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:
- 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.
- 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 the climate zone 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.
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.
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).
A cold climate is defined as a region with between 5,400 and 9,000 heating degree days (65°F basis).
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).
A very cold climate is defined as a region with between 9,000 and 12,600 heating degree days (65°F basis).
States that are partially or entirely within the Cold and Very Cold climate zones:
Portions of the cold climate are subject to frequent and intense rain and snow storms, 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. The region is at low risk of earthquakes except for localized areas in Idaho, Wyoming, and Utah and at the border of Tennessee and Missouri. The cold and very cold zones are at low risk of volcanic eruption except in Alaska, Washington, and Oregon. Portions of the cold climate are prone to landslides, especially in the Rocky Mountains and Appalachian Mountains. The region is at low risk for hurricanes except along the Eastern seaboard (USGS 2010)
These two zones cover a huge 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 region you should mainly focus on:
- Moisture and precipitation management
- Air Sealing
- Thermal control techniques for foundations, walls, and roofs
- Hurricanes, Tornadoes and Strong Winds
- Solar radiation
- Wildfires in risk zones
- Earthquakes in risk zones
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).
Unintentional air flow due to poor assemblies at the seams (walls, roof, foundation plates), through-wall penetrations (electricity, plumbing, nails), leaks around doors and windows, and cracks in the roof, robs a home of warm or cool air.
It is important to note that air sealing is a complementary effort to insulation and moisture control. All three are different systems and must work well together to provide a resilient, durable, safe and comfortable environment.
In addition to thermal and energy control, air leaks also serve as a pathway for moisture flow, poor air, pests, and decrease overall comfort levels.
Controlling air infiltration is one of the most cost-effective and simplest energy-efficiency measures in modern construction practices. Air sealing is required by the 2018 International Energy Conservation Code (IECC) which identifies several areas for air sealing and requires verification with a blower-door test or visual inspection.
The materials and approaches mentioned below are common and time tested. However, these measures must be carefully installed to be effective and must be installed in the proper construction sequence before cavity areas are covered up by insulation, moisture control layers, fixtures or walls.
Health and safety are essential factors to consider when air sealing, especially if the home contains combustion appliances. See Building America’s Air Sealing guide for more information. Sealing against air leakage is primarily done for thermal reasons, but when coupled with appropriate mechanical ventilation, this procedure also assists in maintaining good indoor air quality for the occupant.
Air leaks also carry water vapor; if this water vapor condenses, it can cause mold and other moisture problems. An important job for air barrier systems is separating conditioned spaces from unconditioned. The key to the control of airflow is the use of a continuous air barrier. This barrier may be made up of several types of materials as long as it provides an unbroken barrier between conditioned space (indoors) and unconditioned space (outdoors, attic, crawlspace, and garage).
Building America researchers have worked with three building approaches that push the air and thermal barriers toward the exterior of the building shell:
- Conditioning crawl spaces and basements or using slabs,
- Installing insulated exterior sheathing, with sealed seams, and
- Conditioning attics.
These approaches make it easier to provide an uninterrupted air barrier. In addition, in homes where ducts need to be placed in the basement or attic, it is better to have these spaces conditioned. This will result in better energy efficiency, air quality and moisture control.
Air barrier components:
- Mudded and taped gypsum board serves as an air barrier on the home’s interior.
- Sidings such as Stucco may serve as an air barrier on the home’s exterior.
- Some Sheathing materials can act as air barriers
- Some house wraps / membrane can serve as both the moisture / water control barrier as well as an air barrier
- Caulk, tape and in some cases insulation foam are air barriers used in cavities, seams and through-wall penetrations
- Air flow needs to be controlled from the outside in (e.g. wind) and inside out (e.g. air conditioning) to protect both the interior thermal and air quality as well as the structure of the house from moisture which travels with air
- Different climate zones command the usage of different air barrier materials
- Building codes and building standards define the performance which air barrier materials should meet (note that the materials, the assembly and the entire enclosure may have different performance requirements.)
