Everything you need to know to construct a stationary rooftop louver.

Figure 1
Louvers come in all different shapes and sizes, and are used for many different applications. One very common example in the HVAC and roofing industries is the stationary louver.

Used primarily for ventilation, its only function is to allow air to pass through, while not allowing water in. It's called a "stationary" louver because all the blades are in a fixed position.

As shown in Figure 1 and Figure 2, the way the individual louvers are constructed and placed within the frame keeps the water out. The individual louver blades are fastened to the frame at a 45-degree angle and as shown in Figure 2, the bottom of the blade (A) overlaps the top of the louver blade directly below itself (B).

Note when looking at Figure 2, the profile of the louver, it is important to add and bend the additional material to the top and bottom of the louver because the additional three-eighths-inch bend, with the one-eighths-inch return on the top and bottom, will serve as a stiffener. More importantly, the top profile will keep water from migrating up the louver and inside, which sometimes happens in driving rains (shown by the blue arrows).

Figure 2


There are many different types of screens and methods for attaching them to keep insects and other animals from entering through the louver blades. The louver in this article uses a clinch edge, built on the frame for holding the screen in place. This louver is for natural transfer of combustion air or cross ventilation. It is not intended for fan-assisted makeup air or exhaust, which may have different considerations.

Start laying out the louver by developing the sides and then the top and bottom pieces. This will give you the necessary information for the individual louver blades. All four sides of the frame will be laid out for the use of the clinch method in attaching or fastening the screen.

Start by determining the total width of the louver as it is shown in Figure 3. The shaded area in Figure 3 represents two 1-inch parallel vertical lines that when folded becomes a clinch connection. Beyond this shaded area is the actual part of the louver that is placed into the opening; the width is labeled "X."

Draw another vertical line 2 inches from the clinch edge line, shown as the shaded area. The 2-inch measurement comes from the spacing of the louvers. The distance from Point A to Point C is 2 inches, as is Line CE and the rest of the louvers. If you space the louvers 3 inches apart, then the distance of the vertical line would change to 3 inches from the edge.

At Point A, draw a line at 45 degrees until you intersect the vertical line established 2 inches from the clinch edge. Where the line intersects at Point B, draw a line horizontal to Point C, perpendicular to the clinch edge, as shown. Repeat this and draw a 45-degree line starting at Point C to where it intersects at Point D, and again draw a horizontal line connecting Point E, perpendicular to the clinch edge.

Figure 3


Repeat these steps until you have reached the top. These lines have established the edge where each louver will meet the side of the frame. On each end of the louver, there is a half-inch 90-degree bend. If you are using pop rivets to attach these louvers, you can pre-drill the holes in the side of the frame, as shown in Figure 3, by making reference marks one-fourth-inch parallel to the Line AB, shown as A1 to B1, C1 to D1, etc.

Figure 4

Reference marks

Once all the reference marks have been made, the holes need to be established. Take one of the reference lines, as shown in Figure 3, and mark off from the edge of the line - the edge of the center line on the louver - for the placement of the holes. Draw two vertical lines parallel to the face of the frame as shown in points 1A and 2A. Where they intersect the 45-degree reference line (shown in red), drill the hole for the pop rivet. Carefully lay out the bottom and top part of the frame as both described in Figure 4.

Figure 5

The last step

Making the louver is the last step before assembly. Lay out each louver as shown in Figure 5, noting the 45-degree notch in the corners of each half-tab. Once you have this drawn out and cut as shown, refer back to Figure 2 for the profile on how they should be folded. The holes are marked as they were in the sidepiece shown in Figure 3. The top louver blade may have to be adjusted in length, depending on the separation between each louver blade and the size of the louver frame.

All louver frames must be made watertight by solder or weld. The louver blades can be attached by pop rivets as described in this article, but soldering, welding or even spot-welding are frequently used. The minimum gauge that should be used in louver blade and frame construction is 24-gauge galvanized steel for widths up to 24 inches. Where the louver blades are greater then 36 inches wide, a one-eighth-inch by 1-inch-wide bar should be attached to stiffen the louver blades.

(For more information on manual sheet metal layout, write to The Sheet Metal Shop Resource Center, 516 Chicago Ave., Waukesha, WI 53188, or visit www.thesheetmetalshop.com.)