Wood and composite deck construction field guide

Deck building, and why the ledger and the guard are life-safety

A deck is a structure that holds people up in the air, and that one fact changes how you have to think about every connection in it. A patio sits on the ground. If the base under a patio fails, the surface settles and somebody calls you back. A deck is different. If the deck fails, people fall, and they fall with the whole structure coming down on top of them. So a deck is built to a code standard the way a floor is, because that is what it is: an exterior floor, elevated, attached to a house that was never drawn to carry it.

Two parts of that structure fail catastrophically, and they are the two parts you cannot get wrong. The first is the ledger, the board that bolts the deck to the house. When the ledger lets go, the deck pulls away from the wall and collapses, and ledger failure is the leading cause of deck collapse on record. The second is the guardrail. When the guard is too low, too weak, or has gaps a child fits through, somebody goes over the edge or through the rail. Everything else on a deck is craft. These two are life and death.

The rest of the work serves those two. You set footings below the frost line so the structure does not heave. You attach and flash the ledger so it carries load and the house band joist behind it stays dry. You frame the joists and beams to the span tables so nothing sags or breaks under the crowd. You detail the guardrail and the stairs so nobody falls. This guide walks that sequence and hedges the load-path and life-safety calls to the IRC deck provisions, the AWC DCA 6 prescriptive guide, the engineer, and the product manufacturers, because those are the sources that actually control. For the surface a deck often connects to, see the paver and hardscape patio guide; for the railing details, see the metal railing and guardrail guide.

What is the most common cause of deck collapse?

The most common cause of deck collapse is failure of the ledger connection, specifically a ledger nailed to the house instead of bolted, or a ledger that was never flashed so the band joist behind it rotted and let the fasteners pull out. Failure investigations going back two decades keep landing on the same thing: the deck separates from the house at the ledger and drops, usually when the deck is loaded with people, which is the worst time for it to go.

Nails are the original sin here. A nailed ledger relies on the withdrawal strength of smooth shanks in end grain and cross grain, and that is nothing close to what a loaded deck pulls with. Since the 2009 IRC, the code has required the ledger to be fastened to the band joist with 1/2 in lag screws or bolts, not nails, and that requirement has carried through every edition since. The second killer is water. A ledger that is not flashed traps water against the house band joist, the wood rots, and the bolts that were sized correctly withdraw from punky lumber. The connection that passed inspection on day one fails three winters later because the wood behind it turned to mush.

So the ledger and the guardrail are the two items to get right above all others. Bolt and flash the ledger or the deck comes off the house. Build the guard to the height, the load, and the baluster spacing or someone goes over it. Treat both as engineered, code-governed connections, not as carpentry you eyeball. The IRC R507 deck provisions and DCA 6 give the prescriptive path; for anything outside that path, the structure and the attachment go to an engineer.

How do you attach a deck ledger?

Bolt the ledger to the house floor band joist with 1/2 in lag screws or through-bolts on the spacing the code table gives for your joist span, and never with nails alone. Through-bolts are the most reliable connection because they clamp the ledger and band joist between a head and a nut on a washer, and they do not depend on thread engagement in wood that may be old or wet. Lag screws are accepted when they fully penetrate the band joist and bite past it, but if you cannot confirm what is behind the sheathing, through-bolting or a different approach is the safer call.

The fastener spacing is not a guess and not a habit. DCA 6 and IRC R507 give a ledger fastener table that sets the spacing by the joist span the ledger carries: the longer the joists, the more load each fastener sees, and the tighter the spacing gets. The table also sets the edge distances, top and bottom and from the ends, so the fasteners do not split the ledger or the band joist. Use the minimum ledger size the code calls for, commonly a 2x8 or to match the deck joists, and stagger the fasteners in the rows the table shows.

What you are bolting to matters as much as the bolts. The ledger has to land on solid house framing, the rim or band joist of a floor, not on brick veneer, not on a cantilevered floor, not on the rim of a bay window, and not over a layer of foam sheathing that holds the ledger off the structure by an inch. When the wall has continuous exterior foam, there is a specific detailed approach for fastening through it that the code and the connector manufacturers cover; do not just run longer lags and hope. And when you cannot get a sound ledger connection into reliable house framing, you build the deck free-standing on its own posts and beams instead of hanging it on a connection you do not trust.

