09. January 2018

Thermal bridging and healthy humidity levels

from Brent Chancellor
Cold winters bring low relative humidity levels.


Ever hear that dry crackle or feel the effect of static electricity as you remove your coat or sweater in the middle of winter? Maybe have dry itchy skin, cracked lips, or even nose bleeds? Why is it that we associate these things with cold weather like we associate holidays and fruitcake? In one word, humidity.

Cold air holds less moisture than warmer air. Therefore, in late fall or early winter, just as we begin to think about heading out to the ski slopes, we begin to feel the effects of the dry, cold air. This cold air enters our homes and is then heated, resulting in air with a very low relative humidity level.

For human comfort and to prevent dry skin, cracked lips, and nose bleeds, relative humidity levels in the winter should be between 20-80%. However, relative humidity levels should be kept below 50% to discourage microbial growth (e.g. dust mites).

As we design and construct our buildings to be more and more airtight, healthy, comfortable humidity levels will be easier to achieve and maintain during winter months. However, what happens when we combine healthy humidity levels that rise to around 50% relative humidity with building designs that do not eliminate thermal bridges?


Thermal Bridging in Today’s Buildings

Thermal bridging allows heat to escape from our homes and offices and results in localized cold interior surfaces. If these surfaces get below the dew point, then condensation, and potentially mold growth, is the result. Mold risk conditions are actually present even before any condensation is visible. For relative humidity levels of  50% and normal indoor temperature of 70°F (21°C), the dew point is  52F (11C). These conditions mean that at cold interior surfaces, – such as the floor slab of a continuously poured concrete balcony – there is a high likelihood that condensation will form. To prevent this condensation from forming and resulting in mold growth, the slab temperature needs to be increased. One of the best ways of accomplishing this is to use a structural thermal break.

Using a structural thermal break significantly slows the rate of heat loss through the balcony slab. This improved thermal performance results in more comfortable floor temperatures, but most importantly helps to prevent condensation from forming and potential mold growth from occurring by raising the floor slab temperature. Using a structural thermal break can increase the floor slab temperature by as much as 13F (7C) – a welcome comfort as we move into the colder months, and a safety buffer to ensure there is no possibility of mold growth.


No STB balcony
When no structural thermal break is installed, balconies allow significant heat loss through thermal bridging.


With STB
With structural thermal breaks installed, thermal bridging and therefore heat loss is significantly reduced.


Visit the Schöck North America website for more information about structural thermal breaks for concrete and steel connections. Explore the full range of Isokorb® products for balcony, canopy, steel beam, exposed slab edge, parapet and rooftop connections.

Considering structural thermal breaks for an upcoming project? Have a Schöck Engineer call you to answer your specific design questions.  



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