Note that this information is of a general nature and is not a substitute for the language in the code. Code compliance for a particular project is determined based on materials submitted in a permit application. Also be aware that all work is required to comply with the code, regardless of whether a permit is required.

• General application of the Residential Energy Code
• Changes of occupancy or changes of space conditioning
• Changes of space heat type to electric resistance from other fuels
• Best ways to show compliance
• Residential space heat types
• Residential glazing requirements
• Residential insulation requirements
• Residential space heating and cooling system requirements
• Residential service water heating system requirements
• Residential lighting requirements
• Energy efficiency tips

GENERAL APPLICATION OF THE RESIDENTIAL ENERGY CODE:

• Group R occupancy. The Residential Energy Code (Chapters 1-10) covers all Group R occupancy as defined in the Building Code. This not only includes single-family dwellings, but also multi-family dwellings, and the guest rooms portions of hotels and motels, both low-rise and high-rise. It also includes spaces, such as corridors, that are considered accessory to the main use by the Building Code. Other occupancies are subject to the Nonresidential Energy Code (Chapters 11-15).
• Space by space determination. Occupancies are determined on a space by space basis, NOT on a building basis. Thus, in a building with three upper floors of apartments, one street level floor of retail shops, and two floors of below-grade parking: the apartments would be subject to the Residential Energy Code and the retail and parking would be subject to the Nonresidential Energy Code.
• Insulation exemptions. Spaces which are unheated, such as single family garages, are not required to be insulated. (Note, however, that the Building Code requires habitable spaces in Group R occupancy to have heating equipment, thereby triggering the building envelope requirements of the Energy Code.) Be aware that, even if a space is exempt from the building envelope requirements, all the other equirements in the Energy Code must be complied with. Thus, a water heater must comply with the efficiency requirements regardless of where it is installed, and there are requirements for efficient lighting in parking garages.

CHANGES OF OCCUPANCY OR CHANGES OF SPACE CONDITIONING:
For the most part for existing buildings, only the altered portion is subject to the Energy Code requirements. However, there are two key cases which trigger full compliance: one which is for full compliance with all sections of the Energy Code and the other is for full compliance with the building envelope section. Consequently, for these cases, please refer to the new construction requirements.

• Change of occupancy from Other than Group R (nonresidential) to Group R (residential): Section 101.3.2.3 specifies that spaces with this type of change of occupancy "shall be brought into full compliance with this Code".
• Change of space conditioning: Changing a space from one that was exempt from the building envelope section to one that is subject to the code requires full compliance with the building envelope requirements. Examples of this type of change from unconditioned to conditioned space includes:
  - change from unheated and uncooled to heated,
  - change from unheated and uncooled to cooled,
  - change from unheated and uncooled to heated and cooled.
  Note that simply adding air conditioning to a space that is already a heated space does NOT require changes to the building envelope. (However, if alterations are made to the building envelope, they shall comply with the appropriate requirements.)

CHANGES OF SPACE HEAT TYPE TO ELECTRIC RESISTANCE FROM OTHER FUELS:
From 1986-2007, the Energy Code has had more stringent building envelope requirements for spaces having electric resistance space heat than for other fuels. (See the discussion below about residential space heat types for more information on how these categories are defined.) Section 101.3.2, which addresses the application of the code to existing buildings, states that "in no case shall building envelope requirements or mechanical system requirements be less than those requirements in effect at the time of initial construction of the building".

• Requirements to convert to electric resistance space heat. Consequently, for spaces constructed in 1986 or later, the space heat type cannot be changed to electric resistance from other fuels unless the space is brought into full compliance with the Energy Code at the time that the space was constructed. This primarily means the glazing and insulation requirements. (See the Seattle Energy Code History page for a summary of the requirements in effect at various dates.)
  Please note that Seattle City Light also has Service Requirements for new or enlarged electrical service which require that for spaces being converted to electric resistance space heat:
  - roofs and floors must be insulated to the current code, and
  - EITHER all walls OR all windows must comply with the current code.
  These City Light requirements apply to all conversions, including cases where the Energy Code does not.
• Other changes of space heat type. Other changes of space heat type are subject to the requirements for alterations.

