Steel Deck Framing: Complete Guide

Building a deck is a great way to increase your outdoor living space and add value to your home. If you’re worried about lumber quality, moisture damage, rot, and the maintenance of a wooden deck frame, consider using steel deck framing. Not sure what metal deck framing is or if it’s right for you, we’re here to help!

Steel deck framing won’t rot and is resistant to insects, mold, and mildew. It won’t sag over time, is more durable, easy to use, and can last 3 to 4-times longer than wood with less maintenance. It is more expensive, but in the long run, you’ll actually save money.

In this guide, we’ll explain what steel deck framing is and its benefits, and discuss the different components that make up a metal deck frame. We’ll explain installation and explore compatibility with different types of decking. Plus, we’ll look at the leading brands and where to buy them. Our aim is to provide you with the information to make the best decision for your deck project.

What is Steel Deck Framing?

Steel deck framing is made of 12 to 20-gauge steel, so is often referred to as LGS (light-gauge steel) framing. It consists of metal posts, beams, and joists made of various gauges or thicknesses of galvanized, powder-coated, or painted steel to prevent corrosion. Its strength-to-weight ratio is better than that of wood, so components are lighter, will span greater distances, and are easier to use.

Metal is also straight and true and doesn’t swell, twist, or warp with temperature and moisture changes, making decks easier to square and build. It can be screwed, bolted, or welded together too.

Metal framing comes in stamped, structural, and tubular formats. Stamped framing is shaped from thin gauge steel sheets, is the least expensive choice, and is often covered with concrete.

Structural framing is cold-formed steel framing shaped in boxed or 3-sided beams, joists, and posts and is stronger and more durable than stamped. Tubular framing is extruded square or rectangular steel tubes and is much stronger and more durable than the other two types, and also the most expensive.

Benefits of Steel Deck Framing

Metal deck framing has been around for decades and has undergone improvements over time, and now is more popular than ever before. It offers many advantages over wooden framing. It will last longer, is stronger, can be reused or recycled, and won’t rot, swell, twist, or warp like wood, so it’s safer too. Some of the key benefits are explained in more detail below.

Strength and Durability

Metal deck framing is typically structural light-gauge steel (LGS) or extruded tubular steel. Both forms offer a greater strength-to-weight ratio than that of wood. This means components are lighter and will span greater distances, plus it’s easier to use.

The metal is triple-coated galvanized, stainless, painted, or powder-coated to prevent corrosion. Metal decking is not only stronger, but it is also more durable. LGS framing won’t warp, sag, split, or bow, and is resistant to rot, wind, and weather damage.

Longevity

Untreated steel can last for hundreds of years in certain environments. The light-gauge steel used for deck framing is treated to protect it from moisture and other climatic issues, so it will last 100+ years with minimal maintenance.

It’s important, though, that all cuts, welds, bolt and screw holes, and any scratches are treated to prevent corrosion. Tubular steel should also have drain holes to remove condensation and caps to keep insects and moisture out.

Greater Spans

The strength of steel deck framing is greater than that of dimensional lumber, so it can span further with less weight. A 20-foot 14-gauge 10” deep LGS joist can span 19’-6” feet at 16” O.C. without support and weighs about 67 lbs.

A similar 16-gauge joist will span 18’0” and weigh 53 pounds. Comparatively, a 20’ length of 2×10 Southern pine will weigh over 90 lbs and span 14’-0” under the same conditions. Longer spans translate into fewer support posts too, which helps reduce overall costs.

Low Maintenance

Steel deck framing requires less maintenance than timber framing. Check for scratches or chips in the coating every one or two years and seal with an appropriate coating. While checking for scratches, also check that fasteners are tight.

Keep the steel free of dirt and debris seasonally to protect the metal frame and deck material. Steel won’t rot, shrink, or expand like wood, so it requires less servicing or maintenance.

Fire Resistance

Steel deck framing is non-combustible and has a Class-A fire rating. It resists flame and meets the Wildland Urban Interface and Building Code requirements for certain wildfire States, as well as many insurance companies. However, much depends on what is stored under and on the deck, as well as the elevation of the deck above grade level.

Cost-effective

The cost of building a deck depends on its size, elevation, and even your ZIP or postal Code. Lumber and steel are both commodities and their price per linear foot fluctuates, so comparative costs are subject to change.

Before COVID, steel deck framing was about $6 to $12/sqft and lumber between $3 and $5/sqft. However, since 2021, timber has increased in costs, so it is more on par with the price of 18 to 22-gauge steel deck framing. This makes steel framing much more cost-effective since it is stronger, spans further, requires less support, and lasts longer.

Components of Steel Deck Framing

Building a metal deck using modern structural or tubular steel components follows much the same practice as building a wooden frame. The main difference is weight, straightness, and ease of squaring and leveling.

