Building Science

What Is Thermal Bridging & How to Reduce It?

The exte­ri­or wall of a build­ing is the bar­ri­er that keeps tem­per­a­ture, mois­ture, wind, and pol­lu­tion out­side and cre­ates a com­fort­able and healthy indoor envi­ron­ment. A pri­ma­ry goal of con­trac­tors and archi­tects is to design a wall assem­bly with a ther­mal bar­ri­er that resists heat trans­fer between the inside and out­side. There­by the inte­ri­or of a build­ing stays warm in cold win­ter months and cool in the sum­mer. A build­ing’s wall assem­bly resis­tance to this flow is mea­sured by its effec­tive R‑value. The effec­tive R‑value includes all the mate­ri­als used in its con­struc­tion: the dry­wall, studs, fiber­glass batts, ply­wood or OSB sheath­ing, water con­trol plane, and sid­ing. The larg­er the R‑value, the low­er the con­duc­tiv­i­ties of the wall assem­bly. Prob­lems in a wall’s assem­bly, such as ther­mal bridg­ing, increase the wall’s con­duc­tiv­i­ty, which leads to increased air flow through between the inte­ri­or and exte­ri­or of the build­ing. Build­ing exte­ri­or walls with low con­duc­tiv­i­ty and high effec­tive R‑values will keep unwant­ed out­door ele­ments out­side and ensure a com­fort­able indoor envi­ron­ment.

Thermal Bridging Reduces the R-Value of a Building's Exterior Walls

A ther­mal bridge is a more con­duc­tive area of a wall assem­bly, com­pared to the sur­round­ing space, like the stud space and the exte­ri­or insu­la­tion. Heat and ener­gy flow through the ther­mal bridge at a high­er rate than the sur­round­ing areas; which reduces the effec­tive R‑value of the wall assem­bly. Ther­mal bridg­ing typ­i­cal­ly occurs near high­ly con­duc­tive mate­ri­als like wood studs, met­al studs, steel, and con­crete. For exam­ple, wood studs allow heat to flow through the wall at a rate that is three times faster than the heat flow through the insu­la­tion. So, even though the insu­la­tion has a nom­i­nal R‑value of 19, the building’s effec­tive R‑value is low­er. Steel fram­ing is even more con­duc­tive than wood. In fact, steel fram­ing typ­i­cal­ly reduces the sur­round­ing insu­la­tion’s R‑value by as much as 50%, while wood fram­ing reduces the sur­round­ing insu­la­tion’s R‑value by less than 10%. Deter­min­ing and pre­vent­ing poten­tial ther­mal bridges with­in a wall assem­bly is essen­tial for con­struct­ing a com­fort­able and ener­gy effi­cien­cy build­ing.

Continuous Insulation Layer Stops Thermal Bridging

Wrap­ping a building’s enve­lope with a lay­er of con­tin­u­ous insu­la­tion cuts off ther­mal bridg­ing. Stop­ping ther­mal bridg­ing saves ener­gy and low­ers the risk of mold and rot by elim­i­nat­ing or reduc­ing con­den­sa­tion. Con­tin­u­ous insu­la­tion is installed on the exte­ri­or of all areas of the build­ing enve­lope except open­ings for win­dows, sky­lights, doors, and build­ing ser­vice sys­tems. Con­tin­u­ous insu­la­tion is required by ASHRAE 90.1 and 2015 IECC. ASHRAE 90.1 is the U.S. ener­gy stan­dard for all com­mer­cial and res­i­den­tial sin­gle or multi‐​family struc­tures greater than three sto­ries in height above grade.The stan­dard defines con­tin­u­ous insu­la­tion as insu­la­tion that is con­tin­u­ous across all struc­tur­al mem­bers with­out ther­mal bridges oth­er than fas­ten­ers and ser­vice openings.The amount of insu­la­tion required (as indi­cat­ed by the R‑value) by the stan­dard depends upon its cli­mate zone. Con­tin­u­ous insu­la­tion com­plies with build­ing codes, elim­i­nates ther­mal bridg­ing and increas­es the effec­tive R‑value in a wall assem­bly.

Bautex Block Continuous Insulated Wall System

The Bau­tex Wall Sys­tem con­tin­u­ous insu­la­tion stops ther­mal bridg­ing and exceeds the ener­gy effi­cien­cy require­ments of the most strict build­ing codes. The R‑value for Bau­tex Blocks is R‑14, with­out exte­ri­or or inte­ri­or fin­ish­es. A build­ing with Bau­tex Block con­tin­u­ous insu­la­tion with brick veneer is an R‑18 sys­tem; far exceed­ing ASHRAE 90.1 rec­om­men­da­tions. In warmer, south­ern cli­mate zones, ASHRAE 90.1 min­i­mum R‑value require­ments for con­tin­u­ous insu­la­tion (above grade, mass walls), are less than R‑8. The Bau­tex Block is also fire-rat­ed, noise-reduc­ing, storm-resis­tant and easy to install. Inte­ri­or and exte­ri­or walls of res­i­den­tial and com­mer­cial build­ings can uti­lize Bau­tex Walls. The use of Bau­tex Wall Sys­tem con­tin­u­ous insu­la­tion, stops ther­mal bridg­ing, improves ener­gy effi­cien­cy and saves build­ing own­ers mon­ey for years to come.

Other Sources of Thermal Bridging - the Window and Doors

Ther­mal bridg­ing also occurs through win­dows and doors. The addi­tion of insu­lat­ed shades and storm doors can reduce the ther­mal bridg­ing through these open­ings.

Ther­mal bridg­ing occurs in build­ings near high­ly con­duc­tive, low R‑value mate­ri­als like wood studs, steel, and con­crete. These high­ly con­duc­tive mate­ri­als allow heat to trans­fer through the ther­mal bar­ri­er, usu­al­ly the exte­ri­or wall. A proven method for elim­i­nat­ing ther­mal bridg­ing is con­tin­u­ous insu­la­tion. Con­tin­u­ous insu­la­tion cov­ers all parts of a build­ing, elim­i­nat­ing ther­mal bridges oth­er than those caused by fas­ten­ers, win­dows, doors, and sky­lights. Bau­tex Block is an excel­lent choice for con­tin­u­ous insu­la­tion. Bau­tex System’s light­weight stay-in-place insu­lat­ed con­crete block is a high­ly per­form­ing, strong, and sim­ple-to-install wall sys­tem, with an R‑value far exceed­ing indus­try rec­om­men­da­tions. The Bau­tex Block gives con­trac­tors and archi­tects an effi­cient method to elim­i­nate ther­mal bridg­ing; reduc­ing ener­gy loss and ensur­ing sav­ings for own­ers of both res­i­den­tial and com­mer­cial build­ings.