BEST WAYS TO SHOW COMPLIANCE:
The Residential Energy Code contains three options for demonstrating Energy Code compliance. The options listed in order of preference are:

• Prescriptive Option (Chapter 6). ALWAYS use this option if it works for your project. It requires the least calculations on your part, which means fewer for the plans examiner to review. Prescriptive requirements are based on standard construction techniques and there are many commonly available products to choose from. No matter how sophisticated your design process is, that does not mean that you need to choose a complicated compliance process. The Prescriptive option Building Envelope requirements for Seattle are in Table 6-1. (Seattle is in King County and so is included in Climate Zone 1. For other portions of Washington State, see the Climate Zone categories in Section 302.3.)
• Component Performance Option (Chapter 5). Consider this option if you have have a multifamily project and the glazing area in your project exceeds 25% of the gross conditioned (heated and/or cooled) floor area or if you want to install windows with a higher U-factor or less insulation (such as at the perimeter edge of intermediate floor slabs) than the Prescriptive option requires. Be aware that the basis for tradeoffs is a glazing area that is 15% of the floor area and that you'll need to improve the energy-efficiency in some other area to make up for those areas that do not meet the Prescriptive requirements. Also be aware that metal studs provide a significant thermal bridge and that you'll also need to make up for this. Use the Group R Occupancy Target UA form.
• Annual Energy Analysis Option (Chapter 4). Consider this option if neither the Prescriptive option nor the Component Performance option works and your project has most of its glazing on the south side and the site has good solar exposure. Use one of the computer programs listed in Chapter 8.

RESIDENTIAL SPACE HEAT TYPES:
From 1986-2007, the building envelope requirements varied depending on the space heating system type. Starting in July 2002, the requirements were made the same for all residential space heat types using the Prescriptive compliance options, however, the electric resistance criteria were more stringent for the Component Performance (Target UA) and Annual Energy Analysis compliance options.  Starting in 2007, the requirements are the same for all residential space heat types for all compliance options.  (Note, however, that there are still differences in criteria based on space heating system type for nonresidential spaces.)

• Requirements more stringent for electric resistance space heat. Of the two categories of space heat type (Section 502.2.2), the requirements are the most stringent for spaces having electric resistance space heat. "Electric resistance" includes any and all kinds of electric heat (electric baseboard, electric wall units, electric furnaces, electric radiant heat, etc.), except heat pumps. The "other fuels" category includes everything else. An exception for other fuels allows up to 1.0 watt of electric resistance heat per square foot of conditioned floor area or 1,000 watts. For example, in an 800 square foot house or apartment, this would permit up to 1,000 watts. The intent was to allow a small electric radiant heater in the bathroom. (Conditioned floor area does not include unheated spaces such as a garage. However, if heating is provided for the garage, then the garage doors must be insulated to meet the Energy Code requirements, as must the walls, floors, etc.)
• Applies to additions and alterations as well as new construction. Alterations and additions must also comply with requirements based on space heat type. For example, if windows are replaced in a space with electric resistance space heat, such as a hotel guest room, the U-factor must be 0.35 or less. (A typical U-0.35 glazing product is described in the section on alterations involving replacement glazing only.) Also, if an existing house is heated with a gas or oil furnace, but a new room or second floor is to be added and heated with electric resistance space heat, then the new addition must comply with the building envelope requirements for electric resistance space heat.

RESIDENTIAL GLAZING REQUIREMENTS:

