Making Houses Work

After a snowy December, Fairbanks has received a respectable (though still below-average) 30 inches of snow so far this winter.

Which makes some residents start pondering snow loads.

Roofs are required to withstand 50 pounds per square foot in the city of Fairbanks.

Snow loads vary across Alaska, depending on where you live. For example, winter snow loads can range from up to 300 pounds per square foot (psf) in Whittier down to 25 pounds in northern Alaska. Many factors affect snow load, including the moisture content of the snow, seasonal accumulation and drifting.

The weight of snow depends on its moisture content, which will vary depending on the conditions. The moisture content of snow ranges from about 1 percent to about 33 percent (water weighs about 62 per cubic foot). Compressed snow, and even snow that simply accumulates over time, will be heavier than fresh snow.

Fallen snow can also pick up humidity from the air and increase in weight.

You determine weight by using a measurement called snow water equivalent (converting inches of snow into inches of water by taking a cylindrical core sample of snow and melting it). You can find the daily SWE for different locations in the state, including Fairbanks, at the USDA Natural Resources Conservation Services website at www.wcc.nrcs.usda.gov/snotel/Alaska/alaska.html. On Wednesday, for example, the snow depth was 16 inches and the SWE was 2.4 inches. To calculate pounds per square foot, you multiply the SWE by a conversion factor of 5.2 (check out the formula here: www.ak.nrcs.usda.gov/snow/data).

That gives you a snow load of roughly 12.5 psf. Keep in mind that this number is designed only to provide an estimate for the region.

Building code in the city of Fairbanks calls for roofs to withstand a minimum of 50 psf, but homes built before 1991 were required to carry 40 psf and older homes even less. Mobile homes can be built to carry just 20 psf.

But keep in mind there is no building code outside of the city limits. Roof snow loads can vary depending upon type of roof, roof slope, melting and re-freezing of snow and ice, among other factors. Sloped roofs that periodically shed snow load present benefits and risks. If snow slides safely onto open ground, there’s no problem.

But if that snow hits a deck on the way down, its force is multiplied many times more than its resting weight and can shear otherwise stable structures right off if they are not supported sufficiently. Or if snow slides onto a flat roof or other surface, its cumulative weight is magnified from than that of normal snowfall. Structures should be designed with overhangs or other features to offer sliding snow a safe path to the ground. The ability of chimneys or utility poles to withstand sliding snow should also be considered.

In addition, decks, sheds, greenhouses, campers and other structures built without permits or an inspection may not be able to handle much if any load depending on the quality of the workmanship.

An underbuilt roof structure may also be at risk for collapse from imbalanced loading.

How do you know if you have a problem? Well, if you’re not privy to the design specifications of your home, the safest route is to hire a structural engineer to inspect your home and do the math. An inspection can also reveal potential weak spots or places where your roof structure, deck, or framing might fail. Consider how additions or modifications might affect your home’s ability to support snow. Wood tends to be very flexible and can withstand a lot of force over time before it snaps. But eventually, if it is not built to the task, it can fail.

Clearing excess snow off your roof or deck is not usually necessary unless you are dealing with an older home, structures that are built to dubious specifications, or an extraordinary buildup of heavy snow. Clearing snow comes with its own risks — like falling off your roof.

Also, the addition of your own weight on an already stressed roof can make matters worse. If you suspect a roof might collapse (you witness sagging or hear creaking), get down immediately.

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.

Refrigerators are often overlooked in the dialogue of energy efficiency. Typically, a new refrigerator with automatic defrost and a top-mounted freezer uses about half the energy of a 1990 version. So if your refrigerator is old and needs repairs, or is close to the end of its expected life, which could be around 15 years, then it makes good sense to replace it.

A new refrigerator with automatic defrost and a top-mounted freezer uses about half the energy of a 1990 version.

