Copper gutter info

There are many things different about copper gutters

When an installer works with Copper gutters there are many things that should be done different that when working with other types of gutters.  One of the most common mistakes an installer makes is the type of fasteners and hangers.  To do the job correctly the installer should use Stainless Steel screws, Copper rivets,  or Copper coated Steel screws.  When choosing a hanger the installer must use either Copper hangers or Brass hangers.  Water that runs off of Copper will corrode a standard Steel gutter screw or an Aluminum or Steel rivet.  This is due to galvanic corrosion.  If an installer uses Aluminum hangers the same thing will happen.  The Aluminum will corrode!  Also it is very important to use a type of sealant that is compatible with copper.  An Aluminized sealant is not ok to use as well as some types of Acrylic sealants.  See our pictures of our work page for some photos of our Copper work. Last there are two common thicknesses of Copper gutter stock that are available.  These are 16 ounce and 20 ounce.  20 ounce is the stronger, thicker, longer lasting of the two being the only (Lifetime) product.

expansion and contraction of sheet metal

Below is an article written by Robert J Boessen of Terracon Consultants

​This is an article written about the expansion and contraction of various types of roofing and gutter metals.

Movement of metal is calculated by the coefficient of thermal expansion (α). The following table provides the calculated increase in 10-foot lengths per 100ºF temperature change.

Metal Type             Coefficient of Thermal        Increase in 10-Foot Lengths 
                             Expansion (α)                   per 100° F Temperature Change 
Galvanized Steel     0.0000067 in./in./F            .080 in. ~¹/16  inch 
Steel                      0.0000067 in./in./F            .080 in. 
Copper                   0.0000094 in./in./F            .113 in. 
Stainless Steel       0.0000096 in./in./F            .115 in. ~ ⅛ inch
Aluminum               0.0000129 in./in./F            .155 in.

Table 1, above, indicates a 10-foot piece of steel moves about one-sixteenth of an inch and aluminum moves more than one-eighth of an inch (almost twice that of steel). When designing/installing sheet metal, it is imperative that the material does not grow into lengths that will cause severe problems. My dad used to say, “Pay Attention Son!” 

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There are many variables associated with perimeter fascia. Keeping the above basics in mind will go a long way to minimizing water intrusion into the roof system as it relates to expansion and contraction under thermal loads.

How many gutter joints have we all observed that leak? No matter the gutter style, a few years after installation there are leaks in some, if not all, of the end lap joints. So a repair techinician is sent to strip in the joints. Whether we use mastic, exposed sealant, EPDM membrane, etc., it’s temporary. Typically, after one cycle of seasons it will need to be repaired all over again.

As with all rigid materials, expansion is a significant design consideration in gutters. The system of gutters, downspouts and their supports must have the flexibility and strength to accommodate expansion. According to NRCA, expansion joints are suggested for gutters to allow movement caused by thermal changes. Long, straight runs should not have expansion joints spaced more than 50 feet apart and no more than 25 feet from any fixed corner. Some types of expansion joints act as a water dam in the gutter. Therefore, the number and placement of downspouts will be influenced by the type of expansion joint used. As stated by the NRCA, “Using metals with high coefficients of thermal expansion, such as aluminum and zinc, should be avoided”.

I am aware there are entities that love to specify and install gutters with a deck flange. However, in my opinion, unless the gutter runs are less than 50 feet, this type of gutter profile should be avoided. I personally have been involved with four separate issues relating to gutters with deck flanges that have resulted in thousands of dollars of corrections.

When I asked a metal building manufacturer representative where his expansion joint detail for the gutter system was, he responded, “Ah Robert, we don’t worry too much about that unless the run is over 150 feet.” Think about that: 15 x 0.080 inch =1.20 inch. Where does he think over one inch of expansion and contraction is going to go? I showed him where every third or fourth section of gutter was leaking. Pop rivets used to fasten the end lap joint were either severed and/or ripped from the face of the gutter.

The following points sum up gutters:

1. Gutter runs that exceed 50 feet must have an expansion joint detail and should not contain a deck flange.

2. End laps may be pop riveted and soldered, or lapped a minimum of three inches, placing two rows of sealant between the lap and installing appropriate type pop rivets and/or sheet metal stitch screws, in two rows, spaced one inch apart staggered.

In closing with this note, if you are a designer or consultant, “pay attention” as my dad says, and give some directions as to how you want the one-eighth inch of expansion and contraction handled in your sheet metal detail. If you are a contractor, “pay attention” when you submit shop drawings as to how you are going to handle the one-eight inch in the shop and the field. If you are a quality assurance representative, you better know how the one-eighth inch is being handled.

Robert J. Boessen, RRC, CDT is a Senior Roof Consultant/Project Manager with the Facilities Engineering Division of Terracon Consultants, Inc.  Robert has been in the roofing industry for 37 plus years. Robert has served as an expert witness in multiple roofing litigation issues, appointed/approved by US Federal District Court as an umpire in roofing issues. Robert has authored papers and presented seminars to his peers on the subject of roofing and sheet metal. Robert has been an active member of RCI for 20 years and serves on the RRC Exam Committee.