Optimize Energy – Design

Energy has been one of the great concerns in house design since the 1970’s. Two great leaps in the cost of oil, one in 1973 and the second in 1979, led the charge for energy efficiency in all parts of the economy.

House designs of the 1970’s and earlier decades were analyzed for their performance, from which new ideas developed to reduce energy use in existing houses and in new house design.

Since then, additional concerns regarding the local and global environment along with the political and economic goals of energy independence has pushed further the desire to improve the performance capabilities of houses.

Today, residential energy use accounts for around 21% of energy consumption in the United States according to the U.S. Energy Information Administration. Making houses ever more efficient goes a long way in reducing the amount of energy we use.

Concepts

The concepts we’ll discuss regarding energy efficiency will include the overall goals of energy use; how energy use is analyzed; how site selection can impact these concepts; how homes are heated, cooled, and powered; and how water is used.

Goals

There are various goals to obtain when considering energy efficiency in your house design.

Energy Use Reduction for Cost Savings

Reducing the amount of energy needed for a house is good environmentally as well as financially.

According to a 2016 study by the National Resources Defense Council, a typical homeowner in the U.S. with an 1,850 square foot home paid around 3.3% of their income on energy expenses, adding up to around $2,200 per year for a $68,000 annual income.

Though not a huge percentage of a homeowner’s costs, a large reduction in energy use can be significant.

A 2015 study by the U.S. Energy Information Administration found the typical energy use of a single family detached house broken down as follows:

• Space heating: 46%
• Air conditioning: 8%
• Water heating: 17%
• Lighting: 5%
• Food refrigeration: 3%
• All other uses (TV’s, appliances, computers, tablets, smartphones, streaming devices, etc.): 26%

The individual percentages for heating and cooling along with their overall percentage of total household use can vary greatly by region, but this gives us a good means of measurement.

Designing a new home that integrates materials, methods, and systems that reduce energy use can be easily justified.

Net–Zero Energy House Design

An ultimate goal is to be able to produce all the energy your house needs without having to rely on utility services, thereby removing any monthly costs for energy use. This is the idea of the net-zero energy house.

This type of design utilizes a combination of passive design concepts that use the sun and wind to help cool the house, and active concepts such as photovoltaic panels, wind turbines, and geothermal systems to heat, cool and generate electricity.

Comfort

Any reduction in energy use or use of ecological systems must allow for the comfort of the house. Reducing energy use means nothing if you’re cold in in the winter and hot in the summer.

Besides using improved construction techniques and more efficient appliances, utilizing the sun in cooler months for heating and shade in the warmer months can help counterbalance energy use.

Analyzing Energy Use

There are several ways to figure out how well a home performs. Let’s take a look.

The Concept of Thermal Bridging

To analyze how your home’s envelope (all of its exterior surfaces) performs, you need to understand the concept of thermal bridging. This term basically means the amount of temperature that can transfer between the interior and exterior of your home through a specific material, system of materials, or at joints between materials and components such as doors and windows.

In summer, thermal bridging means losing cool air to the outside, counteracting the ability to cool the home. In winter it means loosing heat to the outside, counteracting the ability to warm the home.

The easiest example most of us know is windows.

An old metal-framed window with a single piece of glass gets very cold very quickly in the winter. You can touch it and feel the cold, and you can feel cooler air when standing next to it inside. In the summer you can feel the sun’s heat radiating into the room if its facing the sun and there’s no window coverings.

Today’s metal windows counteract such thermal bridging in a number of ways:

• The metal frame is now made in two parts – an inside frame and and outside frame. These are joined together by a material that minimizes any temperature jumping between them. This is called a thermal break.
• Today’s windows use insulated glass. This glass consists of two pieces of glass adhered to either side of a sealed frame. The space between the pieces of glass is typically air-less, acting as insulation between the outside temperatures and inside temperatures.
• Today’s glass has improved performance in relation to solar control. A coating called Low-e, for low-emissivity, reduces the amount of infrared and ultraviolet light getting through the window which helps with cooling in the summer. It also allows in enough solar radiation to warm the room in winter while reflecting interior infrared light back into the room, improving heating. Visible light is barely reduced.

Similar improvements to performance have been made to doors along with the materials and wall systems we use for the exterior walls of our houses.

Home Energy Audit

A home energy audit is an analysis of an existing home’s flow of energy, determining where heat loss occurs and how it can be reduced. This is typically done by a professional inspector who has appropriate equipment to test the components of the house.

For newly-designed houses, the concept of an energy audit can be applied during the design process. The materials to be used to build the house will have performance ratings for their insulation performance. The overall performance of these materials individually and together can be calculated.

