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The Energy-Efficient House

Written by Chuck Eberdt and Edwin Valbert

Since the mid-1970s a new construction technique has become increasingly popular with progressive, energy-conscious builders in the residential housing industry. Responding to the rapid rise in home heating costs, these builders have dramatically increased levels of insulation and tightened the building's shell against penetration by outside air. The result is a house that requires 30% to 50% less heat and is more comfortable, quieter, and cleaner. Building an energy-efficient home isn't Just a good Idea, however. State codes require it.

What Makes an Energy-Efficient House?

• Higher levels of insulation;

• Less air leakage;

• Controlled ventilation;

• Better doors and windows; and

• High efficiency heating and lighting systems, and appliances.

Does an Energy-Efficient House Cost More?

In terms of initial costs the energy-efficient house could cost 2% to 10% more. Once operating costs and reduced heating bills are figured in -- the energy efficient house becomes the more cost-effective option. Other factors may be hard to assign a dollar value to, such as increased comfort and a quieter, cleaner house, should not be overlooked when comparing the cost of building an energy-efficient home to a less efficient one.

Walls

How do you achieve a higher R-value in the wall? Since the R-value of a material is based on its thickness, the more inches of material installed, the higher the R-value. To go from an R- 11 wall to an R- 19 requires making the wall thicker. This is most often done by stepping up from a 2x4 stud to a 2x6 stud. By using the larger size lumber, roughly two more inches of insulation can be installed.

Along with using larger studs, you can increase the R-value by using less lumber and more insulation. A common term for this technique is "advanced framing." Larger studs (2x6) are placed further apart, 24" on center, as opposed to 16" on center. The technique also involves changing framing details at corners and where partition walls intersect to use less lumber and, where possible, using insulated headers instead of solid wood headers. (Changes in corner details can sometimes cause confusion as to what to do with insulation. )

Another way to increase the R-value of the wall is to install a rigid board insulation on either the exterior or interior of the wall. The insulation board not only adds more inches of insulation, but also covers the wood framing members which have a very low R-value.

Floors

You first need to determine when to insulate a floor and when not to. If the floor is over an unheated space, it must be insulated. The level of insulation depends on the type of floor. Concrete slab floors require a different type and amount of insulation than wood floors do.

Since a concrete floor usually rests directly on the ground, you don't have to insulate it to as high a level as a raised wood floor. This is because the soil under the concrete does not change temperature as much as air does. With this in mind, concrete floors are insulated to R-10. It's important to note the insulation doesn't have to be under the whole floor (unless it's a radiant heated slab) but should extend completely around the perimeter and in toward the center of the slab for a combined distance of 24". You should take care to ensure the slab edge is insulated. The most commonly used material for slab insulation is extruded polystyrene. Extruded polystyrene is not as prone to moisture absorption as other foam board products are.

Insulating a raised wood floor is very much like insulating a wall. The types and amounts of insulation used are similar. The floor should be insulated to at least R-19 (R-30 is required for homes with electric resistance heat). The insulation is placed directly under the floor between the floor joists. This effectively isolates the crawl space below from any heat, so you will need to insulate any pipes and ductwork located in it. In addition, you are required to cover exposed dirt in the crawl space with black 6-mil plastic, and vent the crawl space to the outdoors. This is necessary to keep moisture levels down. The ventilation should consist of at least two opposing vents with a Slab Insulation with Interior net free vent area of one square foot of vent for every 150 square feet of crawl space floor area. The term net free vent area refers to the amount of air that can be moved through a vent once the screens and louvers have been accounted for. For this reason, a one square foot net free vent will measure larger than one square foot.

Higher Levels of Insulation
Insulation is measured in R-values. The higher the R-value, the better the material is at stopping heat loss. The more insulation put in the walls, floors, and ceiling of a house, the less heat it will take to keep that house warm. The optimal amount of insulation installed depends on the climate, how well the house is to perform, and the cost of energy.

Historically, older homes had no insulation in the walls. Then, starting in the late '50s and early '60s, the walls were insulated with R-8 material. Now the requirement is R-l 9, with many builders going to R-26 or higher. This increase in R-value reflects the rising cost of energy and the growing desire to have a more comfortable and efficient house.

Ceilings

Historically, building insulation started with attics or ceilings. The difference now is the level of insulation being installed. While older houses will have 3" to 4" of ceiling insulin (about R-9 to R-12), a new energy-efficient house will have 13" to 21" of insulation (R-30 to R-49, depending on the type of insulation used). These higher levels of ceiling insulation lead to a few adjustments in how the ceiling is put together.

In a vaulted or cathedral ceiling the framing members have to be large enough to hold the insulation and allow an air space for ventilation. A minimum 1" air space or "clearance" is required. Since this could involve a very large framing member, it's often done by using a scissor truss or using high-density batts.

