The NCRB and Standards Australia describes “deformation” as a shape of structural member or structure, resulting from the applications of load(s). In addition to deflection includes any plastic, non-recoverable movement.

Often the change will not be noticeable, but result in trivial defects and in some cases in defects of appreciable magnitude.

Roof framing and roofing.


Movement of the roof is commonly caused by the roof not adequately resisting wind uplift forces. Often the roofing is not adequately secured to the roof framing or the roof structure to the wall structure.


Distorting of flat roof decks is caused by condensation. The condensed water can wet ceiling joist in contact with the deck, increasing the risk of fungal decay. It can also drip, damaging the ceiling below or wetting electrical cables.

Widespread sagging

Sagging of a pitched roof will be visible where roof coverings have dished, and ridge lines are bowed over strutting points. Deforming will commonly result from: initial poor design; increase in roof covering loading; corrosion of fixings; long term loading, lack of support; or timber damage.

Localised sagging

Sagging of the roof at the eaves is often caused by excessive cutting (birdsmouth jointing) of rafters or sagging of the roof in the vicinity of services is often caused by excessive cutting and removal of framing members for the installation of services, especially plumbing vents and flues.

Wall structure:

Framed and masonry construction

Vertical bowing and horizontal bending or even collapse of walls. Deformation is caused by the wall not resisting vertical pressure from foundations or upper floors and roofs, and horizontal pressure from strong winds and retaining earth.

Suspended concrete slabs.

Excessive deflection: A reinforced suspended concrete floor ma deflect production side- effects such as failing to continue to provide support for walls build on them. In such cases a horizontal crack may often be found at the base of the wall, though it may be covered by skirting board. Deflection in suspended concrete floors will most commonly result from one or more of the following reasons; initial poor design; substandard workmanship and practice; drying shrinkage; or the floor loading exceeding the design loading.

Suspended timber ground floors

Sagging or springiness of the floor underfoot Deformation will most commonly result from one or more of the following reasons: under- design or floor framing members; insufficient structural support; defective timber connectors or fastening methods; poor workmanship; overloading; or timber pest damage