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Frequently Asked Questions
What is the trade running through all of these?
Protection against free area.
Every screen and baffle removes opening.
Fine insect mesh removes a great deal.
The ventilator still looks the same size.
Size the opening for the screened free area.
Nominal dimensions mislead badly here.
Why is fine mesh worse than a coarse screen?
It blocks far faster.
Dust, seeds and nesting material catch in it.
A blocked screen removes free area entirely.
The ventilator looks normal from the ground.
Nothing indicates the loss.
Use fine mesh only where insects must be excluded.
When are weather baffles necessary?
On exposed and high-rainfall sites.
They exclude driving rain and snow.
They cost free area like any obstruction.
Sheltered positions often manage without.
Snow ingress is the case people underestimate.
Specify for the actual exposure.
What do dampers add?
Control over a permanently open hole.
Winter heat loss through it can be significant.
Manual, thermal and motorised options exist.
Motorised versions link to a control system.
They add cost and a maintenance item.
Fit them where winter loss justifies it.
Why do dampers fail?
Because they are never operated.
A damper left in one position seizes.
Roof exposure accelerates it.
It then cannot close when wanted.
Exercise them on a schedule.
Annual operation is usually enough.
What does the curb or upstand do?
Raises the ventilator above the roof finish.
The covering turns up against it.
That keeps water out of the opening.
Height follows the roofing system.
It is the same requirement as any roof equipment.
Coordinate with the roofing contractor.
What inspection do these need?
An annual look from the roof.
Check screens for blockage and nesting.
Check baffles for corrosion and distortion.
Operate any dampers fitted.
Confirm fixings and flashing are sound.
Most failures are visible and cheap to correct.