Copper, 7 min read
Copper gutters and flashing: what 80 years of service looks like
Why soldered copper outlasts almost everything else on a house, the details that make it fail early, and what it costs to do properly.
By Joaquim Duarte, Copper shop lead
Walk down Commonwealth Avenue and look up. The copper bay roofs, conductor heads and cornice gutters you see were mostly installed between 1870 and 1910, and a good number of them are still working. That is the promise of copper: install it correctly once and it can outlive everyone who paid for it.
It is also why failed copper work is so frustrating. When a copper gutter leaks after 15 years, the copper is almost never the problem. The details are.
Why copper lasts
Copper forms a protective oxide layer as it weathers. It turns from bright penny to brown within a year, then slowly develops the green patina known as verdigris. That patina is stable and protects the metal underneath. A 16 ounce copper sheet loses only a tiny fraction of its thickness over a century in normal New England air.
Just as important, copper can be soldered. A soldered seam is a continuous metal joint. It does not dry out, shrink or crack the way sealant does after a few freeze and thaw cycles.
The four details that make copper fail early
Almost every early copper failure we repair comes down to one of these:
- Caulked or riveted seams instead of soldered seams, which open up within a few winters
- No expansion joints on long runs, so the gutter tears itself apart with seasonal movement
- Contact with steel or aluminum, which causes galvanic corrosion at the joint
- Copper that is too thin, such as 12 ounce stock used where 16 or 20 ounce is needed
Hung gutters versus built-in gutters
Hung gutters, usually half-round on older houses, attach to the fascia with hangers. They are the simpler and less expensive option. We use copper hangers screwed into rafter tails at about 24 inch spacing, which keeps them straight under snow load.
Built-in gutters, often called Yankee or box gutters in New England, are troughs built into the cornice itself. They are elegant and invisible from the street, but when they leak, water goes straight into the wall. The fix is a soldered copper liner with properly placed expansion joints, installed after any rotted wood in the trough is replaced.
Flashing is where copper earns its keep
Chimney, valley and dormer flashing is the most common source of leaks on old roofs, and copper is the best material for it. For chimneys, we use step flashing woven into the roofing with counter flashing set into a sawn reglet in the mortar joint. It is more work than surface-mounting a strip of metal and caulking the top edge, but it does not fail every five years.
Valleys on slate and tile roofs get 20 ounce copper, open or closed depending on the roof. On long valleys we pre-form and solder sections in the shop so there are no laps where water can back up during heavy rain.
If you can see caulk on a copper detail, that is the part that will leak first.
What it costs
Copper is a premium material, so the question is always value over time. As a sample range, hung half-round copper gutters run about $42 to $95 per linear foot installed, depending on access, conductor heads and downspout runs. Built-in gutter relining varies more, because it depends on how much wood needs to be rebuilt.
Compared with aluminum gutters at a third of the cost, copper that lasts three to four times longer is usually the better investment on a house you plan to keep, and on historic facades it is often the only option a commission will approve.
Caring for copper
Copper needs very little. Keep gutters clear of leaves, check downspouts after big storms, and do not let anyone attach steel brackets, aluminum downspouts or satellite mounts directly to it. If you want the bright color to last, a clear lacquer can slow weathering, but most owners come to love the brown and green.
Our copper shop fabricates everything in Dorchester and our installers solder on site. If you are not sure whether your gutters are built-in, hung, copper or something painted to look like copper, our free inspection will tell you.
This article is general information for homeowners and is not legal, insurance or engineering advice. Figures are illustrative for this demo site.
