Air barrier between attics?
Hi…we are in North Idaho one hundred miles south of the Canadian border near Coeur d’Alene in Climate Zone 5. We use AC in July & August and heating October to May.
I apologize in advance that this isn’t a brief question. I tried to condense this as much as possible, but it’s a complicated situation regarding energy efficiency strategy. I would really appreciate any help you might be able to offer.
冬季确实在今年2月1日左右去了，三周内我们的降雪量为65英寸。我们于2018年3月购买了房屋，这是我们的第一个冬天，所以自然而然地，我们在楼上的主卧室里遇到了非常糟糕的冰坝，一些水分和损坏。
I am planning extensive energy upgrades with the objectives of avoiding future ice dams and water damage as well as improving energy efficiency and comfort.
My main question is whether I should isolate the three attics in the house which are now all open to each other. Details follow…
这所房子建于1991年，没有任何能源升级。房屋的主要部分是两层楼，上面有几个大型复杂的窗户，一间用于主卧室的床，另一个用于前廊（请参阅照片）。这两个楼层的部分有一个分裂的俯仰屋顶 - 前部12/12，后部约为4/12（本质上是一个大型棚屋）。房子的后部是单一的故事，有厨房，餐厅和一个角落。2007年的后部增加了一个单层的补充（包括两居室，洗衣房，一个浴室，储藏室，长大厅）。单个故事部分有三个阁楼。在两层楼的部分；和车库。目前，在这三个阁楼中的任何一个中，没有任何霉菌或霉菌生长的证据。
Attic inspections have revealed lots of energy shortcomings:
1.原始区域和加法区域中的绝缘层不足（爆炸）。似乎平均可能是R30，但是在许多区域中，绝缘材料被堆积起来。它可能被吹扫，安装不佳，或者可能是由有线电视或安全系统的人员移动的。有几个区域，可见裸露的天花板板岩。
2. Maybe 10% of the cardboard rafter baffles are partially down
3. Inadequate ventilation around the second story dormers. Little air can enter near the dormers and the dormer front gable wall blocks air entry to the rafter bays.
4. Inadequate second story ridge ventilation – there are only two small turtle vents at the ridge (see aerial photo). The single story part has a continuous ridge vent which gets covered with heavy snowfall in this region.
5. Lots of can lights (IC, not AT) and ventilation fans (all fans vent outdoors).
6. Utility room combustion air in the ceiling opens to the single story attic – dumps heat into the attic.
7. An auxiliary gas-fired furnace plus supply and return ducts over the addition. The furnace and ducts are insulated, but that’s a lot of heat going into the attic when the furnace runs.
8. The three attics are open to each other and air can freely flow from one attic to the other. Moisture from warm cars in the garage can leak into the garage attic and flow to the attic over the rear single-story section. Air from the single story-attic can flow up to the second story attic through a huge opening where the return ducts go from the second story attic down to the utility room.
9. Very leaky and uninsulated hatches to both the first floor and second floor attics.
I have a big project ahead. The retrofit plan I’m thinking about is:
1. remove the cellulose insulation in the living areas; leave the existing cellulose over the garage.
2.增强房屋前侧窗户附近的第二层通风入口；我不确定我们目前有多少入口区域或如何添加入口区域（在左侧的大型上窗附近发生了进水区域）。后棚室内有连续的拱腹入口，因此入口区域很好。
3.在第二层山脊附近添加几个屋顶出口通风孔（查看通风最大的冲天炉风格的通风孔不会被雪覆盖）。我将平衡入口和出口区域。
4. seal all electrical & plumping penetrations from living spaces to attics.
5 add can light covers sealed with foam.
6. replace can lights with Cree LED CR6 or LR6 retrofits and seal flanges to sheetrock.
7. add two inches closed cell foam over the ceiling sheetrock in both first floor and second floor attics; build up a 4 inch foam “berm” over the exterior perimeter top plates and up to the bottom of the rafter baffles
8. replace failing cardboard baffles with site-built foam or OSB baffles with 1-1/2 inch air space to roof sheathing; seal baffles to top plates
9. close off the utility room combustion air inlet to the attic.
10. seal the supply and return ducts (most of them are insulated flex)
11. possibly abandon the attic furnace and switch to wall electric heaters or add a ductless mini split system.
