Back when I lived in the countryside, one of my neighbors pointed to a fence post on the depression side of his holding that stood half-dozen in. higher than the other posts. "I drove that post back downwards iii years in a row," he said, "only it still keeps popping up." It wasn't a persistent woodchuck at work. It was the almanac work of winter-time frost.

Frost, the same light, delicate stuff that periodically coats your window glass in winter, is a surprisingly powerful natural force. It lifts the soil, cracks rocks and snaps copse, altering the landscape in almost every neighborhood that has freezing weather. Sidewalks crack and pop upward similar logjams; concrete driveways, front end stoops, and steps rhythmically rise, autumn or begin to pitter-patter away from houses or garages; and decks and patios begin to tilt. Fences lean to the side and retaining walls crack also.

Unfortunately, you won't find the effects of frost until the damage is done. Frost usually works slowly just steadily, year later on year, lifting and shifting a wall or driveway until hairline cracks go gaping chasms. Or you'll of a sudden observe that the 1/four-in. gap betwixt the house and porch has grown to a full inch, or the patio door won't open because the concrete slab exterior has risen and pushed upwardly the sill.

In this article, you'll larn how frost works, why it's and so powerful, and what you tin can do to limit its damage.

Why Frost Heave Occur

The frost that can lift and shift an unabridged building is no unlike than what forms on your window, merely it's more mysterious because it occurs hole-and-corner. Fig. A gives you a gopher's eye view of frost in action.

Frost lenses below ground latch onto concrete footing side and push the entire post upward

Frost pockets chosen "lenses" can grade in the wet ground when it freezes. As a lens thickens, it thrusts the overlying soil or foundation upward. Frost can also latch onto the side of foundations and lift them.

When the outdoor temperature drops below 32 degrees F, the moisture in the basis begins to freeze, starting at the top. As you know, the upper level of soil gets rock hard, then that y'all demand a pick to bit through the meridian layer if y'all take to dig a pigsty. Frost gradually works its fashion downward as persistently cold weather cools the soil at e'er deeper levels. If the soil is well-drained and contains trivial moisture, frost spreads evenly through the soil and won't cause trouble. But if the soil is wet, the water will often freeze in a paper-thin canvass, called a lens." Imagine a huge, thin contact lens cached underground.

Depending on the weather, these icy lenses can grow thicker, fed by water rise upward through the soil from wetter soil below or from the h2o table. The water table is the level at which groundwater fully saturates the soil. It tin can begin anywhere from a few feet to more than 100 ft. nether your house, depending on the climate and soil conditions in your locale.)

When h2o freezes, information technology expands nearly 9 percentage in volume (which is why, of course, ice cubes float in your lemonade rather than clunking to the bottom). So when water freezes against the lens, information technology expands, thickens the lens and compresses the soil, eventually thrusting the soil upward along with everything on top of it. This uplift is chosen "frost heave."

Usually, the heave is slow, creeping just a fraction of an inch over days. Even so the power of a frost boost is near unstoppable, because the expansive force of freezing water is huge, somewhere around 50,000 lbs. per sq. in. A frost boost can lift a seven-story building or plummet massive, steel-reinforced physical walls. And then foundations, garages, decks, patio slabs and just about everything else around your firm won't have much of a take chances if a frost heave gets ahold of them.

When temperatures rise and the frost lens melts, the damage is already done. The cracks remain, and foundations, once heaved, never quite settle back to their original place. Each year they move a bit farther off-target until you've got major problems.

Coping With Frost Heaves

People who live in the Southern Gulf States and on the Pacific Declension, where frost rarely penetrates the soil more than an inch or two, don't demand to worry near frost heaves. Simply the residue of u.s.a. would alive in topsy-turvy neighborhoods if builders didn't blueprint homes to prevent frost heaving in the first place.

Frost heaves commonly occur in ii means. Almost frequently, a frost lens forms beneath a foundation or footing and heaves information technology upward. Just ice crystals can as well grab onto the rough or porous surface of a foundation or footing and lift it from the side (Fig. A).

A shifting foundation will quickly ruin a habitation and cost the homeowner big bucks, so builders don't accept chances. When they build a house, they give information technology a "frost footing" made up of foundation walls or piers that extend beneath the "frost line" so a frost lens can't form below it and lift the house. The frost line is the depth in the ground beyond which frost is not likely to penetrate (Fig. B).

Map of frost depth zones in North America

The map shows approximate frost depths during a colder-than-average winter. The actual depth varies widely due to different soil types, the moisture content of the soil, and the ground cover (bare soil, turf, snowfall, etc.). The building lawmaking in your expanse specifies a frost line depth that all local building foundations must meet or exceed.