Ledger flashing and keeping the band joist dry

Flashing the ledger is the single most important step for keeping the deck attached over time, because the water that gets behind an unflashed ledger rots the house band joist and the ledger both, and rotted wood does not hold fasteners. A ledger can be bolted perfectly and still fail if the wood it is bolted to turns soft. DCA 6 shows the flashing details, and the principle is simple: stop water from getting into the joint between the ledger and the house, and give any water that does get in a way back out.

The detail layers from the wall out. The house water-resistive barrier laps down over the top of the ledger, a cap flashing or Z-flashing tucks up under the siding and the barrier and bends down over the top edge of the ledger, and on many assemblies a self-adhered membrane wraps the band joist and the cut sheathing before the ledger goes on. The siding and barrier shed water onto the cap, the cap sheds it onto the face of the ledger, and the water never reaches the joint. Some builders also hold the ledger off the wall on washers or a continuous spacer so the back of the ledger can dry, which is a recognized approach when the fastener length and the connector are detailed for the standoff.

The failure you are preventing is slow and invisible. Water wicks into the unsealed joint, sits against the band joist behind the siding where nobody looks, and the rot spreads for years before the deck moves. By the time the deck sags or pulls, the band joist is gone and the repair is structural surgery on the house, not a deck fix. Flash it right the first time. This is also the reason a ledger should never be caulked-only as a substitute for flashing; caulk is a supplement at best and it fails before the deck does.

The lateral-load connection

The lateral-load connection is the hardware that ties the deck framing back into the house framing to resist the deck pulling away from the wall, and it is separate from the ledger bolts that carry the vertical load. The ledger fasteners are loaded in shear by the weight on the deck. The lateral connection handles the horizontal pull, the force that tries to peel the deck off the house when people move across it or crowd toward the rail. A ledger can carry the gravity load and still need this connection to keep the deck from migrating away from the wall.

The IRC R507 deck provisions added an explicit lateral-load requirement, and the common prescriptive answer is hold-down tension devices installed in pairs, each rated for a 1500 lb capacity, that run from a deck joist through the house rim and anchor to the house floor framing inside. The exact device count, capacity, and placement come from the adopted code edition and the connector manufacturer's listing, so confirm them against the edition the jurisdiction has adopted before you install. DCA 6 illustrates the connection; the connector maker's instructions give the fasteners and the installation.

Where the geometry will not allow the tension ties, or where the house framing cannot accept them, the honest answer is to design the deck free-standing so it does not rely on the house for lateral resistance at all. Do not skip the lateral connection because it is awkward to install. The whole point of it is the failure mode that kills people, the deck pulling off the house, and it is exactly the connection that gets left out on the decks that fail.

How deep do deck footings go?

Deck footings go below the local frost line and bear on undisturbed soil, because a footing above the frost line heaves when the ground freezes and the deck cannot float. The IRC sets the depth at the deeper of the local frost line or a minimum below grade, commonly 12 in, and the frost line varies by region from almost nothing in the south to four feet or more in the cold states. Confirm the frost depth and the minimum with the local building department, because the adopted code and local amendments control the number.

The footing has two jobs. It spreads the load over enough soil that the post does not punch down, and it anchors the post against heave and overturning. The size of the footing comes from the load it carries, which traces back to the tributary area of deck it supports, and the IRC and DCA 6 give footing size tables by post spacing and soil bearing. Bear on undisturbed native soil. If you over-dig, do not backfill with loose dirt and set the footing on it; backfill with compacted gravel or fill the over-dig with concrete, because loose fill settles and the post drops.

