just being short on oxygen.

Carbon monoxide typically comes from in-complete combustion of carbon-based fuels. Since almost every combustion appliance in the home produces some CO, ventilation must be provided to both living areas and combustion equipment. Therefore, the most important action to take in preventing CO buildup is to properly maintain all fuel-burning appliances by making sure they are venting correctly. Get your boiler or furnace looked at every year, and clean your stove or other fuel-burning appliance regularly. Have your ser-vice technician operate your exhaust fan and dryer or other venting appliance while all of the heating appliances in the house are running to make sure no exhaust gases are being sucked out of the ap-pliance and into the living or working space. Use exhaust fans and range-hood vents when cooking with fossil fuels.

Attached garages are also a commonly seen source of CO in the home. The state of Alaska lists the following table of carbon-based, and thus potential CO-forming fuels.

Wood Stove Oil Natural GasCharcoal Waste Oil PropaneCoal Kerosene MethaneLPG & LNG (gas) Gasoline Diesel

TABLE 1. Fuels which can produce CO

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At work, the leading cause of CO poisoning is from generators. Be extremely careful that ex-haust is piped far away from work locations, and make sure that an exhaust catalyst is used when-ever possible.

In general, the higher the carbon content of a fuel, the hotter it must burn to avoid CO produc-tion. Charcoal and coal have high concentrations of carbon. Extreme care should be used when burning charcoal or coal. Dark smoke, creosote or particulate matter are indicative of incomplete combustion but do not necessarily mean that CO is present in the conditioned space, e.g., the living area.

Most fuel-burning appliances, if properly maintained, produce little CO. The small amount of CO produced by fuel-burning appliances is usu-ally vented to the outdoors. However, if anything results in decreased oxygen to the burn chamber or obstructs the chimney, such as a bird’s nest or clogged stovepipe, CO can back up into a house.

Propane ovens often cause CO problems. Whenever a propane stove or oven is used, the range hood exhaust fan should be on. Never block the air supply to a propane oven. CO is also pro-duced by generators, forklifts, etc. If these ma-chines are used in a poorly ventilated space, even outside, CO concentrations can get high enough to cause major injury or death.What are the symptoms?

Table 2 equates the concentration of CO in the air that the victim is breathing with the built-up levels of carboxyhemoglobin, or red blood cells that have attached to CO, and the physical symptoms that accompany this condition. If you suddenly feel lightheaded and nauseous and have a very bad headache, you should remove yourself from your surroundings immediately and contact a medical professional.Carbon monoxide and the law

Alaska Statute 18.70.095, which deals with both smoke detectors and carbon monoxide detec-tors, states, “... carbon monoxide detection devic-es shall be installed and maintained in all qualify-ing dwelling units in the state.” Any housing unit

with an attached garage or installed fuel-burning appliance is covered by this law.

The law requires that CO monitors “must have an alarm, and shall be installed and maintained ac-cording to the manufacturer’s recommendations.”

In the case of rentals, the landlord must supply the detector, and the tenant is obligated to main-tain the detector, test it regularly and not disable it. If someone dies or is injured in a rental where the landlord didn’t supply a working CO detector, it can be considered negligence and the landlord could be liable for punitive damages.Detectors

Unless you get your heat from a district heating system or electricity and don’t have an attached garage or gas cookstove, you should have a CO detector in your home. If you operate machinery at work and think you may be exposed to carbon monoxide, you should consider using a personal CO detector badge.

For the home, a detector with an alarm is a must. Since most CO poisonings occur while the occupants are sleeping, the detector should be loud enough to wake you. For the hearing im-paired, strobelight and bed-vibrating detectors are available. Contact your local hardware store, fire safety supplier or Cooperative Extension agent for more information on detector purchases.Features to look for in detectors

Detectors that use an electrochemical detection method are the current state of the art. We recom-mend purchasing an electrochemical-based detec-tor due to a number of safety-enhancing benefits. “CO Experts” and the KIDDE “Nighthawk” devic-es are considered good electrochemical detectors. A detector capable of displaying CO concentra-tions of under 10 ppm is valuable, since it can sig-nal a problem before it becomes life threatening. Often, a more expensive detector, such as those in the $100 to $150 range, are cheaper in the long run because the chemicals used in the detection pro-cess will last longer than a $25 detector.