Also, once the house is completed an on-site audit can be done to confirm performance and to identify areas that might need some corrections to the installation or to provide suggestions for additional improvements in other areas.

Home Energy Score

The Home Energy Score was developed by the U.S. Department of Energy to rate the energy efficiency of a house. The score is based the structure (materials used to build the house) along with the heating, cooling, and hot water systems.

This was developed as a way to look at an existing home and how it performs, then improving that score through a series of options you can select to improve the house.

This has been extended to new houses as the Whole-House Systems Approach to design, which is discussed below.

Whole-House Systems Approach

This approach to design has the goal of maximizing energy performance before you build. This design method considers the house as an energy system consisting of multiple various parts that work together.

Considerations during design include:

• Site conditions
• Local climate
• Appliances and electronics
• Insulation and air sealing
• Lighting and daylighting
• Windows, Doors, and Skylights
• Water Heating

The goal is to design a house that reduces energy loads as much as possible while maintaining a comfortable home.

Site Selection

The start of your design journey is the property you’ll select to build your house. Most every property is unique, and you’ll need to understand how the site can play into your design.

Site Advantages

Each site you’ll consider will have a specific location from which the sun’s path across the sky can be determined throughout the year, allowing you to take advantage of this free resource.

The site will also have weather patterns such as seasonal winds and storm paths that can impact a house’s performance if not properly designed.

Some sites can have other opportunities that can assist in energy efficient design such as existing trees that can shade the house or act as an effective wind break.

Driving Distances

Though not a part of the house design and its energy efficiency, another energy cost to consider is transportation. The sites you’ll look at will have various distances to different activities, so be sure to account for that as part of your overall energy use plan.

Transit Availability and Neighborhood Walkability

A great way to minimize your personal energy use is the ability to use public transit and the ability to walk to local services.

Though not available in most areas, being able to walk to a bus or train, or even a short drive to a train station can save on your energy use and costs. Be sure to consider this with each site.

Also, building in an existing neighborhood or an effectively planned new neighborhood where you can walk to services such as shops, restaurants, dry cleaners, etc., can go a long way in your personal energy reduction.

Indoor Air Quality

As we button up our houses we need to be aware of indoor air quality. Since we’re practically deleting any air leakage we’re also deleting the chance for fresh air coming into the house on a consistent basis unless we specifically decide to open a window or door.

This situation has led to problems of various sorts, including moisture getting trapped in exterior walls causing mold growth and out-gassing of finish materials into the house. Such issues can cause health problems that we didn’t have before when our houses weren’t so tightly enclosed.

This doesn’t mean we should have more air infiltration through our walls. It just means we need to be aware of the materials we select, how we put them together, and how we take on the responsibility of making sure we allow enough fresh air into the house at a rate that allows us to effectively clear out the old air.

A national standard (ASHRAE) recommends houses have a minimum air exchange rate of 35% per hour, and not less than 15 cubic feet of air per minute per person. This means there should be a full exchange of fresh air into the house within no more than a 3-hour period, maybe higher if the family is larger.

You’ll likely need to consider mechanical ventilation that can bring in fresh air at a proper rate.

Energy Use

Energy use is the amount of power it takes to run our houses. This energy will come from electricity, and often also comes from natural gas or oil for heating systems and natural gas for appliances such as stoves and clothes dryers.

Reducing our energy use saves us money. Selecting highly-efficient mechanical systems, water heaters, and appliances is a necessary goal.

The best-case scenario is to have energy that doesn’t cost us anything at all other than the initial expenses needed to install the systems. This is called net-zero energy.

Heating

Traditional Sources

Electricity, oil, and natural gas are the common energy sources we use for heating homes today.

Electricity can be used to heat a house through electric-resistant heating or as part of a central fan unit such as a heat pump.

Oil is often used for boilers, mostly in older homes in the eastern U.S. These boilers are used to create hot water or steam for heating systems via radiators or baseboard heating panels, or for heating a circulating fluid as part of a radiant heat floor system.

Natural gas can be used for boilers as well as in a forced-air system.

Solar Panel Power Generation (Photovoltaic Systems)

Electrical power for heating can be accomplished using solar panels (photovoltaic panels). These panels are typically installed on the roof oriented toward the sun. The panels take sunlight energy and converts it to electricity that can be used in the house for electric-resistant heating or as part of a forced-air system.

Solar Thermal Sytems

A solar thermal system uses solar panels to also heat a fluid that runs in pipes from the panels to the house and back. This heated fluid is then utilized via a number of special pieces of equipment to heat the home and/or to make hot water. Heating the home can be done with an under-floor radiant system, baseboard heating, or as part of a forced-air system.