The post-to-footing connection is where the load path gets interrupted on careless jobs. The post does not just sit on the concrete. It connects through a post base that holds the post up off the footing on a standoff so the end grain can dry, and that resists uplift and provides a positive mechanical connection rated for the lateral and uplift loads. A post set directly on concrete wicks water and rots at the worst place, the bottom where you cannot see it, and a post with no base connection is free to walk off the footing. The footing and its connection tie to the same below-grade thinking as the base under a paver patio; the difference is that a deck footing carries a point load that holds people up, so the bearing and the connection are not optional.

Posts and beams: the load path to the ground

The posts and the beam carry the deck load from the joists down to the footings, and the connections at both ends of the post are where that load path is made or broken. The beam gathers the joist loads and spans between the posts. The posts carry the beam load down to the footings. Size the post for the load and the height, and size the beam for its span and the deck area it carries, both from the span tables rather than from what looks heavy enough.

The post-to-beam connection is a place builders still get wrong. The strong detail sets the beam on top of the post so the load bears directly in compression, with a post cap connector tying the two together against uplift and lateral movement. Notching a post to let a beam sit in the notch is acceptable when it is done to the prescriptive detail with the right fasteners, but a beam simply bolted to the side of a post relies on the bolts in shear and is the weaker arrangement. Bearing beats fastening for carrying gravity load; the connector hardware is there for uplift and stability, not to hold the beam up by itself.

Watch the post height. DCA 6 used to allow a blanket maximum post height, but the guidance now ties the maximum height to the beam and joist spans and the lumber species, with bracing requirements that shorten the allowable height as the spans grow. A tall, unbraced post under a long span is a different animal than a short post under a small deck. When the post height, the spans, or the loads fall outside the prescriptive tables, the post and beam sizing goes to an engineer.

What is DCA 6 and how do the span tables work?

DCA 6 is the American Wood Council's Prescriptive Residential Wood Deck Construction Guide, a graphic document that translates the IRC deck provisions into span tables and connection details a builder can follow without an engineer for decks that fall within its limits. It is the field reference for sizing the joists, the beams, and the posts, and for the ledger fastener spacing, the guard, and the stairs. When a deck stays inside the DCA 6 and IRC R507 limits, the tables are the design.

The span tables work off three inputs: the lumber size, the species and grade, and the spacing, and they output the maximum span. A joist span table tells you how far a 2x8 of a given species can span at 16 in on center under the deck design load, which the code takes as 40 psf live plus 10 psf dead. A beam table tells you how far a built-up beam of a given size can span between posts for a given joist span behind it. The longer the tributary area each member carries, the shorter it can span. Do not guess the span. A joist that looks plenty stiff in the shop can bounce and deflect under a crowd, and a beam sized by eye is the kind of thing that fails when the deck is full.

The tables have hard edges. They assume a single, uniform residential load, ordinary species, a defined spacing, and a deck within the height and configuration the guide covers. Hot tubs, planters, heavy stone surfaces, roofs over the deck, unusual geometry, and anything outside the table's range are loads the prescriptive tables do not cover, and those go to an engineer. The 2026 review note here is the same as every year: confirm the tables against the edition of the IRC and DCA 6 the jurisdiction has adopted, because the spans and the connection details have changed between cycles.

Joists, spacing, and the cantilever limit

The joists carry the decking and the live load to the beam and the ledger, and three things size them: the span, the spacing, and the cantilever. The span comes from the table. The spacing is commonly 16 in on center for wood decking and often tighter for composite, which sets how far the joists can span and how the decking is fastened. The joists hang off the ledger and the beam on joist hangers, not on toenails, and the hangers are rated structural connectors selected for the joist size and installed with the connector nails the manufacturer specifies, not with whatever is in the gun.

The cantilever is the overhang past the beam, and it is limited. The IRC and DCA 6 cap the joist cantilever at a ratio of the backspan, commonly one part overhang to four parts backspan, so a joist with a 12 ft backspan can cantilever about 3 ft. Overhang past that and the joist levers up at the beam and the deck springs at the edge, which is exactly where people stand at the rail. The cantilever limit is also why you cannot just push the beam back to make the deck reach farther; past the ratio, the framing has to grow or the beam has to move.

