What about using XPS foam under the footing in a Shallow Frost-Protected Foundation system?
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I’m building a new building that will have radiant floor heat from a boiler. Using a type of foam insulated cement wall — foam is just on the outside. I’m using s shallow frost-protected foundation and wonder about using XPS foam under the footings to stop the thermal bridge that is there.
任何人的想法？
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答复
David,
XPS is used all the time under footings for unheated buildings with frost-protected shallow foundations. See Figure 7 (on page 17) in the NAHB Research Center publication, “Revised Builder’s Guide to Frost Protected Shallow Foundations” (http://www.toolbase.org/pdf/designguides/revisedfpsfuide.pdf.）。只需确保您选择具有足够密度的XPS。
My thought - Consult your structural engineer.
正如马丁提到的那样，你可以用带单片板或加厚的板坯的轻型建筑物，但我还没有满足一个结构工程师，他们将在典型的展开基础下将他的邮票放在绝缘上。我不是说它无法完成，除非你有一个人的人来说，否则你会说的，风险可能是不值得奖励。您可以从内部隔离，并热隔离混凝土霜墙。
David,
Where are you located (what climate zone) and what do you mean by "a type of foam insulated cement wall"?
Are you following the NAHB guidelines (accepted by code) for a shallow frost-protected foundation for your AFI zone? Unless you're in a warm climate, there should also be some horizontal "wing" insulation extending outside the perimeter of the foundation.
With a radiant slab, you must have adequate subslab insulation, along with a vapor barrier and radon vent. You also must have slab edge insulation to isolate the slab from the grade beam. With this edge and bottom thermal isolation of the slab, there is no need to isolate the bottom of the foundation.
谢谢伙计们 - 我一直用工程师调查这一点 - 他和我在他的办公室和更新的ASES指南中经过了建设者指南。但他有点摇摇欲坠。没有谈论的加热建筑指导。关于负载熊问题。我正在寻找100psi xps，其压缩容量较大，而不是正确的地面。我一直在寻找Lite-Form的产品正在进行这些类型的基础 - 它一体化为一个扁平的底部“U” - 只是保持IT水平并用里面的酒吧倒。然后我正在使用一个名为Conform - PVC形成的墙壁的产品，外面有2个“绝缘”。哦，我确实与欧文斯康宁谈论使用XPS泡沫，额定电压为100 psi压缩 - 他们还没有准备好推荐它！那么每个人都认为是什么？谢谢
Robert I'm in Iowa - right at the 2000 degree heat line - so it didn't look like we will need any wings == the wall system is made by nuform.com -- cool idea for animal facility's. There will be a subslab foam of 2 inchs - R-10. The Lite-Form company is here in town so it's very easy to get product. They make and deliver it on the same day! If I was using their product - this wouldn't be an issue - they have 2" of foam on both sides. But I can't find a decent way of protecting it from the dogs in Runs - the wall will be the rear and sides in some runs. Thanks for everyone's thoughts Dave
Using rigid foam directly under concrete footings is much less difficult than one might assume, and 100 psi foam is almost never necessary. Buildings just aren't that heavy!
即使在房屋中有非常重的点负载，数学也不是那么糟糕：例如，36“x 36”脚上的20个kip点负载是20,000磅，超过9 sf或2,222磅/ sf。这只是15.5 psi。
XPS (Dow Styrofoam extruded) has a 25 psi capacity in their standard product, and they make 40, 60 and 100 psi foam as well. Your engineer is most likely being conservative because they haven't done this before, but your soils are much more likely to be a risk with heavy loads than rigid foam will.
From my experience engineers like to see 25 PSI foam under footings - Jesse's math shows how little load there is in reality. Trouble is that most engineers haven't dealt with this and it seems "wrong" to them to build on top of foam. There isn't anything "wrong" with it and your edge loss is always your greatest heat loss - so it is worthwhile arguing for. We use 12" of 25 PSI foam under the footing and then use 15 PSI under the slab...lower density, so lower R-value but also less heat loss then at the building edge. But in your climate and your project you are probably more concerned about keeping your radiant heat in versus your heat loss via the ground. Robert's advice to isolate your slab from your thickened footing area with a vertical thermal break is probably your best bet to start off from. I recommend using EPS vs the XPS as it handles moisture much better. I have seen many heavy water lodged XPS sheets of foam which weight a ton and a half. Of course you keep water away from your foundation anyways.
