Flashing Guidelines for Chimneys

Moving right along, chimney flashing is a must to provide a water-resistant barrier where roof shingles meet a chimney. When rain falls on a roof, chimney flashing will direct water away from the chimney/roof junction.

You can install seamless chimney flashing with the following steps:

  • Pry or scrape off old metal flashing and roof 3cement, if necessary.
  • Cut pre-bent base flashing to fit the front of the chimney.
  • Install pre-bent base flashing against the front of the chimney.
  • Mark chimney edge on the opposite end; snip and bend.
  • Secure with four evenly spaced 1 inch roofing nails to hold the front flashing edge in place.
  • Snip and bend pre-bent 8 in.² step flashing to fit the front chimney corner.
  • Apply caulk where the chimney corner meets the roof.
  • Lay corner step flashing in the caulk and nail in place with two nails.
  • Nail a shingle over the first step flashing; nail a second piece of step flashing over the shingle.
  • Continue this process around to the top chimney corner; cut and bend the final piece of step flashing at the top corner.
  • Fit a pre-bent, soldered chimney saddle behind the chimney; nail directly to the roof at the top edge with 1 inch roofing nails roughly every 6 inches.
  • Shingle over the area where the saddle rests on the roof; leave roughly 2 inches of metal exposed.

For a DIY job, roofing experts recommend buying flashing, especially for a chimney, from a sheet metal fabricating warehouse. Many large roofing companies sell their own sheet metal and will provide a reliable source of flashing and chimney saddles.

The reason that it pays to buy from a warehouse is because it is difficult to make straight, precise bends in sheet metal without a tool like a sheet metal bending brake. Even so, if you’re new to working with sheet metal, it could take extensive experience to bend accurately to properly weatherproof a complicated structure like a chimney or vent.

Once flashing has been installed on a roof, it must be checked regularly, along with all other components in a roof structure.

Flashing should be inspected along walls, plumbing vents, and at the base of a chimney. Check specifically for areas where water can accumulate and leak into a building from bent flashing, holes in the roof, or gaps in materials.

Flashing is a top defense against roof leakage. For this reason, it must be monitored regularly to ensure that it remains securely fastened without any gaps or holes in installation.

If you do find a hole in flashing or roofing materials, it’s time to act immediately.

You can remove old caulk or adhesive with a putty knife and wipe the area clean.

The offending hole can then be re-sealed with roofing caulk using regular caulking application. Nail holes can be filled completely with caulk and smoothed with a putty knife.

For more serious flashing leaks, it’s important not to repair these issues with sealing materials. In more extreme cases, flashing will need to be replaced completely, either by yourself or with the help of a professional.

No matter how you slice it, your choice in flashing materials is of the utmost importance. When you use the proper method of flashing installation, you can guarantee that water will roll off your roof like water off a duck’s back, protecting your property in each season.

Now that you understand the basics of roofflashing, we can move right along to more detailed projects.