Generally, there are three kinds of CO detec-tors available. There are battery-operated detec-tors, wire-in line voltage detectors and plug-in

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detectors. There are also smoke detector/CO detector units available. Since the combination units don’t work when the power is off and should be installed near the ceiling to detect smoke, these units should be used in conjunction with a battery-operated detector.Where do I put a CO detector?

Follow the manufacturer’s recommendations on where to put their detector. The following are general guidelines when more guidance is needed. CO mixes well with air, but is usually warmer than air, since it comes from combustion. Therefore, carbon monoxide often can be found around a ceil-ing. Because of the different situations in which CO can be found, detectors should be placed at breathing level. A detector should be present on every floor of a dwelling. When using a personal

CO detector, keep the detector as close to the head as possible, especially while lying or sitting.

To avoid damage to the unit and to reduce false alarms, do NOT install CO detectors:

y in unheated basements, attics or garages y in areas of high humidity y where they will be exposed to chemical sol-

vents or cleaners, including hair spray, deodor-ant sprays, etc.

y near vents, flues or chimneys y within 2 meters (6 ft.) of heating and cooking

appliances y near forced- or unforced-air ventilation openings y within 2 meters (6 ft.) of corners or areas where

natural air circulation is low y where they can be damaged, such as an outlet

in a high traffic area y where directly exposed to the weather.

CO concentra-tion (parts per million, ppm)

Physiological effects Actions to take

0-7 Normal conditions in and outside Alaska homes.

None.

9 Maximum tolerable outdoor concentration over an 8-hour period (EPA NAAQS).

Reduce physical activity, check HVAC system.

25 Maximum allowable concentration for continuous exposure for healthy adults in any 8-hour period (Health Canada).

Reduce physical activity, call HVAC service immediately.

30 Slight headache possible. Blood concentra-tion approximately 3 percent.

CO detectors must not sound alarm within 30 days.

70 Slight headache possible. Blood concentra-tion approximately 3 to 10 percent.

Open doors and windows. CO detectors must sound alarm within 1 to 4 hours.

70-150 or “Hi” on detector

Early exercise-induced fatigue, impaired fine motor skills. Blood 20 to 30 percent.

CO detectors must sound alarm within 10 to 50 minutes. Vacate house THEN call 911.

200 or “Hi” Headache, fatigue, dizziness and nausea after 2 to 3 hours.

CO alarm must sound within 35 mint-ues.

400 or “Hi” Severe headache, weakness, dizziness, vomiting, collapse.

CO alarm must sound within 4 to 15 minutes.

800 or “Hi” Dizziness, high pulse and convulsions with 45 minutes, death within 2 to 3 hours

1600, “Hi” Respiratory failure. Death within 1 hour.13000, “Hi” Danger of death within 1 to 3 minutes.

Source of some data CMHC Carbon Monoxide Publication CE 25.

TABLE 2

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References

1. Canadian Mortgage and Housing Corpora-tion (CMHC), “Carbon Monoxide (CE 25)”. Published by CMHC, 2005.

2. Haber, Deborah. “A profile of US Poison Centers in 2004: A survey conducted by The American Association of Poison Control Cen-ters”. Published by AAPCC, 2005.

3. Paulozzi, L, MD et al. “Unintentional Poison-ing Deaths — United States, 1999-2004.” J. Am. Med. Assn. 2007.

4. U.S Environmental Protection Agency, Nation-al Ambient Air Quality Standards (NAAQS), June 2000. Available online at http://www.epa.gov/NCEA/pdfs/coaqcd.pdf.

5. See Spring and Summer 2003 Alaska Building Science Newsletters, archived at the website: www.uaf.edu/ces/faculty/seifert.

Content assistance by Garrison Collette.

Battery operated detectors Wire-in detectors Wall plug-in detectorsBenefits Goes anywhere

Sounds an alarm when bat-tery needs replacement.

Most units have a digital readout and fast reset time.

Usually electrochemical based.

Less battery changes.

Many models have battery backup for when power goes out.

Smoke/CO detectors avail-able in one unit.

Goes most places.

Fewer battery changes.

Possibility for vibrating or strobe alert.

Better backup.

Drawbacks Frequent battery changes may be needed.

May be biomimetic instead of preferred electrochemi-cal sensor.

Digital display shuts off when not in use.

These are typically MOS, or metal-oxide-semiconductor detectors, and are less sensi-tive.

Difficult to install.

Damage to wiring may go unnoticed.