The ENERGY STAR for Homes program has compiled the Thermal Bypass Checklist, a comprehensive list of potentially vulnerable spots in the building envelope. The checklist identifies 25 points to inspect throughout the home, covering all major components of the building envelope including exterior walls, floors, ceilings, attics, and shafts. Builders can use the checklist to verify the integrity of the air barriers in the building envelope.
Thermal control techniques for foundations, walls, and roofs
Building America covers many thermal control techniques in their “40% Whole-House Energy Savings in the Cold and Very Cold Climates” guide.
The fundamentals of thermal control techniques are not only about maintaining comfortable temperatures in the house, or the benefits gained from consequential energy saving. While those are critical strategies for your home resilience, the guide also discusses how to properly implement these strategies in order to avoid incidental damages from poor design and implementation.
Here are the key takeaways of thermal control strategies done right:
- Beyond properly insulating these house elements to gain thermal control, all strategies include proper design and implementation to avoid moisture and condensation which lead to either short or long term structural damage (from mold, rot, decay) as discussed above in the Air Sealing section. Throwing tons of insulation without properly understanding how Air and Water flow from the exterior of the house to the inside, and vice versa, will end up in substantial agony and financial loss. Therefore, proper thermal control strategies include:
- Implementation of Air Control layers
- Implementation of Water and Vapor Control layers
- The detailing around cavities, seams and joints, especially where the foundation meets the walls and the walls meet the roof, windows and doors.
- Drying techniques of these elements after they do get wet
- Different foundations - slab, basement, crawlspace - have different thermal control strategies. Insulation is the first step, and it is wise to check out the IECC R value requirements for insulating different types of foundations.
- Same goes for walls and roofs, check out the IECC R value requirements for these house elements based on your climate zone.
- All these strategies also include recommendations to properly design foundations, walls and roofs to reject pests (namly termites).
Floods are the most common natural disaster in the United States. We tend to think that floods happen mainly around coastlines and during hurricanes, but America is experiencing more frequent and devastating floods along creeks and rivers (“riverine floods”), lakes and ponds, and areas with inadequate drainage systems. In some cases, extreme precipitation events (“atmospheric rivers”), in-land tornados, and melting snow/ice can also cause floods in unexpected locations. In flood risk zones consider:
- Elevating your home above BFE (Base Flood Elevation level).
- Build slab-on-grade foundations and grade lots to drain away from the structure. In areas of likely coastal flooding build on concrete or pressure-treated piers.
- Adoption of Water Resistive Materials.
- Elevating Essential Infrastructure.
- Backing up Critical Systems.
- Install a generator-ready electrical service panel to run generator-powered shop vacs, fans, and heaters to dry out the house and reduce water damage during post-storm recovery when electric power outages are common.
- Building Rain Gardens and Barrier Systems.
- Buy flood insurance.
Hurricanes, Tornadoes and Strong Winds
Hurricanes and Tornadoes are not the same. While there are hurricane proof building codes and solutions that can save lives, the same house hit directly by a tornado may endure more damage. Therefore, tornadoes command better choice of materials such as concrete blocks with reinforced steel or Insulated concrete forms (ICFs) walls, scrutinized design of the structural load and assembly, and a shelter room.
Damage from storms varies depending on the category of the storm and the location of the house. The main risks from storms are falling trees, poles, and flying debris, power outages from days to months, major flooding and excess rain, and loss of water supply. In all categories, there is a risk of damage or full removal of the roof, sidings, and other exterior elements, structural damage (walls, roof) to complete displacement or destruction of the house. In storm risk areas:
- Structural load design and assembly
- Designing walls to resist uplift using hurricane strapping and other metal fasteners that provide a continuous load path from foundation to roof.
- Consider steel-reinforced concrete walls.
- Anchoring walls properly to foundations.
- Designing roof geometries that are less prone to wind damage than gable roofs and installing continuous roof underlayment.
