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planning:airtight_construction:general_principles:leakage_problems

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planning:airtight_construction:general_principles:leakage_problems [2015/05/09 21:34]
wolfgangfeist@googlemail.com [Requirements for Airtightness within Passive Houses]
planning:airtight_construction:general_principles:leakage_problems [2019/02/28 10:10] (current)
cblagojevic
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 The external envelope of a building should be as airtight as possible and this doesn’t only apply to Passive Houses. The external envelope of a building should be as airtight as possible and this doesn’t only apply to Passive Houses.
   * building damage caused by water vapour that is transported in air draughts can only be prevented by airtightness of the envelope (see illustration). ​ Building damage is mostly due to the absence of airtightness in the roof area.   * building damage caused by water vapour that is transported in air draughts can only be prevented by airtightness of the envelope (see illustration). ​ Building damage is mostly due to the absence of airtightness in the roof area.
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   * Draughty living spaces and cold air pockets are no longer acceptable for inhabitants:​ a truly airtight method of construction leads to greater comfort.   * Draughty living spaces and cold air pockets are no longer acceptable for inhabitants:​ a truly airtight method of construction leads to greater comfort.
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   * Ventilation systems with supply air and exhaust air spaces only function if the building envelope is sufficiently airtight.   * Ventilation systems with supply air and exhaust air spaces only function if the building envelope is sufficiently airtight.
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   * Airtightness results in better sound protection   * Airtightness results in better sound protection
 Therefore, in accordance with construction technology regulations,​ a good level of airtightness is generally required today, and rightly so.  This applies even more for a comfortable Passive House.\\ Therefore, in accordance with construction technology regulations,​ a good level of airtightness is generally required today, and rightly so.  This applies even more for a comfortable Passive House.\\
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     * A well-insulating building component doesn’t have to be airtight: e.g. one can easily “blow through” a mat of coconut fibre, cellulose filling or mineral wool insulation. These materials are very good insulators, but they are not airtight. The only insulation material that can also be used as an airtight layer is foam glass. ​     * A well-insulating building component doesn’t have to be airtight: e.g. one can easily “blow through” a mat of coconut fibre, cellulose filling or mineral wool insulation. These materials are very good insulators, but they are not airtight. The only insulation material that can also be used as an airtight layer is foam glass. ​
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     * Conversely, an airtight building component doesn’t have to be insulating, e.g. an aluminium sheet is absolutely airtight, but has practically no insulating effect.     * Conversely, an airtight building component doesn’t have to be insulating, e.g. an aluminium sheet is absolutely airtight, but has practically no insulating effect.
  
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 This is a quite demanding requirement,​ but experience has shown This is a quite demanding requirement,​ but experience has shown
   * after some learning gained with first built projects or a Passive House course, these very good values can be achieved regularly. (To see these figures as "very tough" is just a beginners view; we have seen that again and again: after some experience, well designed projects of an experienced team will have n50-values of some 0,3 to 0,5 h<​sup>​-1</​sup>​.)   * after some learning gained with first built projects or a Passive House course, these very good values can be achieved regularly. (To see these figures as "very tough" is just a beginners view; we have seen that again and again: after some experience, well designed projects of an experienced team will have n50-values of some 0,3 to 0,5 h<​sup>​-1</​sup>​.)
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   * the costs for achieving these values are not higher than those to achieve less demanding ones. (To be better than say 1.5 h<​sup>​-1</​sup>,​ you'll need an airtightness concept. But: If you do an airtightness concept, it doesn'​t make a big difference to go for say 0.5 than for 1.5 h<​sup>​-1</​sup>​) ​   * the costs for achieving these values are not higher than those to achieve less demanding ones. (To be better than say 1.5 h<​sup>​-1</​sup>,​ you'll need an airtightness concept. But: If you do an airtightness concept, it doesn'​t make a big difference to go for say 0.5 than for 1.5 h<​sup>​-1</​sup>​) ​
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   * these values guarantee a good performance of the building: moisture problems are avoided this way   * these values guarantee a good performance of the building: moisture problems are avoided this way
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   * the energy conservation by these measures is significant. The influence on peak load is even higher (because of the changing weather conditions). Therefor, building really airtight significantly reduces the risks of missing performance. This is one of the reasons, why there is no "​performance gap" with passive houses - but there seem to be such problems within other ambitious low energy projects. Yes, it's difficult to fully track air infiltration losses and to exactly calculate their influence on the performance. But: The best and easiest (and cheapest) way to cope with this is to build the envelope tight - and avoid all these problems.  ​   * the energy conservation by these measures is significant. The influence on peak load is even higher (because of the changing weather conditions). Therefor, building really airtight significantly reduces the risks of missing performance. This is one of the reasons, why there is no "​performance gap" with passive houses - but there seem to be such problems within other ambitious low energy projects. Yes, it's difficult to fully track air infiltration losses and to exactly calculate their influence on the performance. But: The best and easiest (and cheapest) way to cope with this is to build the envelope tight - and avoid all these problems.  ​
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   * there is an additional benefit for better comfort by avoiding drafts. Persons seem to be especially sensitive to cold drafts (see ISO 7730) - and there are two important causes for such drafts: first, an untight envelope; and second, cold surfaces.   * there is an additional benefit for better comfort by avoiding drafts. Persons seem to be especially sensitive to cold drafts (see ISO 7730) - and there are two important causes for such drafts: first, an untight envelope; and second, cold surfaces.
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planning/airtight_construction/general_principles/leakage_problems.txt · Last modified: 2019/02/28 10:10 by cblagojevic