• Glazing. The definition of glazing (Section 201.1) includes all assemblies that transmit light - not only typical windows and skylights, but also sliding glass doors, translucent plastic panels, and curtainwalls.
• Glazing area. The definition of glazing area (Section 201.1) includes all components of the glazing assembly - glass/plastic, sash, and frame. It generally corresponds to the rough opening area in the wall or roof.
• U-factors and Solar Heat Gain Coefficient (SHGC) to be determined, certified, and labeled in accordance with NFRC procedures. The Energy Code specifies standard rating procedures, certification, and labeling (Section 502.1.5) so that products may be compared on a consistent basis: NFRC 100 for U-factor and NFRC 200 for SHGC. (The National Fenestration Rating Council was specified as the developer of the national system of glazing energy ratings in the 1992 Energy Policy Act.) These rating procedures address the complexity of today's glazing technologies - frames composed of several different materials, low-emissivity coatings, suspended films, argon and krypton gas fills, low-conductance spacers. For additional information about the rating procedures and about obtaining a copy of the NFRC Products Directory, see DPD Client Assistance Memo #403 and the NFRC website. Note that the code requires that ratings be for the entire glazing product, including the sash and the frame. While the information from glass suppliers about glass characteristics may be of interest in the design process, be sure to think about the overall product including the frame. Be aware that the heat loss through the frame can be 10 times more than that through the same area in the center of glass, and that the average heat loss through the entire glazing product can be double what might be expected if only the center of glass was considered. For better comfort and reduced condensation in the winter, look for a frame that performs as well as the glass.
• Default must be used for products without NFRC certification and labels. Energy Code compliance is based on NFRC certification. Products which do not have an NFRC label and which are not certified to the NFRC procedures, as indicated by a label on the product, are required to use the default values (Section 1006). Manufacturer's data is NOT an acceptable alternate.
• Verify NFRC certification and labeling. Be cautious about manufacturers' claims which seem to offer performance which is significantly better than the Energy Code requirements. Verify that the U-factor and SHGC has been determined, certified, and labeled in accordance with the NFRC Product Certification Program (Section 502.1.5.1). Make sure that this requirement is included in the job specifications. Make sure that the performance values are for the entire glazing product, not only for the center of the glass, or for the panel without the frame. A computer simulation or a test report to an NFRC procedure does NOT indicate compliance with the NFRC certification and labeling program. Even though the NFRC procedure may have been used, the sample might be a non-standard size or might not include a frame. If in doubt, ask the manufacturer for a copy of the Product Certification Authorization and contact NFRC (301-589-1776) to ensure that the manufacturer is participating in the NFRC Certification Program.
• Repairing broken glass. In general, provided that the frame AND sash remain:
  - broken single glass may be replaced with single glass,
  - broken double sealed glass units without a low-emissivity coating or without argon gas fill may be replaced with like sealed glass units,
  - broken double or triple sealed glass units with a low-emissivity coating or with argon gas fill must be replaced with like sealed glass units that perform at least as well.
  (In rough terms, the frame is the portion of the glazing product that is attached to the wall or rough. The sash is the portion that the glass fits directly into.)
• Adding storm windows. In general, provided that the frame AND sash remain, storm windows may be added over existing glazing products. (Section 101.3.2.5, exception 1 establishes a U-factor of 0.90 for these assemblies where one is needed for calculation purposes.)
  
• Alterations involving replacement glazing only. Section 101.3.2.5 specifies the reference case as the prescriptive requirement for alterations. The Prescriptive option Building Envelope requirements for Seattle are in Table 6-1. The Reference Case for alterations is Option II. If glazing is simply being replaced in existing openings, and the openings are not being enlarged and no new glazing area is being added, then the key requirement that must be complied with is the one for U-factor.
  - The glazing must have a U-factor of 0.35 or lower. While the U-0.35 requirement can be met in a variety of ways, typically it means:
  (1) an NFRC certified and labeled product*,
  (2) having double glazing*,
  (3) with a 1/2 inch space between the panes,
  (4) plus a very good (sputter) low-emissivity coating or
  having a medium (pyrolytic) low-emissivity coating AND argon gas fill, and
  (5) in a vinyl or wood frame.
  *If the product is not NFRC certified and labeled, then the defaults in Table 10-6A must be used (except for products manufactured by a small business) and this would mean triple glazing in the product specified above.
  
• Alterations where the glazing area is proposed to be increased, but the total glazing area will not exceed the glazing area specified in the reference case (15% of the floor area) . A proposed increase in glazing area (as opposed to the simple replacement of glazing as described in the previous paragraph) triggers additional requirements. Section 101.3.2.5 (referenced in the previous paragraph) states in part that "the result of alterations or repairs
  BOTH: (1) Improves the energy efficiency of the building,
  AND (2) Complies with the...glazing requirements of the reference case in Tables 6-1 and 6-2."
  In addition to the maximum U-factor cited in the paragraph for alterations involving replacement glazing only, the reference case also specifies a maximum area. Where the proposed design qualifies for the option described in this section by not exceeding the maximum area, then the additional heat loss created by adding glazing must be made up for. As even the best glazing has a higher U-factor (heat loss rate) than even an uninsulated wood frame wall, improvements will need to be made to other existing glazing or by adding more insulation to the opaque envelope area.
  - There are three criteria, all of which must be met: (1) the total glazing area cannot exceed 15% of the conditioned floor area, (2) the glazing must have a U-factor of 0.40 or lower, and (3) the overall energy efficiency of the building must be improved. With regards to the first item, if the glazing area exceeds 15% of the conditioned floor area, then you can not use this option. See the next section for other options. For the second item, a typical U-0.40 glazing product is described in the section on alterations involving replacement glazing only. For the third item, improving the overall energy efficiency, see DPD Glazing Calculation Worksheet for STFI for rules of thumb indicating what improvements would need to be made to other existing glazing or what insulation would need to be added for each square foot of additional glazing. Note that insulation must fill the cavity.
  
