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Understanding Frost Depth Requirements for Deck Footings Across the United States

When building a deck, one crucial factor to consider is the frost depth requirement for footings. Frost depth is the distance below ground that soil is expected to freeze in winter. Proper footing depth helps prevent frost heave, which can damage or destabilize your deck. While specific requirements vary by location and can change, this article provides a general overview of frost depth considerations across the United States.

Why Frost Depths Are Important:

Understanding and adhering to frost depth requirements is critical for several reasons:

1. Structural Stability: When water in soil freezes, it expands, causing the ground to heave upwards. If deck footings aren’t placed below the frost line, this heaving can lift and shift the footings, potentially destabilizing the entire deck structure.

2. Preventing Damage: Frost heave can cause cracking in concrete footings, misalignment of support posts, and warping of the deck surface. By placing footings below the frost line, you protect them from these damaging freeze-thaw cycles.

3. Longevity: Properly installed footings that account for frost depth will significantly extend the life of your deck, reducing the need for costly repairs or premature replacement.

4. Safety: A deck that shifts due to frost heave can become unsafe, potentially leading to collapse or injury.

5. Code Compliance: Building codes specify minimum footing depths based on local frost depths. Adhering to these requirements is necessary for passing inspections and ensuring your deck is legally constructed.

6. Resale Value: A properly constructed deck that accounts for frost depth will maintain its value and be an asset when selling your home.

Frost Depth Zones:

The continental United States can be broadly divided into several frost depth zones:

1. No Frost (0 inches): Parts of Florida, southern Texas, and coastal areas of other southern states.

2. Light Frost (0-20 inches): Most of the southern states and coastal areas.

3. Moderate Frost (20-40 inches): Much of the central and eastern United States.

4. Deep Frost (40-60 inches): Northern states and higher elevations.

5. Very Deep Frost (60+ inches): Parts of Alaska and high mountain regions.

General Frost Depth Guidelines by Region:

Southern States:

In states like Florida, Louisiana, and parts of Texas, frost is rarely an issue. Footings typically need to be only 12 inches deep or less, mainly for stability rather than frost protection.

Southeastern and South Central States:

States like Georgia, Alabama, Mississippi, and Arkansas generally require footings to be 12-24 inches deep, depending on local conditions.

Mid-Atlantic and Central States:

In states such as Virginia, Kentucky, Missouri, and Kansas, frost depths typically range from 24-36 inches.

Northeastern States:

New England states and New York often require footings to be 48-60 inches deep due to severe winter conditions.

Midwestern States:

States like Illinois, Indiana, Ohio, and Michigan generally require depths of 36-48 inches, with northern areas potentially requiring deeper footings.

Northern States:

Minnesota, Wisconsin, and the Dakotas often require footings to be 60 inches deep or more in some areas.

Western States:

Requirements vary widely due to diverse climates and elevations. Coastal areas may have minimal frost depth requirements, while mountainous regions may require very deep footings.

Alaska:

Frost depths can exceed 100 inches in some areas, requiring specialized construction techniques.

Important Considerations:

1. Local Variations: Always check with your local building department for specific requirements, as they can vary significantly within a state.

2. Climate Change: Some areas are updating their frost depth requirements due to changing climate patterns.

3. Soil Type: The type of soil can affect how deep footings need to be.

4. Building Codes: Many areas base their requirements on the International Residential Code (IRC), but local amendments are common.

5. Professional Consultation: For complex projects or uncertain conditions, consult with a local structural engineer or architect.

Understanding frost depth requirements is crucial for building a safe, stable, and long-lasting deck. The depth of your deck footings directly impacts the structural integrity and longevity of your deck, making it a critical consideration in the planning and construction process. While this article provides a general overview of frost depth requirements across the United States, it’s important to remember that local regulations always take precedence. Before starting any deck project, consult your local building department for the most up-to-date and area-specific requirements. By properly accounting for frost depth, you ensure that your deck will stand strong for years to come, resisting the challenges posed by freezing temperatures and changing seasons.

Where to find more detailed information about frost depth in your region:

  1. State and local building code websites: Many states and municipalities publish their building codes online, which often include frost depth requirements.
  2. University extension services: Many land-grant universities have cooperative extension services that provide local building and gardening information, including frost depth data.
  3. NOAA (National Oceanic and Atmospheric Administration): They provide climate data that can be useful in determining frost depths.
  4. Local building departments: Contacting these directly can provide the most accurate and current information for a specific area.
  5. Professional associations: Organizations like the American Society of Civil Engineers (ASCE) or the International Code Council (ICC) may have resources or publications on frost depth requirements.
  6. FEMA Frost Depth Map: While not always current, this can provide a general overview.

Deck Materials You’ll Need to Build Your Deck…from the Bottom Up

(c) Can Stock Photo / SafakOguz

When you first start planning to build your deck, you’ll quickly realize there are many options when it comes to figuring out what materials to use. From the footings to the lumber to the fasteners and screws, getting a grip on your materials is a first-step to building a safe deck you’ll enjoy.

Footings

When it comes to footings for your deck, we of course know that in most cases there will be no better or easier option for you than to use RediFootings for your footings. There is no concrete to buy, no mixing, and no waiting for the concrete to dry. You can read more about why RediFooting is your best option for your deck footings here.

Below is a graph that shows the difference between using RediFooting vs using concrete for your footings:

In combination with the ledger attached to the house, the footings support the entire load of your deck. Footings are one of the most critical components of deck construction (as is the soil below the deck footing). But if your footing can’t support the load, it doesn’t matter what materials you use to build the rest of your deck. 

