\n The formation of condensation on the interior surfaces of windows and doors is a highly unpleasant and undesirable issue for customers, which we fully understand. For more sensitive individuals without a technical background and with heightened expectations for quality and detail, condensation on new, expensive, and energy-efficient windows may seem like a disaster, a tragedy, or at the very least, grounds for an immediate claim against the supplier. In this article, we aim to demonstrate that under certain boundary conditions, even a high-quality window or door system, properly manufactured and installed, cannot entirely prevent condensation and will inevitably fall short when pitted against the laws of building physics. <\/p>\n
\n Condensation forms on the interior surface of the structure when its temperature drops to or below the dew point, causing the water vapor in the indoor air to condense on the cold surface. The next step is simply to determine which boundary condition is responsible for the condensation. Once this diagnosis is complete, we have identified the ‘culprit’. <\/p>\n
\n The dew point is most significantly influenced by the following boundary conditions:<\/p>\n
\n Let us examine the basic concepts and explore the relationships between them:<\/p>\n
\n\tAir Humidity.<\/strong> Atmospheric air is always a mixture of two main components: dry air and water vapor. This mixture is referred to as moist air. The amount of water vapor in the air can be expressed in terms of absolute<\/em> or relative humidity.<\/em> <\/p>\n \n\tAbsolute humidity [g\/m\u00b3]<\/strong> represents the mass of water vapor contained in 1 m\u00b3 of air. Air can only hold a limited amount of water vapor, which depends on the air temperature. Generally, as the air temperature decreases, its capacity to hold water vapor also decreases, and vice versa. <\/p>\n \n\tRelative humidity [%]<\/strong> indicates the degree of air saturation with water vapor. It represents the ratio between the current amount of water vapor in the air and the maximum possible amount at a given temperature. <\/p>\n \n A certain level of relative humidity is necessary to create a comfortable living environment. The hygienically acceptable range for indoor relative humidity is 30% to 70%, with the optimal level being around 40%. Prolonged relative humidity above 50% is considered unsuitable from a hygienic perspective, as it promotes the excessive growth of bacteria and dust mites and increases the risk of mold forming on materials with lower surface temperatures. <\/p>\n \n Relative humidity depends heavily on how a building or living space is used. Indoor humidity increases primarily through cooking, drying laundry, bathing, showering, breathing, and transpiration from houseplants. In new builds, it also rises due to the evaporation of residual construction moisture from concrete, plaster, and mortar. A standard household can generate up to 10 kg of water vapor per day. Given the modern demand for highly airtight windows, combined with inadequate ventilation and lower heating settings in winter to save energy, indoor relative humidity often exceeds the 60% to 70% threshold. In one apartment, we even recorded a level of 80%. <\/p>\n \n\tThe dew point<\/strong> is the temperature at which the air becomes fully saturated with water vapor, reaching 100% relative humidity. If the temperature drops below this point, the water vapor in the air condenses. The higher the relative humidity, the higher the dew point. Under standard design conditions\u2014where the indoor air temperature is 20\u00b0C and the relative humidity is \u2264 50%\u2014the dew point is 9.3\u00b0C. Condensation will continue to form until the relative humidity decreases, which simultaneously lowers the dew point. <\/p>\n \n The risk of condensation or mold growth therefore depends on whether the dew point is reached on the interior surface of the window or door. However, the interior surface temperature is not a mandated performance characteristic, meaning it is not included in the Declaration of Performance or the CE marking. Its significance becomes apparent only after the windows or doors are installed in the building. The STN 73 0540-2 standard stipulates that fenestration products must be assessed in their installed state, accounting for the influence of the surrounding structure. The interior surface temperature is determined in accordance with STN EN ISO 10211. Frames and opaque or transparent glazing units in rooms with a relative humidity of \u2264 50% and an indoor air temperature of \u2265 20\u00b0C must maintain a surface temperature above the dew point at all times. The required standardized interior surface temperature to prevent condensation is calculated based on the average outdoor temperature of the coldest month of the year (January) for the building’s location<\/strong>, in accordance with STN EN ISO 13790\/NA. <\/p>\n \n\tAverage outdoor temperatures for the coldest month of the year (January) in selected locations:<\/strong><\/p>\n \n\t\t\t\t\tLocation<\/strong><\/p>\n<\/td>\n \n\t\t\t\t\t\u03b8e <\/strong>[<\/strong>\u00b0C<\/strong>]<\/strong><\/p>\n<\/td>\n<\/tr>\n \n\t\t\t\t\tBansk\u00e1 Bystrica<\/strong><\/p>\n<\/td>\n \n\t\t\t\t\t-3,5<\/strong><\/p>\n<\/td>\n<\/tr>\n \n\t\t\t\t\tBratislava Airport<\/strong><\/p>\n<\/td>\n \n\t\t\t\t\t-1,6<\/strong><\/p>\n<\/td>\n<\/tr>\n \n\t\t\t\t\t\u010cadca<\/strong><\/p>\n<\/td>\n \n\t\t\t\t\t-3,6<\/strong><\/p>\n<\/td>\n<\/tr>\n \n\t\t\t\t\tBrezno<\/strong><\/p>\n<\/td>\n \n\t\t\t\t\t-4,4<\/strong><\/p>\n<\/td>\n<\/tr>\n \n\t\t\t\t\tKo\u0161ice Airport<\/strong><\/p>\n<\/td>\n \n\t\t\t\t\t-3,4<\/strong><\/p>\n<\/td>\n<\/tr>\n \n\t\t\t\t\tLiptovsk\u00fd Mikul\u00e1\u0161<\/strong><\/p>\n<\/td>\n \n\t\t\t\t\t-4,1<\/strong><\/p>\n<\/td>\n<\/tr>\n \n\t\t\t\t\tPie\u0161\u0165any<\/strong><\/p>\n<\/td>\n \n\t\t\t\t\t-1,8<\/strong><\/p>\n<\/td>\n<\/tr>\n \n\t\t\t\t\tPoprad<\/strong><\/p>\n<\/td>\n \n\t\t\t\t\t-5,3<\/strong><\/p>\n<\/td>\n<\/tr>\n \n\t\t\t\t\tPrievidza<\/strong><\/p>\n<\/td>\n \n\t\t\t\t\t-2,8<\/strong><\/p>\n<\/td>\n<\/tr>\n \n\t\t\t\t\tRu\u017eomberok<\/strong><\/p>\n<\/td>\n \n\t\t\t\t\t-3,7<\/strong><\/p>\n<\/td>\n<\/tr>\n \n\t\t\t\t\tSlia\u010d<\/strong><\/p>\n<\/td>\n \n\t\t\t\t\t-3,1<\/strong><\/p>\n<\/td>\n<\/tr>\n \n\t\t\t\t\t\u017dilina<\/strong><\/p>\n<\/td>\n \n\t\t\t\t\t-3,3<\/strong><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \n To prevent water vapor condensation on the glazing, the STN 73 0540-2 standard advises against using aluminum spacer bars in the insulating glass units of rooms intended for prolonged human occupancy.