Investigation of common thermal bridges in walls

Thermal bridges can have a major effect on the thermal performance of building envelopes, significantly increasing winter heat loss and summer heat gain. Further, condensation on thermal bridging elements can result in mold and mildew growth (with accompanying reduction of air quality), staining of surfaces, and serious damage to building components. Significant energy savings and improved structural integrity would result if design practices successfully addressed thermal bridging problems. An ASHRAE research project (RP-785) to address these problems was commissioned and has been completed. Twelve wall assemblies were analyzed through a combination of detailed guarded hot-box measurements and finite-volume heat transfer analysis. Using the measured results to validate the simulation models, additional thermal bridge assemblies were analyzed with the computational method. This paper compares the performance of several different thermal bridges using the results from physical testing and computer simulation. Bridges investigated include steel studs, concrete slabs that penetrate the thermal barrier, screws, masonry ties, anchor bolts, and shelf angles for masonry veneer systems. The effects of the bridges in reducing the overall thermal resistance of the assemblies are examined, and some common solutions to the bridging problems are investigated for their effectiveness.