Structural Deck Inspection

Why this matters

A deck inspection identifies potential safety hazards before they cause injury. Decks built before current code (pre-2009 typically) often don't meet modern requirements; many older decks have ledger attachment failures, missing flashing, undersized fasteners, or framing decay. A contractor who can perform a thorough inspection and document findings produces a valuable service (moderate for typical inspection) and identifies remediation work the customer might not have considered. The customer pays for the inspection; the inspection often surfaces additional work.

When to perform

• Annual inspection (per customer preference)
• Real estate transaction (often required)
• After major weather event (heavy snow, wind)
• Customer reports concern (squeak, movement, sag)
• After other work nearby (landscape, addition)
• Insurance underwriting

What to inspect

A thorough inspection covers:

1. Ledger attachment to house
2. Joist structure
3. Beam and post structure
4. Footings
5. Decking surface
6. Railings and guards
7. Stairs
8. Fasteners overall
9. Code compliance overall

Inspection procedure

Step 1: Pre-inspection conversation

• Talk with the customer about concerns
• Note any specific issues they want addressed
• Note the deck's age and history
• Note any prior repairs or modifications

Step 2: Visual inspection from underneath

If the deck has access underneath:

• Walk underneath the deck
• Inspect ledger attachment (look for fasteners, flashing)
• Inspect joists for rot, splits, sagging
• Inspect joist hangers (proper installation, all nails)
• Inspect beams for spans appropriate to size
• Inspect posts for plumb and condition
• Inspect footings (visible?)
• Look for visible structural issues

For decks without access underneath:

• Note this limitation
• Visual inspection from edge and from above where possible

Step 3: Inspect ledger attachment

The single most-important inspection point:

• Verify ledger is bolted (not nailed)
• Verify fastener spacing (16 inch on center typical)
• Verify fastener type (1/2 inch lag screws or through-bolts)
• Verify flashing is in place
• Look for evidence of water damage behind ledger
• Look for separation between ledger and house

Step 4: Inspect joists

For each joist:

• Visible rot (probe with awl in suspected areas)
• Splits or cracks
• Visible sag (sight along the length)
• End bearing on joist hanger
• Joist hanger condition (all nails, no corrosion)

Step 5: Inspect beams

For each beam:

• Span appropriate to size and load
• Splice locations (if any)
• Beam-to-post connection
• Visible rot or damage

Step 6: Inspect posts

For each post:

• Plumb (use level)
• Connection to footing (visible at base)
• Connection to beam (top)
• Visible rot, especially at base

Step 7: Inspect footings

For each footing:

• Visible above grade
• Cracked or settling
• Post base hardware in place
• Footing diameter appears adequate

Step 8: Inspect decking surface

Walk the deck surface:

• Boards firmly attached
• No loose boards
• No splinters or sharp edges
• No visible rot or damage
• Consistent gap between boards
• Surface drains properly

Step 9: Inspect railings

For each railing section:

• Height (measure; should be 36 inches minimum)
• Picket spacing (4 inch sphere test)
• Post anchoring (test by pushing; should be solid)
• Bottom rail to deck gap (should be less than 4 inches)
• Top rail integrity (push on rail; should hold 200 lb test)

Step 10: Inspect stairs

For each set of stairs:

• Riser heights consistent
• Tread depth consistent (10 inch minimum)
• Stringer attachment to deck
• Stringer attachment at bottom
• Handrail present (for 4+ risers)
• Handrail grippable
• Lighting (if low light)

Step 11: Inspect fasteners

• Spot-check various fasteners
• Visible corrosion (especially below deck level)
• Loose fasteners
• Missing fasteners

Step 12: Code compliance review

Compare findings against current IRC:

• Ledger fastener type and spacing (R507.9, and the ledger fastener spacing table it points to; spacing is set by joist span, so read the table rather than defaulting to 16 in on center)
• Joist hangers and joist-to-ledger connections (R507)
• Beam sizing and beam-to-post connection (R507)
• Footing depth (R403, and the local frost depth, which governs)
• Guard height and opening limitations (R312)
• Stair construction, tread, riser, and handrail (R311.7)

Findings categories

Immediate safety concerns

Conditions that require immediate action:

• Failed ledger attachment (deck could collapse)
• Severely rotted structural members
• Loose railings
• Inadequate fasteners on critical connections
• Stair issues that could cause falls

These are reported as "immediate" with clear urgency.

