Tag Archives: insulation

Moisture Performance of Cellulose Insulation

Blowing dense-pack cellulose insulation into the test walls.

Blowing dense-pack cellulose insulation into the test walls.

Building envelopes have a hard job in Interior Alaska—keeping us warm, dry and healthy at 40-below. CCHRC tests a variety of building designs and products to see how they can be applied in this environment. We recently studied the moisture performance of cellulose insulation to see how it compared to other common types, like fiberglass and rigid foam, and how it performed in a super-insulated house.

First, let’s look at a conventional wood-framed wall with 2×6 or 2×4 studs and an interior vapor barrier. This system has historically worked in the Interior because the vapor barrier limits the moisture allowed into the walls and moisture that does sneak in remains frozen through most of the winter. During the spring, the walls thaw and dry to the outside.

But when you add exterior foam insulation to a house, a common retrofit technique to save energy, the walls can no longer dry to the outside. Is this good or bad for the wall? Depends on how much you add. If you add enough exterior insulation (for example, six inches of EPS foam for a 2×4 wall) the sheathing and framing will stay warm enough to avoid condensation, improving your overall moisture control. If you don’t add enough, however, you move your wall sheathing into the danger zone—above freezing and very humid.

We’ve learned from earlier studies how to use fiberglass and EPS and XPS foam in various wall systems to improve energy efficiency while avoiding moisture problems (See cchrc.org/safe-effective-exterior-insulation-retrofits). This latest study looked at how cellulose performed in different wall scenarios over an 18-month period. These were not standard walls—they intentionally lacked a vapor barrier because we wanted to force moisture into the walls.

Cellulose insulation is made primarily of recycled paper. As a local, rather inexpensive product, it has recently become more popular in building in Interior Alaska. “Dense-pack” cellulose is blown into a wall to a density of 3.2 pounds force per cubic foot, which is designed to prevent the insulation from settling over time. Dense-pack cellulose has an R-value (or insulation value) of 3.7 per inch—slightly higher than fiberglass batts and slightly lower than EPS foam.

Our study shows that cellulose can handle moisture better than fiberglass or EPS insulation when used properly. The test wall that used cellulose as both interior and exterior insulation maintained lower humidity levels (and was less likely to condense or grow mold) than the test wall that used interior fiberglass and exterior foam.

That can be partly attributed to material properties of cellulose. Dense-pack cellulose is actually less permeable to air flow than fiberglass batts. So when used as interior insulation, it reduces the amount of moisture that migrates into the stud cavity.

Cellulose also has the ability to absorb and release water vapor, allowing it to moderate moisture levels within a wall and prevent the large spikes in relative humidity that cause moisture damage.

It’s also more permeable to water vapor than EPS or XPS.  The test wall with exterior cellulose had lower humidity levels than the wall with exterior foam, because it allows faster drying to the outside.

Based on this study, dense-pack cellulose can provide a good option for exterior insulation beyond rigid foam board. In future studies we plan to look at the minimum amount of exterior cellulose needed to keep the sheathing warm and dry.

What are Structural Insulated Panels and considerations for Alaska

SIPsStructural Insulated Panels, or SIPs, are prefabricated building panels that combine structural elements, insulation, and sheathing in one product. SIPs can be used for the walls, roof and floor of a building in place of more traditional construction methods, such as stick-framing. A SIP typically consists of a foam insulation core with a structural sheathing panel bonded to both faces. Sheathing panels are usually made of industry standard OSB or plywood.

Building with SIPs


Constructing a home from SIPs begins at the design phase: builders must work with the SIP manufacturer since the panels are specific to the design. Once the plans are finalized, the SIPs are made and shipped to the job site. The panels are labeled so builders know exactly where each panel goes in the building.

As they are erected, the panels must be joined together according to manufacturer specifications. For instance, many panels are joined with splines that are secured with screws. When the structural connections between panels are being made, workers must take care to seal the joint between the panels to ensure it remains airtight. Air sealing the panel joints can be accomplished using sealing agents such as caulk, adhesive, mastic, spray foam or tape. A tight seal is also necessary in order to prevent moisture from entering the panel, which can lead to structural deterioration of the panel components over time. Some building inspectors may require a 6mil polyethylene sheeting vapor retarder be installed on the interior side (warm side) of the SIPs once the panel construction is completed.


