Replies

1. GBA编辑器
   Martin Holladay|2015年8月11日08:10 AM|#1

   Nick,
   你已经彻底的研究。简单地说,国防部eling heat loss through a basement slab is extremely complicated. Moreover, assumptions about this type of heat loss are controversial. PHPP software often shows higher levels of heat loss through slabs than energy modeling programs written in North America, and the discrepancy is unresolved.

   For a fairly thorough discussion of this issue, read this article (along with the 96 comments that follow):Can Foam Insulation Be Too Thick?

   还应该指出这个问题的答案严重依赖于您的能源成本。

   For a rough guide, I advise you to follow the advice of building scientist John Straube.

   Straube写道，“绝缘成本变得超过了在大约R-60（使用建筑科学公司方法）的7,200-HDD气候中为典型房屋中的墙壁产生能量的成本，以及平板[在等级]关于R-20至R-25，取决于放置EPS的成本（每平方英尺每平方米约10美分）。基础的热量损失较少[比等级上的板坯]，因此截止点更像R-15至R-20，用于基底板。加热带辐射管的板坯将平板的温度从大约68°F或其平均增加到80°F，因此绝缘水平需要增加约50％的辐射加热的板坯。“

   其他专家曾使用其他计算方法来提出建议，以便在基底板下的低于绝缘水平的建议。例如，Gary Proskiw和Anik Parekh已经计算出即使在Yukon领域的黄刀中，基底板也不需要在板坯周边处的R-10垂直绝缘。可以在此处找到完整的详细信息：Optimization of Net Zero Energy Houses。

   Finally, the main reason to install at least 2 inches of rigid foam under a basement slab in your climate zone has nothing to do with saving energy. The main purpose of the rigid foam is to make sure that the slab stays warm enough to prevent condensation. This will (a) make your basement smell better (because it won't be damp or moldy) and (b) make your slab warm enough to allow you to install carpeting if you want to, without worrying that mold will grow under the carpeting.

2. 
   Bob Irving|2015年8月11日09:20 AM|#2

   "the heat from the house will warm the soil and reduce the heat loss." Not quite.
   If you build a well insulated slab, you can raise the temperature of the slab by adding heat, but the soil under your house is thousands of feet deep, not a few inches, and the temperature never changes, so the heat you deliver to the sub-slab soil will be transferred to colder soil in an ongoing process. Your insulated frost walls at the walk out will help with slab temperatures. 4" of EPS (minimum) will give you about R16; 6" will give you R24.

3. Expert Member
   Dana Dorsett|Aug 11, 2015 11:31am|#3

   The soil under the slab has both R-value and thermal mass, both of which vary considerably by soil type and moisture content, making the modeling complex. With the exception of active volcanic areas or flowing artesian water streams the temp of the soil 50-100' down is close to the average outdoor air temp over the past 50-100 years in the area. The temp several hundred or thousands of feet down is much warmer, due to the high core temp of the planet, but that temp is completely irrelevant to this discussion.

   分布式soil-R所以的时间常数il-mass over a season or at most a year is the relevant time period from a slab insulation perspective, and there we are talking a couple tens of feet down at MOST. The slab losses DO raise the temp of the proximate layers of soil, reducing both the rate of loss and the total loss from the slab. The more insulation you put under the slab the less the soil is heated, so the soil stays colder, and the thermal mass of the soil then has diminishing effects on energy use. Putting R10 down instead of only R5 doesn't cut the heat loss by half- not even close, and the difference between R10 and R20 sub-slab foam is even smaller.

   如果已知更多的局部土壤特性，这可以以更高的精度建模，但完全表征位点的土壤的成本超过加入更多英寸泡沫的成本。

   The amount of sub-slab R necessary to mitigate summertime mold and musty-basement issues is pretty modest- R5 -R6 (1.5" of EPS) would be fine even in zone 7. There's still a long term or lifecycle financial energy cost savings argument for R12-R15 or so even for basement slabs, and for on-grade slab edges even up to ~R20 in that climate, but not R25 (unless you expect future energy costs to be several times the levelized cost of solar electricity at today's PV prices.)

4. 
   查理沙利文|2015年8月11日03:14 PM|#4

   上面的伟大答案。我补充说，因为接地温度比外部温度要温暖得多，因此地面的热量损失根据你保持空间的温暖程度强烈地变化，而不是通过墙壁的热量损失更强烈。所以如果你打算让地下室在冬天保持凉爽，你可能会选择一点;如果您计划完全调整它，更多。

   Definitely use EPS, not XPS--you get more insulation value per $, as well as much lower environmental impact.

5. 
   Nick Hall|2015年8月11日05:25 PM|#5

   Thanks for the responses!

6. 
   Brian P.|2015年8月11日06:20 PM|#6

   When planning (and during) our house build, I devoured as much information about other house projects as I could. Anecdotal evidence shows most low energy or net-zero builds in the Northeast US are using at least R20 under slab. Many up to R30 or more.

   4" of EPS seems like a safe choice (versus 2") if planning an energy efficient house in zone 7.

7. GBA编辑器
   Martin Holladay|Aug 12, 2015 05:51am|#7

   布莱恩，
   你没有告诉我们你是否正在谈论地下室平板或等级的平板。

   Nick: basement slabs can get away with much thinner sub-slab insulation than a slab on grade.

8. 
   Nick Hall|Aug 12, 2015 07:59am|#8

   Yes, the slab I'm talking about is below a basement so under the frost line. Except for the edge by the walkout which is more like a slab on grade, but if I insulate the frost wall there does that make it perform more like a basement slab even at that edge? I'm wondering if I should just do the frost wall as ICF since the rest of the wall there will also be ICF?

9. 
   Brian P.|Aug 12, 2015 09:51am|#9

   Correct, I was just offering some general insight into what I learned as a first time home builder/owner and I don't have a solid answer.

   如果尼克因犹豫不决而瘫痪，陷入困境，在建模/计算中陷入困境，并且需要作出决定在现场获取材料.....我想击中R15-20将是他局势的好处？