A reader's Roofs and roofing question: Roof ventilator?

Rita B.   from   Townsville, Australia   had this Roof ventilator question.

Hi Bill
My husband is a plumber. He has been asked by a couple who are renovating an old Queenslander to install an old fashioned roof ventilator on the home.
It was made by a company in Brisbane and is identical to the type of ventilator that used to be installed on these old homes.
We can find lots of photos and history about them but no instructions on how they were attached to the roof. Do you have any info that might help us? Thanks

Bill's reply

Hi Rita,
The old long ridge ventilators were fixed by mild steel brackets bolted to the top of each rafter. The brackets were made out of about 8 x 20mm flat steel bent to the roof pitch. The ventilator was bolted to the bracket with gutter bolts. The purlins were cut around them, or the bracket had a half twist in it so that the thing could be bolted to the side of each rafter.

If it is a standard vent with all the parts pre made he should be OK.
I once had to alter an architect designed one because even though it was normally fully waterproof, in high winds a venturi type effect started sucking water into the building.
So if he has to make up his own brackets, don't make them to high.

If it is not a long ridge vent, but more like a whirlybird or kitchen extractor type hood then it is more a case of maybe making something up or adding timber support between rafters etc.

To give you a better idea you would have to send me a photo or sketch of what the roof and the ventilator looks like.

Cheers Bill.