Electrical outlets and wiring are usually installed into recesses and holes pre-cut into the panels, both on the interior and the exterior as needed. Any special considerations for running electrical systems or other mechanical penetrations through the SIPs should be addressed with the manufacturer during the design phase.

Benefits and Concerns

There are several potential benefits to building with SIPs. For one, the absence of an air permeable wall cavity prevents convective heat losses from occurring within the panels. Large panels will have fewer framing members than a stick-framed wall, which reduces heat losses due to thermal bridging. With a trained crew, SIP buildings can be erected quickly, a big advantage in climates with short building seasons. Properly constructed, a SIP panel home can realize a high level of air tightness and energy efficiency.

On the other hand, builders must take extra care to ensure proper assembly and sealing to prevent any problems due to moisture infiltration and air leakage. Builders also do not have much flexibility in on-site design changes, since panels come pre-cut. An experienced builder who can work through a home design with the manufacturer and who doesn’t cut corners with sealing panel joints is a necessity.

SIPs can be either cost-effective or cost-prohibitive depending on the situation. The design services and shipping costs may drive the price of SIPs above that of conventional framing materials. However, this can pay off in reduced labor costs if a trained crew erects a building quickly, or if several buildings of the same design are being erected.

What is reflective insulation and does it work in a cold climate?

Reflective insulation is typically made of aluminum foil on a backing like rigid foam (pictured here), plastic film, polyethylene bubbles or cardboard.

Reflective insulation is a type of thermal insulation with at least one reflective surface that is installed so that the surface faces an air gap. It is usually made of an aluminum foil installed on a variety of backings, such as rigid foam, plastic film, polyethylene bubbles or cardboard.

CCHRC recently researched the use of reflective insulation in cold climate construction, reviewing other studies and testing two foam insulations with reflective facers. Researchers found that the use of reflective insulation has very little to offer cold climate construction.

To understand how it works, you need to understand the three types of heat transfer: convection is heat transfer through air movement; conduction is heat transfer through solid materials that are touching; and thermal radiation is when heat travels in electromagnetic waves, like energy from the sun.

Reflective insulations are designed to reduce heat transfer through radiation by placing a surface that reflects thermal radiation in combination with an air gap. The reflective surface reflects most of the thermal radiation toward the air space, preventing it from being absorbed by the material. If you don’t have an air space, then the heat is lost by  conduction through the reflective surface. In real life, all these forms of heat transfer occur simultaneously. (Unless you travel to space to remove the atmosphere (air) from the equation. This partially explains why NASA took an interest in reflective insulations, as they faced very different conditions than we do in Alaska.)

In warmer climates, it is common to add reflective insulation in the attic to reduce heat transfer from the roof decking to the underlying insulation, reducing overall solar heat gain within a building. But in cold climates, we have different concerns. For example, homes lose heat primarily from air leaking through the attic and walls and conduction through all components of the house. Because most heat loss occurs this way, reflective insulation would not make much difference in reducing the overall heat loss of your home.

To illustrate this point, let’s examine part of a house where a reflective insulation system is added. If you created a 1-inch air gap into the wall or ceiling with a reflective surface on one side, you could expect to gain around R-2. But walls and ceilings are typically insulated in the range of R-20 to R-60, and reflective insulation faces sharp diminishing returns if multiple layers are installed. Also remember that the air gap needs to prevent airflow and the reflective surface needs to stay clean from dust and moisture.

In addition, many reflective insulations can increase the potential for moisture problems in your home if not placed properly, as they often act as strong vapor retarders. So if you’re using these products, you need to consider not just how they affect heat loss, but also moisture flow.

Watch out for claims about reflective insulations providing benefits that go beyond R-value. All of the product’s insulation value is captured by the R-value, just like fiberglass batts, foam board, and other insulation products. If there are additional benefits, such as reducing air leakage, then those benefits can be measured and compared to other air barrier systems.

In essence, reflective insulation may help in warmer climates but is not a great fit for a cold place like Alaska.