Code violations (not immediately dangerous)

• Picket spacing slightly over 4 inches
• Bottom rail slightly over 4 inches
• Inadequate flashing
• Smaller code issues

These are reported as "should be addressed".

Maintenance items

• Surface refinishing needed
• Some loose boards
• Cosmetic damage
• Aged but functional fasteners

These are reported as "consider for ongoing maintenance".

Monitor items

• Slight settlement
• Minor cracking
• Adequate but aged components

These are reported as "monitor at next inspection".

Report writing

A complete inspection report includes:

Header

• Property address
• Date of inspection
• Inspector name and credentials
• Customer / client

Deck description

• Approximate size
• Material
• Estimated age
• Notable features

Findings by category

For each finding:

• Description
• Location
• Photograph
• Severity (immediate, near-term, monitor)
• Recommended action
• Estimated cost (if appropriate)

Recommendations

• Immediate actions
• Near-term actions (within 1-2 years)
• Monitoring schedule
• Annual inspection recommendation

Limitations

• Areas not inspected and why
• Conditions that limited inspection

Inspector certification

• Inspector name, signature, date
• Statement that report represents conditions at time of inspection

Common deck issues found

Common inspection mistakes

Skipping the underdeck inspection

The most important findings (ledger, joists, beams, footings) are below the deck. Skipping this misses major issues.

Inspecting the ledger from the outside only

You can see fastener heads from below and still miss the failure. What kills people is water behind the ledger rotting the band joist the bolts are anchored into. The bolts look fine because they are fine; the wood they pass through is not. Probe the band joist through any gap you can reach, and treat interior water staining on the wall behind the ledger as a finding in its own right.

Calling a lag bolt a through bolt

They are not the same connection and the difference is what the head is bearing on. Look for a nut and washer on the interior side. If you cannot see the inside face, say so in the limitations section rather than assuming.

Testing a guard with a hand instead of a shoulder

A guard that feels solid to a casual push routinely fails under real load. Lean into it at the top rail with body weight, at midspan and at every post, and do it from the deck side while standing clear of the edge.

Inspecting only the sound-looking wood

Rot hides at connections and end grain, not in the middle of a clear board. Probe every post base, every joist end at the hanger, the cut ends of the beam, the stair stringer where it meets grade, and anywhere two members trap water between them.

Not counting the hanger nails

A joist hanger with half its holes empty is not a joist hanger; it is a shelf. Count them, and check that they are joist-hanger nails rather than deck screws or roofing nails, which is the most common substitution.

Reporting condition without reporting load

An undersized beam or an overspanned joist passes a visual inspection all day. Measure the spans, count the members, and check them against the tables. The deck that has held for fifteen years has held under fifteen years of ordinary use, not under a full party.

Writing findings without photographs and locations

A finding the customer cannot locate is a finding they will not fix, and a finding you cannot locate a year later is one you cannot defend.

Leaving the urgency vague

If a deck should not be used, say that in plain words, in writing, at the visit, and tell the customer directly rather than leaving it in a report they will read next week.

References

• IRC R312 (Guards).
• IRC R311 (Stairs).
• IRC R403 (Footings).
• IRC R507 (Decks).
• North American Deck and Railing Association (NADRA) inspection standards.
• Manufacturer literature: Simpson Strong-Tie, USP.
• Manuall internal: Deck Building Ledger Board Attachment Per IRC, Deck Building Joist Hanger Selection, Deck Building Railing Height Code.