This week we had another inspection on a house that has been re-roofed:
Changing from galvanised iron to Zincalume, the “upgrade” is a whole transmutation from a simple roof structure to one that involves elementary structural forces on the entire building. The inspected home is a timber framed weatherboard cottage built in the early 1920’s that had a corrugated iron roof nailed to a sparse hardwood timber frame. While the roof has provided adequate cover for over 90 years the change of covering and method of fixing has altered the nature of the building to such an extent that it has become structurally unsound.
The original galvanised roof sheeting has been replaced with the current Zincalume roof but no work to the roof frame has been carried out to compensate for the change in characteristics of performance under storm conditions. The original roof would have been nailed to the framing whereby individual sheets could loosen and relieve variance in air pressure between the internal and external areas of the roof covering. The current roof is now screwed together making one cohesive sheet. No tie down restraint strapping between the roof and wall structures has been implemented to comply with the requirements [when completely renewing roof coverings the roof framing needs to be brought up-to current Austrsilian Standards and Buiding Codes] for securing this type of structure. The roof frame is well below the required specification for sheet roofing with rafters being over span and over spacing. Battens for securing the roof sheeting are also spaced too far apart and are not correctly secured to the rafters. The roof frame structure and its fixing methods although suitable at time of the building construction (1920’s) no longer met the Australian Standard’s and Building Codes applicable at the time of the roof being re-covered. When having roofs recovered [sheet metal] it is essential that the roof frame structure, [and any additional framing and restraint strapping required], is installed and secured ensuring that the finished structure and installation meets the Standards and Codes applicable at the time of the works.
While it will, no doubt, be argued that the cottage has stood for all its life without failure the building has been so fundamentally altered that there is now a real risk of total collapse if cyclonic force winds are applied.
The original hardwood frame was constructed with green sawn timber that has dried and shrunk, the drying and movement has caused nails to loosen, and stud framing housed into notched wall plates (top and bottom members of the wall frame) are now also loose. All that is holding the wall frame together is the weatherboard outer cladding and internal wall boarding – both very aged.
If you have any concerns about the condition of your property then speak to a Housecalls team member; [email protected] or 0418 902 240