Venting an existing flat roof
我们在芝加哥有一排房子。这幅图籼te (it seems it was built as drawn) that we have a 1/4″ per foot modified bitumen roof. We don’t have soffits or ridges (just parapets on three sides and a gutter along the back). The roof structure is min 16″ wood roof trusses at the low gutter end and they get bigger at the front. We have R49 Green Fiber blown in cellulose insulation in the trusses. There is no vapor barrier (as the insulation suggested) and there is two layers of 5/8″ drywall at the ceiling. We have mushroom vents at 1 sq. ft. of net free area for every 300 sq. ft. of attic floor space. My questions are: 1) I’ve read online that we need 1sf vent for 150 sf of floor space but there is an exception if you vent ridges and soffits and have a vapor barrier it can be 1:300. It doesn’t really address flat roofs. Do you typically see the 1:300 on flat roofs like the drawings indicate? and would adding more vents always better? 2) The parapets are so low (typically 6″) that we can’t add rigid and keep the min parapet height required by code and to make things worse I don’t think zoning would allow us to add a doghouse if it was taller than the parapets because the building already had to get a zoning height exception. 3) If all we have are the mushroom vents, is there any requirements about where they should be located on a flat roof? The drawings didn’t show their locations (only the net vent area required). Thanks in advance!
GBA详细资料库
由气候和房屋部件组织的一千个建筑细节的集合
答复
Trisha，
根据您的描述绝缘的大量屋顶开发腐烂的护套。
如果您现有的建筑码真的迫使您以几乎保证护套腐蚀的方式将您的建筑物隔离，那么您需要对您当地的建筑部门进行强有力的演示，以获得允许以正确的方式将屋顶隔离。
The best way to insulate a low-slope roof is to install all of the insulation (usually rigid foam) above the roof sheathing. Other methods can work, but they are tricky to execute well.
处理栏杆的最佳方法是永久删除它们。
您当前的通风方法不充分。如果您最终尝试创建通风屋顶装配 - 始终棘手 - 您需要一个突出的狗座，在屋顶的中心，您需要支付非常细致的关注空气密封您的天花板。
有关更多信息，请参阅Insulating Low-Slope Residential Roofs。
在美国气候区5（即您）中，您需要大约40％的总R在屋顶甲板上方的露天点控制中。如果你放下8英寸的II型EPS（R33.6）和一个新屋顶，你就在那里，因为你有R83-ISH总数和R33-ISH以上的R33 /R83 =〜40％。泡沫的成本将运行每平方英尺约3-3.50美元，无法猜测新屋顶的成本是多少。
Ideally the fiber would be in complete contact with the roof deck, but it's not a disaster if it's not as long as you have sufficient foam-R above the roof deck. The air-gap represents a potential thermal bypass between the cellulose and above-deck foam should there be any air leakage, but with R49 in just the fiber layer it'll still meet code from a thermal point of view with just the R49, and incidental outdoor air leakage into that space would be a drying force more often than a wetting force.
将9英寸的EPS放在屋顶甲板上方并取出纤维素，密封通风口将在U-Factor的基础上达到Code-min，但只需将纤维素留到位并且具有超级绝缘的屋顶可能更便宜并且具有更便宜的。
Trisha，在您的情况下可能为时已晚（或者它会涉及一些严重的补救工作
But if you are interested we have written about this subject on our blog:http://foursevenfive.com/unvented-flat-roofs-a-technical-discussion/- 短发泄Fallroofs是非常不可依赖的，会导致马丁指出的损失。
但是，还有除了在屋顶顶部添加泡沫的选项 - 我们的475方法是在内部添加智能蒸汽延迟器智能电池，胶带重叠气密，然后在其上方吹纤维素。我们的安装人员在纽约，新英格兰，新英格兰和其他地方4,5,6的其他地方的许多平顶屋顶上成功地使用这一点。
Trisha，
一些评论：
1. Floris Buisman为475家高性能建筑产品，欧洲膜的进口商作品，他对销售了他正在描述的产品有一种既得利益。
2.他正在描述的方法 - 使用玻璃纤维和纤维素等透气绝缘材料创造一个不打透的屋顶装配 - 在德国可能是合法的，但它将是美国的代码违规行为。