Blocking and a rim joist tie the field together. Blocking between joists at the span and over the beam keeps the joists from rolling and stiffens the deck, and the IRC requires lateral restraint at the supports. The rim joist closes the ends and gives the decking and, on many decks, the guard posts something to attach to. Get the framing flat and consistent now, because every problem in the decking and the rail traces back to a frame that was not right.

How tall does a deck guardrail need to be?

A residential deck guardrail is commonly required to be at least 36 in tall, it has to resist a 200 lbf concentrated load applied in any direction at the top, and the infill cannot allow a 4 in sphere to pass through it. A guard is required once the deck walking surface is more than 30 in above the grade or surface below, and that 30 in trigger is measured to the ground within a set distance of the deck edge. Confirm the exact height and trigger against the adopted code, because commercial work under the IBC and some jurisdictions use 42 in.

The three numbers each guard against a different failure. The 36 in height keeps an adult from going over. The 200 lbf load is what the guard and its posts have to take when someone falls or leans into it, applied at the top where the bending force is worst, and the infill separately has to resist a 50 lb load over a one-square-foot area. The 4 in sphere rule keeps the gaps small enough that a small child cannot fit through or get a head stuck, and it applies everywhere: between balusters, between the bottom rail and the deck, and around the posts. On stairs the triangular opening at the treads has its own larger sphere allowance.

Building the rail itself, the materials, the infill systems like cable or glass or balusters, and the connections, is its own trade, and the metal railing and guardrail guide covers the fabrication and the heights in depth. The point that belongs here is that the guard is the second life-safety item after the ledger, and the geometry and the load are not negotiable. A rail that meets the height but flexes under load, or one with gaps a child fits through, is a guard that fails the moment it is tested. The IBC, the IRC, and the engineer control the numbers; cross-link the railing guide for the build.

The guard post attachment is the weak point

The guard post attachment, not the rail, is where guardrails fail, because a post that is only lag-screwed to the rim joist pulls out under load and takes the rail with it. The 200 lbf at the top of a 36 in post is a serious overturning force at the base, and a couple of lag screws into the side of a rim joist do not have the withdrawal strength to hold it. The post lets go, the rail swings out, and whoever leaned on it goes over. This is the guardrail version of the nailed ledger: the right load, the wrong connection.

The attachment that holds is a through-bolt connection with blocking and tension hardware, not surface lags. The post bolts through the rim with carriage bolts or machine bolts and nuts on washers, blocking is added behind the rim and between the joists so the bolts have solid wood to clamp and the moment is spread into the frame, and a tension hold-down connector designed for guard posts ties the post base down to the joists below the deck. The connector manufacturers make a specific guard-post hardware for this, tested to the load, and DCA 6 shows the blocking and bolting detail. Notching the post over the rim weakens it at the worst spot, so where a post is notched it has to be detailed and reinforced for the reduced section.

Test the thinking, not just the install: where does the 200 lb want to go, and is there a path for it into the frame that does not depend on a few fasteners in withdrawal? If the answer is blocking and bolts and a hold-down, the post will hold. If the answer is two lags and hope, it will not.

The stairs: rise, run, stringer, and handrail

Deck stairs fail people two ways: inconsistent steps that trip them, and a missing or non-graspable handrail that gives them nothing to catch. So the stairs are built to a tight geometry. The IRC commonly caps the riser at 7 3/4 in and sets a minimum tread depth of 10 in, and the rule that matters most is uniformity: every riser and every tread within 3/8 in of the others over the whole flight. The brain learns the step on the first tread and expects it to repeat; a riser that is half an inch off near the bottom is where people fall.

The stringer carries the steps, and there are two kinds. A cut stringer is notched for each step out of a single board, which is fast but removes a lot of the board's depth at the notches; a solid stringer carries the treads on cleats or in routed housings and keeps its full section. Cut stringers have a maximum spacing and need enough uncut depth left below the notches to carry the load, and on wider stairs or composite treads you add stringers to keep the spacing tight enough that the treads do not flex. Attach the stringer to the deck with a proper hanger or connection, not by toenailing it to the rim, and land it on a solid pad at the bottom so it cannot kick out.

