Cool roof on a rigid foam retrofit
Hello,
在开始新家之前，我一直在进行大量研究。我想获得有关如何侵犯我的改建的建议。
The home is a 2600 sq ft contemporary style house. The majoroty of the roof is an unvented catherdral roof assembly. It is a simpole gable roof, although the North face is much steeper. It currently has an aging asphalt roof that will need replacing soon. I am planning a PV array instalation and need advice on what sort of assembly would be the best combination.
Based on research I know that a metal roof is most likely my best option for longevity and performance with the PV array. I saw a few rigid foam retrofit roof details on GBA. These were hot roof assemblies. However, I was curious if anyone had run across a cool roof assembly with a rigid foam retrofit? See the attached image for specifics. The rigid foam has 1×3 battens installed over the top with a pre-galvinized continuous vent installed at the eave.Over this goes the new sheathing, then the ice and water shield. Finally the standing metal seam would go on. There would be a ridge vent installed along the top.
I would like to know if there are any benifits to this type of assembly. I realize that the venting would certainly aid in cooling the metal, however, in seaching for a cost effective solution, I am unsure if any benifits would be marginal and not worth the extra expense. I look foward to any insite on this.
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答复
David,
到目前为止，您描述的方法是隔离大教堂天花板的最佳方法。
使刚性的泡沫层尽可能厚 - R-49并不是太多绝缘，尽管在炎热气候中安装较少的装置是常见的 - 并且您将拥有出色的屋顶组件。
马丁，我感谢立即的回应。
就泡沫厚度而言，我看到5区房屋的建议r值为20。使用XPS，这将转化为4英寸的泡沫。会用胶带和密封的2.5英寸层，上面放着1.5英寸，上面放着停滞的接缝，胶带和密封；有效的侵犯？我假设2x10 afters有玻璃纤维棒，仅基于我在小阁楼空间中看到的隔热材料和房屋中的2x6墙。
David,
如果您相当确定现有的Rafter Bay是用玻璃纤维棒隔热的，则可以将这些Batts的R值计算为您的R-49目标。（当然，安装的质量有所不同 - 大教堂天花板中的许多瓦特板在性能上接近R-0。）重要的是要验证rafter bay没有排气；如果有拱腹通风口和山脊通风孔，则必须仔细密封。
You're right that R-20 rigid foam above the roof sheathing is enough in Climate Zone 5. (For more information on this topic, see如何建造绝缘大教堂的天花板.)
Most green builders avoid the use of XPS because it is manufactured with blowing agents that have a high global warming potential. Either polyiso or EPS would be a better choice; in cold climates, EPS is preferred because it performs better at low temperatures than polyiso.
David and Martin,
由于这是一种改装，在进行这种类型的刚性泡沫屋顶绝缘之前，检查是否有内部塑料板作为蒸气屏障是明智的吗？
直到真正透气的刚性泡沫绝缘材料才能安装在屋顶甲板上.....我们中的许多人注定要有冷泄漏的天花板（除非将内部干墙拆除以撕开Poly屏障）。
Dirk, I had wondered the same thing. At this point, I won't know exact details of the roof assembly until I begin pulling it apart to replace the asphalt shingles. I may be able to gain access possibly in the small attic that is besides the cathedral roof to examine wether there is plastic sheeting underneath the sheet rock.
马丁，解决您提出的几个要点。大部分屋顶上都没有拱形通风口，也没有山脊通风口，房屋西侧的1/4有一个阁楼空间，确实有山脊通风口。我计划将其转换为条件阁楼，因为我目前在那里进行了管道工作。关于泡沫的选择，我被XPS吸引了，因为EPS和Polyisio都有我发现在我的情况下具有劣势的功能。EPS的R值要低得多，因此我需要更多才能达到我想要的R值。就Polyisio而言，我已经读到，由于吹风剂的气体开始凝结，R值性能在寒冷的天气中降低。这不是我想要的不一致之处，因为我宁愿房子在冬天而不是夏天持续的表现。
Finally, I am purchasing the foam second hand, in order to recycle and reduce the impact my choice of insulation has on the environment. I have found a local individual that has factory seconds, surplus, and used sheets of foam.
大卫-安装第一层polyiso跟进ed by a layer of EPS, will keep the polyiso warmer and consequently won't degrade as much in cold weather. You may be able to get these foams second hand as well. Recycled XPS is certainly greener than new, but it could be argued that recycled EPS and polyiso are greener still.
在金属屋顶下，您需要使用Grace的Ultra HT冰和水上保护产品，因为它在夏季高温下的性能较好。
凯文，
EPS does have a muh lower r value and therfore I would need a thicker layer of foam to achieve the desired r value. In the end wouldnt the outer layers of polyisio achieve the same end result as a combination of polyisio and EPS?
Also, how much of an impact do cold temperatures have on the performance of polyisio?
David,
您的美元的最佳组合和爆炸是比poly-ISO的EPS，只需确保水平和垂直的接缝即可。有很多购买二手绝缘材料的地方，并且可以使用许多类型的“轻轻使用”绝缘材料。尝试http://www.insulationdepot.com，他们对我的价格很高，并且可以通过提前通知来提供大量或可以采购。
Don't forget that because XPS is a blown insulation (like Poly-iso) and will lose R-value over time, as the blowing agent off-gases, although it won't get Thermal Drift from cold temps like Ploy-Iso.
EPS, because it is expanded does not degrade over time.
Another aspect of EPS vs. XPS - EPS is semi-permeable, and if it does get water in it, it will shed it. XPS, although more resistant to water and vapor, once it is wet internally can takes months to rid itself of water. Just place a sheet of XPS in a puddle of water for a few weeks, and then take it out after being there for a while and the XPS will still hold the water like a sponge. This further degrades the R-value and long-term studies have been done on XPS that was placed subgrade and then taken out and tested.
每股收益也被部分回收，并且可以在将来。
看到将来的代码簿中外部绝缘材料的R值增加，以防止在中壁中进行凝结问题，如果您将当前代码用作指南，则可以继续进行冷凝问题。
For some further info on insulation thermal drift - check out this GBA article:
//m.etiketa4.com/blogs/dept/musings/cold-climates-r-5-foam-beats-r-6
Another really great article that compares common insulation and the effect of temperature on R-value:
http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/59419/Big-News-The-R-Value-of-Insulation-Is-Not-a-Constant
还有另一个：
http://www.buildingscience.com/documents/information-sheets/info-502-temperature-dependent-r-value/
还有另一个（冗长，数据沉重，但揭示）
http://www.buildingscience.com/documents/special/content/thermal-metric/BSCThermalMetricSummaryReport_20131021.pdf
布拉德，
A very thourough and informative response. That does change some of the details for the roof assembly. I appreciate ypou taking the time to offer some "seasoned" advice.
我会像照片中所示的那种白色的东西。获取一些乳胶错误。