Your local building inspector volition tell you the frost line depth for your area. Information technology ranges from zero in much of California where little or no frost occurs, to 10 in. in parts of Kentucky, to 60 in. in frigid International Falls, MN.

Frost won't normally latch onto the side of a house's foundation because even a small amount of heat from the interior drives moisture in the soil away from the walls. However, frost sometimes grabs onto the foundation of an unheated construction.

Frost can work its mischief on porches, garages and decks too. If these "secondary" structures are connected to a firm, building codes require that they have frost footings too. That's because these connected structures will harm the business firm if they heave. This may seem like a hurting if you're adding a deck or front end porch, but porch floors tin boost up nether doors. and tilting decks tin can pull house walls outward. The toll of repairing a frost heave's damage can easily exceed the original price of a porch or deck.

Floating Structures

It'south usually not economical or necessary to put frost footings nether secondary structures, including garages, decks, sidewalks, patios and retaining walls, if they're non continued to the business firm. With proper precautions, these structures can safely "float" on superlative of the soil without frost footings.

But a mistake here can cause trouble — just inquire my father-in-law. The physical floor of his garage is steadily turning to rubble as it annually shifts, lifts and cracks (more on this later). You may encounter other mutual problems, such every bit concrete patio slabs that elevator under door sills and jam the doors, and deck posts that shift and pull a deck away from the house.

To successfully prevent frost damage to floating structures, y'all have to accept a close look at the soil y'all're edifice on.

Frost And The Soil

Frost heaving doesn't occur automatically whenever the weather turns cold. Information technology requires a certain amount of moisture and a "frost-susceptible" soil. Soils that contain coarse particles of gravel and sand drain well and won't usually heave, considering they don't collect and concur enough water to form frost lenses. They're called "non-frost-susceptible" soils. Soils with finer particles like clays and silts, on the other hand, don't bleed as well and hold a lot of water. They're chosen "frost-susceptible" soils.

Of course, most soils are mixtures of sands, clays, and silts, and then you're not likely to recognize any one type when you dig a ground hole for your deck. Unless you hit gravel or pure sand, it'south usually all-time to assume that your soil is somewhat frost susceptible.

Simply don't despair. Even frost-susceptible soil ordinarily won't boost if you provide good drainage (assuming the water table is far enough underground). Good drainage would solve my father-in-law's trouble. His garage sits near the house in a slight depression that stays wet longer than other parts of the yard. Unfortunately, there'due south no like shooting fish in a barrel style to provide drainage now without major digging. Rather than scraping away the topsoil and putting the concrete slab on grade level, the garage architect should have dumped a foot or 2 of make clean sand or gravel on top of the grade to build up the site. (Builders stipulate "clean" because fifty-fifty a x percentage contamination by silts or clays tin change the character of sand or gravel and make it frost susceptible.) This would take provided enough drainage and stability to keep the concrete slab intact.

To forbid frost heaves, the easiest and least costly solution is to plan in advance for good drainage away from walks, patios, garages, decks and other floating structures (Fig. C).

Using clean sand or gravel under concrete slabs or waxed cardboard tubes around concrete piers will create resistance to frost heaving

A layer of clean sand or gravel nether a physical slab, combined with good drainage, will eliminate most frost heaves. The more frost-susceptible your soil, the thicker the bed of sand or gravel you'll demand. Piers wrapped in plastic, waxed tubes or PVC plastic pipe volition resist frost heaving from the side.

And a bed of sand or gravel underneath improves drainage and decreases frost susceptibility.

Don't hesitate to discuss soil conditions with your local edifice inspectors. They should exist familiar with local conditions and able to warn y'all of potential trouble.

A Deck Builder'south Problem

Information technology's not always feasible to provide good drainage in frost-susceptible soil for post footings for decks. Even if you put the footing downwards to the frost line, frost can all the same grab the side of the post or footing and push it up. In these cases it'due south best to surround the post or physical with a polish surface of plastic, a waxed tube or plastic pipe (Fig. C) to keep frost from bonding to the sides and jacking upward the basis. Refill the hole around the post or tube with the soil y'all dug out, making sure to tamp it downwardly solidly in 6-in. increments as you make full the pigsty. Solidly packed soil, mounded at the top, volition keep water from saturating the soil around the fooling and causing potential heaves. It'south tempting to fill the hole with sand or gravel, thinking yous'll provide good drainage that way. However, unless you also provide undercover drainage, you lot'll actually create a take hold of basin for h2o around the basis, making the potential for frost heaving even greater.