The handrail is required once there are four or more risers, and it has to be graspable and continuous the full length of the flight, mounted 34 to 38 in above the tread nosings. Graspable means a shape a hand can actually close around, the Type I or Type II profiles the code defines, not a flat 2x6 on edge that you cannot grip. Return the ends into the guard or the wall so a sleeve or a strap does not catch on an open end. The stair guard, where the stairs are high enough to need one, follows the same load and sphere rules as the deck guard, with the sloped allowances the code gives for the rake.

Wood or composite decking?

Choose by maintenance, budget, and how the deck is framed, not by looks alone, because the two materials carry different rules. Wood decking, pressure-treated or cedar or a tropical hardwood like ipe, costs less up front, takes any framing layout, and needs cleaning and sealing on a cycle to hold up. Composite and PVC decking cost more up front, clip down with hidden fasteners for a clean surface, and need almost no finishing, but they demand tighter joist spacing, move more with temperature, and get hotter in the sun.

The framing consequence is the one people miss when they switch to composite late. Composite boards are less stiff than wood across the joists, so most composite lines require closer joist spacing than wood: 16 in on center for perpendicular boards on many products and as tight as 12 in on center when the boards run at 45 degrees, with the exact number set by the manufacturer. If the frame was laid out at 16 in for wood and the customer changes to a diagonal composite pattern, the spacing is wrong and the deck feels spongy. Decide the decking before the joists go down, because the decking drives the spacing.

Neither material changes the structure underneath. The ledger, the footings, the framing, and the guard are sized the same regardless of what the surface is. The decking is the wear layer and the look; the safety lives in the frame and the connections.

Wood decking and the gaps that keep it alive

Wood decking lives or dies on drainage and movement, so the gaps between boards are not cosmetic. A wood board sheds water off its faces but holds it where boards touch, so you leave a gap between boards for drainage and air, and you account for how the wood will move. Pressure-treated lumber is often delivered wet from the treatment, so it shrinks across its width as it dries; tight-fit it green and you end up with wide gaps in a month. Kiln-dried or already-dry boards move the other way and want a small starting gap.

The species sets the maintenance and the fastening. Treated southern pine is the budget standard and takes a finish. Cedar is lighter, more stable, and naturally rot-resistant but soft. Tropical hardwoods like ipe are dense, last decades, and resist rot and wear, but they are hard enough that they need pre-drilling and stainless fasteners, and they barely take a film finish, so they are oiled instead. Fasten with screws rather than nails where you can, because nails back out as the wood cycles and become the pop-up that catches a bare foot.

Then keep it sealed. Wood that is cleaned and sealed on a cycle, the interval depending on exposure and the product, sheds water and resists the cupping and checking that come from wetting and drying. Let it go gray and unsealed and it still works, but it weathers, cups, and splits faster, and the cupping traps water on the surface, which is what feeds rot at the fasteners and the joist tops.

Composite and PVC decking

Composite and PVC decking trade up-front cost for almost no finishing, but they hold you to the manufacturer's instructions on three things that wood is forgiving about: joist spacing, expansion gaps, and the fasteners. Composite is a wood-fiber and plastic blend; PVC is all plastic. Both clip down with hidden fasteners that engage a groove in the board edge, which leaves a clean surface with no face screws and sets a consistent gap. Use the maker's clips and the maker's spacing, because the warranty and the performance are written to that system.

The two behaviors to respect are sag and movement. Composite is less stiff than wood, so it sags between joists if the spacing is too wide, which is why the lines require closer joist centers than wood and tighter still for diagonal layouts. And the boards expand and contract with temperature more than wood does, so you leave the maker's end and side gaps, especially on long runs and in hot climates, or the boards buckle in summer and gap in winter. Cutting a board on a cold morning and butting it tight means a buckle by July.

The other reality is heat. Composite, and dark colors most of all, gets hotter underfoot in direct sun than wood does, which matters on a south-facing deck where people go barefoot or where pets and kids use it. It is a comfort and selection issue, not a structural one, but it is the complaint that comes back, so set the expectation when you pick the color. Follow the manufacturer's published spacing, gaps, and fastening for the specific product, because those numbers vary by line and they control.