There are no crowns, bows, splits, knots, or pressure-treatment chemicals to worry about. The biggest decisions tend to be what gauge of metal and the color of the finish, which also affect the costs.

Posts

Posts for wooden or steel frames are commonly attached to concrete footings using post-to-pier brackets. Square structural steel posts or tubular steel posts of appropriate gauge and dimension provide support.

Using 3-1/2” or 5-1/2” square steel posts mimic the look of wooden posts, but are typically stronger than comparable timber ones. The posts are topped with post-to-beam brackets of matching color.

Beams

Structural steel beams are available in different dimensions but a 2”x11” is usually equivalent to a double 2×12 beam. They fasten to the posts with post-to-beam brackets.

While wood beams are solid and leave exposed end grain that must be treated, an endcap of matching color closes and finishes the open ends of the beam.

Ledger

Similar to wooden ledgers, steel ledgers can be fastened to structures. Steel ledgers are available in various lengths and pre-spaced for 12” or 16” joists layouts or blank for alternative spacing formats.

Joists are fastened to and supported by the ledger channel using ledger brackets. Depending on the Brand, they are commonly available in 8’, 12’, and 20’ lengths.

Joists

Metal joists are available in different dimensions depending on the span and design requirements. They fasten to the ledger with ledger brackets, the beam with color-matched brackets and screws, and the rim joist with single hanger brackets or pre-space slots.

Some joists are C-shaped and others are 4-sided 2”x6” structural steel tubes that look like common joists. Available in lengths from 12’ to 20’ or longer and in 12 to 22-gauge steel, they are typically spaced at 12” or 16” O.C. to support common decking options.

Rim Joist

Metal rim joists are 2”x6” C-shaped with or without pre-spaced slots at 12” or 16” centers, or 2”x6” square tubular steel. To accommodate curves, curved rim joists can be purchased, or blank channels notched and bent to take almost any shape created by different lengths of joists.

Commonly available in 8’ lengths, joists are fastened to the rim joist using color-matched hanger brackets or prefab tabs.

Blocking

Mid-span blocking can be accomplished using manufactured blocking strips that maintain 12” or 16” O.C. spacing. Most manufacturers have produced a method for mid-span blocking that fastens to the bottom of the joists to maintain spacing and improve rigidity.

Blocking for the joists resting on the beam is usually a formed steel strap manufactured in set lengths to maintain the correct spacing. Depending on the type used, fastening is usually done with screws.

Stairs

Steel frame stairs come in a variety of options and price points. Stringers can be premade with brackets welded to stringers to support treads and risers. They could be spiral steel frames in ready-made or easy-to-assemble formats.

The easiest and least expensive though, is to build them on site like wooden stairs using 2”x6” steel joists angle cut at the ends to accommodate the required slope and distance. Rise-run brackets are then fastened to the cut joists to form stringers with the necessary number of steps.

Due to the greater strength of the steel stringers, the spacing between stringers can be up to 48”.

Installation of Steel Deck Framing

Adding a deck to a structure typically requires a building permit unless it is free-standing and close to the ground. Permits also require a plan and material list. Some manufacturers and retailers have online design services available for a fee or free if you purchase from them – a helpful service for both the DIYer and the Pro. If you have the skills to build a wooden deck, you should be good to build one with a steel frame – if not, hire a pro.

As with any deck, mark, dig, form, and pour the footings and insert the appropriate post-to-pier brackets. The next step usually is to attach the ledger board to the structure, ensuring that it is level and secured with appropriate fasteners. The steel support posts and beam tend to be next, and can often be fastened together prior to being inserted and attached to the pier brackets and leveled.

The joists are then placed and attached, the rim joist connected, blocking straps installed, and the frame secured to the beam. If stairs are required, they are usually framed and installed too. Depending on the type of railing, additional blocking may be installed and posts attached. The steel frame is now ready for deck boards.

Installing the metal deck frame requires standard tools like a tape measure, level, hammer, rubber mallet, drill, screwdriver, saw with metal cutting blade, chalk, and chalk or string line. Cut joists slightly shorter to make any adjustment and connection easier.

Use appropriate corrosion-resistant nuts, washers, bolts, and self-tapping fasteners. Where possible, install fasteners where they won’t be visible when the deck is complete. Touch up any end cuts, scratches, or holes, and install end caps where necessary.

Compatibility with Decking Types

Metal deck framing provides a strong, solid, level platform upon which to lay your preferred decking. In most cases, special self-drilling 410 stainless steel epoxy-coated screws are recommended for 12 to 18-gauge steel and 1/8” to 1/4″ aluminum framing.

Steel deck framing comes in different finishes to mimic the look of solid wood and improve aesthetic appeal. Regardless of the finish, though, metal framing is compatible with most decking materials.