Short battery backup life.

Short battery backup life.

Wall socket may be located in unsafe location.

May be MOS or gel-plate based (biomimetic) instead of preferred electrochemi-cal.

Avoid wall switch-con-trolled outlets.

TABLE 3

Note: Carbon monoxide detectors do not last forever! Replace your detector every 3 to 5 years, depend-ing on the model.

SAFE AND EFFECTIVE EXTERIOR INSULATION RETROFITS: PHASE I

The following research report by the Cold Climate Housing Research Center focuses

on a longstanding question about vapor barrier location and the effect of vapor barrier integrity (or whether there is even one present) on mois-ture accumulation over a season. The results are very instructive and demonstrate that old rules of thumb — such as the one-third/two-thirds rule for vapor retarder placement for 7–10,000 degree-day climates and the one-quarter/three-quarters rule for subarctic climate zones — are fairly good concepts. The research also shows that the more insulation placed outside the moisture retarding surface in the wall, the better the moisture control, and that is the desired function of the wall.

The editor

(Article begins on page 9)

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Safe and EffectiveExterior Insulation

Retroits: Phase IColin Craven and Robbin Garber-Slaght

September 14, 2010

CCHRC Snapshot RS 2010-03

Cold Climate Housing and Research Center, P.O. 82489, Fairbanks, AK 99708. Phone: (907) 457-3454, Fax: (907) 457-3456, Email: [email protected]

Introducti onCCHRC staff oft en receive questi ons from property owners interested in retro tti ng their home using additi onal insulati on so as to save money on heat-ing bills. A common method for retro tti ng walls is adding rigid foam insulati on to the exterior. How-ever, determining how much exterior foam to add can be tricky.

The conservati ve approach is to add enough exte-rior insulati on so that the wall framing never cools to the dew point. In Fairbanks, this approach would require 2x6 walls to receive between six and 10 inches of exterior foam board (depending on the type) to compensate for the insulati ve eff ect of the existi ng insulati on. Unfortunately, this approach is oft en prohibiti vely expensive. Based on practi cal experience, it seems that less exterior insulati on can work, but exactly how much less is unknown. CCHRC researchers’ concern is that the installati on of a thin layer of exterior insulati on may be prob-lemati c because it has the potenti al to allow con-densati on within the wall while also reducing the drying potenti al of the wall.

A further complicati on is the fact that most resi-denti al constructi on in Alaska contains a plasti c va-por retarder between the interior nish, e.g., gyp-sum board or paneling, and the wall framing. This plasti c sheeti ng is used to restrict air and vapor ow through the wall and keep water vapor from condensing within the walls during winter. In older homes, unsealed seams or penetrati ons have oft en compromised the vapor retarder. This is parti ally miti gated because the wall can dry to the exterior during the summer, allowing an escape path for moisture that collects in the winter.

Please visit the CCHRC website for more publicati ons: www.cchrc.org/publicati ons-catalogue

Promoting and advancingthe development of healthy,

durable and sustainable shelter for Alaskans and other

circumpolar people.

Gypsum wall board

Six-milpolyethylene (interior vapor retarder)

2x4 stud wall

R-11 berglass batt insulation

1/2 inch plywood structuralsheathing

Exteriorair barrier

6 inches EPS foam board(exterior vapor retarder)

1x2 furring strips

Lap siding

Window

Outlet box

Exterior foam insulati on can signi cantly inhibit drying. Because foam in-sulati on is relati vely impermeable to water vapor, the combinati on of an interior vapor retarder and exterior foam insulati on is commonly called a “double vapor barrier.” If the amount of exterior insulati on does not prevent condensati on in the wall, moisture may accumulate over ti me.

In this context, CCHRC staff designed a study to answer two questi ons:Based on eld studies of best- and worst-case scenarios, what dis-• tributi ons of interior-to-exterior insulati on prevent signi cant con-densati on within retro tt ed walls?Does a double vapor barrier cause moisture problems in the dry • and cold Interior Alaska climate?

Figure 1A general depicti on of the wall system used in this study (not to scale). Variables across the nine wall secti ons include the presence or absence of an interior vapor barrier, 2x4 or 2x6 stud constructi on and the amounts of stud wall insulati on and exterior foam insulati on.