• Alterations where the glazing area is proposed to be increased and the total glazing area will exceed the glazing area specified in the reference case (15% of the floor area). The glazing area cannot be increased above the limits in the reference case unless the entire building envelope complies with the new construction requirements (i.e. all opaque areas are insulated as specified for the proposed glazing area and glazing complies with the appropriate U-factor for the proposed glazing area). The new construction prescriptive options are described below.
  
• Prescriptive options for new construction, including additions. The Prescriptive Building Envelope options for Seattle are in Table 6-1. Options I and II are applicable to all occupancies and have a maximum allowed glazing area of 12% or 15% of the gross conditioned floor area. For single-family (R-3 occupancy), Option IV allows an unlimited glazing area. For multifamily (R-1 and R-2 occupancy), Option III has a maximum allowed glazing area of 25% of the gross conditioned floor area, and Option V allows an unlimited glazing area. (Note that the glazing area is specified as a percent of the wall area for nonresidential spaces.) New construction and additions can use any of these options. As the allowed glazing area increases, the maximum allowed U-factor decreases - thereby necessitating a better product. Options for glazing areas for the reference case and for maximum area allowed in the prescriptive tables are as follows:
  - For the reference case: (1) the total glazing area cannot exceed 15% of the conditioned floor area, and (2) the glazing must have a U-factor of 0.35 or lower. A typical U-0.35 glazing product is described in the section on alterations involving replacement glazing only.

RESIDENTIAL INSULATION REQUIREMENTS:

• Nominal R-value. The definition of nominal R-value (Section 201.1) indicates that it is the thermal resistance of the insulation according to recognized standards. Some insulation literature (particularly for rigid insulation) rates insulation R-values at several different temperatures. The R-value for insulation used for the building envelope is to be determined at 75° (NOT 40° or other temperatures). Note that some rigid insulations, due to the use of certain blowing agents, will lose R-value over time.
• Metal frame roofs, walls, and floors where the insulation is to be installed between the metal framing members are not allowed to use the Prescriptive option (because of the significant thermal bridging of the metal) and instead these assemblies must comply with the overall assembly U-factors in Table 5-1 using the default U-factors in Chapter 10 (except for multifamily buildings complying with the component U-factors listed). The Prescriptive option is based on wood-frame construction and assumes insulation installed between wood framing or in a continuous manner uninterrupted by framing. Insulation installed between metal framing achieves only roughly half of its rated nominal R-value due to the thermal bridging of the metal framing.
• While the Prescriptive option is based on wood-frame construction, even wood framing elements act as a minor thermal bridge and reduce the effectiveness of the insulation. To simplify compliance, the R-values specified throughout the code are for the insulation alone. Be aware that all framing reduces the effective R-value of the overall assembly, because the framing acts as a thermal bridge to bypass the insulation. For instance, wood only has a value of approximately R-1.25 per inch of thickness, much less than a batt insulation rated at R-3 per inch or a rigid insulation rated at R-5 per inch. The ASHRAE Handbook of Fundamentals, a respected engineering text, estimates that 25% of a wood framed wall is framing for studs, headers, plates, sills, cripples beneath windows, framing over doors, other bracing, etc. Consequently, the effective R-value for a wall with 2 x 6 wood studs at 16 " on center with R-19 insulation in the cavity and gypsum board on the inside and plywood covered by beveled wood siding on the outside is R-16.1 (U-0.062) for the overall assembly - only 85% of the insulation R-value. For metal framing, it can be much worse. For a similar wall with metal studs and the same R-19 insulation in the cavity, the effective R-value is R-9 (U-0.11) for the overall assembly - only 48% of the insulation R-value! Thus, to minimize thermal bridges and achieve full insulation R-value, install insulation in a continuous manner over the framing members, especially if they are metal. (The U-factor is the thermal transmittance - an inverse rating of sorts, but one which addresses the overall assembly and includes the effects of thermal bridges such as that due to framing members.)
  
