Air Ventilation Screens
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Ventilation is a Building Code requirement
Homes provided with insulation on the attic floor (directly on the top surface of the ceiling barrier (typically sheetrock a/k/a drywall or plaster) most building codes require soffit vents.
The standard code formula requires 1 square foot of net free ventilation area for every 300 square feet of attic floor area, assuming that 50% of the ventilation openings are located in the soffit, and 50% along the ridge.
If a roof has only soffit vents and no ridge vents, most codes require 1 square foot of net free ventilation area for every 150 square feet of attic floor area. The 'net free' ventilation area should take any restrictions into consideration such as louvers or the percent of open area allowed by the selected screen for the exclusion of insects or pests.
Note: Preliminary research has shown that the net free vent areas reported by many manufacturers is  exaggerated, as many fail to consider the loss of useable open area due to the addition of vent louver and insect screen air flow restrictions.
To obtain the best source of attic ventilation requirements and information may be to seek advise from a reputable attic repair specialist or roofing contractor having extensive experience working within your regional climatic area.
Crawl Space (below floor) Ventilation May soon become an obsolete requirement
Recently a new approach has been developed that has proven to be successful involving the removal of existing vent screens, followed by permanently sealing the openings to block air flow, moisture and insects.
After undergoing several trial installations. long term tests and numerous independent investigations the concept of completely sealing the below floor crawl space areas has proven to prevent moisture accumulation while reducing seasonal cooling and heating requirements. This new approach has demonstrated its effectiveness in eliminating the growth of mould which has long been attributed to moisture entrapment.
To obtain additional information search Google using the keyword phrase 'crawl space ventilation'  or more specifically  'crawl space vapor barrier'
Continuous Length Soffit Screens
The use of Continuous length vents provide the maximum amount of area that screening may be installed within.  The typical installation consists of a slotted opening located under the roof eave running along the entire length of roof.  The typical width is within the range of 2" wide upward to 4" in width.  The screening is fastened either directly to the bottom surface of the roof joists before the soffit panels are installed which allows the staples to be concealed by the soffit panels which results in a clean appearance. The alternate method involves stapling the screens on the bottom exposed surface of the soffit panels which are then trimmed by nailing thin firing strips that conceal the staples is covered (trimmed) with staples placed along the outside edges of the screening.
When selecting which type material to use, the local environment should be considered.
Costal applications, when screens are subjected to direct salt sprays  may contact the screen or salt air breezes (ocean air) are detectable, copper or copper based alloys such as brass or bronze should be the  first choice due to superior life expectancy. The use of Monel 400 (a nickel copper alloy) screens which are impervious to salt sprays salt air and many chemical environments are also worthy of consideration, especially when price is no object.
Commercially Pure Copper Vent Screens
Copper vent screens are best suited for ocean front applications subject to salt spray.  Copper is also frequently specified based solely on cosmetic appearance.
Copper Soffit Vent Screens
Data Sheet

Openings Per Linear Inch

Soffit Vent Screen Opening

Stainless Steel Wire Diameter

Open Area

Inches

M.M.

Inches

M.M.
PDS 4 0.203" 5.516 0.047" 1.194 65.9%
PDS 8 0.097" 2.464 0.028" 0.711 60.2%
Copper vent screens are custom slit to width according to customer requirements
Inland applications are somewhat less challenging than Costal applications although air pollutants such as acid rain or airborne chemicals should avoid using screen materials such as bronze, copper, nickel and galvanized.
Stainless Steel Vent Screens
Stainless Steel has some major advantages over Galvanized Steel as the life expectancy is much longer in addition to the benefits of superior strength and smooth surface condition.  When considering the labor required to replace a vent screen, stainless steel can be well worth the investment.
When larger pests such as rats, squirrels, bats, birds, raccoons and skunks are not considered a threat the standard duty stainless steel specifications listed below will provide insect exclusion down to 0.041".
Standard Duty Stainless Steel Soffit Vent Screens
Data Sheet

Openings Per Linear Inch

Soffit Vent Screen Opening

 Wire Diameter

Open Area
T-304 T-316

Inches

M.M.

Inches

M.M.
PDS PDS 14 x 14 0.062" 1.575 0.009" 0.229 76.4%
PDS PDS 16 x 16 0.053" 1.358 0.009" 0.229 73.3%
PDS PDS 18 x 18 0.046" 1.168 0.009" 0.229 70.2%
PDS PDS 18 x 14 0.046" x 0.062" 1.168 x 1.575 0.009" 0.229 73.2%
PDS PDS 20 x 20 0.041" 1.041 0.009" 0.229" 67.2%
Commercial and Industrial applications requiring a higher level of strength and security in addition to a much longer life expectancy should consider the specifications listed in the table below.
 Commercial and Industrial Grade Stainless Steel Soffit and Ground Vent Screens
Data Sheet

Openings Per Linear Inch

Soffit and Ground Vent Screen Opening

 Wire Diameter

Open Area
T-304 T-316

Inches

M.M.

Inches

M.M.
PDS PDS 4 x 4 0.215" 5.461 0.035" 0.889 74%
PDS PDS 6 x 6 0.138" 3.505 0.028" 0.711 69.2%
PDS PDS 8 x 8 0.108" 2.743 0.017" 0.431 74.6%
PDS PDS 8 x 8 0.105" 2.667 0.020" 0.508 70.6%
PDS PDS 8 x 8 0.100" 2.540 0.025" 0.635 64%
Galvanized Vent Screens
With a proven history of performance, Galvanized Soffit vent screen is a specification group utilized in many light commercial and residential building applications.
Galvanized vent screens usually last a minimum of ten years, up to a maximum of twenty years depending on the environment which they are exposed to.  The hot dip galvanized wire surface tends to be somewhat rough which causes dirt and grime to adhere and eventually build up to the point where considerable open area is lost, restricting air flow to the ventilated area.  Periodic cleaning with a soft brush will remove the surface buildup.

Many Soffit and Ground Vent Screen are difficult to access for maintenance or replacement, for superior service life, Stainless Steel soffit and/or ground vent screens often prove to be more cost effective.

Galvanized Soffit and Ground Vent Screens
Data Sheet

Wires Per Linear Inch

Screen Opening

Gauge

Wire Diameter After Galvanizing

Open Area

 Stock Roll Widths

Inches

M.M.

#

Inches

M.M.

 Also Available In Custom Widths
PDS

4 Mesh

0.224"

5.69

23

0.0258"

0.66

80.4%

 2.5" 2.75" 3" 4" 6" 8"
PDS

8 Mesh

0.108"

2.74

27

0.0173"

0.44

74.2%

 - - 3" 4" 6" 8"
 
As you will note in the table above, the standard galvanized soffit vent bug screen  specifications include two aperture choices, 0.224" and 0.108".  Either opening will exclude rodents, birds and squirrels but neither can prevent insect entry.  For smaller insect level exclusion, standard galvanized screen can be applied inside the primary vent screen, however the addition of the second smaller aperture screen will cause a slight reduction of the useable open area. Any reduction of open area should be avoided without the advice of your architect or builder.
To access additional information we suggest you visit the links shown below:

Residential Ventilation by Joseph Laquatra

To view our complete list of Insect Screen specifications , click here
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Last modified: April 11, 2017