Common site errors
The nature of the faults
Section titled “The nature of the faults”They are not spectacular, they cause no immediate problem, and they disappear behind the lining. That is what makes them dangerous: the consequence emerges years later or under an extreme load.
The typical faults
Section titled “The typical faults”Wider or omitted screw fixing
Section titled “Wider or omitted screw fixing”The screw pattern is a designed value. Opened up on a “that will do” basis, the capacity of the connection falls proportionally. Self-drilling screw connections.
Missing bracing
Section titled “Missing bracing”An omitted strap or a diagonal not pulled taut weakens the bracing system. Bracing with steel straps.
Missing hold-downs
Section titled “Missing hold-downs”The uplift component at the end of a shear wall is small and cheap — which is why it is often left out. Hold-down anchorage.
Members of the wrong thickness
Section titled “Members of the wrong thickness”With mixed material thicknesses the marking is structural information. A swapped member looks no different. Marking and assembly logic.
A punctured vapour control layer
Section titled “A punctured vapour control layer”A cable, a socket box, a fixing — every puncture is a point where moisture collects. The principle of vapour control.
Omitted cavity barriers
Section titled “Omitted cavity barriers”A cheap, small component that cannot be added afterwards. Cavity barriers.
Substituted lining
Section titled “Substituted lining”If the lining has a bracing role, substituting it changes the structure. Sheathing diaphragm.
Tolerances not taken up
Section titled “Tolerances not taken up”A panel forced onto an inaccurate base loads the connections.
Why they happen
Section titled “Why they happen”Rarely out of ill will. Typically because:
- the contractor does not know that a given member has a structural role,
- the drawings do not say so unambiguously,
- or the situation on site forces improvisation with nobody to ask.
How to prevent them
Section titled “How to prevent them”- Unambiguous drawings: mark the screw pattern, the bracing and the anchorage.
- A short, practical briefing for the erectors on day one.
- Inspection before covering, with a record.
- An available designer: if there is a question, somebody to ask.
The point
Section titled “The point”Concealed faults are the most dangerous, because there is no feedback. Prevention is cheap: unambiguous drawings and one inspection before the lining goes on.