Building in a Cold Climate Zone

Building in a Mixed-Dry Climate Zone

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One of the main reasons we build houses is to protect ourselves from the environment. Setting aside extreme environmental events, climate (which is part of the environment) is the overarching system that surrounds our homes. When designing or retrofitting a home, one of the first steps you should take is understanding the climate system as well as the microclimate around your home. 

Two key merits of designing a home for the respective climate zone it’s in:

  1. Maintain thermal comfort for house occupants at all times with minimal active heating and cooling, resulting in great energy savings as well as resilience since the dependency on the power grid is low.
  2. Keeping the house resilient and durable for many years with minimal impact from mold, decay, and pests, which ensures a healthy and safe environment for occupants. The key here is keeping water, in all its forms, away from the house structure and using designs and materials that allow wet elements to dry quickly.

 

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 constructed homes, and can be significantly reduced in existing homes depending on the scope (and budget) of retrofitting projects.

Data from recent years shows the acceleration of extreme climate events, and that we will be experiencing significant changes in the climate, some subtle and growing slow (rising temperatures, droughts, sea-level rise) and some harsh and unexpected  (extreme storms, precipitation, wildfires).

Designing a home based on historical data or for today’s climate is a good starting point and that’s what building codes help us achieve. However, assuming houses are built to last two to three generations (say 80 years) the goal should be to ensure those designs can meet the future challenges and demonstrate the same efficiency and durability throughout those years. To reach true sustainability, it is important to adopt best practices that adhere to local climate zones, micro-climates, and predictable extreme events. 

Setting aside extreme events, this blog focuses on the basic need of adhering to your local climate zone. You cannot design the same home in Arizona and 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, the risks from wildfires, floods, and earthquakes differ. Therefore, we want to convey two key takeaways: 

  • First, all the mentioned climate factors command a thoughtful approach to the design and alignment of house elements, such as the location of rooms, windows, and solar panels, the slope of your roof and the size of the overhangs, the elevation of the house and location of key energy and water systems. A design that considers climatic adaptations will keep the house cool in the summer and warm in the winter. It will also help your house dry quickly after exposure to water which will improve resistance to mold, decay, and pests. These are just a few examples.
  • The second takeaway is the use of materials, assembly, and detailing. For example, a humid climate poses different challenges compared to a dry climate. Different materials and how you assemble them can make a difference between a house that quickly accumulates moisture and develops mold and decay versus a house that dries quickly and serves you for many years and in a healthy fashion. 

 

What about the cost? The difference between a true resilient house and standard construction isn’t necessarily the cost. Many times the difference is being aware, asking the right questions, choosing the right professionals and then properly designing and assembling the house, using the right materials. 

 

U.S Climate Zones

Building America”, a program funded by the Department of Energy (DOE), has divided the U.S into 8 climate zones and provides ample information and data on design and building practices based on those climate zones. Their main aim is to help homeowners achieve the most energy-efficient homes, but they also provide key strategies for durability and adaptation to the relevant climate zone, providing further safety, comfort, and cost savings.

 

Extreme Precipitation and Climate Change

 

To determine the climate zone relevant to your property, check the Building America Best Practices Volume 7.3 Guide to Determining Climate Regions by County (DOE 2015) for a list of counties and climate zones.

 

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


HOT-DRY and MIXED-DRY

A hot-dry climate is generally defined as a region that receives less than 20 in. (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 in. (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 Hot-Dry and 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

Hot-dry and mixed-dry climates bring several challenges for home building. The intense solar radiation imposes a large 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 major moisture source; leaks can cause significant 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 various 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 (use less energy) and resilient (reduce 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 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 for the lives of people who live near those ecosystems and their homes. Moisture is one of the main factors that determine wildfires 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 roof, 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 noncombustible 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.



Pest control

Pests do not only risk your property, they 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 defence 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 studying the threats in your location. You can learn about the main or common threats from local building codes and other local public resources. 
  • Once you gain knowledge, either hire a professional or try to monitor and identify if you have any ongoing infestation.
  • Whether you have an ongoing infestation or not, 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 when necessary, selecting appropriate poisons for identified pests.
  • Termites and carpenter ants are a threat to your home structure. Main strategies here are keeping your structure and the soil around it (18 inches or so) 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 (which is part of the environment) is the overarching system that surrounds our homes and one of the main reasons we build houses - to protect ourselves from weather and natural phenomena. 

 

The main impacts of the climate on our homes have to do with how we handle moisture and water so house elements dry quickly and do not develop mold and decay. How we handle pests such as termites. 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. 

 

Setting aside extreme environmental events, homes should be designed in a way that adheres 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 reach 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. 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, those - “one in a century events” - which now occur more often. These require additional measures and planning.

 

KEEP COOL. BUILD RESILIENCE. EAMPACT.


References:

https://www.eia.gov/energyexplained/use-of-energy/homes.php

https://www.ncdc.noaa.gov/billions/

https://basc.pnnl.gov/

https://www.energy.gov/sites/default/files/2015/10/f27/ba_climate_region_guide_7.3.pdf

https://www.energy.gov/sites/prod/files/2013/11/f5/40percent_hot_humid.pdf

https://www.energy.gov/sites/default/files/2013/11/f5/40percent_mixed_humid.pdf

https://www.energy.gov/sites/default/files/2013/11/f5/18899.pdf

https://www.energy.gov/sites/default/files/2013/11/f5/cold_climate_guide_40percent.pdf

https://www.energy.gov/sites/default/files/2013/11/f5/marine_40_guide.pdf


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 temperature mean is above 65°F, we subtract 65 from the mean and the result is Cooling Degree Days. If the temperature mean is below 65°F, we subtract the mean from 65 and the result is 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 air tightness, 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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