What happens if some type of insect or animal decides to make a home in the sub-footing foam? That could affect the structural integrity of the foam. Although the chances of this happening are pretty slim, the potential downside risk would make me look for other options.
Graham,
In cold climates, footings are usually 4 to 6 feet below grade. You don't get ants that deep.
马丁，
But FPSF is typically only 12" deep, still probably too deep for most ants.
昨天对Lite-Form的人进行了良好的访问。我们确实查看了FPSF的ASCE标准。他们确实在未加热的建筑物中使用泡沫。他们不会在加热的建筑物中使用它，但这并不意味着它无法使用。我们将使用XPS而不是EPS - 更少的湿度渗透和高压缩数字。工程师一直在研究数字 - 压缩此处的土壤中的土壤中的3000磅/平方英尺，每平方英尺超过20磅 - 具有较高密度XPS泡沫的性能水平。Lite-Forms系统是8英尺的部分，水泥通道是工程师选择的高度和宽度。然后是2“泡沫。然后回到脚踏板上的新墙壁上方的脚踏上方的6英寸。看起来我们将使用24英寸宽水泥脚 - 8“墙上。如果我们将墙放在偏远的中心 - 那么我们将有一个12“翼绝缘，放在脚踏顶部。这将在内部留下一个4”壁架用于板块。 There will be 2" of foam under the slab and it will have radiant heat installed in it. So that will make the 8" high cement footing, 2" of foam under and 2" of foam on top than 6+" of back fill on top of that so there is plenty of slope away from the building. anyone seeing anything that is not making sense? Or other thought? Thanks Dave
Dave,
几件事没有意义。你在三个单独的浇注中做了一个浅地基础：脚踏，阀杆和平板。如果你真的想在周边下方隔离，而不是为什么单倒入的厚度边板块？
我更喜欢通过两次浇注将周边级光束隔离，特别是因为我对板坯的不同混合（具有光纤，并且通常，颜色），并且因为我构建了一个12“厚壁系统，我可以使用12“宽的梁（这对于两层楼的房屋而言，除了最严重的土壤之外，这是一个足够的轴承。我总是设计一个浮动板。轴承上的边缘要求亚拉峰填充物如此良好压实，使得在土壤/脚交界处导致破裂可能是差动沉降。
But, if you're doing this offset wall-on-footing design, then all you need for insulation is the exterior vertical board required for your AFI zone and sub-slab and slab-edge insulation to isolate the heated concrete from the ground and from the footing. No sub-footing insulation is necessary as long as you have a good capillary break on top.
Robert - thanks for your thoughts. The reason for the mulitable pours - the Wall of the building is a single pour pvc form with 2" of foam on the exterior but still in the pvc. This is for a Vet clinic. And a lot of the interior wall need a very durable exterior because dogs are equal to hogs when it comes to destroying things. These walls will be 14 to 21 (front of building) feet tall. The entire exterior wall will be done in one pour. So the footing have to be done before the walls are built and poured. As for the slab -- it gets pretty complex with all the dog runs having some slope to in floor trench drains. Multiple 12ft by 20ft rooms (separation of animals reduces barking). I'm consernered about your comment about the slab -- if it is place on the inside 4" of the footing and the area under the floor is not compressed really well -- then the slab will crack and settle at those edges --- that will not be good because that is right where the trench drains are!! -- thanks for your thoughts Dave
Dave,
Edge-supported slabs are commonly done and, with proper sub-slab crushed stone fill, sub-slab vapor barrier, sufficient steel reinforcement, appropriately-located control joints, expansion joints and bond-breakers at edges, are not problematic. I design my slabs to be both thermally and structurally isolated from the foundation because it reduces the potential for failure, but my strategies often vary from conventional approaches.