Passive Heating

Passive heating uses the sun itself to warm the home. The house is designed to maximize the “collection” of sunlight through windows in cooler months. The light is used to heat floor and wall surfaces during the day that can then radiate the heat back into the house at night.

Cooling

Traditional Systems

Most air conditioning in the U.S. involves either window units for individual rooms or a central-air ducted system that blows cool air into multiple rooms. These use a refrigerant that is circulated and compressed to cool air which is then blown out into the home. After the air is cooled, the heat of the warmer refrigerant is expelled to the outside.

Another version that’s mostly used in dry climates is the evaporative cooler, sometimes called a “swamp cooler”. This uses a box with evaporative pads on three sides. Water is circulated through the pads while a fan pulls warm outside air in through the pads, cooling the air. The fan then blows the conditioned air out of the unit into the house.

Each of these systems require a large amount of electricity to operate the fans, circulation pumps, and condensers of the units.

Passive Cooling

Passive cooling is the age-old method of beating summer heat. This requires effective design to keep solar radiation out of the home through effective shading, creating exterior walls that keep summer heat from making its way through walls, providing cross ventilation of outdoor air through the rooms to create cooling breezes, and preferably a means of releasing hot air through the top of the house via skylights or cupolas.

In homes with basements, you can take advantage of somewhat cooler temperatures at that level by circulating that air through the main part of the house.

Cooling can be augmented through the use of geothermal systems that circulate a fluid from deep underground up to the house, taking advantage of the cooler temperatures at those depths.

Solar Cooling

Newer systems have been developed that use solar energy to cool the house. These are relatively newer systems for residential use and aren’t as common as traditional cooling systems, but they’re making headway.

I won’t get into technical aspects, but will give a general overview of these systems. Let’s take a look:

Solar Hybrid Air Conditioning

This system uses a home’s solar-panel-generated electricity to power an air conditioning system. This can include a central-air ducted system such as a heat-pump system, or smaller individual units, called mini-splits, that cool individual rooms.

Solar Thermal Air Conditioning Systems

This system uses solar panels to heat and circulate a refrigerant fluid instead of using an air conditioning compressor for the same process. The heated refrigerant from the panels is cooled through a heat exchanger, with the cooled refrigerant then passing through a fan unit to cool the home, cycling back to the solar panel for reheating.

Water Heating

As mentioned earlier, heating water for domestic use can use around 17% of your energy expenditure for a typical 1,800 square foot house.

Traditional Systems

Most water heating is done by heating water in a tank by using gas or electric resistant heating. Though tried-and-true, they’re expensive to operate.

Let’s take a look at alternatives.

Solar water heating

Using the sun to heat domestic water is a great way to cut money out of your annual budget, as sunlight is basically free to use.

There are various solar water heating options available, with many variants to each depending on the components used. Below are the general methods of heating domestic water.

• Direct water heating: This system uses the water pressure of your domestic system to circulate water to the solar panel for heating. The heated water is then piped directly to the plumbing fixtures in the house.
• Direct circulation hot water storage: This system uses an insulated box of flat-plate heat collectors with a dark bottom plate, located to capture solar energy. Water is circulated through this box for heating. The heated water is then pumped to a storage tank for later use.
• Circulating fluid water heating: This system uses a non-freezing fluid which is heated in a solar panel and circulated to a water storage tank. The heat of the fluid is transferred to the water in the tank using coils. Once the heat transfers off the coils, the cooled fluid is circulated back to the solar panel to be heated.
• Direct heating of water storage tanks: This system places two or more water storage tanks in a glazed enclosure outside of the house. The tanks are painted black to absorb heat, which then heats the stored water.

House Construction Types

Houses can be built in a variety of ways with numerous materials. Each type of framing / structural system and enclosure system needs to be designed for energy performance. Below are some various construction types we’ll discuss.

Wood Frame

Most houses in the United States are built of wood framing. Wood stud framing is typically enclosed with wood sheet panels over which a waterproof membrane is placed. The exterior finish material is then applied directly to the membrane or in front of the membrane with a cavity between them, such as for a masonry veneer wall or rainscreen system.

To help keep the house warm, batt insulation is placed between the studs prior to the interior being finished out.

Today, newer systems have been developed to make wood-frame houses more energy efficient. These include increased insulation, the use of building wrap to keep out moisture but allow for the expulsion of trapped water vapor, and interior vapor barriers to keep inside moisture from penetrating into the walls.

