Q–My house was recently re-roofed. However, leaks are still present at a chimney and where a lower roof meets a second-story wall. I was able to get up on the roof and look around. The metalwork around the chimney and along the wall was not replaced. It is old and rusty. However, I discovered fresh silicone caulk and roofing cement in and around this metalwork. Was the caulk installed incorrectly?
A–Yes, the caulk was installed incorrectly. It should never have been used in the first place. Caulk is simply not an acceptable material for sealing the seams in metal roof flashings. Caulk can be used in emergency situations or as a temporary measure until such time as you or the roofer can break out the soldering iron, stick solder and red ruby acid flux. It is best to leave caulk and caulk guns in the hands of painters, not roofers.
Roofing shingles are a fantastic product. Many of them are easy to install and will create a leakproof covering in normal weather conditions. When installed properly, shingles shed water like the feathers on the back of a duck. As long as nothing is sticking up through the roof, you should rarely, if ever, get a leak.
However, almost every roof has something sticking through it, including plumbing vent stacks, skylights, roof vents, exhaust fans, and walls. Wherever such objects penetrate a roof surface, metal flashings must be installed in conjunction with the shingles to prevent leaks. The flashings are transitional roofing materials. That is, they connect something that is not a roof to the actual roof.
These flashings are almost always two-part systems. They are called different things in different parts of the country. In most instances, the system consists of a base or step flashing, which can be “laced” into each shingle layer, and a counter flashing that covers the base or step flashing. The flashings can be made from tin-coated steel (terne), galvanized steel, copper, lead or any other metal that can be easily soldered, brazed or welded. Aluminum should never be used as a flashing material if it will come into contact with mortar in brick or stonework because the alkaline chemicals will corrode the aluminum.
There are several reasons why these flashings need to be a two-part system. Roofs, as well as houses, have a great tendency to expand and contract in reaction to seasonal moisture and temperature differences. The things that stick through roofs, however, do not always expand or contract at the same rate. Some things, such as chimneys, barely move at all.
This expansion and contraction must be allowed to occur without creating the potential for a roof leak. The two-part flashing system allows this to happen. Because of how the two pieces of metal flashing overlap, they can slide past one another and still keep rain from entering your house.
The caulk that was used in an attempt to seal the rusted flashing does not have the ability to handle the movements that will occur on a regular basis during the next 20 years or so. Soldered metal flashings can withstand repeated expansion and contraction cycles without leaking.
Remember how I mentioned that the technology has been around for hundreds of years? Professional roofers have never depended upon caulk in the past. They instead soldered or brazed the seams or joints in their metalwork. This method permanently melds the metal pieces so they act as one. Caulk, on the other hand, relies strictly on its ability to stick to something. If that “something” is dirty, oily, dusty or rusty or if it expands and contracts a great deal, the caulk may have trouble adhering. You can depend on solder. Call your roofer back and have new flashings installed that are soldered.
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Have questions about the remodeling process? Write to Tim Carter, c/o The Chicago Tribune, P.O. Box 36352, Cincinnati, Ohio 45236-0352.
For photographs of properly installed roof flashings and other tips on installing roof flashings, send $2 to Tim Carter at the above address. Ask for Builder Bulletin No. 24.
For a list of past Builder Bulletins and a wide variety of individual job bid sheets, send a business-size, stamped, self-addressed envelope to the same address.
Ask the Contractor can also be accessed via the Internet at http://www.chicago.tribune.com/homes/articles/askcon.
