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.