12. blow R60 fiberglass into the living space attics and add fiberglass to the garage to R39
13. tightly sealed and insulated attic hatches
对不起，所有漫长的背景！是的，有一些问题，这是我真的很感谢您的建议：
1.我应该彼此隔离这三个阁楼，以便它们是独立的，并且不会在它们之间传达空气？换句话说，我是否应该阻止从车库到一楼阁楼的空气流，并阻止从一楼阁楼到二楼阁楼的气流？即使在5度户外温度之夜，车库也悬停在冰点附近。但是进入车库的汽车带来了大量的热量和水分，可以流入这两个阁楼。
2. What’s the best approach to adding air inlets on the front of the house given the dormers?
3.我们在单层餐厅和厨房区域中有12英寸深的船上天花板；绝缘的最佳方法是什么？
4.我还应该考虑其他能源考虑吗？我想念什么？
事先感谢您对此可能有任何意见或想法！我想明智地花钱。
GBA Detail Library
由气候和房屋部分组织的一千个建筑细节的集合
答复
Steve,
Lots of problems here. Your approach makes sense, but you may have bigger challenges than your realize.
If this were my house, I would certainly abandon the furnace and associated attic ductwork, and I would install ductless minisplits to handle the load now carried by the attic furnace.
如果座舱阻止所有r架被排气，那么您可能会有一些after柱，需要使用未通风的方法隔离。如果是这样，您可能必须卸下屋顶和屋顶护套，以便您可以用上面的闭孔喷雾泡沫将某些after湾隔离。
Thanks, Martin. Appreciate your reply. I forgot to mention that there is a knee wall to the right of the porch dormer on the front 12/12 roof. These are (I think) 10 inch rafters over the knee wall area and the rafter bays have fiberglass batt insulation in them (kind of like a cathedral ceiling design). I don't recall if there is an air chute above the batts (I don't think there is). So it's even more complicated in this area.
If I have a cold, unconditioned attic, does it make sense to insulate individual rafter bays with CC foam as you suggest? Are you suggesting changing to a conditioned attic and insulate the entire roof sheathing assembly? I briefly considered that and rejected it.
What about the air communication between the three attics? Would I be better off isolating these to prevent airflow from 1) the garage attic to single story attic and then from 2) the single story attic to the second story attic? Right now, these are all open to each other.
Steve,
Q. "If I have a cold, unconditioned attic, does it make sense to insulate individual rafter bays with CC foam as you suggest?"
答：不。如果阁楼被排气，并且在阁楼地板上有一个完整的R-49绝缘层，则无需在after架上进行绝缘材料。然而，这是事情变得棘手的地方：如果您的阁楼缺乏适当的排气口，因为从拱腹到阁楼没有空气通道，或者如果after空间被压缩得如此之高-49在阁楼地板上进行的绝缘材料，您必须确定其他方法是否更有意义。
Q. "Are you suggesting changing to a conditioned attic and insulate the entire roof sheathing assembly? I briefly considered that and rejected it."
A. It's one possible approach, but I'm not recommending it -- it's hard to say if that approach makes sense without a site visit. But it may still make sense to have a vented unconditioned attic above most of your house, while insulating a few rafter bays with an unvented approach.
Q. "What about the air communication between the three attics? Would I be better off isolating these to prevent airflow from 1) the garage attic to single story attic and then from 2) the single story attic to the second story attic? Right now, these are all open to each other."
A. I think this matter is mostly irrelevant. Your are focusing on the wrong issue. What you need are the following: (1) An air barrier between the interior conditioned space and the attic, and (2) R-49 insulation in direct contact with the air barrier. If you can get that, then the air mixing issue is irrelevant.
Ice dams are almost always a combination of conductive and convective heat loss. I bet folks on GBA get tired of me and Martin (and others) saying this but:
尽可能保持密闭；与您选择的绝缘水平一样重要，即使不是更重要。
彼得
谢谢你,彼得。我读过很多论文和文章on GBA, JLC, and others about this problem and understand the importance of air sealing. That's why I'm going to the considerable expense of sucking out the existing cellulose over the living areas -- it's the only way to get access to do a good job of sealing. We are going to do individual leak seals, fill chases, drop ceiling soffits, recessed light covers, covers over ventilation fans, etc, then spray the 2 inches of CC foam over the ceiling sheetrock to really encapsulate and air seal it.
I just asked Martin this: should I isolate the three attics from one another? Right now, the garage attic is open to the single story attic and the single story attic has a huge hole into the second story attic around the return air ducts. This strikes me as a path for fire spread, for humidity spread, and for convective air flow to rise to the upper-most roof assembly. So I think it makes sense to isolate these from each other. What do you think?