Fasteners and structural connectors

The fasteners and connectors on a deck have to be hot-dip galvanized or stainless steel, because treated lumber corrodes ordinary and electro-galvanized steel, and the connectors are rated structural hardware, not generic brackets. A deck is outdoors, in contact with treated wood, and loaded with people, so the metal in it is doing structural work in a corrosive environment. The wrong fastener does not announce itself; it quietly corrodes inside the connection until the connection lets go.

Match the coating to the exposure. The common standard for fasteners in treated lumber is hot-dip galvanized to ASTM A153, and for connectors the heavier G185 galvanized coating, or stainless steel throughout. Stainless grades 304 and 305 cover most inland work, and 316 is the call near salt water, where even hot-dip galvanizing gives up over time. Do not mix metals in a single connection: galvanized fasteners in stainless hardware, or the reverse, set up galvanic corrosion that eats the less noble metal faster than either would corrode alone.

The structural connectors are the joist hangers, the post bases, the post caps, the hold-downs, and the tension ties, the Simpson-type hardware that makes the load path continuous from the decking to the footing. These are tested, rated products, and they only carry their rated load when they are installed with the specific connector nails or screws the manufacturer lists, in every hole the design requires. A joist hanger half-filled with the wrong fasteners, or filled with drywall screws, is not the connector on the label. Use the rated fastener, fill the holes the listing calls for, and the connector does what the table says.

Why treated lumber eats the wrong fasteners

Modern pressure-treated lumber corrodes regular steel fast because the preservatives are copper-based, and copper in contact with steel in a wet environment drives galvanic corrosion that strips an uncoated or lightly coated fastener. The industry switched away from the old chromated arsenical treatments years ago to copper-based chemistries like ACQ and copper azole, which are safer to handle but markedly more corrosive to fasteners than what they replaced. A bright or electro-galvanized screw that lasted in the old lumber rusts through in the new.

The mechanism is the part that bites you later. The copper and the steel form a galvanic cell whenever moisture is present, and the steel is the part that gives up its metal. An electro-galvanized coating is thin and burns through quickly in this service, leaving bare steel to corrode inside the wood where you cannot see it. The fastener thins at the shank, loses strength, and one day the connection it was holding fails under load with no warning on the surface.

The fix is to specify the metal for treated lumber from the start: hot-dip galvanized to the right standard or stainless, in both the fasteners and the connectors, every fastener in the deck. This is not a place to use up the box of deck screws from the last job if you are not sure what they are. The cost difference between the right fastener and the wrong one is small. The cost of a connection that corrodes out under a loaded deck is not.

Water management and rot prevention

Rot is the slow killer of decks, and it concentrates at a few predictable places, so the water management is about keeping those places dry and able to drain. The ledger joint is the first, covered above, and it is the worst because the rot there attacks the house. The second is the post bottoms, where a post set on concrete wicks ground water up the end grain and rots from the bottom; the standoff post base that holds the post up off the footing on a gap is what prevents it. The third is anywhere two pieces of wood trap water between them with no path out.

Keep wood off the ground and let air move under the deck. Posts on standoff bases, joists and beams up off the soil, and ventilation in the space under the deck all let the framing dry between rains. A low deck skirted tight to the ground with no airflow stays damp underneath and rots faster than a high, open one. Where the deck is close to grade, slope the ground to drain away and keep a vented gap rather than sealing the underside up tight.

On the surface, the joist tops are a quiet rot site on wood-framed decks: water sits in the gap between deck boards and soaks into the top edge of the joist right where the fastener goes. Joist-top flashing tape, a self-adhered membrane run along the top of each joist before the decking goes down, sheds that water off the joist and protects the fastener penetration. It is cheap insurance on the part of the frame that gets wet every time it rains, and it has become standard practice on decks built to last.

Do you need a permit to build a deck?