What to look for in an energy efficient house

Shopping for a home in Fairbanks can be difficult, especially if energy efficiency is a priority. With heating oil prices volatile and resale value at stake, finding the most fuel-efficient home makes sense.

Following are just a few of the things to look for in an efficient home.

Site Location

  • South-facing slopes that are exposed to sunlight will be warmer in the winter and require less heating than comparable homes on north-facing slopes or obscured by dense tree canopies. Deciduous trees, such as Alaska birch, are desirable because they lose their leaves in winter and allow sunlight to shine through.
  • Ideally, homes should be situated lengthwise east to west in order to take advantage of the sun.
  • Protection from wind, provided by trees or hills, can help to conserve heat in winter. Low-lying evergreens or shrubs placed on the sides of a house that are exposed to wind will also help conserve heat.


  • Houses that share common walls with other structures, such as townhomes, lose less heat than standalone homes.
  • The overall shape of the house will affect heat loss due to the amount of wall space exposed to the elements. L-shaped, H-shaped, or U-shaped homes, for example, will tend to lose more heat than rectangular homes.

  • Arctic entryways that are sealed from the outside and the inside living areas by separate doors can help retain heat.

  • South-facing windows are preferable to windows on any other axis because they can collect sunlight and minimize heat loss.

  • Plumbing should be run inside heated or indirectly heated areas and consolidated as much as is practical. Sinks, baths, and laundry should be close to the water heater to minimize standby heat loss or, alternatively, on-demand water heaters can be used.



  • There’s a saying among energy raters in Alaska – “You can’t over-insulate, you can only under-ventilate.” When inspecting a house, ask how much and what type of insulation is in the floor, walls, and attic. Other than airtight construction, no other single factor will affect a home’s energy use more than insulation. But insulation without adequate ventilation will invite moisture problems.

  • All gaps and cracks in the house should be well sealed or caulked.

  • Doors and windows need effective weather-stripping.

Mechanical Systems

  • The performance of heating appliances such as boilers can vary widely and replacing an aging existing system can be expensive.  It’s not uncommon for heating systems to be oversized in relation to a homes energy needs, which can also contribute to efficiency losses.  Consider having the heating system professionally inspected to assess reliability and performance.
  • Doors and windows need effective weather-stripping.

  • Previous years’ fuel bills can help gauge heating costs, but be aware that the presence of a woodstove, pellet stove, or other heating appliance other than the boiler can make heating oil usage numbers misleading.

Home Inspections

  • Check to see if the home has already had an energy audit done.  An energy audit will provide a detailed assessment of the home’s energy performance and will help identify problem areas.  If energy efficiency is a priority, an audit/home inspection by a state certified energy rater can provide valuable insight into a home’s real world performance.


Should you insulate your basement or crawl space?

The foam board in this basement is in the process of being air sealed with tape at the joints and corners.

Concrete basements in many older homes are inadequately insulated by today’s standards (or not insulated at all). For new construction, both state and local building codes require a minimum R-value of 15 for below-grade walls (walls buried in soil).

This makes good sense as the soils in our region are relatively cold; even below the frost line, soil temperature may only reach a high of 36°F.

This means that in a poorly insulated basement, significant heat losses can occur year round. Basement walls that are well sealed and insulated, on the other hand, can save money and make yourhome more comfortable.

In older homes, it is often more practical to insulate the basement from the inside. If there are any problems with water penetration, make sure you fix them first or any work you do on the inside will be compromised.

If gutters and good site drainage don’t solve a water problem, then unfortunately excavating the exterior and applying a coat of waterproofing and resolving drainage issues may be necessary.

Rigid foam board or high-density spray-applied foam insulation make good choices for basement walls. Both products are resistant to air flow and can tolerate occasional exposure to small amounts of moisture. Depending on the type of foam, it will take between 3 and 4 inches to produce the minimum R-value of 15. Remember that the concrete behind the insulation is cold and will attract condensation if it is exposed to inside air.

If you use rigid foam board, then the joints should be tight, taped and also staggered if you are using several layers.

Be aware that building codes are strict regarding exposed foam in living spaces, and almost all foam insulations will have to be protected with some type of fire-proofing.

