May 24, 2018

Building an Energy-Efficient New Home in a Warm Climate with Bautex Wall Assembly

Designing an energy-efficient new home for a hot-humid climate aims to reduce air conditioning bills by preventing the infiltration of warm air and moisture. There are several differences between designing a home in warmer climates (like Texas) versus colder climates (like Michigan). The building envelope of a home in a hot climate has a much smaller Delta-T1 than homes in colder climates. Consequently, homes in more temperate climates require less insolation than homes in cold climates. Hot climate design also more strongly focuses on reducing heat gains from the windows, ceilings, and internal gain (lights, appliances, office equipment, etc.) compared to cold-climate home design.

The one thing both hot- and cool-climate energy-efficient designs have in common is the need to minimize air leaks. In hot climates, air leaks allow cold air to escape and humid, warm air to enter a home. In hot climates, it is essential to design a home with a tight building envelope to ensure the house is energy-efficient and stays cool and dry. The design of an energy-efficient new home in a hot climate also considers the home’s orientation, room placement, and location of ductwork in the house.   

Energy-Efficient New Home in Hot-Humid Climate Needs a Tightly Sealed Building Envelope

A tight building envelope minimizes heat gain and moisture intrusion and is crucial to creating a cool and dry home in warmer climates. Essential design elements for a tight building envelope include continuous insulation (CI) and an air and moisture barrier. Continuous insulation slows down heat transfer, and an air and moisture barrier prevents air leakage and moisture intrusion. Moisture resistance is key to stopping rot and the growth of mold and mildew, which can weaken the structure and degrade the indoor environmental quality (IEQ) of a home. The envelope is made up of the exterior components of the house, including the walls, roofing, foundations, windows, and doors. A tight building envelope must consider all these factors.

The walls are a vital element to preventing heat gains and creating a tight envelope of an energy-efficient home. Several factors affect the efficiency of the walls: conduction, convection, and thermal radiation.

  • Thermal conduction is when warm molecules spontaneously move towards and collide with cooler molecules. The effective R-value of a home's wall assembly is its resistance to conduction (the movement of hot molecules towards cooler molecules). The walls of an energy-efficient building should have low-conductivity and a high effective R-value.
  • Thermal convection is the transfer of heat from a warmer space to a colder space by the flow of liquid or air molecules. A tightly sealed building envelope stops this flow, often with an air and moisture barrier.
  • Thermal radiation transfers heat from a warm area to a cooler area by electromagnetic waves, which for homes is mainly the sun’s rays. The design of an energy efficient wall incorporates materials with high reflectivity and low emissivity that limit the absorption of radiant heat.

The Bautex Wall Assembly is a superior, high thermal mass2 system that creates a tight building envelope for an energy-efficient home in hot-humid climates. The Bautex Block meets the thermal performance required of the IRC and IBC and delivers a high-level of continuous insulation that stops the flow of heat by conduction, convection, and radiation and thermal bridges. The Bautex insulated concrete blocks provide an R-14 continuous insulation that meets, if not exceeds, the standards and codes of the (ASHRAE 90.1) Code (2015 IECC). Also, applying the Bautex AMB 20 air and moisture barrier to the Bautex Blocks produces a moisture resistant, airtight house. The Bautex Wall System is the ideal choice for energy-efficient wall construction for homes in hot-humid climates.

  • A cool roof is critical to the design of a home in warmer climates. Cool roofs protect against solar heat gain and keep the home and attic space cool. Low thermal mass materials for a cool roof like tiles, clay, or slate that are reflective or have light colored pigments that cast back the sunlight are good choices for cool roofs.  
  • Concrete slab foundation, along with a continuous layer of rigid foam insulation under the slab, can separate an energy-efficient home from the ground. Separating the home from the ground is an essential component of a tightly sealed building envelope.
  • A tight building envelope must also include energy efficient windows, skylights, and doors suitable to the home’s climate zone.

Site, Room, Window, and Ductwork Location for an Energy-Efficient Home in a Warm Climate

Proper site orientation of a home is crucial for taking advantage of the sun’s energy. For example, in the Northern Hemisphere, homes should be oriented north-south. The north-south orientation minimizes direct sunlight during the summer (which reduces cooling demands) while maximizing sunlight during the winter (which limits heating requirement).

Room orientation is also a critical design consideration of an energy-efficient home.

  • North facing rooms have good sun most of the day and are ideal for the main living spaces like family, living, and dining rooms.
  • East facing rooms have excellent sun in the morning and are cool in the late afternoon, which is wonderful for bedrooms and kitchens.
  • South-facing rooms have low levels of sunlight and are good spaces for service areas such as garages, laundries, and bathrooms.
  • West facing rooms get the late day sun, which is not suitable for kitchens and bedrooms.
  • Windows of an energy-efficient home in a hot climate should face north or south. Limit east- and west-facing windows because they contribute more to overheating than north- or south-facing windows.

For an energy-efficient new house in a hot climate, locate the ductwork inside the home’s envelope. Ducts placed in unconditioned spaces can increase cooling costs by 15 percent.  Furthermore, in hot and humid regions, water will collect on the overheated ductwork.
The design of an energy-efficient new home in a hot climate must include a tight building envelope. The design must also consider the home’s orientation, room and window placement, and location of ductwork in the house.  An energy-efficient home in a hot climate saves the homeowner money and energy and creates a healthy comfortable home.

1The Delta-T is the difference between the outdoor and indoor temperatures. For instance, in Michigan in January 2017, the average low temperature was 17. In Texas, in june 2017, the average high temperatures was 91 . Assuming homeowners follow the Department of Energy’s recommendations to set thermostats at 68 degrees Fahrenheit (℉)  during the cold months and 78 degrees ℉ during the warmer months, Michigan has a Delta-T of 51, while Texas has a Delta-T of only 13.

2High thermal mass materials absorb and store heat energy. High thermal mass materials stabilize temperature shifts within a building by reducing the rate of heat transfer. Concrete, water, brick, and stone are high thermal mass materials. Wood and steel have low thermal mass and not suitable materials for an energy-efficient home.

 


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