The Framing and Structure of Your Deck

For the most part, the main framed structure of your deck–which generally includes the beams, posts, joists, and ledger if attached to a house—will be built from pressure treated lumber. It’s not only the most economical choice but is rot and insect resistant. It’s also easy to find throughout the United States.

An alternative to pressure treated lumber is to use either redwood or cedar, both rot and wood-insect resistant. However, the costs can be double, on average, for redwood or cedar as compared to building your deck with pressure treated lumber.

Initially, pressure treated lumber was preserved with chromate copper arsenate (CCA) added to the wood to make it wood and insect resistant. But because of its high arsenic toxicity levels causing both health and environmental concerns, the manufacturing of pressure treated lumber using CCA was discontinued in 2003. 

The newer pressure treated woods (ACQ) are generally more environmentally-friendly with copper-based compounds, also making them a healthier alternative to the older, discontinued pressure treated woods. 

However, the newer pressure treated lumber is not without its issues. There are still warnings, including the recommendation to wear gloves during handling and to wear an EPA approved dust-mask. 

Additionally, the new pressure treated woods treated with copper are more expensive and also cause issues with the corrosion of certain metals (due to the high copper content). More information is included below with regards to the different types of hardware required for use with pressure treated woods to avoid the dangers of metal corrosion.

Wood Decking

Even if you decide to frame your deck’s structure using pressure treated wood, your options are still wide open when it comes to the actual decking material you can choose to use for the parts of your deck that are visible to you and your guests.

The most popular wood decking options are pressure treated wood, redwood, or cedar. The difference (aside from cost) is that redwood or cedar is naturally rot and insect resistant.

In addition to cedar and pressure-treated decking, there are beautiful hardwood options, also known as “ironwoods” because of their dense cell structure. Because these hardwoods are so dense, they require additional handling and extra work to use them in your construction project. For example, most of the hardwoods will need to be pre-drilled and require different hardware than your typical softwood materials. You’ll notice your saw blade will wear faster when cutting hardwoods.

Hardwoods include Ipe (the most popular hardwood), Cumaru, Garapa, Cambara and Machiche. Although they do not necessarily have to be treated the way the softer woods should, you will extend the life of your hardwood decking by using a surface treatment.

Non-Wood Decking

Both composite decking and PVC decking has taken off over the past few decades, and provides homeowners with a viable alternative to building a deck with real wood.

Composite decking is typically manufactured with a mix of recycled plastic materials and wood pulp. By adding the plastic to the composite, it becomes insect and rot-resistant. Because it is a manufactured product, you will not find the imperfections you will with natural wood products. There is no grain to worry about, and no knots that can often get in the way when cutting and drilling.

Most of the products manufactured today are non-toxic, and have come a long way since the early days when you could spot a deck built with composite or plastic decking a mile away.

Today’s composites and non-wood decking products come in a wide range of colors and styles, and can be an aesthetically pleasing addition to your deck.

There are few downsides to building with composite decking. One is the cost, which is higher than softwood lumber. The other is that some composite decking is more flexible than wood, and often requires closer support spacing, which can increase the overall cost of your deck.

Fasteners, Connectors, Screws and Nails

As deck building codes have changed over the past few decades, using metal fasteners has become more a part of building than your grandfather might ever imagine. Back thirty or forty years ago, a contractor might have used some joist hangers here and there, but otherwise entire decks built with screws, nails, and bolts.

Today, the building codes are written so it is very clear which specific metals and fastener types must be used to build a safer, code-compliant deck. Using the correct fasteners will prevent dangerous failures and provide you with a stronger deck.

Prior to purchasing your connectors and fasteners, you will need to make sure you are choosing the right metal for the material you are using to build your deck. The options used to be limited to either galvanized or stainless steel, but today different woods, such as pressure treated, require coatings and metals specifically designed for the makeup of the wood. The connectors and fasteners are labeled to help you identify which metals you will need.

You can find a wealth of information about fasteners and connectors available for deck construction by visiting the Simpson Strong-Ties website.

Deck Screws

When you walk down the aisle at the hardware store or big box store, you’ll realize there are hundreds of variations, sizes, and materials used to manufacture screws.

As is the case with the fasteners and connectors, screws are manufactured with various materials and coatings to ensure durability and compatibility with the various available deck building materials.

The screws you choose will depend on the type of lumber you’re going to be using to build your deck. Therefore, it’s important to know the differences and why any one screw would be suitable for your construction project.

Galvanized screws were at one-time the go-to, especially with pressure treated lumber. But because of  the newer formulations in pressure treated woods, some screws that were at one time approved will no longer last long enough to be considered useful. Many will break-down over time due to the makeup of the pressure treated lumber.

That’s why there are so many different screw variations on the market today. 

And the differences aren’t just in the material used in the manufacturing. Whether you use galvanized or stainless or ceramic coated is just the beginning of your decision-making.

Because in addition to the material used to manufacture the screws, you will also need to consider the type of screw head you will use. Each will vary from one type of screw to the next, including everything from your typical Philips head screw to square-bit screws to star-head screws to flat-heads, and many others. 

Each screw is manufactured with the goal of improving drive, ease-of-installation, resisting corrosion, and having a durable screw that will last the life of your deck.

As you can see, there are a lot of options when it comes to finding the best building materials for your deck. This article is only a start, and it’s worth doing your own homework once you have your plan together so you can make the most informed decision so you will have a safe and attractive deck you will enjoy for a long time.