Back when I lived in the countryside, one of my neighbors pointed to a argue post on the low side of his property that stood half dozen in. higher than the other posts. "I drove that mail service back downwards 3 years in a row," he said, "just it still keeps popping up." It wasn't a persistent woodchuck at work. Information technology was the annual work of winter-time frost.

Frost, the same low-cal, delicate stuff that periodically coats your window glass in winter, is a surprisingly powerful natural force. It lifts the soil, cracks rocks and snaps trees, altering the landscape in well-nigh every neighborhood that has freezing weather. Sidewalks crack and pop upwardly like logjams; concrete driveways, front stoops, and steps rhythmically rising, fall or begin to pitter-patter away from houses or garages; and decks and patios begin to tilt. Fences lean to the side and retaining walls crack besides.

Unfortunately, you won't discover the effects of frost until the damage is washed. Frost unremarkably works slowly simply steadily, year after year, lifting and shifting a wall or driveway until hairline cracks become gaping chasms. Or you'll suddenly notice that the one/iv-in. gap between the firm and porch has grown to a full inch, or the patio door won't open because the concrete slab outside has risen and pushed upwardly the sill.

In this commodity, y'all'll learn how frost works, why it'southward so powerful, and what you lot tin practice to limit its damage.

Why Frost Heave Occur

The frost that can lift and shift an entire building is no dissimilar than what forms on your window, simply it's more mysterious considering it occurs underground. Fig. A gives you lot a gopher's eye view of frost in action.

Frost lenses below ground latch onto concrete footing side and push the entire post upward

Frost pockets chosen "lenses" can course in the moisture footing when it freezes. As a lens thickens, it thrusts the overlying soil or foundation upwardly. Frost can also latch onto the side of foundations and lift them.

When the outdoor temperature drops below 32 degrees F, the moisture in the basis begins to freeze, starting at the top. Every bit you know, the upper level of soil gets rock hard, then that you demand a pick to chip through the top layer if you take to dig a hole. Frost gradually works its style down as persistently cold weather cools the soil at always deeper levels. If the soil is well-drained and contains fiddling moisture, frost spreads evenly through the soil and won't cause problem. But if the soil is wet, the water will often freeze in a paper-thin sheet, called a lens." Imagine a huge, thin contact lens buried hole-and-corner.

Depending on the weather, these icy lenses can grow thicker, fed by water rising upward through the soil from wetter soil beneath or from the h2o table. The water tabular array is the level at which groundwater fully saturates the soil. It can begin anywhere from a few feet to more than 100 ft. nether your house, depending on the climate and soil conditions in your locale.)

When h2o freezes, it expands about 9 percent in volume (which is why, of course, water ice cubes float in your lemonade rather than clunking to the bottom). So when water freezes confronting the lens, information technology expands, thickens the lens and compresses the soil, eventually thrusting the soil upward along with everything on peak of it. This uplift is called "frost boost."

Usually, the heave is slow, creeping only a fraction of an inch over days. Still the power of a frost heave is most unstoppable, considering the expansive force of freezing water is huge, somewhere around fifty,000 lbs. per sq. in. A frost heave can lift a 7-story building or collapse massive, steel-reinforced concrete walls. So foundations, garages, decks, patio slabs and merely virtually everything else around your house won't have much of a run a risk if a frost boost gets ahold of them.

When temperatures ascension and the frost lens melts, the damage is already done. The cracks remain, and foundations, once heaved, never quite settle back to their original place. Each yr they move a chip farther astray until you've got major problems.

Coping With Frost Heaves

People who live in the Southern Gulf States and on the Pacific Coast, where frost rarely penetrates the soil more than than an inch or two, don't need to worry about frost heaves. Just the rest of us would alive in topsy-turvy neighborhoods if builders didn't pattern homes to prevent frost heaving in the first identify.

Frost heaves commonly occur in ii means. Most often, a frost lens forms beneath a foundation or basis and heaves it upward. Just water ice crystals can also grab onto the rough or porous surface of a foundation or footing and lift it from the side (Fig. A).

A shifting foundation will apace ruin a home and toll the homeowner big bucks, and so builders don't take chances. When they build a house, they requite it a "frost basis" fabricated upwardly of foundation walls or piers that extend below the "frost line" so a frost lens tin can't form beneath it and lift the business firm. The frost line is the depth in the ground beyond which frost is not probable to penetrate (Fig. B).

Map of frost depth zones in North America

The map shows approximate frost depths during a colder-than-average winter. The actual depth varies widely due to different soil types, the moisture content of the soil, and the ground cover (bare soil, turf, snow, etc.). The edifice code in your area specifies a frost line depth that all local edifice foundations must meet or exceed.

