Climate Zone

Climate Zones and Resilience

09-22-2022


 

We build houses mainly to protect ourselves from the surroundings and the environment. Aside from extreme environmental events, remember that climate is part of the environment and the overarching system surrounding our homes. 

Understanding the climate system and the microclimate around your home should be one of the first steps in designing or retrofitting a home. 

Designing your home for the climate zone it is in has two key merits:

  1. It helps maintain thermal comfort for occupants at all times with minimal active heating and cooling, resulting in significant energy savings.
  2. It increases the house's resilience and durability for many years with minimal impact from mold, decay, and pests. It also ensures a healthy and safe environment and lowers maintenance bills.

 

Adapting to Climate Zones

About 50% of household energy in the U.S is used for heating and cooling (space and water). This rate could be dramatically cut to almost zero in new construction and can be reduced significantly when retrofitting existing homes (depending on the scope and budget).

Data from recent years shows the acceleration of extreme climate events. We should expect significant changes in climate, some gradual (rising temperatures, droughts, sea-level rise) and some harsh and unexpected (extreme storms, precipitation, wildfires).

Designing a home for the current climate or based on historical data is a good start. That’s exactly what building codes help us achieve. However, assuming houses are built to last two to three generations, today’s designs should be able to meet future challenges while demonstrating consistent efficiency and durability throughout those years. To achieve true sustainability, we must adopt best practices that adhere to local climate zones, micro-climates, and predictable extreme events. 

This blog focuses on the basic need to adhere to your local climate zone. You shouldn’t design the same home in Arizona, Indiana, Texas, or Oregon. In each region, the trajectory of the sun, the direction of wind and rain, the ranges and fluctuations of temperatures and humidity, the amount of precipitation, snow, and ice, and the risks from wildfires, floods, and earthquakes differ. Therefore, we want to stress two key considerations: 

  1. All the mentioned climate factors command a thoughtful approach to the design and the alignment of a home’s elements. It includes the elevation of the house, the slope of the roof, the size of the overhangs, and the location of rooms, windows, solar panels, and essential energy and water systems. A design that considers its climate zone will perform better while keeping the indoor ambiance cool in summer and warm in winter. It will also help your house dry quickly after water exposure and improve resistance to mold, decay, and pests, to name just a few benefits.
  2. Consider the use of materials, assembly, and detailing. For example, a humid climate poses different challenges from a dry climate. The materials and their assembly can change a house from one that accumulates moisture and develops mold and decay, to a house that dries quickly and healthily serves for many years. 

Our blog is not a substitute for proper design and construction. Awareness, research, and hiring the right professionals will help you make the right choices and save you money and aggravation from day one. 

Which brings us to the prevailing question: what about the cost?

Cost is a leading factor in decision-making for any type of investment. There is a misconception that designing and building with sustainability, resilience, and efficiency in mind increases costs and tends to be above middle-of-the-road solutions. Check out our blog ROI (Return on Investment), which aims to demystify these conceptions.

When calculating your overall costs, you should consider the following in addition to the upfront expenses:

  1. Rising prices of energy and water 
  2. The rising cost of usage (operational costs) of energy as the climate becomes more extreme.
  3. Losses and discomfort due to energy and water grid outages
  4. Maintenance and repair costs of house elements due to climate impact

The difference between a truly resilient house and standard construction isn’t necessarily the cost. Many times it is awareness, asking the right questions, and implementing the knowledge by proper design and assembly, and by using adequate materials.

 

U.S. Climate Zones

Building America, a program funded by the Department of Energy (DOE), provides ample information and data on design and building practices based on 8 different climate zones in the U.S. Its main aim is to help homeowners achieve the most energy-efficient homes. They also provide critical strategies for durability and adaptation to relevant climate zones, providing additional safety, comfort, and cost savings. To learn more about the difference between adaptation vs mitigation climate change, check out our blog about the two terms.

 

 

Resilience-building resources

To determine the climate zone relevant to your property, check Building America Best Practices for a list of counties and climate zones. Or, you can use our tool by submitting your zip code and getting your relevant climate risks and your climate zone.. 

The climate zones defined by Building America are based on heating degree-days*, average temperatures**, and precipitation. The International Energy Conservation Code ( IECC) has a slightly different method for dividing and defining the U.S climate zones. We rely on both resources. However, in this blog as in other sections of our website, we follow Building America’s climate zones.

