Condensation, Ventilation, and Your Metal Roof

在闷热的夏日，没有什么比您最喜欢的饮料的冷杯更令人愉悦的了。我的选择是不加糖的冰茶。而且，当我想象一下那杯冰茶时，首先想到的是凝结的液滴，当我将其携带在玻璃外面时，它们会在玻璃外面迅速形成。

我喜欢这个插图，并在与业主谈论其阁楼空间中凝结的风险时经常使用它。到达露点时，这些液滴在我的杯冰茶外面形成。露点很简单，是水分和温度差异的“正确”组合，导致空气中的水分凝结并形成水。

虽然您最喜欢的饮料杯外面的凝结可能是一个受欢迎的景象，但如果它位于您的房屋或其他建筑物的阁楼中，那就不会受到欢迎。阁楼中的冷凝将导致霉菌，霉菌和腐烂。它还会增加阁楼地板上绝缘的水分水平，随着湿润的潮湿甚至潮湿的效果。

多年来，阁楼中发生的凝结显着增加。一方面，我们在结构中添加了更多的水分来源。诸如植物，洗衣，烹饪，沐浴，气和木炉等植物都会增加建筑物内部的环境水分水平。但是，此外，尤其是自1970年代以来，我们一直在努力使建筑物更加密封 - 我们甚至对它们进行了密封性测试。诸如改进的门和窗户，房屋包裹和其他外墙覆盖之类的东西都意味着，现在，用来通过建筑物信封向外部开车向外面的水分却在建筑物中以对流的气流向上携带，通常最终最终在河边。阁楼。

So, as you think about this warm, moist air migrating into the attic of a building, consider again that cold glass of your favorite beverage. If you introduce it into your attic, condensation will quickly develop on the outside of it, just as it does inside. The same thing will happen with other cool surfaces in your attic. This commonly is the underside of the roof deck. And, of course, that condensation first soaks into the wood, raising its moisture content and making it subject to rot, until it eventually exceeds the wood’s ability to hold moisture and it forms condensation on the surface as well.

真正让我颤抖的一件事是看到金属屋顶安装在较小的建筑物上，例如住宅，而没有胶合板等固体屋顶甲板。当暴露于含水量的阁楼空间时，金属面板的非吸收后侧将用水滴迅速而危险地凝结。我遇到了如此严重的情况，以至于房主认为阁楼正在下雨。

Now, with larger structures such as warehouses, factories, churches, or retail stores, this is less of an issue because you usually have lower ambient moisture levels as well as more air exchanges and therefore a much-reduced risk of condensation.

但是房屋较小，我们在其中产生了很多水分。结果，即使甲板已经到位，这种冷凝的风险也要大得多。一个metal roof在这样的结构上，没有甲板是一个主要问题。

So, what is the answer for condensation control in all buildings? The best solution for most construction methods, excluding those utilizing a conditioned attic space, is ventilation. Another good option and tool in your tool belt against condensation is the use of蒸气屏障to help slow the migration of moisture from the living space into the attic.

Many people I have run into mistakenly do not realize that the living space is the source of the moisture we’re talking about that is at risk of condensing. During most seasons and times, there is higher moisture inside a structure than outside. Moisture naturally tries to drive to drier areas, carried by warm air. If it reaches a cool surface along that path, it condenses, and that is what we want to avoid.

适当的通风由进气口和排气口组成。进气口位于阁楼的下部边缘。然后，排气口最好位于屋顶的山脊或山峰。我喜欢想尝试创建流动空气的“河流”，遍历整个屋顶的整个底面，在保持屋顶甲板干燥和健康的同时进行水分和热空气。

Oftentimes, the intake vents are in the eave soffits of the structure. Care must be taken to ensure that they do not get blocked with insulation over the years. Baffles are sometimes used in the attic to help keep the airways clear and open. These vents are commonly installed by the same contractor who installed siding, fascia, and gutters on the structure. The exhaust vents are then often part of the roof system and installed by the roofing contractor.

If the structure does not have soffit overhangs and therefore no room for attic air intake vents, roofing manufacturers sometimes offer vented starter/drip edge pieces that extend out the eaves a couple of inches to bring air into the attic.

Both intake and exhaust vents should carry an NFA rating. This stands for Net Free Area and quantifies the amount of open area that allows air to pass through the vent. You ideally want an even balance of NFA for intake and exhaust or, if anything, a somewhat pressurized system with slightly more intake than exhaust. Local building codes will specify the total amount of NFA based upon the building size, with the guideline that it is split evenly between intake and exhaust.

采取适当的预防措施，这种凝结可以留在属于的地方 - 在您最喜欢的夏季饮料的外面。

这是以赛亚工业总裁托德·米勒（Todd Miller）的来宾帖子，他在金属屋面行业工作了35年。他经常回答有关屋顶，通风和其他主题的问题教育网站。