Additionally, rigid insulation panels have been developed that can act as both the insulation for the home and the enclosure of the framing. This provides for more consistent insulation values across the wall compared with batt insulation, where the wood studs have less insulation value than the batts.

Several exterior finish products have also been developed that have their own integrated insulation to augment the overall wall performance.

Advanced House Framing / Optimum Value Engineering (OVE)

This is a framing technique developed to minimize the amount of wood used in framing, which minimizes construction waste. It also replaces lumber with rigid insulation where applicable to improve energy performance.

Advanced framing can include the following differences from traditional framing:

• Using two-foot planning modules to make the best use of common construction material sheet sizes and to reduce waste and labor.
• Using wall stud spacing of 24 inches on center to work with common sheet sizes of construction material.
• Spacing floor joists and roof rafters at 24 inches on center, again to work with common sheet sizes.
• Using two-stud corner framing instead of three-stud or four-stud corners.
• Using drywall clips or scrap lumber at corner framing for drywall backing instead of using more studs.
• Using in-line framing where the floor, wall, and roof framing members align vertically to transfer loads directly to the foundation.
• Using single-piece lumber headers and top plates at non-load-bearing locations.
• Eliminating headers in non-load-bearing walls.

According to the U.S. Department of Energy, such construction can result in material cost savings of hundreds of dollars for a typically-sized house, can save labor costs from 3% to 5%, and can reduce annual heating and cooling costs by up to 5%.

However, the framing system must comply with all wind, seismic, and other requirements of the jurisdiction the house is in.

Timber Frame

Timber frame construction was very common up to the development of wood stud framing. However, it has become popular as an aesthetic style. This framing system uses large-sized wood framing members to create columns, beams, and roof rafters.

Today, such a system would typically be enclosed with a framed wall or masonry and stone wall outside of the timber frame so that the timber can be fully exposed on the interior.

The use of structural insulated panels, called SIP’s, has become common to enclose timber frame construction. These panels consist of thick rigid insulation sandwiched between wood panel sheets, typically OSB (oriented strand board). Together this creates a strong well-insulated panel that can come in large sizes (up to 8 feet x 24 feet) and used as the exterior walls.

Log

Log homes are just that – stacked logs that act as the enclosure, structure, and the exterior and interior finishes of the home. There are several performance issues to consider with log homes:

• Wood has less thermal resistance than typical insulated wood-frame construction. A 6-inch softwood log wall has an R-value (thermal resistance value) of around 8. A typical 2×4 wood stud insulated exterior wall has an R-value around 14, which is significantly better.
• Logs do have some thermal mass benefit to offset the lower R-value, but not much.
• Logs will shrink over time, even if kiln-dried, they shrink and expand with weather and temperature changes. Therefore, you’d need to watch for gaps that can open up between the logs, causing air leakage.
• The best trees to limit shrinkage, starting with the best, are cedar, spruce, pine, fir, and larch.
• Logs are susceptible to moisture, which over time can lead to rot and insect infestation. Use waterproofed and insecticide-treated logs, and be sure to reapply the treatment regularly.

Light-Gauge Steel Frame

This framing consists of thin metal “studs”, similar to wood studs. The same enclosure and insulation concerns apply here; however, being metal, these studs are prone to greater thermal heat transfer than wood studs when wall insulation consists only of insulation batts placed between the studs. It’s best to use continuous exterior insulation for this framing system.

Another consideration has to do with different expansion and contraction rates with temperature compared to wood. This will require attachments between the two, such as wood sheathing, that allow for the differing movements of the materials.

Heavy-Steel Frame

Heavy-steel framing uses large structural steel members for columns, beams, and roof rafters, similar to timber framing. The same enclosure options apply to both framing options.

Masonry Structure

Building a house from brick has been a time-honored method for centuries. Today, a masonry structure usually consists of concrete masonry units (CMU) as the structural wall and enclosure for the home.

Masonry walls have great thermal mass properties, but not good insulation value. Thermal mass allows the walls to soak up the sun during the day and then radiate the warmth into the house at night, which is good in colder months. Thermal mass using CMU would require solid CMU blocks or CMU cavity blocks filled with mortar.

Since high insulation values are required for most codes, building a thermal mass wall might not fly with local authorities.

Today, masonry walls can be covered with rigid insulation board to get the insulation values that are required. There are also insulated CMU blocks which incorporate rigid foam within the unit. However, these have an issue with discontinuous insulation due to the fact that the insulation cannot abut with the insulation in the adjacent unit.

Concrete Structure

A concrete structure typically consists of columns and horizontal slabs for the structure. Concrete walls might act as structure as well.

This type of structure isn’t common in the U.S. due to the high labor costs required, but has been common in other parts of the world where labor costs are significantly less.