Here is a summary of considerations in designing or building in the different climate zones in the U.S:

All content below is credited to Building America and the DOE, although we have refined and added some nuggets! Building America is a professional, reliable, and motivating source to follow for further information.

 

HOT-HUMID

A hot humid climate is generally defined as a region that receives more than 20 inches (50 cm) of annual precipitation and one or both of the following occur:

Houses in the hot-humid climate need to withstand large solar gains in the summer and significant levels of moisture in the ambient air most of the year, along with torrential downpours and high winds, including hurricanes. 

States with a hot-humid climate experience a yearly average of 40 to 70 inches of precipitation. Temperatures typically stay above freezing, with variations of approximately 30 degrees between the average summer and average winter temperatures (NOAA 2010). Parts of the hot-humid climate zone experience frequent and intense rain, tropical storms, severe thunderstorms, tornadoes, and hail. The majority of the region is at high risk for hurricanes and high winds. Large parts of the Southeast have been subject to flooding.
The hot-humid climate zone is considered at low risk for earthquakes, volcanic eruptions, and landslides. Except for a small area on the southwest Alabama border, all hot-humid climates are at low to moderate risk for forest fires. 

When designing or retrofitting a house in this climate region, it’s important to consider strategies to manage moisture, moss, solar gain, protection from hurricanes, flooding, and hail, as well as wildfires in risk zones.
Explore strategies for building properly in a hot-humid climate in our blog.

 

MIXED-HUMID

A mixed-humid climate is defined as a region that receives more than 20 inches (50 cm) of annual precipitation, has approximately 5,400 heating degree days* (65°F basis) or fewer, and where the average monthly outdoor temperature drops below 45°F (7°C) during the winter months.

Parts of the mixed-humid climate zones are subject to frequent and intense rainstorms, severe thunderstorms, and hail. Some areas are at high risk for tornadoes and high winds. Large parts of the Midwest and the South have been subject to flooding. The mixed-humid climate is subject to hurricanes along the Eastern seaboard. The region is at low risk of earthquakes except for localized areas around Arkansas and South Carolina (USGS 2010). Precipitation in the mixed-humid climate varies widely, from 20 inches in the drier parts of Kansas, Oklahoma, and Texas, to more than 50 inches in Tennessee and North Carolina. 

In this climate region, water and flood-resisting strategies, moisture management, solar gain and shading, high wind/tornado/hurricane mitigation strategies, and hail protection should be top of mind. Read more about building adequately according to a mixed-humid climate in our blog.

 

HOT-DRY and MIXED-DRY

A hot-dry climate is generally defined as a region that receives less than 20 inches (50 cm) of annual precipitation and where the monthly average outdoor temperature remains above 45°F (7°C) throughout the year.

A mixed-dry climate is generally defined as a region that receives less than 20 inches (50 cm) of annual precipitation, has approximately 5,400 heating degree days* (65°F basis) or less, and where the average monthly outdoor temperature drops below 45°F (7°C) during the winter months.

Hot-dry and mixed-dry climates bring several challenges for home building. The intense solar radiation imposes a considerable thermal load on houses, increasing cooling costs, adversely affecting comfort, and damaging home furnishings. Annual precipitation in these climates is typically less than 20 inches. Nevertheless, a brief period of heavy rain can deposit several inches of water onto and around a building. Besides rain, improper irrigation can be a significant moisture source; leaks can cause considerable damage, and indoor sources of moisture can be a problem. If water collects in an area that cannot quickly dry, deterioration of building components may occur. 

In this climate, consider moisture management, solar gain, fireproofing, and pest control. Read further on strategies for building properly according to a hot dry climate and mixed dry climate in our blogs.

 

COLD

A cold climate is generally defined as a region with approximately 5,400 heating degree days* (65°F basis) or more and fewer than approximately 9,000 heating degree days (65°F basis). Read further in our cold climate blog.

 

VERY-COLD

A very cold climate is generally defined as a region with approximately 9,000 heating degree days* (65°F basis) or more and fewer than approximately 12,600 heating degree days (65°F basis) and with between 9,000 and 12,600 heating degree days (65°F basis). 

 

Portions of the cold climate are subject to frequent and intense rain and snowstorms, severe thunderstorms, and hail. Some areas are at high risk for tornadoes and high winds. Large portions of the Midwest and Northeast have been subject to flooding, with most of the counties of these areas experiencing four or more presidential disaster declarations due to flooding since 1965. 

