Building in a Mixed-Dry Climate Zone

 

We build homes 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, in addition to adaptation and climate change:

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, durability, and climatic adaptations 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.

 

 

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.

 

MIXED-DRY

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.

 States that are partially or entirely within the Mixed-Dry climate zones:

• North-West Texas
• North-West Oklahoma
• New Mexico
• Arizona
• East and central California
• South Nevada
• South-East Colorado
• South-West Utah

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 region you should mainly focus on: 

• Moisture and precipitation management
• Solar radiation
• Wildfires in risk zones
• Pest control

Moisture and Extreme Precipitation

Probably the biggest challenge for maintaining a durable home is keeping its structure dry. Water in its various forms - liquid, solid (ice), vapor (moisture) - finds its way onto the exterior (rain, snow, ice), interior (floods, showering, cooking, breathing), and within the structure (leaks). Here are some key strategies to explore with your architect and contractors when designing or retrofitting a waterproof house:

• Most importantly: properly design and build your walls, roofs, and the foundation floor (crawl space/basement). A solid design will help drain water quickly and allow materials to dry. The design defines the layers you should use such as sidings, vapor, air, and water barriers, insulation, drywall, etc., the order by which you will lay them from the outside in, and the materials you use. The build is how well you attach them and run the detail so there are no cavities/leaks and thermal bridging. Check our blog on “water” for further details.
• Design the right size and angle of overhangs (eaves and gables) with a proper gutter and drain system that is capable of routing water from heavy storms away from the house.
• Landscaping is key. By digging a ditch or creating a small barrier/slope, and planting the right plants, you can help stop excess rainwater from running off and ending up damaging your property or overwhelming the local sewer system or water reservoirs. 
• Use door jambs that are designed for water and rot resistance.
• When installing windows use sill wrap, corner shields, and adhesive flashing tape to protect against water intrusion.
• Use cement backer board behind tubs, showers, and kitchens
• Install a dehumidifier - these systems suck wet air, cool it down, and condense the water back into a container or a pipe system and back into the world, preferably for good use and/or away from the house.
• Install a thermostat with humidity controls.
• The EPA still allows the use of paints containing mildewcide which potentially can repel bacteria but is also deemed toxic. Instead, look for VOC-free, or Low-VOC (some of the low-VOC become free after drying for a couple of weeks). 

 

Solar radiation

Simply put, solar radiation heats up the roof, walls, windows, and doors, and that energy then heats up the interior of the home. In order to have an energy-efficient home (that uses less energy) and resilient (that reduces the dependency on the energy grid and cooling systems, even during extreme heat waves), you should:

• Install a reflective roof and use light or reflective exterior wall colors.
• Install a radiant barrier in the attic.
• Install overhangs, covered porches, awnings, pergolas, or shade trees to minimize solar heat gain (avoid shading the roof due to moss).
• Place the air handler and ducts in a conditioned space or go ductless with mini-split heat pumps.
• Install high-performance, low-emissivity windows with low solar heat gain coefficient.
• Locate windows on the sides of the house that can catch coastal breezes.
• Create a tight thermal envelope and install a positive-pressure ventilation system.
• Use non-heat-producing Compact Fluorescent Light (CFL).
• Install ceiling fans and look for solar-powered fans (as backup).

 

Wildfires in risk zones

Wildfires pose a risk to the lives of people who live near those ecosystems and their homes. Moisture is one of the main factors that determine wildfire frequency and since the changing climate in recent years brings dryer winters, the consequences of wildfires are becoming more devastating, and the fire season becomes longer.
In fire risk zones consider:

• Avoid new construction in WUI zones and choose a location that is not at high risk of wildfire. 
• Use non-combustible or fire-resistant materials for exterior components such as roofs, sidings, windows, doors, vents, and gutters. For example, use Class A-rated roof shingles and borate pressure-treated lumber in framed homes.
• Create defensible space by surrounding your property with non-combustible materials and remove vegetation away from the house.
• There is no “fire-resistant” vegetation. Design the landscaping around the house with high-moisture plants that grow close to the ground and have a low sap or resin content. Choose plants that resist ignition such as rockrose, ice plant, and aloe. Plant hardwood, maple, poplar, and cherry trees that are less flammable than pine, fir, and other conifers.
• Install interior and exterior fire sprinklers.
• Find more information in our Building Resilience Against Wildfires blog.
   

Pest control

Pests do not only pose a risk to your property but are also a threat to your family’s health. As with other hazards, prevention and being on the offense is a better strategy than being on the defense after pests have gained access or control over parts of your property.

The following methods are layers of protection that perform well together to reduce the threats from pests.

• Start with researching the threats in your location. You can learn about the main or common risks from local building codes and other local public resources, or use our tool. 
• Once you gain knowledge, either hire a professional or try to monitor and identify if you have any ongoing infestation. Either way, the main objective is to create an environment that rejects or eliminates pests;
• Use pest-proof building materials;
• Eliminate food sources, hiding areas (cracks), and other pest attractants;
• Use traps and other physical elimination devices; and only when necessary, select appropriate poisons for identified pests.
• Termites and carpenter ants are a threat to your home structure. The main strategies here are keeping your structure and the soil around it (about 18 inches) dry, and creating barriers to block easy access: 
  • Use the Termite Infestation Probability (TIP) maps to determine environmentally appropriate termite treatments, bait systems, and treated building materials for assemblies that are near soil or have ground contact.
  • Keep all wood (including siding, decking, and fencing that attaches to the house) from soil contact to minimize the presence of wet wood, which attracts carpenter ants. 
  • Use termite flashing and insulation products with termiticides or use fiberglass rigid insulation when insulating slab edge or exterior foundation walls
  • Provide roof drainage to carry water at least 3 feet beyond the building.
  • Apply decorative ground cover no more than 2 inches deep within 18 inches of the foundation.
  • Keep plantings at least 18 inches from the foundation with supporting irrigation directed away from the finished structure.
  • Specify and install an environmentally appropriate soil treatment and a material treatment (treated wood, termite blocks) for wood materials near grade.
• The CDC provides a good starting guide to help protect your home and the health of your family from various pests such as rats, flies, roaches, mosquitos, and fleas.
   

 

Summary:

Climate is part of the environment and the overarching system that surrounds our homes. The main reason we build houses is to protect ourselves from weather and natural phenomena. 

 

The main impacts of the climate on our homes have to do with handling moisture and water so house elements dry quickly and do not develop mold and decay,  handling pests such as termites, insulating and providing comfort while minimally utilizing heating and cooling systems, taking advantage of solar energy as well as protecting ourselves from it, and handling winds, earthquakes, wildfires, and floods. 

 

Homes should be designed to adhere to the local climate zone characteristics and the micro-climate around the home, in order to achieve: 

1. Thermal comfort for house 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 - ensuring a healthy and safe environment for occupants (even when the power grid is down) as well as lower ongoing 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 houses 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. 

To achieve true future sustainability - research and understand your climate zone and study how to mitigate the risks it poses. Tap into information from local governments, communities, and neighbors. Lastly, hire certified professionals that will help you achieve these goals in the most cost-effective way. 

Remember, working with the environment and adhering to the local climate zone is the necessary first step. The next step is being ready for future extreme events which now occur more frequently. These require additional measures and planning.