<\/p>\n \n\tSurface Condensation and Interior Space Usage.<\/strong> With new windows that meet the requirements of the STN 73 0540-2 standard upon installation, surface condensation should not occur under the conditions mentioned above. If it does, users should first evaluate how they are using the interior space, as this fundamentally impacts the factors outlined at the beginning of this article: 1) indoor air temperature and circulation, 2) indoor relative humidity, and 3) outdoor air temperature. To mitigate this, they should adhere to the following guidelines: <\/p>\n \n a) Ensure adequate ventilation. The fresh air supply in living areas should be 25 m\u00b3 per person per hour, or the recommended air exchange rate of n = 0.5 per hour should be maintained. Condensation on the window glass is a clear indicator of an inadequate indoor environment. To minimize heat loss, ventilate intensively several times a day rather than leaving windows slightly open. Using the micro-ventilation handle position for prolonged periods is not advisable, as it cools the interior structures. For optimal energy efficiency, consider installing a mechanical ventilation system with heat recovery, which significantly reduces heat loss while maintaining air quality. <\/p>\n \n b) Heat the building to the designed temperature, and no lower, as this helps maintain higher surface temperatures on the interior structures.<\/p>\n \n c) Position radiators directly beneath the windows. The upward flow of warm air increases the interior surface temperature of the glass and frames, effectively preventing condensation. <\/p>\n \n d) Do not obstruct the flow of warm air to the windows. Closed or lowered interior blinds, deep window sills, covered radiators, or an abundance of plants on the sill significantly reduce the surface temperature of the window structure, thereby increasing the risk of condensation and mold growth. <\/p>\n \n If these guidelines are followed but condensation still forms to the extent that it runs onto adjacent structures, the window supplier should be contacted. The cause could be improperly adjusted window or door hardware, causing the sash to sit incorrectly against the frame. This compromises the sealing system and allows cold outside air to lower the interior surface temperature. It is also possible that the installed windows are simply unsuitable for habitable rooms. The manufacturer certifies the window’s parameters via a Declaration of Performance; if the declared values meet standard requirements, the product is deemed fit for purpose. However, window manufacturers are not obligated to assess the lowest interior surface temperature (temperature factor) of the window. A more serious issue is condensation forming on the building structure itself (the installation joint), which is typically caused by improper installation, missing thermal insulation on the outer reveal, or other thermal bridges. This scenario poses a genuine risk of mold growth. In such cases, the user should consult the building designer, who is responsible for resolving all structural details. If the homeowner did not hire a designer prior to the window replacement, they should request the installation details from the window supplier or follow the guidelines set out in STN 73 3134. If no formal window replacement project was drafted, the homeowner bears full responsibility for the correctness of the installation details. <\/p>\n \n\tThe impact of the window installation method on the lowest internal surface temperature.<\/strong> A window in a non-installed state typically has its lowest internal surface temperature at the interface between the frame and the glazing\u2014specifically where the glazing spacer is located. After installation, the temperature at the frame-glazing interface usually remains unchanged. If the detail of the window’s connection to the perimeter structure is well-insulated, a slight increase in surface temperature may also occur at the glazing joint. In the case of an inappropriately designed connection detail, the temperature at the connection joint and the reveal drops significantly. <\/p>\n \n Source: Window Maker’s Handbook, SLOVENERGOokno<\/p>\n","protected":false},"excerpt":{"rendered":" The formation of condensation on the interior surfaces of windows and doors is a highly unpleasant and undesirable issue for customers, which we fully understand. For more sensitive individuals without a technical background and with heightened expectations for quality and detail, condensation on new, expensive, and energy-efficient windows may seem like a disaster, a tragedy,…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[150],"tags":[],"class_list":["post-10654","post","type-post","status-publish","format-standard","hentry","category-technical-articles"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.aluplast.sk\/en\/wp-json\/wp\/v2\/posts\/10654","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.aluplast.sk\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.aluplast.sk\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.aluplast.sk\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.aluplast.sk\/en\/wp-json\/wp\/v2\/comments?post=10654"}],"version-history":[{"count":0,"href":"https:\/\/www.aluplast.sk\/en\/wp-json\/wp\/v2\/posts\/10654\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.aluplast.sk\/en\/wp-json\/wp\/v2\/media?parent=10654"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.aluplast.sk\/en\/wp-json\/wp\/v2\/categories?post=10654"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.aluplast.sk\/en\/wp-json\/wp\/v2\/tags?post=10654"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}\n\n
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