Tag Archives: CCHRC

How to build and maintain efficient, healthy walls

Are you curious about what’s in your walls, but not quite ready to tear them apart to find out? We’ve dissected a standard wall system to see what’s inside, and what it tells us about your home energy performance and the durability of your envelope.

Whether you’re building a new home or retrofitting an existing one, this video will show you the key to tight, long-lasting walls. It will give you an understanding of the three main issues facing walls in a cold climate: air leakage, moisture movement, and conductive heat loss. CCHRC building educator Ilya Benesch will show you how these effects are at play in yours walls, how to spot them, and how to deal with them. Enjoy!

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 a combined/integrated heating system?

Many homeowners use the same appliance to heat both their house and their domestic hot water. These multipurpose appliances are called combined or integrated systems.

 

Hot water for space heating goes into a hydronic distribution system or to coils for forced air distribution, while domestic hot water goes to a storage tank or directly to the faucet. Combined systems work with several types of appliances, including boilers, ground source heat pumps or solar thermal systems.

 

Combined systems offer several advantages over distinct systems. Since an integrated system provides both domestic hot water and space heating, you have fewer appliances to maintain. During the heating season, it’s more efficient to have a single appliance providing both hot water and heating because you have fewer on-off cycles. It also saves space.

 

On the downside, combined systems can be less efficient when the heating appliance only fires occasionally—in summertime, for example. In addition, it’s tough to measure the efficiency of combined systems because the rating on the appliance (known as the AFUE) only applies to space heating, not domestic hot water. A heating contractor or someone who owns the same appliance can give you a better idea of the actual efficiency.

 

There are two types of combined systems—storage tank and tankless. Storage tank systems are most popular. In this setup, the appliance simply sees the hot water tank as an additional zone, but one that is separated from the space heating system to avoid contamination of the drinking water. When the domestic hot water tank calls for heat, the appliance sends heat to that zone. Having a storage tank forces the appliance to fire only a few times a day to provide hot water. This design is more efficient than a tankless coil system because the appliance doesn’t have to fire as often, which is an energy-intensive process. Also, since there is no burner on the storage tank you can add extra insulation to the tank to save energy.

 

A tankless coil system has an extra heat exchanger that fits into the appliance. Water is heated when it flows through the heat exchanger. Tankless coil systems are most efficient when the appliance is already being used for space heating. During summer months, however, the on-off cycling that occurs every time domestic hot water is needed can waste energy. To avoid this, some homes use a tankless coil system during the winter and a separate domestic hot water system during the summer.

 

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.

 

Winter Punch List

The punch list arsenal

Winter is looming, but there is still time to attack a fall home maintenance punch list before it gets too cold.  In addition to a boiler tune-up and chimney inspections, there are a few more details worth considering.

Now is the best time to make sure your roof system is in good working order.  It’s not too late to replace shingles, add snow stops, patch leaks, or replace any missing fasteners on metal roofs.  Now that the leaves are down, the gutters are ready for inspection. In the spring, gutters clogged with frozen debris are virtually impossible to clean and can cause melt water to overflow and run down next to the foundation and into the basement or crawlspace. Check the downspouts too. They should be unobstructed, firmly attached, and pointed to direct water away from the house.  While you are walking around the house, check the grade for drainage.  Surface soils will remain unfrozen for a little longer so it’s not too late to do any last minute dirt work to ensure spring run-off is directed away from the house. Inspect any heat traces to make sure they are in good (and safe) working order.  Replacing a heat trace now is a lot less hassle than a frozen waste or supply line in the winter.  If you have any concerns about the safety of a heat trace – particularly if it’s older—consult a professional.  A malfunctioning heat trace can be a fire hazard.

If you have an HRV system, make sure all parts of the system are in good working order.  Alaskans tend to spend a lot more time indoors during the cold periods, and good ventilation is critical.  An inspection should include a look at the supply and exhaust grilles on the outside of the house – not just those belonging to the HRV, but also dryers, range vents, and bathroom fans, especially if they are close to the ground where the intake can become clogged with leaves, grass, or other debris.  If an exhaust damper is present, make sure it is operating smoothly.  Open up the HRV and examine both the filters and the core. The cores can be removed and washed out if they’re dirty. The condensate drain and drain line under the HRV should be free of obstructions; if a trap is present, it should contain water. A properly installed HRV is designed to bring in and exhaust the same amount of air.  The system should provide enough fresh air to ensure occupant health and control humidity but not over-ventilate, as excess air flow is simply wasted energy.  If you’ve never had your system professionally balanced and inspected, now is the time.

