Frost protected foundations - essential in cold climates
Protecting homes and buildings in cold climates from structural damage caused by frost heave is essential for durability.在加拿大和美国北部的大部分地区，在冬季的几个月里，地面结冰深度达几英尺。这种地面冻结会导致位于其上方或附近的建筑物隆起，甚至会导致水平移动，而不仅仅是垂直移动。
在建造新住宅时，适当隔热的地下室和在住宅的等级地基上设计板不仅可以防止地基开裂，还可以减少能源消耗和全球CO²排放。The negative environmental aspects of concrete use can be mitigated by good engineering to use finite quantities based on structural need, and by using it proactively forthermal mass．
There is hardly any limit to the force that can be exerted by water when it freezes; even the weight of tall buildings cannot withstand the damage that can be caused when ice forms below them. A force of 19 tons per square foot has been measured with one seven-story reinforced concrete frame building on a raft foundation that heaved more than 2 inches. But, preventing frost heaving is actually a breeze as long as you design properly, and here we tell you how.
What causes frost heave and where?`
Ground frost heave, at its most simple, happens when ground water in cold climates changes from a liquid to a solid．水结冰时会膨胀9%，所以对于任何位于霜冻线以上的结构——甲板、棚子、平地板或地下室地基，当膨胀的土壤迫使它向上时，如果没有适当的设计或保护，它就会被吹走。这导致地基开裂，甲板移动，损坏地下室和平板的平房。
While the solutions to preventing frost heave are the same, the ‘actual’ cause of frost heave is somewhat misunderstood. It is mostly thought that the upward expansion of existing moisture in soil is what causes frost heave, but it’s slightly more complicated. So, for building nerds who want the real skinny on what’s going on, it’s a bit like this -
There is latent heat in the ground from summer months, so when winter arrives, ground freezing it is a progressive effect that happens as the temperature drops over many months. The freeze begins to move downward as air temperatures begin to stay consistently below zero, but there is always soft and warmer soil below.
冰的形成很大程度上是因为下方未冻结土壤中的水被吸收到冻结区，并附着在现有的霜晶体上，形成越来越厚的冰层。The key phrase for this phenomenon is "ice segregation"．这就是导致土壤颗粒分离的膨胀和导致地面向上隆起的原因。但你真的有必要知道吗?是的。当你在晚宴上说出那句话并给你的朋友留下深刻印象后，你可以在评论区感谢我。
冻胀会引起什么问题?
The pressure of frost heaving can crack basement walls - especially when built of CMU or brick- or with the lifting forces of frost heave caused by "adfreezing," which occurs when soil freezes to the surface of a foundation.
冻结区底部形成的隆起压力通过加冻黏结传递到地基上，产生抬升和分离力，通过接近冻融深度的水平砂浆接缝的垂直位移将CMU拉开。This is very important to consider wheninsulating a basementorinsulating a crawlspacein an older home from the inside.
The forces involved in frost heaving can also be very destructive to lightly-loaded structures and cause serious problems in major ones - so when there are both within the same overall home structure (like a deck attached to a house with a basement), the differential movement can literally rip elements of a home apart.
Another aspect of frost heaving we have seen, especially in clay soils, that's highly inconvenient if not as destructive as a deck separating from a house, is where fence posts move around over winter and then never quite settle back - leaving the fence in a sorry state by the spring.
Frost heave prevention when building a home
Preventing frost heave is not difficult; you simply need to add sufficient insulation for your climate to prevent frost from getting underneath the base of your structure.Sufficient drainage is also important to keep water away from what you're building, this is also important for basement durability to reduce the chances of damage caused by flooding or high levels of humidity.
First, we should dispel any myths – you don’t ‘need’ to put dirt against a home to prevent frost heave. A slab on grade is not at greater risk from frost heave than a basement if it is built properly - in which case the correct term is aFrost Protected Shallow Foundation - or FPSF．
So if a general contractor tells you that you 'must' have a basement, they are simply wrong. That’s often someone who doesn’t know how to build a FPSF slab but still wants your money, so they may try to fill your head with their own misconceptions to get the job.
In most cold climates we have grown accustomed to having basements, and adopted the notion that a house needs to be in the ground to be below the frost line. That just isn’t so. You also do not need to pile dirt against the side of your house to stop it from tipping over. It’s just that dirt has always been used as insulation against frost heave, so it has been ingrained in us for centuries as essential. But, thanks to modern building practices, you can also use ‘insulation’ as insulation against frost heave!