A concrete structure would typically be enclosed by masonry. However, infill walls of wood or steel studs could be used, as could walls of glass.

Concrete has great thermal mass properties, but the same code issues apply as with masonry construction.

Panelized Construction

Structural panels have become more common for house construction due to lower labor costs and shorter time frames for installation. SIP (structural insulated panels), are most common. This integrates rigid insulation between two boards, typically OSB board.

Together these create a strong wall that can handle structural loads. Since the wall is built with insulation, the system creates its own continuous thermal barrier.

Ecological Design

The best way to optimize energy for your house is to use ecological design concepts. This means utilizing readily available regional materials and planning the house for optimal use of the sun for heating. Using on-site power generation is a positive.

Let’s take a look at options for ecological design.

Passive Solar Design – Methods

Passive solar design utilizes the sun’s energy for home heating, using the sun’s path during the day and during the seasons as part of the home’s planning.

Below are some options for passive solar design.

Direct Gain

Direct gain is planned such that all living spaces receive adequate sunlight to heat the house during the day. It also uses materials that can radiate that warmth back into the house at night. Any glass for this purpose would be shaded in warm months.

Indirect Gain (Trombe Wall)

Indirect gain is the concept of using sunlight to directly heat a large thermal mass wall that’s inside the house so that the house can receive radiant heat from all sides of the mass. This type of thermal mass is called a Trombe wall, named for a French engineer who pioneered the use of such thermal mass in the 1970’s.

Isolated Gain (Sunspaces)

Isolated gain uses specifically-designed spaces to collect solar heat that can then be distributed through the rest of the house. Such spaces are similar to greenhouses. The distribution can occur through radiation of the collected heat, conduction of heat through material, or the movement of air through the use of fans.

Comfort in Warm Seasons

Though passive solar design is planned for heat gain during cold months, you need to be cool and comfortable during the warm months. This can happen through architectural design that shades windows and surfaces in the warm months, and uses landscaping such as deciduous trees that allow light into the house in winter while providing shade in summer.

Passive Solar Design – Implementation

Design is in the details, especially with passive design. Let’s review.

Properly-oriented Windows

To maximize solar gain, the house should be generally broad east-to-west and shallow in the north-south direction, orienting the day-to-day living spaces on the long side that faces the sun. This long side should have enough windows so that each living space can be warmed using solar energy.

Thermal Mass

Thermal mass should be used when allowed by the local authority. Thermal mass allows for the collection of radiant energy into an appropriate material which will then radiate into the house at night. If you can’t use thermal mass for the exterior walls, use a Trombe wall and heat-absorbing materials inside the house.

Heat Distribution

Heat distribution is putting the sun where its needed for warmth. The day-to-day spaces such as living rooms, dining spaces, and kitchens benefit from direct solar gain into the rooms.

Bedrooms don’t typically need as much direct gain since they’re occupied mostly at night, so radiant heat from thermal mass or from isolated-gain spaces might be adequate.

Little-used spaces might not need anything other than heat from the other spaces. Such spaces could include a laundry room, pantry, or other storage room.

Sunlight Control

An important consideration in passive solar design is sunlight control. In cooler months you want as much sunlight in the house as you can get so that the house stays warm. Conversely, you want little radiant solar energy during warmer months. Luckily the sun is lowest in the cooler months. The higher sun in the warmer months allow for shading to cool the house.

Glare can become a problem, especially during the colder months while the sun is lower.

In warm months the sun begins heating the east side and the light is more intense while low. The side facing the sun is warmed next, and then the west side of the house. This can cause the west side of the house to be much warmer due to the extended period of heat gain, and the light will be more intense while the sun is setting.

Designing walls and windows that address this can be challenging. South windows need to be shaded to block out the higher sun in warmer months while allowing light in during cooler months. East-end and west-end windows should be smaller or screened to minimize the intense sunlight in the morning and evening.

Living in direct sunlight during the heating season might be great, but be aware how light and glare can impact the space and how furnishings are arranged.

Design Methods Utilizing the Sun

Designing a house to maximize its energy use effectiveness and livability is important. Below we discuss two approaches to analyze energy-efficient house design.

Whole-house Systems Approach

This approach looks at all elements of a house together to analyze potential energy performance. This can work for more traditionally designed houses as well as for solar design houses. We discussed this approach in more detail earlier in this article.

Benefits of this approach can be a design that:

• Reduces utility and maintenance costs
• Increases comfort
• Reduces noise
• Creates a healthier and safer indoor environment
• Improves the durability of the house.

Due to the complexity of such analysis its best to hire a professional to provide the review of your design as well as the built house.

