June 20, 2022

Built-in Box Gutter FAQs

These built-in box gutter FAQs were written as a companion piece for Episode #78 (beginning 5:11). Many thanks to the author, Jason Lamb, for taking the time to compile this information and for joining me during the listener Q&A segment. -Stacy

What was originally used to line my built-in gutters?

Many of the built-in gutters in America would have been lined in terne metal. This was a light gauge steel with a coating of lead and tin. It is a good, long-lasting material so long as it is kept painted and well maintained.

What are the best materials to use when restoring a built-in gutter?

Copper can be bent and formed into complex shapes, it doesn’t rust, you can solder pieces together, and it doesn’t need to be painted. It’s preferable to use a heavier 20oz weight. The heavier gauge will have more columnar strength, last longer, and the amount of thermal expansion and contraction will be less severe.

Stainless Steel is also an excellent material that will last forever. This may be ideal for situations where you need to connect the gutter to a metal roof that would not be galvanically compatible with copper.

I could also give Zinc an honorable mention here. It is a very popular roofing material in Europe.

Is there a less expensive material I could use?

There are no inexpensive materials that work well for built-in gutters. I strongly suggest you do not fixate on raw material costs since the cost of labor will be the most expensive portion of your project. It would be false economy to invest so much time and labor into this work only to use an inferior material.

What about EPDM, TPO, and other rubber/elastomers?

Many built-in gutters have been re-lined with rubber membrane products. The problem with this approach is that these thick rubber materials aren’t well suited to being formed into sharp bends, corners, and complicated shapes that a built-in gutter requires. You’re also adding this thick material on top of the existing (old) gutter and so the rainwater capacity will be somewhat diminished.

It is a solution that can certainly buy some time if a full restoration isn’t in the budget. You can expect this to last 15 to 20 years.

How long should a copper built-in gutter last?

A copper built-in gutter that is well designed and detailed should last more than 70 years with little to no maintenance. The key words here are “well designed and detailed.” The sad truth is that copper work done with improper fabrication techniques may have a lifespan that is cut drastically short. Many of the copper gutters being replaced today are no less than 20-30 years old. It’s also important to note that this work may look beautiful but still have dubious details that make it doomed to premature failure.

How can I repair damage to my built-in gutter?

Small tears and gashes caused by falling objects can be patched with a tape designed for roofing applications. One product called EternaBond (affiliate link) is a thermoplastic and non-curing rubber tape. It is super strong and has a UV-stable backing—which is kind of important for something that will bake in the sun on top of your house.

When the soldered joints of a built-in gutter have split, these can sometimes be re-soldered but it is very difficult to solder copper that has aged to a patina. One might also question why the soldered joints continue to split open. Often, there has not been an allowance for thermal expansion and contraction. Re-soldering and therefore strengthening the joint may only transfer that thermal stress elsewhere, causing more splits and tears.

Do most roofers know how to work with built-in gutters?

No. This is a highly specialized area even among roofing professionals who specialize in traditional roofing for historic properties.

What about fabrication and technical detailing?

How should these pieces of gutter be soldered together? How much should the pieces overlap? How are rivets used? How are the sections of gutter connected to the drip edge? How far should the new gutter extend under the roofing material? What is thermal expansion and how do we create an allowance for it?

The good news is that much of this information is readily available to anyone who’s interested in reading it. The Copper Development Association’s Design Handbook
https://copper.org/applications/architecture/arch_dhb/ is a thorough guide for these technical details. Think of this as a pre-med course for anyone interested in performing architectural sheet metal work. Although it focuses on copper, much of the information is also applicable to roofing in other metals.

What about problem-solving and design decisions?

Once you’ve gained an understanding of the basics of architectural sheet metal work (the pre-med reading I mentioned) you can begin to think about how this applies to your own gutter.

Is the existing pitch of your gutter adequate? How long will the new gutter pans be before they terminate into expansion joints? Will this work with the existing downspout locations? Does the built-in gutter system connect to any other architectural features such as chimneys or dormers? If so, how are these connections detailed?

This is highly customized work that will be tailored to your house. Chances are, your built-in gutter isn’t going to look like anyone else’s. You will have problematic situations that are unique to your house.

Even if you never plan on doing this work yourself, becoming well-read on these topics will enable you to hire the right professionals and, at best, help you weigh in on these important decisions from a position of knowledge.

About Jason

Jason works as a graphic designer and has a passion for building restoration, woodworking, and traditional roofing. His knowledge of architectural sheet metal comes from obsessive study, hands-on practice, and friendships with talented roofing professionals.