• Alterations. Section 101.3.2.5 specifies the reference case as the prescriptive requirement for alterations. The Prescriptive option Building Envelope requirements for Seattle are in Table 6-1. The Reference Case is case II in Table 6-1.
  - The total R-value of the insulation for each of the altered portions of the building envelope, after the alteration, must be no less than that specified in the Reference Case. Where alterations are made, such as adding insulation, the alteration must result in the altered portions complying with the Code. For example, it is not acceptable to only add R-11 insulation between the floor joists over a crawlspace where there is no existing insulation as this would not bring the floor up to the minimum insulation requirements. Similarly, it is not acceptable to only add R-11 insulation insulation in attic space that only has R-11 to start with as the total of R-22 is still less than the minimum insulation requirements.
  - For attics and most other roofs, R-38 minimum. R-30 is the minimum for insulation installed in single-rafter, joist-vaulted roof/ceilings PROVIDED that the this single-rafter area does not exceed 500 square feet per dwelling unit. If the single-rafter area exceeds 500 square feet, then that area must be insulated to R-38 insulation minimum.   To achieve R-30, while still maintaining the required 1 inch vented airspace, typically requires a 2 x 12 rafter if batt insulation is to be used. (Note that metal frame roof/ceilings where the insulation is installed between the metal framing are not allowed to use the Prescriptive option. These assemblies must comply with the opaque roof/ceiling U-factors in Table 5-1 using the default U-factors for steel truss framed ceilings in Tables 10-7A to 10-7E or calculated in accordance with Chapter 10, Section 1007.)
  - For walls, R-21 minimum. Section 602.2 contains three alternate wall assemblies that are deemed to comply with the R-21 requirement. (Note that metal frame walls where the insulation is installed between the metal framing are not allowed to use the Prescriptive option. These assemblies must comply with the opaque wall U-factors in Table 5-1 using the default U-factors for metal stud walls in Table 10-5A.)
  (1) 2 x 6 framing with R-21 fiberglass batts,
  (2) 2 x 4 framing with R-15 fiberglass batts plus R-4.0 rigid foam sheathing, or
  (3) 2 x 4 framing with R-13 fiberglass batts plus R-5.0 rigid foam sheathing.
  - For walls below grade, R-21 minimum if insulated on the interior and R-10 minimum if insulated on the exterior. The R-21 assemblies for interior insulation are described in the preceding section. R-10 exterior insulation is typically achieved with 2 inches of rigid insulation.
  (1) 2 x 6 framing with R-21 fiberglass batts,
  (2) 2 x 4 framing with R-15 fiberglass batts plus R-4.0 rigid foam sheathing, or
  (3) 2 x 4 framing with R-13 fiberglass batts plus R-5.0 rigid foam sheathing.
  - For floors over unconditioned space, R-30 minimum. R-30 typically requires a 2 x 10 rafter if batt insulation is to be used. Also, be aware that Section 502.1.4.7 specifies that the insulation must be installed tight against the floor so that there are no air gaps above that allow convective loops to bypass the insulation. Consequently, it is not acceptable for R-30 to be held in place at the bottom of a 2 x 12 floor joist. (Note that metal frame floors where the insulation is installed between the metal framing are not allowed to use the Prescriptive option. These assemblies must comply with the opaque floor U-factors in Table 5-1 using the default U-factors for metal joist floors in Table 10-4A or calculated in accordance with Chapter 10, Section 1004.)
  - For slab on grade floors, R-10 minimum for spaces with electric resistance space heat and R-10 minimum for spaces heated by other fuels. R-10 typically requires 2 inches of rigid insulation. This insulation must extend downward from the TOP of the slab for 24 inches or downward from the TOP of the slab and then horizontally below the slab for 24 inches total. If the slab has heating elements within or under the slab, then the R-10 insulation must continue under the entire slab or under the heating elements so as to isolate the heating elements from the soil.
  
• Prescriptive options for new construction, including additions. The Prescriptive option Building Envelope requirements for Seattle are in Table 6-1. The options for maximum allowed glazing area range from 12% to 15% of the gross conditioned floor area, with an unlimited glazing option for R-3 occupancy, single-family. (Note that the glazing area is specified as a percent of the wall area for nonresidential spaces.) New construction and additions can use any of these options.