Passive House

Passive house is a voluntary standard and a design process for energy efficiency, the goal of which is to reduce the house’s ecological footprint. Areas of review include:

• Passive solar design, including the impact of landscaping.
• The use of superinsulation to rid of any thermal bridging.
• The use of high-performance windows, typically requiring double-insulated glazing (triple-pane glass units)
• Airtightness of the house design.
• Use of natural ventilation
• House heating using passive solar design, heat recapture from internal mechanical heat sources, considering body heat as part of the analysis.
• Energy conservation throughout the design
• Using passive daylighting while using light fixtures at night that minimizes energy use.
• Using appliances that meet the high standards of Ecolable certification.

A Passive House does not require any specific design style to obtain its goals. Rather, it encourages whichever design you want that can successfully integrate and obtain the goals.

Many Passive House homes manage to obtain net-zero energy use.

Ecological Construction Options

Ecological construction uses readily available materials such as soil, straw, and discarded material. Combined with effective passive solar design, this construction type can significantly reduce a home’s overall energy needs, and often allows for a home to become completely independent of any outside need for energy. Below are the most common types of construction.

Soil Construction

Soil construction uses dirt to build thick walls with good thermal mass. This is an age-old means of building that can utilize a couple of methods:

• Masonry construction: The most well-known example in the U.S. is the adobe construction found in the southwest, especially in New Mexico. This traditional method forms on-site mud bricks mixed with straw as a binder, and then dries them in the sun. The brick is then stacked and covered with mud plaster. There are contemporary variations to this method.
• Rammed Earth construction: This method of construction uses vertical forms in which soil and binders such as straw are placed and then compacted, creating a strong wall. The wall is also covered in a mud plaster.

Earth-sheltered Construction

Earth-sheltered construction uses soil to protect a house from the elements, especially wind. Soil is not a great insulator, so insulation will still need to be considered where walls intersect with the soil in temperate and colder climates. Houses using this design often use passive solar concepts for heating during the winter.

There are three general methods for this type of construction:

• Bermed-Earth Design: This system uses soil placed against a strong structural wall, typically made of concrete, with the soil sloping down and away from the wall. Some designs extend the soil onto the roof, while others build partially into a slope.
• Penetrated bermed-earth design places soil on all sides and top of the house with only doors, windows and skylights penetrating through the berms.
• Underground Design: This design digs down into the earth for the house, covering the roof with soil. A central atrium open to the sky is used for light and ventilation.

Strawbale Design

Strawbale design uses rectangular bales of straw tied with wire that are stacked to form a wall. The wall is then covered with wire mesh stretched across the face of the bales that’s then covered with stucco and plaster. These walls can be structural, used to hold up the roof, or used as infill construction for timber-framed houses.

The stucco (exterior) and plaster (interior) provide fire resistance as well as thermal mass. The straw provides significant insulation. This system can be combined with passive solar design to heat the house.

Earthship Design

Earthship design takes on the goal of creating a fully-eco-positive design for houses, using natural and recycled materials along with various processes for heating, cooling, and electrical generation. This design is created for self-reliance.

The most common element of earthship design is the use of tires as the “formwork” for walls. There are mountains of discarded tires throughout the world, and this design takes advantage of that.

The tires are filled with dirt, which is compacted as the wall is built up. The wall is then covered in mud stucco and plaster for the surface finish material. This creates a thermal mass wall.

The house is designed with these walls on three sides, sometimes using bermed-earth for further weather protection. The fourth side has a lot of glass oriented toward the sun . The sun is used to heat interior floor and wall surfaces built of materials that collect heat that can be radiated into the house during the day and evening.

A variety of passive and geothermal cooling, on-site electrical generation, and water collection systems complete the self-contained design that is claimed to work for any climate.

House Planning & Design

To optimize the use of energy, appropriate planning of the house can go a long way in reaching the goal. Additionally, how the house is enclosed is important. Below we’ll discuss aspects of this.

House Orientation

The orientation of your house on the property is the starting point. Taking advantage of the sun for heating and energy production is a must. Passive solar heating can work with traditionally-built houses of any style, as well as with more unique ecological construction methods.

Room Placement

In temperate and cold climates the daytime living spaces should face the sun to take advantage of its energy during the colder months. Bedrooms can be placed on the side away from the sun as they’re mostly occupied at night.

Placing support spaces such as the laundry room, pantry, storage rooms, and the garage at the east and west ends can provide protection from morning and evening heat during the hot months.

In hot climates the house is best oriented with living spaces facing away from the sun to reduce the potential for heat gain. Having the bedrooms face the same direction is advantageous, placing all support spaces and the garage toward the sun for protection from daytime heat.