You can also enhance the efficiency of your fridge through proper maintenance. Seals can become brittle or lose their compressive memory, which can cause small gaps. As a rule of thumb, you shouldn’t be able to take a piece of paper and slide it between the seal. Another way to test the seal is to stick a flashlight inside the fridge. If you turn off the lights in the room and can still see light coming out of the fridge, then it’s probably time to replace the seals.

The refrigerator compartment should be between 36F and 38F and the freezer should be between 0F and 5F. You can’t always trust the dial in the fridge, so if you really want to be sure, put a thermometer inside and use the dial setting as a point of reference to make sure everything is working as it should. You may also want to clean the condenser coils, which are located at the back or bottom of the fridge. They can collect dust and force the fridge to work harder to do its job.

The location of your fridge is also important. If it’s sitting in the sun, next to the stove, or in any other warm spot, it will use more energy trying to stay cold. A fridge in a cold space will work the opposite way and save energy.

When you’re preparing food to go into the fridge, let it cool down fully before storing it away. Remember, a refrigerator is a temperature-regulating appliance. Hot food will raise the temperature inside the compartment and the fridge has to work harder to bring that temperature down to the level it is set for.

If you’re considering buying a new fridge, top and bottom units tend to be more efficient than side-by-side units. However, the bottom line when buying a fridge, or any appliance, is the yellow Energy Star tag. Energy Star information will tell you kilowatt hours per year for your model, which you can compare with other models.

CCHRC recently released the pilot for “Your Northern Home,” a series of educational videos geared toward Alaska homeowners. The 12-minute video focuses on crawl spaces–the very important but often overlooked space underneath your home where moisture problems often originate. Host Ilya Benesch describes how to maintain a dry, healthy crawl space through insulating, air sealing, heating, and waterproofing.

If you’re thinking about replacing your heating system, here are some questions to ask yourself.  A “yes” to any of them may warrant a call to an energy rater or heating contractor.

Have you recently upgraded the thermal envelope of your house?

The thermal envelope of your house is everything that separates the living space from the outside, including walls, doors, windows, insulation and the roof. If you’ve been sealing leaks, eliminating drafts, replacing old windows with double-pane or triple-pane models, or adding insulation, you’ve been making your home more energy efficient.

With thermal envelope upgrades, the home will lose less heat in the winter and therefore the heating appliance won’t need to provide as much. This means your heating appliance is probably oversized and it may be time to replace it with a properly sized one that will operate more efficiently.

oil-fired space heater

Is your current heating appliance more than 20 years old?

Technology marches on. Appliances made today are far more efficient than older models. Not only do they use less fuel, they are also safer and come with more advanced controls to improve efficiency. Also, the methods to size a heating system are better and can be tailored to individual homes.

Is your house uncomfortable?

Do you have rooms that are always too hot or too cold? This can be the result of air leaks, inadequate insulation, an improperly sized heating appliance, or lack of zoning in your heating system. Start with a call to an energy rater to find out which improvements you can make to solve this problem. If you need to add insulation or seal leaks, take care of that before upgrading your heating system so that the heating system will be sized properly for your home.

Who do you call?

Energy raters will look at your entire house, measuring doors and windows, checking insulation levels, assessing your heating system and checking for drafts and leaks. The rater will input the data into AKWarm, software maintained by the Alaska Housing Finance Corporation that calculates energy ratings. The rating describes how efficient your house is and suggests ways to improve the rating, which may or may not include the heating system. The rating will help prioritize upgrades, show the energy benefits of each one, and may qualify you for the Alaska Home Energy Rebates Program.

Heating contractors will focus specifically on your heating system, evaluating its current efficiency and whether it is sized properly. A contractor can sometimes test for the efficiency of the distribution system (depending on the type). The contractor will provide you with information on improving your current system and purchasing new appliances.

A hot fire burns more efficiently than a smoldering fire.

Just like skiers ride best with the right sized boots, your house needs a properly sized heating system to perform at its highest efficiency. Oversized heating systems are inefficient and cost more, both upfront and in ongoing maintenance, than a heating system that fits your home.