RESIDENTIAL SPACE HEATING AND COOLING SYSTEM REQUIREMENTS:

• Space heating and space cooling equipment to be sized no greater than 150% of the design load. Section 503.2.2 limits the oversizing of equipment. Correctly sized equipment consumes less energy (even though it operates longer hours) and provides better comfort through this more-continuous operation that mixes the air more thoroughly within the space. Oversized equipment cycles on and off more frequently, meaning more cycles of standby losses and causing more wear and tear on the equipment. The larger blasts of hot or cold air more quickly reach the thermostat causing it to shut the system off sooner. This limits the amount of air mixing, which can result in more cold spots and hot spots.
  - Seattle design temperatures are 70° inside and 24° outside (46 degree temperature difference) for heating and 78° inside and 82° drybulb/66° wetbulb for cooling.
  - For spaces with electric resistance heat, the design heating loads for new construction in Seattle are commonly 3 W/sf. For an 800 square foot apartment, this means that 2400 Watts or 2.4 kW of electric baseboard could satisfy the heating load at the design conditions.
  - For spaces heated by other fuels, the design heating loads for new construction in Seattle are commonly 10 Btuh/sf. For an 1800 square foot apartment, this means that a furnace with a 18,000 Btuh output could satisfy the heating load at the design conditions.
  - Natural gas- or oil-fired equipment may allowed to be sized within the range of 150-250% provided that the equipment has an AFUE of 90% or greater.
• Ducts to be securely fastened and sealed with welds, gaskets, mastics (adhesives), mastic-plus-embedded-fabric systems. Duct tape is not permitted as a sealant on any ducts. UL181A and 181B tapes are allowed when installed in accordance with their listing.

RESIDENTIAL SERVICE WATER HEATING SYSTEM REQUIREMENTS:

• Electric water heaters to be installed on R-10 surface. Section 504.2.1 requires that electric water heaters in unheated spaces or on concrete floors be placed on an incompressible R-10 surface. The purpose is to minimize conductive standby losses from the tank into the concrete floor. The R-10 can typically be achieved by a 2 inch thickness of rigid insulation.
• Heated swimming pools to have pool cover. Evaporation is a significant source of heat loss from swimming pools. Section 504.5.2 requires that heated pools be equipped with a pool cover approved by the building official. The cover needs to contain a vapor retardant material so as to minimize evaporation. To be most effective, it should be located on the surface of the water.

RESIDENTIAL LIGHTING REQUIREMENTS:
The residential lighting requirements are contained in Section 505, with alterations addressed in Section 101.3.2.8.

• Group R-3 occupancy (single-family and duplex). Strictly speaking, the Residential Energy Code does not contain requirements for lighting for single family and duplex as Section 505, exception 2 exempts R-3 occupancy from the lighting power allowance requirements.
• Group R-1 occupancy (multifamily). While Section 505, exception 2 exempts the dwelling unit portions, the lighting power allowance requirements in Table 15-1 do apply to other spaces in R-1 occupancy, such as corridors and other common areas.
• Group R-1 occupancy (other, including hotel and motel). The lighting power allowance requirements in Table 15-1 apply to all spaces in other R-1 occupancy, such as hotel and motel guest rooms, corridors, and other common areas. In addition, hotel and motel guest rooms are required to have a master switch at the door to turn off all permanently installed luminaires and switched receptacles.
• Exterior residential lighting for all Group R occupancies (single-family and duplex, multifamily, other including hotel and motel.  Luminaires providing outdoor lighting and permanently mounted to a residential building or to other buildings on the same lot shall be high efficacy luminaires (incandescent is not allowed) or shall be controlled by a motion sensor with integral photocontrol photosensor.
• Parking garages. Parking garages are not considered Group R occupancy so lighting in that portion of a multifamily building, for instance, is subject to the requirements in Chapter 15 of the Nonresidential Energy Code (such as the limit of a maximum installed lighting wattage of 0.20 W/sf in Section 1532).

RESIDENTIAL ENERGY EFFICIENCY TIPS:
The Energy Code only establishes minimum requirements for energy efficiency. There is much more that can be done to achieve greater energy efficiency. In order, here are some suggestions to consider.