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58%Inside Sheathing

42%OutsideSheathing

Insulati on Distributi on Insulati on Distributi on

41%Inside Sheathing

59%OutsideSheathing

Insulati on Distributi on

31%Inside Sheathing

69%OutsideSheathing

58% %42%

Moi

stur

e Co

nten

t (%

)

Insulati on Distributi on58% Inside/42% Outside



R-11 R-11 R-11R-8 R-16 R-24

Mold Threshold

Figures 2The stud cavity insulati on (interior) and exterior insulati on distributi ons in several of the Mobile Test Lab test wall secti ons. The illustrati ons do not represent cross-secti onal thicknesses, rather the distributi on of interior and exterior R-values relati ve to the total R-value for each wall secti on. For example, Figure A has a total insulati on R-value of 19, of which 58% is within the stud cavity (R-11) and 42% is exterior to the wall sheathing (R-8). NOTE: Figure 2 and Figure 3 refer to three wall secti ons which have corresponding lett ers.

Figure 3The wood moisture content of studs in select Mobile Test Lab wall secti ons over the winter of 2009-2010. The moisture content of concern for initi a-ti on of mold growth (16%) is illustrated for comparison to the test wall data. Dott ed lines connecti ng peaks in the red data series represent inferences of wood moisture content during a period when the sensor area was below the freezing point of water. When frozen, the sensors falsely show a de-crease in moisture content. The insulati on distributi on for each data series, identi ed as A, B and C, are shown above.

A B C

A

B

C

What does a 41%/59% R-value distributi on mean in terms of constructi on materials?

2x4 w/R-11 requires 4.0 inches EPS• 2x6 w/R-19 requires 6.8 inches EPS•

Hint

www.cchrc.org


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The Mobile Test LabTo answer these questi ons, we began an experiment in our Mobile Test Laboratory (MTL) in the fall of 2009. The MTL is a road-worthy trailer with nine 4x8 test wall bays. For this ex-periment, all nine test walls were built using typical building practi ces with 2x4 or 2x6 frame constructi on. Eight of the nine walls were covered with either polystyrene or polyurethane exterior insulati on, with the ninth test wall kept as a control, with no exterior insulati on. Photograph 1 shows the MTL dur-ing constructi on and installati on of the test walls. The test walls have diff erent distributi ons of insulati on in the interior (yellow berglass batt s lling the wall cavity in Figure 1) relati ve to the insulati on on the exterior of the wall (rigid board foam in Fig-ure 1). Most test walls have an interior vapor retarder. Some were left without to provide a means for comparison.

The interior conditi ons of this phase of the MTL experiment were designed to mimic a worst-case situati on for homes. The trailer interior was maintained at 40% relati ve humidity, 70°F and with a slight positi ve air pressure (1 - 7 Pa) over the win-ter of 2009-2010. The test walls were monitored for moisture content of the wall framing, heat ux, temperature and stud cavity humidity over the course of the winter. This snapshot presents select wood moisture content ndings from Novem-ber 2009 to March 2010.

A Balance of R-ValuesDetermining the amount of exterior insulati on required to re-move the condensati on potenti al within a wall is a functi on of the local winter temperatures and the amount of insulati on in the stud bays. Because insulati on properti es vary, we refer to the distributi on in terms of the insulati on R-value in the stud caviti es (interior) to that placed on the exterior (see Figures 2a -2c). For this study, we varied the distributi on of interior to ex-terior R-values from 31%/69% to 70%/30%, and report select data within this spectrum of R-value distributi ons.

Figure 3 shows the wood moisture content for three of the test walls from November 2009 to March 2010. The reading is from the stud beneath the electrical outlet. All three test walls had interior vapor retarders with unsealed penetrati ons around the electrical outlets to simulate older constructi on practi ces. Compared to a conservati ve threshold for concern of 16% wood moisture content (when mold growth can initi -ate), it is readily apparent that a 58% interior and 42% exterior R-value distributi on is problemati c given the laboratory condi-ti ons maintained for this experiment. Note that most drops in moisture content during the winter do not represent periods of drying in this wall during relati vely warm winter days, but instead indicate that the moisture content sensors were freez-ing during relati vely cold periods. When the area surround-ing the moisture content sensor freezes, the resulti ng signal falsely shows a decrease in moisture content.

In sharp contrast, both the 41%/59% and 31%/69% R-value distributi ons show robust resistance to condensati on and water vapor absorpti on that kept the wood moisture content below the threshold of concern throughout the enti re test pe-riod. No freezing at the wood moisture content sensor was recorded for these test walls throughout the monitoring pe-riod.

