Library

The ABIS library is a collection of useful reference material relating to buildings and their problems as well as timber pests such as termites.

The library is a combination of material written by ABIS as a result of our own research and practical experience together with useful information gleaned from other authorative sources.

 

Deformation

Thu, 16/04/2009 - 11:29

Deformation of Roof Structures

Pitched Roofs

Widespread sagging is visible where roof coverings have dished and ridge lines are bowed over strutting points commonly resulting from:

  • Poor design with under-design of roofing members sizing, spacing and support
  • Overloading the roof framing e.g. replacing corrugated iron by terracotta tiles
  • Corrosion of roof fixings where water has penetrated the roof covering or where nails and plate connections are subjected to an aggressive salt environment near the coast
  • Inadequate or incorrect support of roof trusses
  • Timber pest damage with weakened structural timbers unable to support normal roof loading

Around Eaves

Symptoms in the form of localized sagging around the eaves, resulting from excessive cutting of rafters to fit over wall plates or excessive cutting or removal of roof framing members for installation of services.

Flat Sheet Metal Roofs

Distortion and lifting resulting from failure of galvanized roofing nails with movement of the sheeting caused by wind pressure or uplift, or deterioration of the fixing battens from timber pest attack.

Deformation of Wall Structures

Vertical bowing and horizontal bending or even collapse of walls is caused lack of resistance to vertical pressures from foundations upper floors or roofs or horizontal pressures from strong winds and retained earth.

Framed Construction

  • Under-design of wall framing through use of under-sized or under-specified structural timbers
  • Overloading the wall
  • Foundation movement with failure of walling, piers and stumps or posts to bearer level due to differential movements of supports on expansive soils or foundation failure
  • Wind damage
  • Timber pest damage with weakened structural timbers unable to support normal loading
  • Poor workmanship with excessive cutting or removal of wall framing timbers for services

Masonry Construction

  • Poor design with insufficient wall thickness for height of wall or under-design of footings
  • Overloading
  • Foundation movement
  • Inadequate engaged pier stiffness resulting in low resistance to bending and buckling of long unsupported lengths of walling
  • Corrosion where rusting wall ties in coastal areas cause the wall to bow and become unstable

Masonry Retaining Walls

Cracking and horizontal movement with inadequate resistance to lateral loads due to:

  • Initial poor design
  • Untradesmanlike workmanship and use of substandard materials
  • Forces not accommodated for by design
  • Lack of maintenance

Deformation of Floor Structures

Suspended Concrete Floor Slabs

Horizontal cracking at the base of the wall results from:

  • Initial poor design
  • Untradesmanlike workmanship where the slab is stripped too quickly or overloaded during building
  • Drying shrinkage
  • Floor loading exceeding the design loadings

Timber Ground Floors

Sagging or springiness of floors underfoot is commonly due to:

  • Under-design of floor framing members with under-sized or under-specified bearers and joists
  • Insufficient support with inadequate spacing of walling piers or stumps or posts to bearer level
  • Defective timber connectors or fastenings including insufficient blocking
  • Untradesmanlike workmanship with excessive notching of floor framing for service installation
  • Overloading
  • Timber pest damage causing structural timbers to become too weak to support normal loading.

Timber Upper Floors

Sagging or springiness of the floor or even cracking of the ceiling due to:

  • Under-design of floor framing members
  • Untradesmanlike workmanship
  • Defective timber connectors or fastenings
  • Overloading
  • Timber pest damage

Stairways

Defective treads and landings, loose newel posts, handrails and balustrades or stairway instability and collapse frequently result from:

  • Poor design
  • Untradesmanlike workmanship and substandard materials
  • Timber pest damage
  • Defective timber connectors and fastenings and metal corrosion
more