• Reduce the space heating load. For residential buildings, space heating is the largest energy enduse. The way to reduce energy consumption is to reduce the space heating load, and then to improve the efficiency of how that load is served. With Seattle's cloudy winter climate, the best way to reduce the load is to install better windows. Glazing is available with U-factors as low as 0.25 (lower is better for U-factor) - this product might have two layers of glass with a plastic film suspended in between, a low-emissivity coating, argon or krypton gas in the sealed glass unit, the glass layers separated by a low-conductance (insulating) spacer, all installed in a very good frame. Make sure that the U-factor is NFRC certified and labeled (this is your assurance that the data is independently verified). Adding more insulation (high is better for R-value) is another option, though this will not have as much of an effect as better windows.
• Optimize passive solar design. Having minimized the heat loss through the building envelope, the next step would be to optimize the passive solar gain by orienting windows to the south. Note, however, that for a well-insulated building with good windows in Seattle's cloudy climate, the optimum south-facing glazing area is 7-10% of the gross floor area (70-100 square feet for a 1,000 square foot house or apartment). More glazing than this and the unit will tend to lose more heat through the windows at night than it gains from the sun during the day. Don't mistake high temperatures in a space due to solar gain as meaning good solar design. Actually, it indicates the opposite. High temperatures mean poor solar design because there is not enough mass in the space. Good passive solar design has enough mass in the space to moderate the temperature swings - storing the heat to keep the building from overheating during the day and slowly releasing the heat at night when it is useful.
• Meet the remaining load efficiently. The next step, after minimizing the heat loss and optimizing the passive solar design, is to improve the efficiency with which the reduced load is served. The first priority here is to locate all ductwork and other heating distribution equipment within the insulated shell of the building. Many people do not realize that ductwork typically leaks a surprising amount of air and heat with it. In two otherwise identical houses, the one with ductwork in the attic or crawlspace will use 30-40% more energy for space heating than the one with all the ductwork inside the insulated shell of the building. (Note that this is not as much of a problem where piping is used as the heating distribution means because water leaks are usually quickly apparent.) Other steps are installing an automatic setback thermostat and higher efficiency heating equipment. The primary reason that people pay the higher cost of keeping all rooms heated to daytime temperatures throughout the night (when they are asleep and not using these rooms) is that they don't want to wake up to a cold house or apartment in the morning. While a person can manually turn the thermostat down at night, the chief advantage of an automatic setback thermostat is that it will turn the thermostat back up so the space is reheated by the time one gets up. Higher efficiency heating equipment produces the same amount of heat using less energy. Gas and oil furnaces and heat pumps are available with efficiencies 15-20% higher than the Energy Code minimums. Also, be very careful if considering radiant heat to be installed in a floor slab. The slab needs to be very well insulated from the soil below. Otherwise, much of the heat energy will go into the ground and be conducted away as our damp soil in western Washington is not a good insulator.
• Use water heating carefully. After space heating, water heating is usually the second largest energy enduse. Spas and hot tubs use an incredible amount of energy, especially if located outside. Spas and hot tubs should be well insulated on the sides and bottom, and should have a thick, insulating cover on top. Consider that the average year round temperature in Seattle is approximately 50°. Therefore, if heating a house to an average of 65° (70° during the day and 60° at night), there is an average temperature difference of 15 degrees (65° - 50°) between the heated space indoors and the air outdoors. Now think about a hot tub heated to 105°. Here the average temperature difference between the water in the hot tub and the outside air is 55 degrees (105° - 50°): 3-4 times as much! Using a setback thermostat can save lots of energy. Even if the hot tub is installed inside the house, the 40 degree temperature difference (105° - 65°) between the water in the hot tub and the air in the house is still 2-3 times the 15 degree difference between the air in the house and the outside air. While this extra heat will offset some of the space heating needs in the winter, it will also make the space warmer in the summertime, thereby increasing fan or cooling energy consumption.
• Pick energy efficient appliances. The third largest energy enduse in dwelling units is for appliances. Refrigerators consume the most energy because they run 24 hours/day, every day of the year, maintaining a 30 degree temperature difference (65° - 35°) between the air in the kitchen and the air inside the refrigerator, and perhaps twice that between the air in the kitchen and that in the freezer (65° - 0°). The best refrigerators can be 25-30% more energy efficient than the worst in any particular size category.
• Use efficient lamp sources, especially for exterior lights and hallway lights in multi-family buildings. Lighting is fourth on the list of enduses. Compact fluorescent lamps use 1/3-1/4 of the energy of incandescent lamps and the color rendition is improving all the time. While most lights within a dwelling unit may only be on several hours each day, exterior lights are often on all night (12 hours/day) and hallway lights in multi-family buildings and in hotel and motel corridors are on all the time (24 hours/day) providing good opportunities for energy savings.
• Additional information. For additional information, see Sources of Information on Energy Efficiency.