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Roofing/Copper valley nailing



I had copper valleys installed for my new roof.  Each copper valley was nailed--with copper nails--about 2" from each vertical edge. My concerns: 1) Shingles were then nailed onto the copper using electro galvanized nails (dissimilar metals), 2) these nails were about 10" from valley center, 3) what is to stop water from flowing underneath copper and into these nails holes (e.g. if/when the copper corrodes around these zinc nails?  Should I be worried? In the literature, there seems to be some confusion or differences on these issues. Thank you!

Great question! The bad news is that you are correct that galvanized steel (the shingle nails) and copper are quite far apart on the galvanic scale and thus the potential it quite high that there will be electrolysis. Regarding the placement of the shingle nails, NRCA states "Generally, fasteners should be kept back from the center of the valley a minimum of 8 inches. However, on low-slope roof valleys or in climates where freeze-thaw cycling or intense rainfall may be regularly anticipated, holding nails back farther from the center of the valley is no uncommon."
I would recommend that you contact your roofing contractor and have him replace the valleys. When this is done he should install new underlayment under the valley, install new copper valleys and insure that the new shingles are installed extending onto the valley 4" and set in a bed of sealant. The shingles should provide a tapered valley such that the distance between the center of the valley and the edge of the shingles is greater on the eave side of the roof then at the ridge side (approximately 1/8 inch per lineal foot of valley).
One additional note - you may consider during the replacement having the contractor hem the edges of the valley and install clips in lieu of mechanically-attaching through the valley. This will allow easier expansion and contraction of the sheet metal, and the hem will aid in preventing water from getting outside of the valley metal. This is obviously a bit more labor than originally expected, and the roofing contractor will likely ask for (and be entitled to) a few more dollars for this extra measure - I believe that it is money well spent.


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Aaron Nelson


All types of questions with regard to roofing, waterproofing and sheet metal. This includes commercial and residential buildings, along with the various aspects of the construction means and methods, ventilation, steep-slope or low-slope, code requirements, installation errors and other such problems


I started in roofing fabricating and installing sheet metal flashings out of high school for a large commercial contractor. I worked for the same contractor in the office estimating and project managing commercial project for 10 years. I left the construction side of roofing and now work as a roof consultant, which I have been doing for 8-years.

RCI, Inc.

I am a Registered Roof Consultant (RRC) and a Registered Roof Observer (RRO) through RCI, Inc. RCI is a international group of building envelope professionals. I am an approved instructor for RCI educational programs.

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We have worked with many local school districts, insurance companies, HOA's, building management companies, and we have a national client with buildings located throughout the US.

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