土壤的绝缘值约为每英尺R3，其中泡沫绝缘将在每英寸R3和R5之间。这就是为什么你可以在冬季霜冻深度为4英尺的地区建造房屋，使用4英寸的保温材料而不是4英尺的泥土。As a quick caveat – there are many types of rigid insulation but they aren’t all suitable for below ground;see here to find the right rigid foam insulation for foundations．
How much does frozen ground heave?
Terrain with high water tables and particularly expansive soils such as peat or clay often suffer from frost heave and damage buildings.It’s not uncommon to see a deck or shed move as much as 7 or 8 inches, and in some cases much more than that, even up to two feet. Buildings of 3 or 4 stories can easily be forced upwards by several inches. How severe the shifting can be depends on the soil type and its ability to contain moisture or bulk water, and of course the weight of the building or part of a structure to be lifted.
In very harsh winters, we've seen sidewalks and roadways heave up 6 inches or more, and separate blacktop vertically from curbing, which is embedded deeper and on a gravel base. Both the extra drainage and the deeper depth were keeping the water away from under curbing that was obviously present and freezing under the porous blacktop.
Does gravel prevent frost heave?
Yes, a good drainage base will help prevent frost heave. Gravel or crushed stone does not hold moisture, so it makes an excellent base.Sand works as well; it takes a layer of about 4 to 6 inches to be safe.
As mentioned above, a slab on grade is not at any greater risk of frost heave than a basement, full stop. Read more here –Choosing between a slab on grade and a basement．你可以建地下室，无论对错，你也可以建楼板。只要做对了，你就不会有问题。
And if you happen to have bought some swamp land in a cold climate somewhere while you were drunk in a bar, don’t give up hope; see here forhow to build on problem soils like clay soils that are susceptible to frost heave．也许你的购买是明智的。: )
There are general rules for given areas on how deep the frost line is, ranging from a few inches in the Southern States to as much as 6 or 7 feet in the far north.Find out what buillding climate zone you are in, and be sure to check with local-municipality building inspectors to know for sure how deep you might need to go to get under the frost line.
This is, of course, great as a general rule if you are building something without permits or building inspectors, but for anything of greater consequence like full home construction, don’t chance it in the least. Buildings should be engineered properly for their specific climate.
Will frost heave go away?
Generally yes, if you have a smaller building or structure that has experienced frost heave, it will often settle back down close to its original position.But as quick as it drops in spring, it will lurch back up in the winter if you don’t deal with it.
冻胀通常在1月或2月开始发生，因为寒冷穿透地面，春天来了，当它融化时，它通常会回落到原来的位置。“接近”它，但不总是。这对于像木棚这样的小室外建筑来说可能是可以的，它们可能不会受到太大的破坏。更大的东西，比如房子，会受到永久性的损害。另一个问题是，水管、污水管、天然气管或电气连接等设施都是在地下建造的。
Recap: the essentials to prevent frost heave
To prevent or fix frost heave, you have to either deal with the water in the ground, or the temperature of the ground, and ideally both.You need to make sure water drains away from the problem area, not towards it. Start your forensics and solution-hunting first with the roof’s storm water runoff, and direct it someplace where it does no harm. That can be with eavestroughs or gutters directing water towards swales, dry wells, orrainwater collection barrels．
There is also the option of directing water towards the street, and that’s better than towards your house. But on a grand scale, directing water to hard surface municipal water runoff has negative ecological consequences of its own. Best is to学习如何管理雨水径流，并实际利用这些水为你的优势;read more here．
一旦你限制了任何从你的屋顶流下来的水的潜在破坏性输入，你需要适当地分级你的景观设计，以引导降雨。即使是远离房屋、甲板、棚屋或其他地方2%的坡度，也能将水转移到更安全的方向。如果是像粘土这样的膨胀土，挖开顶部几英寸，铺上某种防水膜是一种额外的措施，可以帮助保持土壤干燥，但要小心——因为干燥膨胀土也会导致老房子的地基下沉和开裂。
裙摆保温也能起到同样的作用，它包括铺设一块坚硬的EPS泡沫保温材料(倾斜于建筑物外)，以防止土壤湿润，但更重要的是如何移动霜线。所以这里真正的要点是，水和冷水会破坏东西，但保温和水分流能节约东西。只要你记住这一点，并据此设计，就没有理由担心霜胀。
Now you know more abouthow to protect foundations and slabs from frost heave．Learn more aboutbest practices for energy efficient and durable basement construction and renovationsin these pages:
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