Icicles on foam insulated house
We just moved into our house in W. MD in mid Dec. The house is completely foam insulated, walls and roof system. The insulation job was performed as well as it could have been done. After 30 days of below 25F temperatures and several feet of snow, we are getting icicles around the entire house, some places worse than others but I suspect roof area in the worse spots as the reason. I think am getting heat transference through the 8-10 inches of roof foam and probably more likely through the 2×12 roof rafters that is causing melt under the snow and then icings as it hits the 2ft overhangs. Does this sound like a reasonable deduction and does anyone have suggestions other than heat tape on the overhangs? Thanks Derek
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德里克（Derek），南侧最差的冰柱吗？
No. There doesn't seem to be any solar effect. I still have 12 inches or more of snow on the entire roof. No bare spots at all, perfectly even melt on top of the snow cover.
德里克,
One way to determine whether your icicles are forming due simply to your weather, or are due to heat loss through the roof, is to compare your icicles with those on unheated buildings like garages, barns, and equipment sheds.
如果您的冰柱确实比附近未加热的建筑物还差，那么您的屋顶正在泄漏。这表明需要致电建筑绩效承包商来确定热量如何通过屋顶泄漏。
Hi Martin,
It is definitely in the heated portion of the house as there are no icicles over the bonus room above the garage which we keep at about 55F. The icicles are pretty uniform around the heated house. I am doing a blower door test and shooting the house with a thermal camera tomorrow but I don't think I will find much as the house was well built and insulated. I think it is a performance characteristic of the foam that no one has done any research on that I can find. Over time, the heat from inside has to be making its way through the foam and raising the roof temp. The snow is insulating the exterior of the roof so there is not a lot offset of the freezing temperatures keeping the roof cold. In addition, the 2x12 rafters are a week point.
雪实际上是一个很好的绝缘体，例如每英寸R-2，或12英寸的R-24。假设R-39是8-10英寸的开放式泡沫。这意味着您的R值的38％现在位于屋顶表面之外。如果您考虑在after子中进行热桥接的问题。
With an outside temp of 25°F and an inside temp of 70°, you have a 45° differential. 38% of 45° is 17°. The surface of your roof is (in theory) 25° + 17°, or 42°. Obviously, warm enough to melt snow.
Meanwhile, your 55° bonus room only has a 30° differential. 38% of 30° is 11°. 25° + 11° is 36°. Still above the melting point, but you get the idea. The snow is raising the temperature of your roof surface. That's why in heavy snow areas, vented roofs are prefered. Washing the underside of the roof surface with cold air keeps the snow frozen.
您的选择是：
保持屋顶相对较不雪 - 有一个特殊的工具。屋顶上很难。塑料版本不如金属版本那么糟糕。
Use metal roofing so the snow pack does not get very deep before sliding off.
Vent the roof.
Use heat cables at the eaves.
Increase the amount of insulation you have inside the house.
嗨，迈克尔，
That makes sense. Do you think installing the radiant bubble foil to aattic ceiling would be enough to solve it? I was also kicking around celulose on the attic floor?
有回音吗?: -)
德里克, if you stand in your attic now, what are you looking at? Rafters and foam?
德里克,
Michael is right...
My knowledge of Maryland geography is not so good, but don't the Appalachian Mountains run through West MD? I'm assuming your have about 6,000-ish HDDs in your area?
You said you have 8-10 inches of open-cell spray foam in the attic. So about R-29 to R-37. I don't think this is sufficient for your climate.
从你的描述项目,我m assuming the house is new. Thus a new roof is not an option. Neither is venting. Your only option appears to be adding more insulation.
Sorry about the triple post, I am on my phone doing this.
Michael, yes rafters and foam.
James- Yes we are in the mountains at about 3100 ft. I wa4 told by several foam contractors that after a certain amount of foam there is no additional benefit? I guess I could fill the rest if the cavity with closed cell? There are still some area that would be tough to get to due to the roof system geometry.
I think you're in a mixed wet-humid climate, which is tricky. The roof and wall assemblies need to be able to dry to both sides, so you don't want closed cell foam on the inside. More open cell might be the answer. No such thing as "no additional benefit" to additional insulation, just diminishing returns. Martin's suggestion of getting an energy specialist to look at your house is probably the best route to a solution for you.