The Double Vapor Barrier Eff ect To address the questi on of whether exterior insulati on retro- ts can pose a problem due to the double vapor barrier eff ect, we constructed the same three test walls with and without

Sources and Control of Moisture

Acti viti es of everyday life are the common sources of wa-ter vapor in homes. Breathing, showering, and cooking are signi cant sources, while pets and plants are less ob-vious ones. Generally, the more occupants in a home, the more water vapor is generated.

The amount of water vapor in air is commonly expressed as relati ve humidity, which is a rati o of water vapor mass in the air to the mass in water saturated air at the same temperature. In winter, it is recommended that homes in very cold climates be kept around 25% relati ve humid-ity*. Higher relati ve humidity promotes condensati on within the building envelope, and lower relati ve humidity can cause occupant discomfort.

The primary means for moisture control in cold climates is venti lati on, which is most eff ecti vely achieved by a heat recovery venti lati on system. In winter, the incoming fresh air contains signi cantly less water vapor than indoor air.

*Lsti burek and Carmody (1994) Moisture Control Handbook: Prin-ciples and Practi ces for Residenti al and Small Commercial Build-ings. John Wiley & Sons, Inc.

Photograph 1The Mobile Test Lab during installati on of new test wall secti ons,August 2009.

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CCHRC Snapshot RS 2010-03 www.cchrc.org

Cold Climate Housing and Research Center, P.O. 82489; Fairbanks, AK 99708. Website: www.cchrc.orgPhone: (907) 457-3454, Fax: (907) 457-3456, Email: [email protected]

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Insulati on Rati o58% Inside/42% Outsidew/Vapor Barrier



Insulati on Rati o58% Inside/42% Outside



interior vapor retarders. The resulti ng wood moisture con-tent data from November 2009 to March 2010 is illustrated in Figure 4. This graph shows the same data as Figure 3 for the test walls with interior vapor retarders (bold colors), and also includes the corresponding test wall insulati on distributi ons without interior vapor retarders (light colors).

When considering the test walls based on the presence or ab-sence of vapor barriers, the wood moisture content is consis-tently lower for walls with a greater percentage of R-value on the exterior. This result was expected, as more exterior insula-ti on provides greater resistance to condensati on within the wall. However, when comparing walls of the same insulati on distributi on, the results are more complex. For test walls with the majority of the R-value on the exterior (Figure 3, blue and green), the walls with vapor retarders have lower moisture contents. For the test wall with the majority of the R-value within the stud bays (red), the opposite was observed. Fur-ther discussion on these observati ons will follow in a subse-quent technical report.

The practi cal implicati on is that wall constructi ons with great-er exterior R-value distributi ons are more eff ecti ve at con-trolling moisture, not that homeowners should remove an existi ng interior vapor barrier. While an interior vapor barrier drasti cally increased moisture accumulati on in the test wall with the least exterior insulati on, both test walls with this

R-value distributi on (58% interior, 42% exterior) remained above the threshold of concern for nearly the enti re test pe-riod. The presence of an interior vapor barrier was bene cial to walls with greater exterior R-value, e.g., 59% exterior or greater, than within the stud bays for the data shown in Figure 4. However, wood moisture content at other locati ons within the test walls show con icti ng results. Evaluati on of the test wall moisture content during the summer season, when dry-ing is anti cipated, will help to determine the signi cance of the double vapor barrier eff ect. As for moisture accumulati on during winter: the greater the exterior R-value of a test wall, the less an interior vapor retarder in uences moisture accu-mulati on.

More Results PendingThe moisture content of the test walls will be monitored over the summer, and results on the amount of drying with the test walls will be reported in the fall of 2010. In winter of 2010– 2011, the experiments will conti nue at 25% relati ve humidity and neutral-to-slight negati ve pressure. These conditi ons are representati ve of a best case scenario that balances the needs of occupant comfort and durability of the building envelope.

CCHRC would like to thank the Alaska Housing Finance Cor-porati on, Demilec and GW Scienti c for their support of this project.

Mold Threshold

Figure 4A similar illustrati on to Figure 3 with additi onal test wall secti ons displayed. The graph shows three pairs of test wall secti ons of diff erent interior to ex-terior R-value distributi ons disti nguished by color, each with an interior vapor barrier (bold color) and without an interior vapor barrier (pale color).

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