- If you decide to go with a gable roof, properly planning the length and width of the gable overhang, strengthening gable ends, and outlooker attachments at gable ends.
- Eave designs with extended fascia providing drip edge, and recessed soffit vents (Zoeller 2006).
- Adequately securing chimneys to the structure.
- Ensuring windows and doors meet appropriate design pressures (“impact windows and doors”) in addition to being protected from windborne debris.
- As with windows and doors, there are hurricane-proof garage doors and tracks. You may also reinforce an existing garage door using a garage door bracing kit.
- Safe-room / Shelter - according to the Federal Emergency Management Agency (FEMA), a safe room is a: “hardened structure specifically designed to meet the FEMA criteria and provide near-absolute protection in extreme weather events, including tornadoes and hurricanes. Near-absolute protection means that based on current knowledge of tornadoes and hurricanes, the occupants of a safe room built in accordance with FEMA guidance will have a very high probability of being protected from injury or death.”
- Outswing doors.
- Hurricane shutters.
Hail is a form of precipitation consisting of solid ice that forms inside thunderstorm updrafts, sometimes building rapidly and without advanced warnings. Hail can damage homes and landscaping and can be deadly to people, livestock, and pets. In Hail risk zones consider:
- Harden your roof using impact-resistant shingles (Go for Class 3 or 4 UL2218 tested shingles)
- Protect windows and skylights with either permanent or temporary shutters.
- Cut trees around the house that may fall on the house during hail storms.
- Stowaway (indoors) all backyard and front yard furniture during the storm.
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.
Earthquakes in risk zones
If you are planning a new construction, you need to design and build the house with enough strength and stiffness to properly perform during an earthquake. According to FEMA, “actual earthquakes can generate forces considerably higher than those used for code-prescribed design.”
As a minimum, build your home according to local and state codes. But based on the specific risk zone you are in, consider above-code techniques that can be applied to further enhance a structure to obtain minimal damage and best protect the occupants and belongings. These would be:
- Adopting I-Codes from the International Code Council (ICC) where local codes have not yet adopted them, or no code is currently required.
- Codes define the measures or factors for strength and stiffness. Discuss with your experienced architect, engineer, or contractor if you need to go above these metrics.
- Designing strength and stiffness to both vertical and lateral movements. Many times focus is on vertical, although lateral loads pose the same if not higher risks, therefore, adding strength and stiffness to lateral movement can be beneficial.
If you are retrofitting, there are many measures you can take to make your house more susceptible to earthquake forces. Here are some options you can explore:
- Replace unreinforced masonry or deteriorating concrete foundations with reinforced concrete.
- Add steel frame and structural sheathing to a soft-story wood-frame.
- Secure frame to the foundation with anchor bolts.
- Inspect exterior masonry walls periodically for cracks and reinforce them; In case of chimneys, brace them to the roof structure.
- Inspect for loose roof tiles and properly anchor roofing material to a braced roof frame.
- Strap water heaters to the building frame.
- Secure bookshelves to walls with screws or straps.
- Secure light fixtures and fans to ceiling joists.
- Secure bookcases to wall studs.
- Strap computer monitors and televisions to walls or desks.
- If your home is heated by natural gas, use flexible pipe connections for gas appliances.
- Install a seismic actuated gas valve, which shuts off the gas during severe earthquakes.
- Manufactured homes should be tied-down and anchored
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.
Setting aside extreme events, homes should be designed in a way that adheres to the local climate zone characteristics and the microclimate around the home and meet the following objectives:
- A resilient and durable home with minimal impact from mold, decay, and pests - ensuring a healthy and safe environment for occupants
- Provide thermal comfort for house occupants at all times with minimal active heating and cooling, resulting in great energy savings and resilience (less dependency on the grid)
- Provide ongoing supply of quality Air and Water
Achieving these objectives require the right design, choice of materials and proper construction. 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
- 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.
* 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.