Learn how a sagging roof can be a danger to home owners.

Sagging roof danger and economical means of rectification. QBIS.

Considerable sagging to corner of roof (hip) due to insufficient support to part of the roof structure.


Inadequate support below a roof structure.

Props supporting this under-purlin (horizontal timber member, between the props) are too widely spaced the purlin is also undersize.

How to fix.

This can be rectified by fitting addition props for support where the purlin span is too wide, provided the props are supported off an internal wall or an appropriate size roof beam.

Sagging roof danger. What you need to know about roof construction to ensure safety.

  • Purlins must be supported off internal walls, not ceiling joists otherwise collapse can happen.
  • Alternatively a strut may be fitted, with support off top of the external wall and propped off another nearby wall, if close by.
  • A product known as a Barap Bolt can also be used.


Poor method of roof construction causing considerable sagging of ceiling joists.

How to fix:

  • Temporary props to lift and straighten the ceiling from below.
  • A webbed truss or laminated beam would be required with hangers down to the ceiling joists for their support.
  • Ceiling battens and linings may also require resecuring if also sagging.


Weight of roof tiles is causing sagging of roof and beam to tilt presenting a potential danger of collapsing. 

  • Beam requires blocking or bracing to avoid further tilting.
  • The roof structure requires straightening and restructuring.

This is a common problem with buildings around the 1940’s to 1980’s. “They don’t build them like they used too”

Economical alternative to the expense of having a roof restructured

It would be worth considering replacing the roof tiles with metal sheeting.


  • New roof.
  • Choose color.
  • Metal sheeting has far fewer joints therefore is less likely to leak.
  • Offers the opportunity of fitting insulation below the roof sheeting.
  • Would not require restructuring.
  • In some cases, cheaper than restructuring.

Disadvantages of metal roof sheeting as opposed to tiled roof.

  • Noisy in heavy rain.
  • Although more prone to being damaged from hail, unlike like tiles it is not likely to leak because of hail damage.
  • Requires more securing of structure to avoid uplift in a storm.

Related information to sagging roofs.

QBIS: Roof components and location

Roof Technical Information

Tafe: Building terminology

QBIS: Barap Bolt roof supports

For independent Building Inspections Brisbane in all suburbs, Qld Home Buyers Inspection Service. qbis.com.au