Look out over any Duro-Last roof and you will see many white cylinders dotting the rooftop.  These tiny towers are a signature part of every Duro-Last roof.  You may ask yourself, “Why does Duro-Last require vents to be installed on their roofs?” In this blog we will explore the theory of operation of the two way vent and how it benefits those who select Duro-Last to protect their biggest investments.



Reason 1: Pressure Equalization

The majority of Duro-Last roofs are mechanically fastened the roof deck. This leaves a tiny air gap between the membrane and the insulation or decking.

When wind rushes over the edge of a building, it creates vortexes of wind, like mini tornadoes.  These wind vortices cause pockets of low pressure to develop above the roof surface.  The air inside the roof system has a higher pressure relative to the air above the roof when the wind is blowing. The air wants to equalize the pressure but Duro-Last is air tight as well as water tight.  So the pressure differential causes the ballooning of the Duro-Last. Ballooning stresses the membrane causing it to stretch and wear more quickly.

Wind Over Parapet-01

Wind Vortices Cause Membrane “Ballooning”


Duro-Last has cleverly designed a solution to this problem by designing a two-way roof vent.  The vent allows the air to escape out of the Duro-Last during pressure changes.  It literally sucks the air out from under the roof membrane causing it to stick tight to the underlayment.

Wind Over Parapet with Vent-01

Vents Allow Pressure to Equalize


Reason 2: Moisture Control

Duro-Last is often used as a re-cover roofing solution. That is to say, it is installed directly over top of an existing roof.  If there is any moisture trapped in the existing roof system, it will condensate on a cool surface.  At night, the membrane will act as that cool surface and will collect moisture.  This can cause mold, mildew, and premature degradation of the underlayment and fasteners. The two-way vent allows for that moisture to escape the roof system without causing lasting damage.

Wind Over Parapet with Vent and Moisture-01

Vents Prevent Moisture Related Damage

Real-World Performance

Duro-Last has put a lot of thought into the design of their two-way vents. It has paid big dividends in real world performance of their products. Below are two case studies describing how Duro-Last Roofing survived direct hits by tornadoes and survived!


Pierce City, MO


Indianapolis, IN

To find out if a Duro-Last PVC roof is right for you, Contact Jewett Roofing Today!

Jewett Commercial Roofing Contractor