These two zones cover an enormous territory with broad and varying challenges. Notable weather phenomena are extreme, prolonged low temperatures and snow accumulation in the winter, extreme and sudden precipitation events, high winds, and high humidity (along the Mississippi). Extreme natural events that can occur in these climates include flooding, earthquakes, and forest fires.

In this climate, prioritize water and flooding resistant strategies, moisture management, air sealing, and thermal control techniques for foundations, walls, and roofs. Fireproofing in certain areas of the western part of this zone is required. Taking advantage of solar gains in the summer is also a key strategy. Seismic proofing and landslide protection are required in risk zones. Read further in our very cold climate blog.

 

SUBARCTIC

A subarctic climate is generally defined as a region with approximately 12,600 heating degree days* (65° basis) or more. The only subarctic regions in the United States are found in Alaska.

At this point, we are not covering Subarctic climate zone characteristics and strategies.

 

MARINE

A marine climate is generally defined as a region that meets all of the following criteria:

  • The mean temperature of the coldest month is between 27°F (-3°C) and 65°F (18°C).
  • The warmest month’s mean temperature of less than 72°F (22°C).
  • At least four months with mean temperatures of more than 50°F (10°C)
  • A dry summer season. 

The marine climate covers a narrow band paralleling the West Coast from the Canadian border south to the county boundary separating Ventura and Los Angeles counties in California. In some stretches, this band is only one county deep inland from the Pacific Ocean. The marine climate was designated in recognition of the mild temperatures and moist conditions found along the coast. However, the marine climate borders the cold climate in the north and the hot-dry climate in the south. Therefore, the conditions of these neighboring climates are found in some inland areas. 

Homes in the marine climate are faced with high levels of moisture, often in the form of rain, fog, or snow. Extreme weather conditions that sometimes occur in the marine climate include heavy precipitation, high winds, flooding, lightning, earthquakes, droughts, and forest wildfires. The marine climate is at low risk for hurricanes and tornadoes.

In this climate region, moisture management, moss, solar gain, fireproofing, seismic proofing, and pest control should be top of mind. Read more in our marine climate blog

 

Summary

Our homes should be designed and constructed in a way that adheres to the local climate zone characteristics and the micro-climate around the home, to achieve: 

  1. Thermal comfort for occupants at all times with minimal active heating and cooling, resulting in great energy savings.
  2. A resilient and durable home for many years with minimal impact from mold, decay, and pests. It also ensures a healthy and safe environment for occupants and lowers maintenance bills.

Building codes are a good starting point, however, they set the minimum requirements and don’t always cover all the best practices. Assuming homes are built to last 50 - 100 years, the goal should be to ensure their design can meet future challenges and demonstrate the same efficiency and durability over such time. 

It is essential to consider the way we handle moisture and water so house elements dry quickly and do not develop mold and decay, the way we handle pests such as termites within our home, and how we insulate and provide comfort while minimally utilizing heating and cooling systems, how we take advantage of solar energy as well as protect from it, how we handle “average” winds, earthquakes, wildfires, and floods. 

Remember, working with the environment and adhering to your climate zone is the necessary first step. The next step is to prepare for future extreme events, those “one in a century events” which now occur more often. These require additional measures and planning. To read more on building strategies for each climate risk, explore our risk blogs.

 

KEEP COOL. BUILD RESILIENCE. EAMPACT.

 

Footnotes:

* Heating and Cooling Degree Days

NOAA defines: “Degree days are based on the assumption that when the outside temperature is 65°F, we don't need heating or cooling to be comfortable. Degree days are the difference between the daily temperature mean, (high temperature plus low temperature divided by two) and 65°F. If the mean temperature is above 65°F, we subtract 65 from the mean and the result is Cooling Degree Days. If the  mean temperature is below 65°F, we subtract the mean from 65 which results in Heating Degree Days.”

A degree day is a solid gauge to calculate if your home improvements have merit. After you take measures to improve your energy efficiency with the proper home insulation and airtightness, energy-efficient HVAC systems (or a “passive house” ventilation system), you will be able to observe how the new energy bills fare against the past. While extreme events of high or low temperatures at any given year might skew the results, you should still be better off after installing proper insulation and taking advantage of energy-efficient HVAC systems or “passive house” strategies.

 

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