We took down the triple wall chimney recently during a rebuild and I decided that the old chimney cap had to go. It never really worked right being that it was square and, of course the chimney was round. (See photos.) Replacement chimney caps can be quite costly, running into the hundreds of dollars. Even more considering I wanted it to work with the already installed 18 inch wide storm collar. My budget was a maximum $50-$75.

Due to the restrictive budget, I decided to build something myself and though the design process took me several months, the end product looks very much like my original design. To begin, I had to make this with nuts and bolts as I didn't own a welder. My budget also forced me to create with ready available materials (nothing special order.) When the idea hit me to use ready made galvanized garbage can lids, the thing sort of designed itself.

The standard garbage can metal is 28 gauge, and a quick check in with some engineers said that this should be sufficient to repel rain and hold as much as 3-6 inches of snow.

The materials list:

2 Galvanized Steel Trash Can Lids (21" size)
5 lengths of galvanized steel, 36" x 3/4" x 1/8"
28 bolts, 1-1/2" x 3/8"
24 nuts 3/8"
4 Spring clip nuts
1 roll of 19 gauge 1/2" hardware cloth
High Temp Putty
Thread Lock Liquid
Paint and Primer

Before things get started, I took time to research the code required for a chimney cap for my area. The code stated a 5/8" opening or smaller, which is why I went with this hardware cloth. If you plan on trying this for your house, I recommend taking the time to check this for your exact area beforehand. I make no claims as to whether this is any particular class covered in any area.

Step 1: Cutting the Lids

The first thing I did was to cut the handles off both lids. I then covered the resulting holes in one lid using the high temp putty. It smooths down with a touch of water so that it's very thin. A bit of putty on the underside assures a permanent fit. This lid is set aside to dry.

The 2nd lid is cut using an angle grinder. I made two cuts creating 3 pieces. The center piece will not be used, and the resulting hole is 9" across, to match the size of the center flue of my triple wall chimney.The 2nd cut is made 1-1/2" from the outside edge, leaving an 18" cut out. This creates the base of the cap, as well as an inner ring. The circular center ring will be used later.

Using a 3/8" bit, holes are cut uniformly around both lids on the outer edge. The circumference of the lids was exactly 65" so the holes ended up being 8-1/8 inches apart.

Step 2: Cuts, Struts and Crossbucks

The galvanized struts are cut to the following lengths:

4 pieces 12 inches long

8 pieces 9 inches long

4 pieces 3 inches long

4 pieces 2 inches long

All of the pieces are drilled 3/8" from each end with a 3/8" bit.

4 of the 3 inch pieces are given a slight 15 degree bend 1" from one end. The angle is designed to match the angle of the rise of the center ring. These pieces will support the center ring across the bottom of the chimney cap creating a secondary rain shield.

4 of the 2 inch pieces are given a 90 degree bend.

8 of the 9 inch pieces are given a slight bend of 10-15 degrees on the ends to match the flare of the outer edge of the lid and base.

The 4 struts that are 12 inches long are given a gentle curve as they will run form the crossbucks which will keep the unit from helixing over time. The curve is slightly wider than the curve of the lid itself.

Lastly, the hardware cloth is cut to give a piece 65" x 9" and set aside.

Step 3: Prepare Storm Collar

The storm collar is prepared by first cleaning off the old paint. Then 4 holes are cut into it which will allow the chimney cap to be attached and removed easily for cleaning. Location of the holes from the edge is determined by the spring clip nuts. The 4 spring nuts are spaced evenly around the outside of the storm collar.

The 4 brackets bent to 90 degrees are test mounted to the spring nuts.

As much as I would like to trust my measurements and know that if (when) the chimney cap is removed for cleaning or painting, that the 4 brackets will match up easily when it is put back, there is the possibility that it could be off by enough to cause problems. So, each hole is given a number designation and the hole is marked with a set of dimples on both the collar and the base of the cap.

Step 4: Assemble - Temporary

Now is a good time to check all the struts and crossbucks for measurement size. The entire thing is assembled finger tight. In this way, adjustments can be made easily.

Step 5: Prime and Paint

The parts are laid out and primed. It is important again to note that though the parts are all made of galvanized steel, the cuts are not galvanized and could rust; so a good coating or two of primer and paint is important.

Once the primer has dried, the parts are painted with the finished color (in this case, a finish called 'hammered copper.') While the parts dry, the storm collar is painted to match. Then the primed pieces are painted with the copper color.

The secondary rain shield is only colored on top, as the color is not needed on the unseen underside, so an extra coat of primer is applied there.

Step 6: Full Assembly

The parts can now be assembled (again, only finger tight) along with the hardware cloth. The hardware cloth length should be trimmed so that only an inch or so overlaps behind one of the struts.

Once fully assembled, the hardware cloth is painted to match

A final step is to remove each bolt, one at a time and apply threadlock. (I used Loctite Blue 242) Then the bolts can be tightened using two socket wrenches. The bolts for the 90 degree mounting brackets on the bottom of the chimney can be removed to attach the secondary rain shield.

The same bolts which hold the 90 degree mounting brackets will hold the straight brackets to support the secondary rain cap. The end of the bracket with the slight bend is attached to the base of the chimney cap. Use threadlock to finalize this install. The secondary rain shield rests on top of the 4 three inch brackets and is bolted into place. Apply threadlock and tighten all bolts in the secondary rain shield.

Note: the secondary rain shield rises up in the center adn therefore the rise should be to the center of the cap. Rain that makes it into the chimney cap and lands on the secondary rain shield will run AWAY from center of the chimney.

Step 7: A Final Look

Here is he finished piece attached to the storm collar, ready for installation when the chimney is installed. Here is also a shot of the secondary rain shield from below and a close up of the rain shield inside the chimney cap.

I have now added the final picture of the chimney cap installed. It has rained a couple of times and the rain runs off the cap beautifully (though, to be honest, I did not go up on the roof in the rain to check this out.)