Vernacular Design

Vernacular design is a term for historic designs adapted to the materials and climate of a region. It’s good to understand how materials were used in the region you’re building as well as the design methods they used to keep houses warm in winter and cool in summer.

You don’t have to design an ‘old house’. Instead, learn from them so that you can apply the principles to your house design, especially in terms of natural heating and cooling. Today’s materials and technologies can augment the historic materials and designs to allow you to create a unique and well-performing design based on historic climate adaptation.

Foundations

Any foundation, whether for a basement or for a home built on a concrete slab, can transfer cold temperatures into the house. Properly insulating the foundations is important to minimize this.

Rigid board insulation is used for foundations, and can be placed in a variety of positions depending on the design of the foundation in relation to the floors.

Basements / Lower Levels

Today basements are always seen as “bonus space”. There are different types of basements:

• Full-depth basement: This basement is essentially completely underground with no windows. If this basement aligns with an outside wall, windows would have to occur in “light wells”, which are small areas dug into the ground next to a foundation wall deep enough to install a window.
• Partial-depth basement: This basement is mostly underground but might extend above the ground enough to allow for some small windows.
• Walk-out basement: This basement is typically used for sloped sites. The side of the basement on the lower part of the site is placed such that you can access an outdoor patio using a standard-height door. Sizable windows are also placed on this wall.
• Full basement: A basement that is the same size as the footprint of the house.
• Partial basement: A basement that is smaller than the footprint of the house.

Insulating a basement that extends to an exterior wall of the house is important. Soil can freeze down to several feet during winter, so counteracting that cold is important. Insulating under a walk-out basement slab will be necessary as well.

Even partial basements will need insulation since soil temperatures at these depths can remain cool in winter.

Having outdoor light in a basement can reduce lighting costs over time. A walk-out basement using large windows at the yard level can be a good source of natural light.

The small windows used for partial-depth basements and in light-wells for full-depth basements don’t provide enough natural light, so supplemental lighting is required.

For full and partial-depth basements consider using a large light well or large open stair that has windows and a skylight above it that can bring down enough daylight to reduce the need for electrical lighting in the active spaces.

Also consider using a series of tubular skylights throughout the basement. These are also known as light tubes and solar tubes.

A light tube has a small round skylight at the top that’s attached to a round metal tube with an inner reflective surface. The tube travels from the roof through the attic to the ceiling of the space below. The bottom of the tube typically has a translucent panel to help distribute the light into the room.

These tubes are typically smaller than a typical skylight, with the tube sizes typically ranging from around 10 inches to 14 inches in diameter. Tube lengths can reach up to 30 feet, so using this for basements isn’t a problem as long as the roof is not too tall.

Never place a bedroom in a basement unless it can have full-sized windows on the yard side of a walk-out basement.

Exterior Walls

The main issues with exterior walls are thermal insulation, protection from exterior moisture, and protection from interior vapor. Exterior rigid insulation is best to create a uniform insulating enclosure with minimal, if any, thermal bridging if it has a high-enough insulation value (its R-rating, for resistance rating).

There are numerous methods to build exterior walls, and tons of material options for the exterior finishes. A lot of research will be necessary to determine the best materials for your house design.

Thermal Mass

Since most energy codes require a high R-value for exterior walls, using these walls for thermal mass is likely not viable. Some rural jurisdictions might not have an issue, especially in warmer climates, and areas with a tradition of such construction might be OK with it. Be sure to investigate your options from a code and energy performance standpoint.

If you can’t use exterior walls for thermal mass to take advantage of solar energy, you can always use interior thermal mass using a Trombe wall or windows and skylights placed for maximum benefit to heat wall and flooring materials that can absorb and radiate heat in winter.

Rainscreen

A rainscreen wall is an exterior wall system where:

• the finish (exterior) material is pulled away from the main wall such that rainwater doesn’t hit the main wall (which is the main job for any finish material).
• any moisture that might penetrate through the finish material can drain on the cavity side before reaching the main wall.
• air can flow behind the exterior material to help in drying out any moisture along with the finish material.

The gap between the back of the finish material and the face of the main wall is at least 3/8″. This minimizes the potential for capillary action that would allow water on the back of the finish material to reach the moisture barrier of the main wall.

Rainscreen walls basically consist of the same materials as any standard wall, with the only difference being furring strips or drainage netting to create the gap, insect screening at the top and bottom of the gap, and a few miscellany depending on the final materials and installation methods.