In a situation where there is an attic space, it's usually easy to get enough insulation in place. The one problem spot is the outer edge where the rafter or truss sits on the outside wall. In a typical case there would not be room to install 12" to 15" of insulation in this location. One solution is to use an oversized truss or "raised heel truss." In an oversized truss, the top and bottom chords come together beyond the exterior wall and typically have a steeper roof pitch. This allows enough room for both the insulation and ventilation.

Remember you must vent the space above the insulation in either the vaulted ceiling or attic. This ventilation reduces summer heat buildup, which prolongs the life of the roofing material and prevents moisture problems in the winter. You should divide the vents: half up high on the roof and half down low. An example of this might be a continuous ridge vent combined with continuous soffit vents. You need one square foot of net free vent area for every 300 square feet of attic floor.

Less Air Leakage

The next step in an energy-efficient house is to control and reduce the amount of warm air escaping and cold air entering the house. In addition to making a big difference in energy consumption, sealing the house significantly improves comfort level. The house becomes virtually draft-free. Air sealing can also improve the life-span of the home by reducing the chances of rot due to moisture. Air leakage is controlled in a number of ways.

Seal around doors, windows, and other penetrations that go through the exterior walls and install an air barrier.

Two advanced air barrier systems are a polyethylene wrap and an airtight dry wall system. With the polyethylene wrap system, you install a layer of poly against the studs with all edges and penetrations sealed. Then you install dry wall, thereby reducing air leakage to a minimum. With the airtight dry wall system, you reduce air leakage by installing gaskets or sealants between certain framing members and then sealing the dry wall to the framing members.

Because it's important to keep insulation dry and because the major source of problem moisture is from inside the house, you must also install a vapor retarder. This vapor retarder is always placed on the warm (or living) side of the insulation. With poly wrap, the vapor retarder is the same as the air barrier. And with the air-tight dry wall, the dry wall is sealed with a vapor retarder paint and a combination air/ vapor retarder is created.

One technique used to ensure good air leakage control is to test the house as it's being built. By using a device called a fan door, the house can be pressurized or depressurized. You can then inspect the house with a smoke stick that will point out unwanted air leaks. These leaks can then be sealed up before they are lost behind the dry wall.

Controlled Ventilation

While sealing up the house might at first seem like a bad idea from a ventilation standpoint, it's in fact very helpful. In the past, ventilation has been left up to unplanned holes and cracks in the house with little thought given to when or where ventilation was occurring. But it turns out that even "leaky" older houses often have very little ventilation taking place when it's warm outside or when there's no wind blowing. This means a good part of the time older homes are receiving little or no ventilation. By sealing up the leakage points and planning the ventilation, the energy-efficient house has the right amount of ventilation at the right time and at the right location where it's needed.

Ventilation systems in energy-efficient houses take two basic forms:

• Mechanical ventilation without heat recovery;

• Mechanical ventilation with heat recovery.

The choice to recover heat or not depends on the cost of the system and the climate. With heat recovery, the system is designed to recapture heat from warm air before or while it's being vented to the outdoors.

Whether heat recovery is included or not, the system should provide "spot" ventilation in the kitchen, bathrooms, and laundry room. This will exhaust stale air, moisture, odors, or other contaminants at the site as it's generated. In addition, a "whole-house" system will be needed to provide fresh air, while generally exhausting stale air.

The system should have a combination of automatic and manual controls. Typically, the automatic control will be either a time clock that turns on the system at certain times of the day or a dehumidistat that turns the system on when the moisture level in the house gets too high. The owner should also have manual controls to turn the system on, off, or to a higher speed as needed.

Along with installing some type of ventilation system to control indoor air quality, you also need to maintain control over the products used in the house to begin with. One of the best ways to prevent an indoor air quality problem is not to introduce pollutants into the house to begin with. Some examples of this would be avoiding the use of products that contain formaldehyde and airing the house out before moving in, so fumes and moisture left over from construction will be reduced. Hobbies or activities that produce fumes should be done in areas with adequate ventilation.

Better Doors and Windows

Doors in an energy-efficient house should have both a lower U-value (higher R-value) than older standard doors, and a good weatherstripping package to prevent air leakage. One example of a higher quality door would be a metal, wood, or fiberglass clad door with a foam core. The foam core lowers the U-value of the door from .40 to .20 or less.

Because windows are such poor insulators when compared to the rest of the home, you should give careful consideration to their use in the energy efficient house. You should look at four areas:

• Window orientation;

• Amount of window area;

• Type of glazing;

• Frame details.

Window Orientation
Due to the high heat loss of windows, the goal should be reduce the number of windows used. (The Washington State Energy Code limits the amount of glazing area.) Also, it's important to place the windows so they will help heat the house. The best way to do this is to locate the majority of windows on the south side, while minimizing windows on the north, east, and west. This will not only allow the sun to provide additional winter heat, but will help to prevent overheating as well. You should take care to position the windows so the rooms will have enough light and will meet code requirements. (The Uniform Building Code requires 10% glazing in habitable rooms.)

