Half-Round Copper Gutter Installation Guidelines
BY DON MILLER, THE COPPERWORKS OF DON MILLER
as written for Slate Roof Quarterly Magazine

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Following are a few of the installation guidelines for installation of half-round copper raingutters, which are available in an expanded form from the INSTALLATION INSTRUCTION BOOKLET by The Copperworks of Don Miller. (877) 633-9308.
Most contractors size rain gutters and downspouts based on intuition and experience of what works or doesn't work in a particular region. However, if you want some solid numbers to follow, use the formulas found in the ARCHITECTURAL SHEET METAL MANUAL (ASMM) published by S.M.A.C.N.A., 4201 Lafayette Center Drive, Chantilly, VA (703) 803-2989.
One of the first considerations in raingutter planning is downspout placement, which is largely an esthetic consideration.
In any given desired downsput location there is a good chance that the location will work for the following reasons:
A. The roofline may be sloping towards the downspout - Good.
B. The roofline may be level towards the downspout - OK perhaps.
C. The roofline might be sloping away from the downspout location, but perhaps the region is hot and dry, so that any standing water will dry fast, and maybe the roof area drained is small.
D. The roofline might be sloping away from the downspout location, but there is enough space on the facia and esthetic considerations make sloping the gutter downward in relation to the roofline acceptable, or if the raingutter is large enough, it might be possible to solder a second bottom into the raingutter to force the flow towards the downspout.
The option of soldering a second bottom into the gutter to induce flow is easy to provide in a half-round gutter. First fill the low area with water. Using a grease pencil, draw the outline of the edge of the water. Drill 1/4" holes in the bottom of the gutter to drain the water from the gutter and every three feet to ventilate the cavity that will be created. Measure the width between the grease lines on each side of the gutter for every six inches of the length of the double bottomed area. Cut out pieces of copper using the width measurements obtained. Solder the pieces in.
Although having a little pitch to the gutter might slightly reduce the buildup of dirt and ice, this is often not practical or necessary, as it is only essential that the gutter be able to dry out in a day or so to reduce corrosion and to prevent the breeding of mosquitoes. In a galvanized steel gutter, keeping the gutter dry is key to its longevity, although in a copper gutter, dryness is not too critical in its longevity.
A rule of thumb for expansion of copper gutter (in relation to the expansion rate of the structure) is 1/8" per ten feet of copper per 100°F temperature change. The raingutter and its fastening systems must be able to allow for its rate of expansion and contraction. This is a critical consideration where the gutter is going around or butting into corners. Be sure to allow for expansion seams where necessary as per the ASMM. Cast bronze facia brackets are ornamental, exceedingly strong, and allow for a great deal of gutter expansion.
Copper is at the top of the galvanic scale. Other metals such as steel, aluminum or zinc will corrode more quickly when in contact with copper or the flow from a copper pipe. The copper will not be harmed by these other metals. Compatible metals for copper are most bronzes and brasses, and some some alloys of stainless steel. If the copper is contacting a very thick piece of steel or iron in a dry location, the effect on the steel or iron may be negligible. If the surface of the other metal is large and the surface of the copper is small, the effect on the other metal may be negligible. If a copper gutter is being slipped behind a steel flashing, separate the metals electrically and maybe the flashing will be OK until it is time to reroof. If a large surface of copper is contacting a small surface of the other metal, or if water drops from a copper surface onto the surface of another metal, the other metal may not last long.
Copper gutter seams should be riveted on 1-1/2" centers and soldered. Soldered seams without rivets over time can crack, especially where exposed to the expansion forces of two long lengths of gutter. If fascia mount gutter brackets are used, then any seams may be placed behind the brackets through a little advance planning. Care should be taken that the pin in a copper pop rivet is solid brass, and is not plated steel. If it sticks to a magnet, it has no place in a copper gutter.
The cleanest looking gutter miter is a cut into the stock material itself. Three-quarter inch tabs are allowed on one side. The seam is riveted and soldered on the outside surface. Any exposed rivets or solder on the outside surface may be ground flush, and exposed solder may be easily copper plated using a special plating fluid. Gutter ends that do not abut a flat surface look much more beautiful if they are provided with mitered, or return, end. The tabs on gutter miters and mitered end caps can be cut to overlap opposite to the way that shingles on a roof would overlap, so that solder will flow down into the seam effectively.
Continuous lineal gutter screens are useful where broad leaf trees are dumping large quantities of leaves into the gutter. However, small dirt and silt and things like conifer needles build up anyhow below the screens, and the screens will need to be removed once in a while for cleaning, so outside of locations with broadleaf trees, it often is a better choice to not have screens.
Raingutters should have drop outlets soldered into them, that drop down at least one inch, to insure that water will drop down and not travel along the underside of the gutter.
It is a beautiful option to use a gooseneck that follows a French S-curve down from the raingutter and back to the wall.
Leaderheads are also known by a number of other names. Collectors, collector heads, conductor heads, scupper heads, rainwater heads. If leaderheads are being used, then they are usually placed at the top of the downspouts where the gooseneck or downspout elbow contacts the wall. While there are a number of practical reasons why leaderheads are used, most clients choose to use them purely from the standpoint of ornamentation. Some of the more practical reasons are: a location to collect debris; a vaccum brake for tall downspouts; to reduce freezing up of the downspout.
Copper downspouts may be fastened to the wall using cast bronze downspout brackets, which are ornamental and exceedingly strong, or with a simple copper strap. Fasteners for downspout brackets or straps, such as toggles, must be of a compatible metal to copper.
It is recommended to contractors that lengths of gutter and downspout stock be scrubbed with scotchbrite and water, and dried immediately with paper towels prior to installation. Use latex gloves during installation. This process is not only a good preliminary to achieving a good chemical patina, but even if a chemical patina is not being used, the first several months that copper is installed, fingerprints and factory residue stand out in bold and intense colors. This ugly situation is usually of no long term concern, but it can make collecting a payment from a homeowner difficult.
The progression of patina colors on copper varies greatly with conditions of climate. In most regions this might mean a month or so for copper to lose its shininess and go to a russet brown, and perhaps five to ten years to develop a natural green patina. In order to speed up this process a chemical patina can be used. The usual goal of a chemical patina is a slightly spotty olive green over a brown undersurface. If using Copperworks patina chemical or chemicals of other companies, best results are usually obtained by first applying the chemical very diluted with water, and through a series of applications, gradually increasing in concentration.
In some special locations with salt spray, or acid fog, copper will first turn a strong red terra-cotta color, and then go rather quickly to a lime green even without a chemical patina. In these situations copper is less durable than usual and heavier gages should be used
Don Miller of the Copperworks of Don Miller has a complete ornate raingutter hardware catalog which includes Don Miller's unique bronze and copper products, Copperworks Green Patina Formula, and a national source list for lineal raingutter stock manufacturers and suppliers.

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