A masonry veneer wall is non-structural, has a cavity between the brick and the wall of the house, and is attached to the main wall by wire ties or special clips. It can act as a rainscreen as long as the gap is ventilated.

Rainscreens help reduce energy use by providing a solar radiant screen that eliminates any radiant energy thermal bridging between the finish material and the main wall. It also stops the effects of winter winds on the wall system, helping to keep the house warm.

The air gap can also provide some small benefit in summer, acting as a bit of a temperature buffer. The ventilated air will be a bit cooler when the outside air is hot.

Be sure to review any code requirements for rainscreens. Jurisdictions that have wildfires might see this gap as a means for fire to easily reach the main wall, and any natural materials within the gap can be seen as combustible .

Roofs

Roofs get the brunt of solar energy. Making sure the roof is designed to minimize the overheating of attic space is beneficial to reduce energy use.

Roof ventilation is necessary to help moderate attic temperatures. There are a variety of ventilating construction products that can be installed as part of the roof system. There are also mechanical ventilation systems that are available.

Appropriate insulation above ceilings located below attic spaces will be necessary to stop cold or hot air from transferring through to the attic. Flat roofs and any sloped roofs open to the spaces below will require a significant amount of insulation, rigid being best. Ventilation of the rafter spaces will be needed.

Cool Roof

A cool roof is a straightforward concept. This type of roof uses roofing material that can reflect light and radiant heat. Such roofs are very light in color, and a wide array of standard roofing materials can be used for cool roofs.

Green Roof

A green roof incorporates plants, typically seedums but can include most any type of plant, to cover the roof and keep it cool in the summer. These roofs are used on flat roofs or roofs of minimal slope.

Green roofs can be as simple as placing soil-filled trays placed on the roof to more complex systems that integrate with the roofing, insulation, and drainage components to maximize the positive impact, provide for rainwater capture, and to provide a usable garden space you can occupy.

The benefits of green roofs can be many, depending on the methods used to build them. They can:

• Help to manage and reduce storm water runoff from the roof.
• Provide insulation from solar heat by way of the plant materials intercepting the solar radiation before it can hit the roof.
• Reduce cooling needs.
• Reduce the heat island effect in urban and suburban areas.

Green roofs will be more expensive than traditional roofs, and the structure will need to be designed to support the additional weight. However, it can improve comfort and provide savings over time.

Windows and Doors

Needless to say, doors and windows are the weakest points in the thermal envelope of your house. Selecting energy efficient windows with high performance glass is a necessity. Doors should be insulated when using metal as the finish material and effectively sealed at the frames and door sill.

Landscaping

Landscaping can be an important component of your home’s energy performance. Let’s take a look at how this can work.

Tree shading

Deciduous trees, which drop their leaves in autumn, can be used as a means of providing shade in the summer and allowing in light in the winter. This is particularly beneficial for passive solar houses that use a lot of glass on the sun side of the house.

Trellises with vines at windows can also be a means of providing shading in summer along with light in winter.

In hot climates, the use of tall and large coniferous trees such as large junipers planted in groups next to the house can provide some shading for the walls of the house that get a lot of sun.

Windbreaks

Another use for large coniferous trees is as windbreaks. Planting these in a line along an edge of your property, one next to the other, can reduce the amount of wind hitting your house during the winter months, taking some of the heating load off of your house.

Green Roof

As discussed above, green roofs used on flat roofs can increase the efficiency of a roof system by minimizing the amount of sun that reaches the roof surface.

Water Conservation

Finding alternate methods of collecting and using rain water can reduce water utility bills and any electrical costs for water pumping. Below are some of these methods.

Rain Capture – Domestic Use

Rain is one of those free things nature gives us, so collecting it for our use is beneficial.

Capturing rain requires your roof drainage system to be tied to water storage tanks, which can be located at ground level or be below ground as cisterns. Ground-level capturing methods from non-asphalt paved surfaces (also excluding driveways due to the oils from your car) or from rain gardens might also be used.

This collected water is not technically “potable” – meaning usable to drink and cook – unless its filtered and treated properly. Otherwise, the water can be used in a separate water system for toilet flushing and for washing clothes, or used for landscape watering or washing your car.

Rain Capture – Irrigation

Using captured rainwater for your yard minimizes the amount of water needed from a utility or pumped from underground sources.

Xeriscaping

Xeriscaping uses only regional plants and vegetation for your landscaping. These plants are adapted to your local environment and therefor should require no or minimal irrigation. This minimizes any costs needed to obtain water for your landscaping.

Note: Photos and graphics are by Cayl Hollis unless noted otherwise.

Top Image: Photo by Fips.

Featured image on home page by Mark McCammon.