How to Buy Chimney Flashing
Making sharp, straight bends in sheet metal is tricky unless you have access to a tool called a sheet metal bending brake. Even then, you need experience to bend complicated shapes. That's why we’re recommending that you order your chimney flashing from a sheet metal fabricating shop. Large roofing companies often have their own sheet metal shops and are the best place to buy the chimney saddle and flashing; they'll know exactly what you need. Otherwise, check the Yellow Pages under “Sheet Metal.” We used 26-gauge galvanized sheet steel for our flashing and saddle, but prefinished steel or copper are other possibilities.
Most chimneys have a small rooflike structure behind them, called saddle (Photo 6), that diverts snow and water to both sides of the chimney. Whether your chimney has a wooden saddle covered with shingles, a sheet metal saddle or no saddle at all (like the chimney in this story), we recommend installing a new custom-made sheet metal saddle (Photo 6).
Custom-made saddles are soldered together at critical spots that are hard to seal on saddles that are built in place. Soldered sheet metal saddles less than 3 ft. wide are self-supporting and easier to install if you just tear out any existing metal or wood saddle. Most old saddles were built right over the top of the roof boards and need no patching. Otherwise, fill in the missing boards before installing the new saddle. Saddles wider than 3 ft. may need additional support. Ask your sheet metal fabricator for advice.
Bending and soldering a saddle is complicated, but sheet metal shops need only two pieces of information from you to bend up a saddle: the width of the chimney and the slope of the roof (see “How to Find Your Roof Slope,”).
In addition to the saddle, you'll need the following sheet metal parts (see Figure A):
- Front base flashing. Order about 12 in. more than the width of the chimney. Some lumberyards stock a “dormer flashing” that will work in this location. You may have to adjust the angle by bending it to match your roof slope.
- Prebent step flashing, 8 x 8 in. Roofers call these “shingle tins”. You’ll need one for each shingle along the edge of the chimney plus a few extra. Most lumberyards stock these.
- Front cap flashing and side cap flashing. Some sheet metal shops stock a flashing for this purpose, but you’ll probably have to have it made. Measure at the front of the chimney from the roof to the third mortar joint and add about an inch to determine the height you’ll need. The shape is relatively simple, so you could buy flat sheet metal, called “coil stock,” and bend these yourself.
- Back cap flashing. This flashing is identical to the front and side cap flashing.