Why Sheds Fail

1. Connection Failure

The #1 cause of shed failure. The individual members (columns, rafters, purlins) are usually strong enough, but the connections between them are the weakest link. Under-designed connections fail before the members reach their capacity.

Common connection failures:

• Base plate uplift — holding-down bolts too few, too small, or not embedded deep enough in the footing. Wind uplift pulls the column out of the ground.
• Knee connection — the column-to-rafter joint is under-bolted or the gusset plate is too thin. The frame opens up under wind load.
• Purlin-to-rafter connection — tek screws or clips can't resist the uplift. Purlins lift off the rafters, taking the roof sheeting with them.
• Apex connection — the ridge joint fails, allowing the two rafter halves to separate.
• Bracing connections — bracing gusset plates tear or bracing rods/straps snap, allowing the shed to rack and collapse.

2. Inadequate Bracing

Bracing prevents the shed from racking (leaning sideways like a parallelogram). Without adequate bracing, even moderate wind loads cause progressive lateral displacement until the shed collapses.

• No bracing installed — surprisingly common in DIY and unengineered sheds
• Bracing in one direction only — sheds need bracing in both the portal direction and the longitudinal direction
• Tension-only bracing with no capacity — light strap bracing that stretches or snaps under design loads
• Bracing removed for access — owners remove bracing to fit equipment through, not realising it's structural

3. Foundation Failure

The shed frame transfers all forces to the footings. If the footings can't resist these forces:

• Uplift — footings not deep or heavy enough to resist wind uplift. The column pulls out of the ground.
• Bearing failure — the footing is too small for the soil's bearing capacity. It sinks into the ground.
• Sliding — horizontal wind forces push the shed sideways along the ground surface.
• Reactive clay movement — footing depth insufficient for the soil's reactivity, causing differential movement that distorts the frame.

4. No Engineering

Sheds built without engineering are essentially guesswork. The builder estimates member sizes, bolt numbers, and footing depths based on experience rather than calculation. This might work for small, sheltered sheds in benign conditions. But for any shed of significant size, in exposed locations, or with openings, the forces are simply too complex to estimate.

5. Construction Defects

• Missing bolts — bolts left out because they were hard to install
• Wrong bolt grade — Grade 4.6 used where Grade 8.8 was specified (half the strength)
• Holding-down bolts misaligned — bolts cast in wrong position, column can't be properly secured
• Under-compacted backfill — loose soil around pier footings reduces uplift resistance
• Insufficient concrete cover — reinforcement too close to surface, corrosion accelerated

6. Material Deterioration

• Corrosion — unprotected or damaged galvanised coatings allow rust, reducing member capacity over time. Particularly aggressive in coastal, industrial, and high-humidity environments.
• Roof sheeting fatigue — repeated wind cycling loosens tek screw connections, eventually pulling through the sheeting.
• Timber decay — in older timber-framed sheds, rot and termite damage progressively weaken members.

Frequently Asked Questions