Your local building inspector will tell you the frost line depth for your surface area. It ranges from zilch in much of California where little or no frost occurs, to ten in. in parts of Kentucky, to 60 in. in frigid International Falls, MN.

Frost won't usually latch onto the side of a house's foundation because even a minor amount of oestrus from the interior drives wet in the soil away from the walls. Withal, frost sometimes grabs onto the foundation of an unheated structure.

Frost can work its mischief on porches, garages and decks too. If these "secondary" structures are continued to a business firm, building codes require that they accept frost footings as well. That's because these connected structures volition damage the house if they heave. This may seem similar a pain if you're adding a deck or front porch, but porch floors can heave upward under doors. and tilting decks can pull house walls outward. The toll of repairing a frost heave's damage tin can easily exceed the original price of a porch or deck.

Floating Structures

It's ordinarily not economical or necessary to put frost footings under secondary structures, including garages, decks, sidewalks, patios and retaining walls, if they're not connected to the house. With proper precautions, these structures can safely "float" on elevation of the soil without frost footings.

But a mistake here tin cause problem — just ask my begetter-in-police. The concrete floor of his garage is steadily turning to rubble every bit it annually shifts, lifts and cracks (more on this after). You may encounter other common bug, such as concrete patio slabs that lift nether door sills and jam the doors, and deck posts that shift and pull a deck away from the house.

To successfully prevent frost damage to floating structures, yous have to take a close expect at the soil y'all're edifice on.

Frost And The Soil

Frost heaving doesn't occur automatically whenever the weather turns cold. Information technology requires a sure amount of moisture and a "frost-susceptible" soil. Soils that contain coarse particles of gravel and sand bleed well and won't commonly heave, because they don't collect and hold enough water to grade frost lenses. They're called "not-frost-susceptible" soils. Soils with effectively particles like clays and silts, on the other manus, don't drain likewise and hold a lot of water. They're called "frost-susceptible" soils.

Of course, about soils are mixtures of sands, clays, and silts, and then y'all're not likely to recognize any one type when you dig a basis hole for your deck. Unless you hit gravel or pure sand, it's commonly all-time to presume that your soil is somewhat frost susceptible.

But don't despair. Fifty-fifty frost-susceptible soil normally won't heave if you provide practiced drainage (assuming the water table is far plenty hush-hush). Expert drainage would solve my father-in-law's problem. His garage sits nigh the house in a slight depression that stays wet longer than other parts of the yard. Unfortunately, there's no easy way to provide drainage now without major digging. Rather than scraping away the topsoil and putting the concrete slab on grade level, the garage builder should have dumped a foot or two of clean sand or gravel on height of the grade to build up the site. (Builders stipulate "clean" because even a 10 percent contamination by silts or clays can change the character of sand or gravel and make information technology frost susceptible.) This would have provided enough drainage and stability to keep the concrete slab intact.

To prevent frost heaves, the easiest and to the lowest degree plush solution is to programme in accelerate for good drainage abroad from walks, patios, garages, decks and other floating structures (Fig. C).

Using clean sand or gravel under concrete slabs or waxed cardboard tubes around concrete piers will create resistance to frost heaving

A layer of clean sand or gravel under a physical slab, combined with skillful drainage, will eliminate about frost heaves. The more frost-susceptible your soil, the thicker the bed of sand or gravel you'll need. Piers wrapped in plastic, waxed tubes or PVC plastic pipe will resist frost heaving from the side.

And a bed of sand or gravel underneath improves drainage and decreases frost susceptibility.

Don't hesitate to talk over soil conditions with your local building inspectors. They should exist familiar with local weather and able to warn y'all of potential trouble.

A Deck Architect'south Problem

Information technology's non always feasible to provide skilful drainage in frost-susceptible soil for post footings for decks. Fifty-fifty if you put the basis downwardly to the frost line, frost tin still grab the side of the mail or basis and button it upwards. In these cases it's best to surroundings the post or concrete with a smooth surface of plastic, a waxed tube or plastic pipe (Fig. C) to continue frost from bonding to the sides and jacking up the basis. Refill the hole effectually the postal service or tube with the soil you dug out, making sure to tamp information technology downward solidly in half dozen-in. increments every bit you fill the pigsty. Solidly packed soil, mounded at the top, will continue water from saturating the soil around the fooling and causing potential heaves. It's tempting to fill the hole with sand or gravel, thinking you lot'll provide good drainage that fashion. However, unless you also provide hugger-mugger drainage, you'll actually create a grab basin for water around the footing, making the potential for frost heaving even greater.