Once the foam is in place, then wood framing or furring can be used to run wiring and plumbing, and to provide an attachment for Sheetrock (which is a fire protection). Often, using a plastic vapor retarder is not advised if you will be insulating the basement walls with foam board. If properly sealed, the foam provides a good air barrier, and a layer of plastic sheeting will only reduce the wall’s ability to dry out, should moisture ever make its way in.

Basement walls that are well sealed and insulated can result in big energy savings and increased comfort. But because this area of your home will become much tighter, you may need to consider some form of mechanical ventilation to insure good air quality and humidity control.

What is causing all the black spots in my attic insulation?

attic insulation stained with dirt

Although mold can’t be ruled out, it is quite probable that it may be caused by something else.

Just because you have dark spots on your insulation doesn’t mean you have a festering mold problem. Air leakage from inside the house through the walls and ceilings can produce some pretty dramatic localized black spots in fiberglass batts.  Typically, fiberglass batting isn’t good at stopping air leakage, but it does act as a very effective filter material for airborne dust particles. Dirty insulation is a phenomenon that is especially common in older, leaky houses in the Interior.

In a recent attic inspection of a 30-year-old home, CCHRC found batt insulation riddled with dark streaks. The source of the streaking was a lot of air leakage through electrical outlets, wiring penetrations, gaps in the vapor retarder, gaps around furnace ducting, chimney, and other sources.

Particulates released by combustion appliances, such as wood stoves, boilers, furnaces, diesel heaters or auto exhaust, can produce very fine soot that can build up over time in insulation. Tobacco smoke can also contribute.

Look for clues in the pattern of the dark stuff. Does it match up with an air leakage pathway? For example, air from inside the home can exit through an unsealed electrical penetration in the ceiling and follow the wiring through the insulation, depositing dirt in the surrounding fiberglass along the way.

Does the wood framing or sheathing around the insulation also have black spots? If not, it is more indicative of dirt than mold.

If you are still concerned that you may have a mold problem, call a mold expert to make a positive identification.


Which energy efficiency investments are best for my house?

foam insulation on the wall of CCHRC's Mobile Test Lab

That’s what an energy model will tell you.

How much insulation to use is one of the most common questions in the construction industry–among both contractors and homeowners. A steady increase in energy prices, along with growing material costs, makes it important to find the sweet spot between energy efficiency and affordability.

The Alaska Housing Finance Corporation provides standards, called Building Energy Efficiency Standards, or BEES, for different regions of Alaska to help guide these decisions. Home builders using AHFC mortgage loans must comply with these standards, but they also provide a good reference for anyone building in Alaska.

An energy model will tell you if you meet these standards. It’s a computer modeling program that runs a series of heat-loss and performance calculations for every single component of your house. You plug in the dimensions and construction details of all the exterior walls, roof, windows, foundation and floor, along with info about your heating and electrical systems, and you end up with a model of your home’s performance. The program also factors in climate data. You can change insulation values, construction types, heating appliances, and fuel prices to test a variety of conditions.

The best time to do the modeling is before you build, as it gives you the most flexibility to make changes. The best approach is to hire a state-certified energy rater to plug your house plans into the program, which should run between $350-$700 (but probably toward the lower end). You are required to get an energy rating anyway if you are using an AHFC funded mortgage loan to make sure you meet their standards. If you want to try energy modeling yourself, you can download a public copy of the AK Warm modeling program here (the one used in the state of Alaska).

Energy modeling is a powerful tool that can provide long-term savings and peace of mind with minimal up-front investment. Remember, though, that occupant behavior and awareness will also have a great impact on your home’s performance. A house bursting at the seams with teenagers will perform differently than the same one occupied by a retired couple.

Reflective Insulation-not a big help in cold climate construction

adding an aluminum facer to a 1-inch piece of EPS (expanded polystyrene)

CCHRC has just released a report on the effectiveness of reflective insulation in a cold climate. The insulation, which has a reflective surface, is commonly used in hot climates to reflect heat from the sun away from a building. For example, a home in Florida could add it to the roof decking to divert heat from the attic insulation and save on air conditioning.

But our researchers found that the insulation is less effective in a cold climate because it doesn’t add much r-value to an already well-insulated building.

Check out the full report here