I have sprayed homes and diagnosed such homes. I would recommend an energy home performance expert that has many years of hands on experience in the energy field to look at your home and do a blower door test as well. With the attic hatch open and with it closed.
THe way your home was sprayed indicates that the heating cooling system is in the attic. Ecspecailly open cell foam expands so quickly that it sometimes does not fill all the voids but leaves pockets and holes that allow heated air into and out. Attention to detail has to be done. Most homes even if spray foam is done had ridge vent and soffit vents added. THese can and will be direct paths for any air leakage to contribute to your problem. Ductwork in the way along the soffit could have caused a less than ideal spray job that is allowing air leakage. A good connection has to be made from the soffit/roof deck to the top-plate of the exterior wall. By the way if you do have more open cell spray foam added make sure its not the "I" word brand becasue it does not stick to itself. If you have a blower door and even an infrared done on the roof deck from the inside, with the blower door running and then not running I think you will see your problems. You can attack them with a 16lb tank of minimal single componet expanding foam. Curious what is your fuel usage and square footage? Dan A+ Energy
嘿，丹，感谢您的投入。我们的热系统都是辐射地板，我确保HRV管道不会侵入屋顶系统。没有交流电，因为它在我们地区的湿度非常低，如果夏季达到85F，那就是热浪。我们的加热空间约为4000平方英尺。我们用丙烷的蒙克金锅炉加热。我们将丙烷用于瞬时热水，然后在厨房里煮顶。到目前为止，在非常寒冷的月份使用燃料（高温从未超过25F），我们使用了200加仑。
德里克,
不幸的是，您已经成为像丹（Dan）这样的人的受害者客户会吹牛）。
对“热屋顶”有很好的研究，您已经发现了它们的几个问题之一。您的after架上有相当大的热桥，小于区域4的最低IECC规定的R值，屋顶上的降雪量只有8英寸，在25°的屋顶上，您会在隔离的腔体和融化中融化在afters处低至10°的室外温度。
If the ice damning results in roof leakage, the open-cell foam can hold a good deal of moisture against the roof deck, causing saturation and potential moisture problems when temperatures rise.
除了最潮湿的气候外，排气的屋顶除了最潮湿的气候外，都会胜过“热屋顶”，并消除大量潜在的水分和热问题。
The only simple solution to your current situation is to add at least one inch of rigid XPS foam board to the underside of your rafters to increase the R-value and reduce thermal bridging. Either that or use a roof rake to remove the snow at the eaves before it can melt.
Snow-melt cable rarely takes care of the problem.
哇……我just built a home in Upstate NY. Cold area. Icynene sprayed right to roof sheathing and over trusses. 5 inches. Walls 5 inches. floor joists 5 inches. Has a cellar. Roof is not vented. Attics are conditioned space.
根本没有雪融化。第三冬天。房子很紧。漫长的方向是东西方的，向南窗户示例...在北部更少。
Propane 95% efficient basic furnaces. 3000 plus square feet. two 500 gallon propane tanks. When I go to the home to work on it... once the sun comes up.. the heat stays off for the day as far as I know.
I am over the top happy with this build. And the Icynene is making me very happy. The main reason I went with low density foam.... is because it does breath.... I like the fact that it is more permeable. I really feel moisture trapping could be a huge problem with 2lb foam.
我现在对闪光和纤维素的1磅泡沫感兴趣。
Also... the guy making water filled windows beat me to my idea... I love the idea of a window being a net plus btu producer.
aj
再次感谢您提供的所有输入，非常有趣的东西。
Adkjac- It does not sound like you are full time at this house? I would look at some of the suggestion if you are still in construction phase as the icicles really did not start on my house until about two and half week of constant indoor temperatures of 68-70F.
I am going to take some remedial action but the icicle proplem I have is not terribly bad even under what I consider a pretty bad weather month. I will continue to experiment.
也许UpStateny屋顶的A的区别是他的屋顶的桁架结构。通常，屋顶桁架将具有2x4或2x6顶和弦。因此，他的喷雾形式封装了顶部的和弦，并且没有屋顶结构的正式桥接。
adkjac，
If you're in climate zone 6, your 5" of open-cell foam doesn't even come close minimum IECC standards, which are R-49 ceiling, R-20 walls, R-30 floors. If you're in northwestern NY, zone 5, the requirements are 38/20/30.
You've got, at best, R-18 all around.