If you’re planning any air sealing with spray foam, the cut-off temperature for most expanding foams is above freezing, although a few brands may go lower. Last but certainly not least, make sure your home has operating smoke alarms and at least one operating carbon monoxide detector.

I’ve heard stack effect can cause problems with indoor air quality. How is this possible?

Stack effect (also called chimney effect) involve the air flow into, out of, and through a building. This air flow can produce some unwelcome side effects. An enclosed heated building in winter will have different air pressures at different heights (the result of differences in air density caused by of differences in indoor and outdoor temperature). To complicate matters, a taller structure such as a multi-story house will contain a taller column of air with greater pressure differences.

Everything starts with the fact that warm air rises and cold air sinks. Inside a home this means that warmer air moves towards the upper regions near the ceiling, producing positive air pressure at the ceiling level. It doesn’t end there though, because what’s going on outside the house influences the air pressures inside the house. When it gets very cold, the outside air is much denser than the heated indoor air. As a result, the positive pressure in the upper regions of the house can increase dramatically. Things are fine, however, until you have an air leak somewhere in the positive pressure zone. At this point, the warm air will rapidly exit the house through the leak. As warm indoor air leaks through the walls or roof, it cools and deposits moisture along the way and loses heat. It doesn’t stop there. New air to replace the air lost must come from somewhere. Replacement air will tend to take the path of least resistance. Typically air is drawn in through the lowest regions of the house, which is why problems with soils gases, such as radon, tend to increase in winter. Replacement air isn’t always just drawn in through the lower parts of the structure. Air can also come through poorly sealed or malfunctioning combustion appliances such as wood stoves and boilers.

The key to reducing potential problems with stack effect is good air sealing around penetrations in the building. If you are considering sealing air leaks in your house, it’s very important that you start at the top. If you start at the bottom, then you are potentially increasing the chances that the air leaking out of the top will pull air from other sources such as combustion appliances. Always be sure that you have a functioning carbon monoxide detector in your home and that your boiler and wood stove have a dedicated source of combustion air.

Do you need a vapor barrier on a raised floor?

I-beams for a new home built on post-and-pad

Post and pad foundations are a common sight in Fairbanks, as they represent one of the least expensive approaches to building on unstable soils – of which we have no shortage. Usually the floor is raised several feet off of the ground, and air flows freely underneath.

It is standard practice in cold climate construction to install a vapor retarder on the “warm side” (indoors) of the exterior walls and ceilings. This keeps the water vapor generated in the living spaces during the cold seasons from entering the insulated cavities, where it can condense and lead to mold and rot. Installers typically use polyethylene plastic sheeting in a “6 mil” thickness, which is mandated by local building codes.

With post and pad construction, it may seem logical to also install plastic sheeting over the tops of the floor joists before laying down the subfloor sheathing.  In some cases however, it can do more harm than good.

If any rainwater leaks through the joints in the subfloor before the roof is on, it will be stopped by the plastic, and the floor may not be able to dry out quickly enough to avoid mold and decay. The same risks hold true if liquids are spilled on the floor once the house is finished, or if a major plumbing leak occurs. The plastic also prevents the use of subfloor adhesive between the joists and sheathing, which is designed to prevent squeaks in the floor. Modern subfloors are usually sheathed with industry-standard ¾-inch tongue and groove exterior-rated plywood, or oriented strand board (OSB).

With post and pad construction, the subfloor sheathings are less at risk for moisture issues to begin with. That’s partly because warm indoor air leaves at the top and is replaced by outside air drawn in at the bottom, so water vapor moves upwards – away from the floor. In addition, the combination of thickness and types of glues used in ¾-inch plywood and OSB subfloor sheathings means they are less likely to absorb any moisture that might be forced into the house.

