Please help me decide which option to go with for my encapsulated crawlspace retrofit.
I am in Nashville, TN – zone 4. I just bought a two story house that was built in 1997 and is on a crawlspace. The current crawl is in “good to great” shape according to the various contractors and energy professionals that I have had down there giving me bids. This is even though I have already fixed numerous issues with overflowing gutters or gutters with downspout connections at the ground level that did not correctly meet up with the black pipe to take it away from the foundation. Despite these issues, and despite that the house is 20 years old with a traditional vented crawl with batt insulation in the floor joists, there is very little to almost no hanging insulation or the “normal” look of a vented crawl. No standing moisture and no mold, there is some condensation on the ductwork. BUT… the hardwood floors above did show significant cupping, which we have since fixed with sanding and refinishing them. (The previous owners were just a man and woman and apparently they kept the house REALLY warm… around 80 from the looks of the programmed modes on the thermostat and the resulting cooling and heating bills) We dont want this cupping to come back, and want to do what is best for the house in the long term. The main level of the home is around 3,600 sq feet. I have crawlspace encapsulation bids that range from about $5,400 for a sealed and taped vapor barrier only that includes a “Mega dry cs70” dehumidifier to bids for encapsulating and then foaming the walls (closed cell below rim joist / open cell in rim joist area) and a 70cfm or so exhaust fan along with a transfer grill somewhere in the house. And variations in between. Some want a dehumidifier, some want to cut supply and return, and some want to vent. I have read and read and read and cannot decide which is the best option.
I am also getting bids to put open cell in my rafters of the whole house as part of this project. Some want to do 5″, claiming any additional is a tiny improvement for the money, all the way to a contractor who will simply “fill the rafters”.
And one last wrinkle… I am having low voltage wiring installed, and along with that a chase of a couple of small pipes running from the crawl to the attic. I was wondering if NOT foaming them in and allowing air to be pulled out from the new crawlspace from the foamed attic would help with any off gassing that could occur in the newly foamed attic space. Is that any kind of a good idea?
So… in a nutshell, I like the dehumidifier idea since it seems energy efficient, even when the dehum runs, since I am not “Wasting” my conditioned air by sending it to the outside from the small fan, but I like the small fan exhaust idea since I feel that would get rid of off gassing from the attic or new crawlspace foam, as well as radon, etc. (radon test in this home upon moving in was a very low 1.1).
I know that is a lot, but I wanted to get all the variables and decision points into the question. Thanks so much for any help and advice!
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由气候和房屋部分组织的一千个建筑细节的集合
Replies
John,
In most cases, a properly sealed crawlspace should not need a dehumidifier. For more information on this issue, seeBuilding an Unvented Crawl Space.
If your climate zone, building codes require a minimum of R-49 of roof insulation. If you want to use open-cell spray foam for this, you'll need about 13.5 inches of spray foam to meet minimum code requirements. (There are cheaper ways to do this, by the way, but I don't recommend skimping on R-value to save money.)
有关此问题的更多信息，请参阅
It’s OK to Skimp On Insulation, Icynene Says
How to Build an Insulated Cathedral Ceiling
Open-Cell Spray Foam and Damp Roof Sheathing
谢谢，我将再次阅读这些文章。由于我只有2x8架，因此我将无法更深地超过〜7.5英寸，并且能够在屋顶的内部干燥墙壁，以便将来建造一个房间，这是我想要做的事情。我想7.5英寸的封闭牢房几乎是“把我带到那里，但是由于“无法检测到泄漏”问题，这将是非常昂贵的，而且似乎不推荐。
John,
作为我的文章（How to Build an Insulated Cathedral Ceiling）解释说，如果需要，可以增加腔深度的深度，以提供更多的绝缘层。在所使用的方法中：在after子的内侧，您可以在90度以90度安装2x4（16英寸O.C.），以加深腔体。或者，您可以使用胶合板的毛刺来支撑现有afters的新2x4“ afters”（在同一平面上）。或者，您可以在after子的内侧安装连续的刚性泡沫，然后在中央16英寸处安装1x4绑带。
好，谢谢！我会回顾一下...我在我的区域中为R49拍摄吗？我当时认为R38在这里是代码。
John, I am in Knoxville and the house here had a very wet crawlspace. First I dug a curtain wall: a 4' deep trench (well below the grade of the crawlspace interior), lined with geotectile fabric, perforated solid pipe on the bottom with slight pitch, filled with crushed rock. Put this all across the back, at the foot of the downslope that drained toward the house. Ran solid pipe from the low end to daylight. Connected downspouts to the solid pipe. This significantly reduced moisture below the house.