Window Area
This is one decision where smaller is better. As mentioned earlier, windows are a major source of heat loss due to their low R-value. The best way to counter this problem is to minimize the overall amount of glass put into the home. As a rule of thumb, the glass area should run no more than 15% of the floor area. In a conventional home, glazing runs about 13% to 18%. (The Washington State Energy Code limits glass area to 21% in gas-heated homes but for more efficiency you'll want to go lower.) These numbers may seem low compared to solar houses of the past. But remember the house is being built better so it will require less heat and can afford to capture less sunlight. Whether the house will be dark depends more on the placement of the windows than on the amount of window area.

What's an R-Value? A U-Value?
Some building components, such as walls, floors, or ceilings, are given R-values to indicate how well they perform thermally. An R-value measures the thermal resistance of a material. In other words, it measures how slowly heat flows through a material. The higher the R-value, the better an insulator the material is.

Although R-values have been applied to windows as well, current practice is to use U-values to describe their thermal performance. U-value is just the opposite of R-value. It measures how quickly heat flows through a material. Thus the lower the U-value, the better an insulator the material is.

The terms are interchangeable by the formulas R=1/U and U=1/R.

Glazing Type
Glazing describes the transparent material used in the window (typically glass or plastic). You need to decide both the number of glazing layers and the type. The minimum choice would be a plain double-glazed window, with a U-value of .65 for a gas heated home, and .40 for an electric heated home. The next step up is a triple-glazed window or a double-glazed Low-e window, both around U-.33. Low-e refers to a manufacturing process that enables the window to retain more heat inside the house.

The window's thermal performance depends not only on the number of glazing layers, but also on the air space between the glazing layers. A spacing of 1/2" to 3-1/2" is recommended. One advantage of using a higher-efficiency window is that you can add more window area for views and daylighting without increasing the heat loss.

Frame Details
Common frame materials are wood, vinyl, metal, and fiberglass. Like other parts of the window, the R-value of the frame varies among materials. Wood, vinyl, and fiberglass are about the same, and metal is much lower. Insulated metal frames are usually referred to as thermally improved frames and have a better R-value than uninsulated metal frames. They also are less likely to produce condensation. But even with a thermal break, insulated metal frames are not as efficient as wood, vinyl, and fiberglass frame options. Regardless of the framing material, you should look at the weatherstripping and check to see if the window has been tested for air leakage.

Heating, Lighting, and Appliances

Since the energy-efficient house will use less heat than a conventional one, you should take care in choosing a heating system. The two important issues to consider are the size of the system and controls, While undersizing the heating system will lead to comfort problems during cold periods, oversizing can cause discomfort, a loss of efficiency, and premature equipment failure. You or your mechanical system installer should do heat loss calculations to ensure the right size system Is installed. Having the ability to control the temperatures within different rooms in the house will also lead to higher levels of comfort and lower heating bills.

Because of the reduced heating load, lighting and appliances will play a larger part in the overall energy performance of the house. Taking the time to lay out and choose an efficient lighting system will keep the house working as an efficient unit. Examples would be using task lighting, and fluorescent lighting along with multiple switches to achieve acceptable levels of light while reducing energy consumption.

Choosing energy-efficient appliances will also contribute to an overall lower energy bill. Energy-guide labels on refrigerators, dishwashers, washing machines, and hot water heaters will help you choose the most efficient appliances. The hot water heater is the largest energy consumer of the appliances, so it demands the most attention. Consider where the tank will be in relation to where the hot water is used, and choose a tank with a higher insulation value to reduce losses. Also, setting the tank on an insulated pad will help reduce heat loss. Insulate hot water pipes and install low-flow showerheads and faucets.

Suggested Reading

Energy Efficient House Construction Techniques Manual, Energy Business Association of Washington, Washington State Energy Office, Olympia, WA 98504, 1984.

Fine Homebuilding, Hughes, John R., The Superinsulated House, June/July 1982. Good description of how to efficiently put together a double wall. Step by step, with features.

Low Energy Home Designs: Design Guidelines and Plans for Energy Efficient Housing, Alberta Agriculture, Print Media Branch, 9718 107 Street, Edmonton, AB, T5K 2C8, 1982 94 p.

New House Planning & Idea Book, Brick House Publishing. This is the American version of the above book from Alberta agriculture. This book works from a variety of floor plans and highlights construction details through them.

Superinsulated Design and Construction, Lenchek, Thomas Mattock, Chris and Raabe John, Van Nostrand Reinhold, 1987

The Superinsulated Home Book, Nissan, J.D. and Gautam Dutt, and Sons,1985.

Solar Age, "Super Saskatoon," Jane Meyer and Craig Sieben, January 1982, and "The Latest in Superinsulated Houses," David Godolphin, November 1982.

Washington State University Cooperative Extension

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