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Some degree of ventilation is always a good idea when designing architectural metal panel systems.  The exchange of air on the back side of panels will reduce the risk of corrosion propagated by trapped moisture vapors.  While stainless steel and titanium are quite forgiving in this regard, zinc is not.

    Zinc panel systems must be sufficiently ventilated so as to prevent the collection of moisture on the interior surface of the material, and thereby prevent premature failure.  Many factors govern the amount of free air space required, including: 
 

• Roof Slope

The higher the pitch, the greater the air flow.  Therefore, less free air space is required.  Free air space is defined as the amount of clearance between the metal panels and the vapor barrier.  Guidelines for free air space appear in Table 1.

Ventilation Guidelines

                         
                             Table 1

• Complexity of the Roof Design

If there are a number of different planes that intersect, creating a complex multi-faceted roof design, the individual panel sets of each planar section need to be analyzed for required ventilation.  Provided each section flows freely to a higher point and the ultimate air exhausts are of sufficient size to balance with the air intakes depending on them, there will be no problem.  Difficulties occur when joining details inhibit airflow at the junctions of different roof sections. 
 

• Air Inlets & Outlets

Air inlets should be installed at the lowest point in the panel system and outlets should be placed at the highest.  Ridge vents are quite suitable.  Ventilation caps are also appropriate.  These openings should be as evenly spaced as possible, ideally integral to each panel, as is the case with a ridge vent.  The percent open area of the ventilators should be 50% of the cross sectional area of the free air space prescribed.  If a panel is 24" wide and requires 3" of free air space, the area of the cross section is 24" x 3", or 72 sq. in.  Therefore, 36 sq. in. of open area needs to be provided at each opening (air inlet and air outlet).

• Degree of Insulation

Our recommended clearances for free air space assume the building is insulated with a vapor barrier in place.  Care must be taken to avoid direct contact of bituminous material with zinc.  If there is a limited degree of insulation that will allow the air in the ventilation space to heat up, or if moisture from the interior of the building is free to migrate to the free air space, substantially more clearance is required.

• Climate

The guidelines we have discussed thus far relate to temperate mesothermal climates with moderate relative humidity.  Air space clearances must be increased substantially in tropical climates and may be relaxed in arid ones. 

     At this point, if you are designing a zinc panel system, you may have quite a few questions regarding the proper amount of free air space for your project.  Since the aforementioned factors all contribute to moisture conditions, it is difficult to create a set of standards to cover every unique situation.  We recommend that you contact us to address any concerns about your application.

     If the material in this section has you on the verge of looking for a less mettlesome metal, do not be discouraged.  These special ventilation requirements can be ignored if back-coated material (see PRODUCTS - ZINC PRODUCTS - InvariTique^TM With Back Coat ) is used.  However, we do recommend a nominal amount of ventilation.