Heating appliances are sized by the amount of heat they can provide in one hour. This heating capacity is measured in BTUs per hour (one BTU is about the amount of heat energy produced by burning one match).

The heating capacity of your system should match the peak hourly demand of your house. Peak hourly demand is the maximum heat required by a house in one hour on the coldest day of the year. For a rough estimate, a well-insulated, two-story house in Fairbanks might require 60,000 BTUs per hour on the coldest day of the year, so a heating appliance should be rated to produce that much heat.

A properly sized heating system will run continuously on the coldest day in order to keep the home at its set temperature. This means the system is running at its steady-state efficiency, the stride it hits after warming up. Steady-state efficiency is like the miles-per-gallon your car gets cruising on the highway as opposed to riding in stop-and-go traffic.

Oversized systems, on the other hand, tend to cycle on, produce lots of heat, and turn off. The cycling on and off wastes fuel (as the appliance repeatedly ramps up and cools down) and causes wear and tear on the mechanical system (which ultimately requires more maintenance).

Wood- and coal-fired devices can also be oversized. When a wood stove is too large, residents tend to burn fires at a low smolder to prevent overheating the house, which is not only less efficient but also emits more particulates than a hot fire.

Domestic hot water systems should also be properly sized. For example, storage water systems are sized by their First Hour Rating (FHR), the amount of hot water in gallons the heater can supply per hour, starting with a full tank of hot water. The FHR (determined by the size of the water tank, source of heat, and size of the burner or element) should be within a few gallons of a building’s peak hourly hot water demand. F

or example, a household of three who routinely shower at night while running a dishwasher may have a peak hourly demand of about 45 gallons. So the house would need a domestic hot water heater with a First Hour Rating of 40-50 gallons. For tankless water system, the size depends on water usage, fuel input and the temperature of the incoming water.

The size of a heating system is directly related to the efficiency of your home. So if you make any building envelope upgrades to your home, you’ll require a smaller heating system—a good reason to make upgrades before replacing your heating appliance.

Sizing your system

Rule-of-thumb methods should not be used to size a heating system because today, sophisticated computer software exists that can help contractors with this task. Contractors in Alaska should use one of two methods to determine the proper size of your heating system:

–ACCA Manual J by The Air Conditioning Contractors of America

–AKWarm software, maintained by the Alaska Housing Finance Corporation, provides sizing methods for heating systems.

Don’t be afraid to ask your contractor how he will size your heating system, and ask to see the calculation.  Remember: a properly sized heating system will save you money.

You can calculate your hot water peak hourly demand for a storage water heater at the U.S. Department of Energy website on hot water heaters: http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12990

contractor sprays interior walls with low-density polyurethane foam

We’re building a new set of walls in a testing trailer to see how well open-cell spray foam performs in the extreme cold.

The Mobile Test Lab is a trailer with nine wall sections, each a different combination of studs and interior and exterior insulation. Last year we tested wall systems with interior fiberglass insulation and exterior EPS foam board  to see how they handled moisture. We were wondering how much exterior insulation would be needed to prevent the sheathing from reaching dew point (the temperature at which vapor condenses into water). Researchers found that as long as a wall has 65 percent of the insulation on the cold side, the wall cavity stays pretty dry and no mold growth occurs. All of the walls with less than 65 percent on the outside had some degree of mold on the sheathing. We also found vapor barriers made a big difference, as walls with vapor barriers were much less humid and featured only small areas of mold near holes in the plastic. (For more results, read the project Snapshot here.) 

This time we’re testing open cell spray foam to see how it handles cold weather and indoor humidity. This winter we’ll set indoor conditions at 70 degrees, 40 percent relative humidity  and positive pressure (a rather exaggerated condition for homes in Fairbanks, which will force moisture into the walls).

Q: What is bow-roof construction and what can I build with this design?