To minimize air leakage through the floor, the unsupported seams can be caulked with an adhesive sealant, such as a silicone, that bonds well with wood. The decision of whether to use or omit a plastic vapor retarder in floors using post and pad construction ultimately rests with the engineer or the local code official, who may have reasons specific to the project or building site.

Policy Researchers Head Southeast to Meet with Building Communities

infrared image shows heat loss in the east end of the CCHRC Research Testing Facility

CCHRC is presenting one of the keynote addresses at the Alaska Municipal League (AML) Summer Legislative Meeting in Sitka this week. The AML, a statewide advocacy organization of 140 municipalities, meets each summer to discuss common issues and set legislative priorities at the state and federal levels.

CCHRC Senior Researcher for Energy Policy, Dr. John Davies, will present on energy efficiency as a resource for the sustainability of Alaskan communities. This will be a great opportunity to advance discussion of state energy efficiency policy recommendations that are part of work CCHRC is performing under a contract with the Alaska Energy Authority.  A long-term commitment to improving the energy efficiency of our buildings, appliances, and vehicles can reduce our need for energy by such large amounts that it should be considered as equivalent to large energy resources such as natural gas pipelines, hydroelectric dams, or coal-fired power plants.

Davies, along with Policy Research Director, Dr. Kathryn Dodge, will also visit Juneau and Ketchikan to meet with members of the building community about energy efficiency standards and the programs used to measure them. They will discuss and obtain feedback from builders, energy raters, and regulators on proposed policy recommendations, such as a statewide energy code, and present updates to a range of CCHRC programs.  One agenda item will be AkWarm, an AHFC computer program used to model energy use in homes and commercial buildings. AkWarm’s calculations are based on insulation levels, air tightness, and other thermal characteristics, and it is used to certify building for loans, rebates, and other purposes.

Hot roofs, cold roofs, and common roof problems

Cold roof on the CCHRC building.

In severe cold climates, roofs face two important challenges; retaining heat effectively, and controlling moisture trying to escape from the living space.  The colder the weather and the longer the winter, the more pronounced the issues can become.  Deficiencies and poor building practices that are overlooked in a more forgiving climate become very apparent here in Fairbanks.   A basic understanding of your roof system and the challenges it faces can help to identify the sources of problems.


Roofs fall into two categories: “cold” and “hot.”  They can suffer from the same ailments.


 A properly constructed “cold” roof maintains a continuous air space between the underside of the roof and the insulation. This air space is designed to do two things.  To some degree, it allows an exit path, through vents, for moist air that has leaked from holes in the ceiling vapor barrier into the insulation cavity. The space also creates a thermal break that helps prevent escaping interior heat from conducting directly to the roof’s underside, where it can cause the snow above to melt.


A “hot” or unvented roof relies on high levels of insulation to slow down heat transfer to the exterior.  The other critical component in a hot roof system is a near-perfect vapor barrier that keeps moisture-laden air from entering the roof cavity, where it can become trapped.

If either type of roof fails to retain heat, one result is ice damming, a fairly common sight in Fairbanks in mid-winter. The classic symptoms are large icicles hanging off of eaves and exposed spots on the roof where snow has melted away. Roof problems are more pronounced in our climate because we have an increased “stack effect.” Rising warm inside air will try to exit the building through leaks at the ceiling level. To replace it, dense, cold, outside air is drawn through cracks in the bottom of the house like a chimney. The greater the temperature difference between inside and outside, the stronger the stack effect, amplifying the heat loss.

Water vapor abides by similar laws. During winter there is a huge imbalance between moist, heated indoor air and extremely dry, cold outdoor air. Because water vapor molecules by nature try to reach equilibrium, they will move through any vulnerable areas (including solid wood) to balance the moisture levels. This is called vapor drive. The greater the temperature difference, the more intense the vapor drive. When a house has high indoor humidity, the combination of stack effect and vapor drive can cause severe moisture problems inside the roof if it is poorly sealed.   Gone unnoticed, this can lead to structural damage as well as mold and its accompanying health issues.

Whether your roof is hot or cold, three elements will keep problems at bay: good indoor moisture control, adequate insulation, and good sealing.