I sealed the crawlspace with reinforced plastic sheeting, taped and caulked for an airtight application. I did not remove the R-13 in the floor joists, and I did not insulate the perimeter walls.
考虑了选择后，我不希望发霉的地下室空气与我们的条件空间通信，因此我没有将被动通风口猛击到房屋上，也没有将HVAC从HVAC放入爬网空间。我考虑过将低CFM风扇添加到外部，但决定简单地将其作为第一步，也许以后再添加风扇。
The third option is to dehumidify only. Instead of getting one of those $1600 dehumidifiers that the crawlspace specialists recommend, I went with a small $150 unit with an energy star rating. Ran the condensate line to the sump.
Result: the house still smelled moldy—but significantly less so—during the first year. Ever since the house has smelled clean and fresh—and my wife has a real nose for mold. The dehumidifier does not turn on much anymore either. By the way, the HVAC ducts are all in that crawlspace, so you can imagine why the house would smell moldy!
Finally, I built a fully gasketed access door, and I added one of those toggle clamps to suck the door against the weatherstripping to make it airtight. Works like a charm.
Personal gripe: when I go on the Parade of Homes tour around here, even the high-end homes have ventilated crawlspaces, with block walls that are below grade and not even waterproofed. When I peek, saturated soil and damp stem walls are common. And again, ductwork in unconditioned space that is destined to become moldy. I wish continuing education was required to keep up a contractor's license.
John,
The R-49 minimum comes from the 2012 International Residential Code (IRC). If your jurisdiction uses a different code -- and that's entirely possible -- the requirements might be different. If you are uncertain about local code requirements, call up your local building department.
大卫，
您写道：“个人gripe：当我参加这里的房屋游行时，即使高端房屋也有通风的爬网空间，砌块墙的墙壁低于坡度，甚至没有防水。墙很普遍。同样，注定要发霉的无条件空间中的管道。”
I couldn't agree more. I continue to be astonished that high-end homes, including homes costing between $500,000 and $1,000,000, have the same lousy construction details as $180,000 starter homes. This happens because (a) code requirements aren't enforced, and (b) buyers are unaware of how poorly built these homes are.
Thanks for all your help here Martin... if I may, two more questions:
1.我的想法是否想到了现在从爬行空间到阁楼在我家中安装的两条电线追逐管，可以让阁楼空气（因此，从即将到来的开放式填充泡沫中安装的任何瓦斯）都可以与泄漏的房屋混合空气将从70cfm风扇外部存放在房屋外面，该风扇将安装在密封和绝缘的爬网空间中？
2.在我泡沫之前，我应该付钱给一家屋顶公司以从屋顶上卸下所有通风孔，然后“重新安装”该区域，还是将它们和泡沫放在当前通风口下方和周围？我的假设是，通风口区域只是要求在道路上泄漏，但我的妻子认为我们应该独自一人留下足够好的泡沫，只有泡沫。
再次感谢！
John,
I'm not a fan of your plan to deliberately leave wiring chases that connect your crawl space with your attic unsealed. Sealing these wiring chases (at the top as well as the bottom) is the best practice, in my opinion, especially since future changes to your house are unpredictable.
如果您打算在屋顶护套的底面安装喷雾泡沫，从而形成一个未通风的阁楼，那么您阁楼中的空气就无法视为“泄漏的房屋空气”。它将只是“房屋空气”，因为您的阁楼现在将在室内。
Here is my cheapest option... is installing JUST the vapor barrier and not any foam in the crawl but keeping the existing batt insulation a viable option?
Here is what the contractor proposed:
• Remove the existing vapor barrier and debris from crawl space.
•安装12-mil plasti(20毫升可用)c vapor barrier to cover the entire crawl space floor. (approximately 3,600 SF)
• Seal off the foundation vents.
• Extend the vapor barrier up the perimeter foundation walls within 1” of the top of the top block.
• Wrap the 25 support piers a minimum of 16” above the crawl space floor.
• Seal all joints in the vapor barrier.
• Install a dehumidifier and electrical outlet near the center of the crawl space.
• Install ¾” diameter PVC discharge line to discharge in the positive drain at the rear right corner of the crawl space.
• Dispose of debris off site.
John,
我支持我的文章中提供的建议Building an Unvented Crawl Space.
我认为在大多数密封的爬网空间中不需要除湿机（尽管有时除湿机在新建筑工作的头几个月中是有意义的）。
I am a strong believer in insulating crawl space walls.
The other measures mentioned in the article include efforts to reduce water entry into a crawl space (good exterior grading, roof gutters, etc.).