Simonson's shed has a clear poly-carbonate roof. The end walls will be conventionally framed and will include doors and vents.

We typically think buildings should be made with vertical studs and gabled roofs.

Yet alternative designs offer many advantages over conventional construction. Common materials can be used in new ways to make a wide range of structures, from tool sheds to insulated cabins.

The gabled-arch bow-roof shed is one of these innovative designs.

Bow-roof sheds are free-standing arched frames that are easy to build, light-weight and low cost. Structural strength comes from the arch shape formed by their bows.

They can be 10 to 20 feet wide and any length. The free-standing frame allows covering with any sort of roofing, including plastic sheeting.

Even the foundation can be light and simple. A sill plate may rest simply on ground stakes or just a row of railroad ties. Concrete blocks with adjustable cradles also work.

Your flooring could be anything from bare dirt to conventionally framed floor joists. Pea gravel offers one low-cost, easyto- build floor. Place plastic sheeting under the gravel to keep moisture and dirt from coming through.

Individual bows are mass-produced on a jig.

They consist of two bent wooden strips separated by wooden blocks. The 1-by-3-inch strips, cut to match the width of the bow-roof shed, are bent around these blocks. The strips are fastened using bolts and screws. When the bow is lifted from the jig, it holds its arched shape.

Each bow stands up on the sill plate and is connected to a top ridge beam. Bows may be placed up to 4 feet apart. The erect bows create the classic Gothic arch. Lateral structural strength comes from horizontal purlins fastened to each bow. You can also attach diagonal supports if the roofing has little shear strength.

You can use almost any bendable, water-shedding material for roofing. For example, clear, UV-inhibited plastic sheeting can make a great cover for a greenhouse. One economical option is thin plywood covered by conventional asphalt shingles. Metal roofing makes a strong, permanent roof for a reasonable price. You only need to consider the snow load when selecting roofing materials.

Once the roofing is installed, the bow-roof shed is a strong, waterproof structure. The final step is closing in the walls on the ends. The end walls are typically framed in with conventional vertical studs, although you can use almost any material since they don’t hold up the arch. Doors and windows can be placed within the walls.

Although bow-roof sheds are typically just storage space, they may also serve as heated living space. The floor, end walls and roof could be insulated using conventional techniques; just be sure to use an inside vapor barrier and provide air ventilation under the roofing if you are building in a cold climate such as Fairbanks.

These Gothic arches provide enough strength to allow you to use lightweight, affordable materials and to get creative with your design.

Building manager Dave Shippey gives a tutorial on how to operate the masonry heater. The unit is made from 12,000 pounds of local rock and heats 1/3 of the building. It burns at 2000 degrees with 98 percent efficiency, produces almost no smoke or ash, and uses less than 2 cords of wood in a winter. Dave describes how the stone absorbs heat from the fire and radiates it for 12-24 hours.

PS-Watch until the end for an uncut Halloween scene!

The November snow didn’t stop CCHRC and UAF from beginning the early steps of creating the UAF Sustainable Village: clearing the site.
A half-dozen students joined CCHRC designers and builders as well as UAF workers in the field next to the research center this week. Clad in Carhartts and safety goggles, they chopped trees, dragged brush, chipped wood, and flagged land for the future buildings. They aimed to clear enough trees to create solar exposure for the homes but also to impact the habitat and soils as little as possible.

Four 4-bedroom homes will be constructed on the land this spring. It will serve as a living and learning center, housing students and providing research fodder for them, along with CCHRC scientists and UAF faculty. The homes will demonstrate cutting-edge sustainable building, with passive solar design, energy-trapping thermal mass, and a custom foundation that won’t disturb the permafrost underneath. The project will cost $1 million, showing that a super-efficient 4-bedroom home can be built in a subarctic climate with private financing for $250,000–a stride toward high-performing affordable housing.

Five students will join CCHRC architectural designers this winter to plan the village, after winning a design contest hosted by UAF.