Almost everywhere, a deck attached to a house and above a low height threshold needs a building permit and inspections, because the deck is a structure that holds people and the jurisdiction wants the load path checked before it is covered up. The IRC R507 deck provisions and the AWC DCA 6 guide are the prescriptive standard most jurisdictions build their deck review around, and pulling the permit gets you the inspections that catch the failures this guide is about before they are buried.

The inspections come in stages, and each one looks at a connection you cannot see once the next stage covers it. The footing inspection checks the depth below frost, the size, and the bearing before the concrete goes in. The framing inspection checks the ledger fasteners and flashing, the lateral-load connection, the joist hangers and beam connections, the post bases, and the spans before the decking covers them. The final inspection checks the guard height and infill, the guard-post attachment, and the stairs and handrail. Skip the permit and you risk a tear-out order, and you lose the second set of eyes on the exact connections that put people on the ground.

Pull the permit. The fee is small against the liability of an unpermitted deck that collapses, and the inspection record is part of the document trail if the deck is ever questioned. Confirm the adopted IRC edition, any local amendments, and the local frost depth with the building department before you design, because those control the numbers in this guide.

The build sequence

A deck goes together from the house outward and from the ground up, and the order matters because each stage has to be inspected or made watertight before the next one covers it. The clean sequence is ledger, footings, posts and beam, joists, decking, then the rail and stairs. Set and flash the ledger first so it establishes the deck height and the flashing is done before anything hangs on it. Lay out the footings off the ledger and the building, dig and pour them below frost, and get the footing inspection before backfilling.

Then build up. Set the post bases, stand and brace the posts, set the beam on the posts with the caps, and confirm everything is level and the load path is connected. Hang the joists off the ledger and the beam on their hangers, set the cantilever to the limit, and add the blocking and the rim. This is the framing the inspector wants to see, so call the framing inspection before the decking hides the ledger fasteners, the hangers, and the lateral ties.

Lay the decking to the spacing and gaps the material requires, with the joist-top flashing already down. Then build the guard with its blocked, bolted posts and the stairs with their stringers and graspable handrail, and call the final. Resist the temptation to deck over the frame before the framing inspection to make the job look done; the connections that matter are the ones you would be covering, and that is exactly what the inspection is for.

Maintenance and the annual safety check

A deck is not a build-and-forget structure, because the two things that fail catastrophically, the ledger and the guard, degrade with water and use, and an annual look catches them while they are still a repair instead of a collapse. The maintenance splits into the surface, which is cosmetic and material-specific, and the structure, which is safety.

On the surface, wood gets cleaned and sealed on its cycle to hold off cupping and rot, and composite gets cleaned to keep mold and grime out of the texture. Neither is structural, but a neglected wood surface that cups and traps water accelerates the rot below it. Once a year, walk the structure with a screwdriver and a flashlight. Probe the ledger and the band joist behind it for soft, punky wood. Check the post bottoms and the beam for rot. Push on the guard and the guard posts to feel for movement, and confirm the rail still meets the height and the infill has not loosened. Look at the joist hangers and the fasteners for rust and back-out, and walk the stairs for a loose tread or a wobbly handrail.

The point of the annual check is the ledger and the guard, because those are the ones that hurt people. A soft spot at the band joist or a guard post that moves is a stop-using-it finding, not a someday repair. Catch it at the screwdriver stage.

What to document

The questions that come up later, at sale, after a near-miss, or when a load runs heavy, all land on the connections that are now buried under decking and skirting, so the deck that holds up to scrutiny is the one whose connections went on paper while they were still open to view. Capture the ledger fastener type, size, and spacing and the flashing detail, the lateral-load device and its rating, the footing depth and size and bearing, the joist and beam sizes and spans against the table used, the guard height and the guard-post attachment, the connector models and the fasteners, and the permit and inspection sign-offs.

Photograph the connections before they are covered. A photo of the flashed ledger before the siding closes, the footings before backfill, the joist hangers and lateral ties before the decking, and the blocked guard posts before the rail goes on is the record that proves the deck was built right. A field tool like FieldOS keeps those photos and the spec notes tied to the job and the inspection, so the record exists when somebody asks years later.

