A roofer told us that our hidden gutters can't be repaired. He's suggesting roofing over the gutter and installing new hanging gutters at the roof edge. I don't like this idea. Is there anything that can be done?
Built-in gutters, also referred to as "box gutters" are considered a concealed roof drainage system. Since they are not readily visible, they typically don't alter the historic character of buildings and don't detract from or conceal decorative cornice details. Unfortunately, being unseen often results in neglect. The simplest form of maintenance is keeping them clear of debris. This is necessary for any gutter system to perform its duty, but with built-ins, trapped, standing water can lead to a shorter life and very costly repairs.
A majority of built-in gutters are lined with formed metal. The earliest metal used for the lining is terne-plate. Terne, an alloy of lead and tin, was applied over sheet iron, then later, steel. This gutter lining material needs protection from corrosion. Just like tin roofs, regularly applying an oil-based paint was the traditional method of maintenance.
Another issue is the soldered joints, where sections of the gutter meet and forms a seam. The expansion and contraction of the metal during temperature changes results in failure at the weakest point--the seams. I never find expansion joints in the sheet-metal gutter linings. When a leak is finally discovered, the seams are usually just patched with tar (roofing cement)--which tends to be a messy, temporary repair.
Unfortunately, my experience has shown that a majority of these gutter systems have suffered from the lack of proper repairs and maintenance. Quite often I find that there's also damage to the eaves structure below that requires the skills of an experienced carpenter to repair.
Restoring these gutter systems, even if there is no damage to the wood below, can be quite expensive. Trying to find someone with the knowledge and metalworking ability could also be a challenge. Soldering in some patches might be effective for someone with basic skills, but complete relining with terne requires a highly skilled (and expensive) craftsman. The cost of relining the gutters with copper could be close to the amount one would pay for a new luxury car.
Although it is best practice to restore metal-lined gutters with metal, the availability of experienced contractors and the high cost might prevent some homeowners from making needed repairs. This could allow leaking gutters to cause extensive damage to their home, significantly escalating the cost when repairs are finally made.
If the metal gutter lining isn't too far gone, it might be able to be preserved with an elastomeric coating system. Not the stuff from a home center, but a coating system specifically for historic metal roof preservation. If there are a few bad spots or tar patched seams, a reinforcing fabric can be installed as the coating is applied.
There's another method of restoring built-in gutters that has been successful, when installed with care. This involves applying a waterproof roofing membrane over the existing gutter lining. These membranes are usually either EPDM (rubber) or modified bitumen and are manufactured for "flat" roof installations. Correct installation includes properly adhering the membrane and seams, correctly terminating the edges and installing the downspout outlets so they don't leak.
Built-in gutters, the unseen roof drainage system, was specifically chosen to be installed when the home was built, thus is part of the original historic character. I always try to encourage preserving original elements, even though it might be easier to eliminate the old method for something new and inexpensive.
William Kibbel III is a home inspector and restoration consultant specializing in historic residential and commercial buildings. He is vice president of Tri-County Inspection Company, serving Southeastern Pennsylvania and Central New Jersey.