Wood

Wood decking needs to be screwed to the metal frame using appropriate wood-to-metal deck screws. Hardwoods like Ipe, oak, teak, and mahogany, along with redwood, cedar, cypress, and other softwoods can be fastened directly to the metal joists.

However, the chemicals in pressure-treated lumber can cause untreated and galvanized steel to corrode. To prevent corrosion, many installers use joist tape on any metal that pressure-treated stock will come in contact with.

Composite

Composite decking is available in numerous colors to mimic real wood. The decking can be fastened directly to the metal framework using color-matched epoxy-coated 410 stainless steel corrosion-resistant deck screws for metal framing.

The screws can be driven through the plank to fasten it to the framework, or edge mount clips can be used for invisible attachment. Depending on the manufacturer, predrilling may be recommended, but for most, that isn’t necessary.

PVC

PVC decking, like composite decking, is compatible with metal deck framing. It too can be fastened directly to the metal deck framing. Whether edge or through fastened, though, appropriate corrosion-resistant self-drilling screws should be used.

Leading Brands in Steel Deck Framing

There are a number of domestic manufacturers of steel deck framing with Fortress Evolution and Trex-Elevations leading the pack. Both are warranted for 25 years, and compatible with wood, composite, and PVC decking, but there are key differences.

Fortress Framing

Fortress Building Products manufactures the Evolution line of light-gauge steel deck and stair framing along with a full complement of connectors, posts, and other associated products. The system is designed by and for deck builders and engineered for quick and easy installation by a pro or DIYer.

It’s available in G-60 galvanized steel with a black-sand powder coating. 2’x11” beams come in 8’, 12’, 16’, and 20’ lengths, S-Ledgers in 12’ and 20’ lengths, 2”x6” boxed-joists in 12’, 14’, 16’ 18’ and 20’ lengths, and rim joists in 8’ lengths.

S-Ledger

The S-Ledger is unique to Fortress Framing and is S-shaped for additional strength and fastens to the structure with approved fasteners. It comes in 12’ and 20’ lengths punched to interlock with joists at 12” or 16” O.C. spacing or blank for alternate spacing arrangements.

The ledger is used with special ledger brackets that insert through the punched holes or fasten to the blank face with the same bolts used to fasten it to the structure. Both components are manufactured of G-60 galvanized steel and black-sand powder coated. It’s engineered to make joist placement quick and easy and reduce the number of fasteners.

Trex-Elevations

Trex-Elevations is a complete deck framing system of beams, posts, joists, tracks, brackets, fasteners, and other components. The ledger is a track and requires framing angles to secure the joists, which means more screws and time.

The light-gauge galvanized steel framing is triple-coated in dark brown or battleship gray paint. The 12’, 16’, and 20’ ledger tracks are C-shaped 1.25”x8.15” to receive the 1.615”x8” Box-C joists available in one-foot increments from 8” to 20’. The 2”x8.15” beam comes in 12’, 16’, and 20’ lengths to match the ledger track.

Steel Framing vs Wood Framing

Adding a deck to your home is a matter of planning, lifestyle, aesthetics, and budget. Part of the planning includes compliance with local Building Codes, HOA regs, and insurance requirements. Lifestyle also includes how much maintenance you wish to do yearly and how you’ll use the deck too. Both steel and wood deck framing are compatible with most decking options too.

Steel framing is stronger, more durable, and lighter than comparable dimensional lumber and will span further. Metal is flame, weather, and rot-resistant, straighter, and won’t warp, twist, bow, shrink, or split, so it is easier to install and level. It is installed in a similar manner to wood framing, too.

All cuts, scratches, and drilled holes need to be spray painted to prevent corrosion. Metal requires less maintenance and will last 3 to 4 times longer than timber counterparts.

Wood framing is less expensive and more readily available than metal framing. Wood is also a sustainable and renewable resource. It can be reused, repurposed, and recycled into other products, similar to most metals. However, wood is much easier to customize.

Wood framing is, unfortunately, susceptible to moisture, cupping, bowing, splits, cracks, checking, and warping. Wood will also expand and contract with climatic conditions, and sag and rot too.

If using pressure-treated lumber, all cuts and bolt holes need to be treated to prevent moisture damage and rot, plus special fasteners and brackets are required. Additionally, timber framing will require more frequent maintenance and won’t last as long.

Where to Buy Steel Deck Framing

Steel deck framing components are available from most home improvement retailers like Home Depot, Lowe’s, Menards, TSC Tractor Supply Co., and many others. Many online retailers such as decksdirect.com, deckmart.ca, fortressbp.com, jlconline.com, and Wayfair also carry metal deck framing too.

Check around, and ask about weight and delivery charges if ordering for a DIY project. Most deck installers will also have their own suppliers, so check with them for local suppliers, or hire them to do the job instead.