Common mistakes

• Nailing the ledger to the house instead of bolting it with lag screws or through-bolts, or leaving it unflashed so the band joist rots and the fasteners withdraw.
• Lagging a guard post to the rim with no blocking or hold-down, so it pulls out under the 200 lbf load and the rail goes with it.
• Setting footings above the frost line or on loose backfill, so the deck heaves or the post drops.
• Guessing the joist or beam span instead of pulling it from the DCA 6 or IRC table for the size, species, and spacing.
• Using regular or electro-galvanized fasteners in copper-treated lumber, so they corrode inside the connection.
• Laying composite on a frame spaced for wood, so the boards sag, or butting composite tight with no expansion gap, so it buckles.
• Skipping the lateral-load connection because it is awkward, leaving the deck-pulls-off failure mode unaddressed.
• Building without a permit, so the footing, framing, and guard connections never get inspected.

Field checklist

Standards and references

The IRC, in the R507 exterior deck provisions, is where the residential deck rules live: the ledger attachment and fastener spacing, the lateral-load connection, the footing depth and bearing, the joist and beam span tables, the guard height and load and infill, and the stair geometry. The AWC DCA 6, the Prescriptive Residential Wood Deck Construction Guide, translates those provisions into the span tables and connection details builders use in the field, and it is the practical reference for sizing members and detailing the ledger, the guard post, and the stairs. Both are adopted and amended by jurisdiction, so confirm the edition and any local amendments, and the local frost depth, with the building department before you design.

The hard calls hedge to those documents and to two outside authorities. When the deck falls outside the prescriptive tables, in span, height, load, geometry, or anything carrying a hot tub or a roof, the structure and the attachment go to an engineer. When the surface is composite or PVC, or when the connectors are the rated structural hardware, the manufacturer's published instructions govern the joist spacing, the gaps, the fasteners, and the installation, and the connector's rated load only applies when it is installed to the listing.

Three things carry above everything else in this guide. The ledger must be bolted and flashed or the deck pulls off the house and collapses. The guardrail and the guard post must be built to the 36 in height, the 200 lbf load, and the 4 in sphere or someone goes over or through it. The footings go below frost and the framing is sized to the span tables, not to judgment. Hedge those to the IRC, DCA 6, the engineer, and the manufacturer, and build them like lives depend on the connection, because they do.

Units and terms

Deck construction borrows terms from framing, from the code, and from the connector makers, and the same part can read differently across a permit set, a span table, and a product sheet.

The deck design load most prescriptive tables assume is 40 psf live plus 10 psf dead. Spans, spacing, and heights are in inches and feet on US drawings; the frost depth is a local number in inches. The guard load is a concentrated 200 lbf at the top with a separate 50 lb infill load over a square foot. Fastener and connector coatings are called out by standard, hot-dip galvanized ASTM A153 for fasteners and G185 for connectors, or by stainless grade, 304, 305, or 316.

Deck ledger

The board that fastens the deck to the house band joist; must be bolted or lag-screwed and flashed, never nailed alone

Lateral-load connection

Tension ties from the deck framing into the house framing that resist the deck pulling away from the wall, separate from the ledger gravity bolts

Frost-depth footing

A footing bearing below the local frost line on undisturbed soil so the deck does not heave when the ground freezes

Joist span / DCA 6

The distance a joist spans between supports, sized from the AWC DCA 6 and IRC R507 tables by size, species, and spacing, not by eye

Cantilever

The joist overhang past the beam, limited to about one part overhang to four parts backspan

Guardrail (height / load / 4-in sphere)

A fall barrier, commonly 36 in tall residential, resisting a 200 lbf concentrated load, with infill that blocks a 4 in sphere

Guard-post attachment

The bolted-and-blocked connection with a hold-down that carries the guard load into the frame; the weak point when a post is only surface-lagged

Treated-lumber fastener corrosion

The galvanic attack copper-based preservatives drive on regular and electro-galvanized steel, requiring hot-dip galvanized or stainless metal

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