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How to Cap a Chimney

If your home lacks a chimney cap, you probably want to install one. Chimney caps deflect rainwater from the flue, keep out animals, and contain burning embers from wood stoves or fireplaces. Before learning how to cap a chimney, you must first decide if you’re comfortable working on your roof. After that, the directions vary depending on the shape and number of your flues.

How to Cap a Chimney Instructions

  1. Using the proper safety precautions, set up a ladder to access your roof.
  2. Determine if you have a single-flue or multiple-flue chimney.

For single-flue installations:

  1. Measure the flue.
    1. For a square or rectangular flue, measure width and length.
    2. For a circular flue, measure the diameter.
  2. Select a chimney cap that fits the flue.
    1. Cap dimensions may exceed flue dimensions by up to 1 inch and still fit.
    2. Galvanized metal flues are considered the best option.
  3. Slide the cap over the flue or insert into flue depending on design of cap.
  4. Leave at least 6 inches of space between top of cap and flue edge.
  5. The cap should come with self-tapping screws.
  6. Insert screws into holes on cap and tighten with screwdriver.
  7. Confirm that chimney cap is tightly fitted and not shifting.

For multiple-flue installations:

  1. Measure the combined width and height of the flues.
    1. Choose the height for the tallest flue and the width of the widest flue.
    2. These dimensions are needed to ensure that you buy a cap that fits over all flues together.
  2. Measure the width and length of the chimney crown, which is the masonry slab around the flues.
  3. Select a cap that fits the crown, covers all flues, and leaves a minimum of 5 inches between it and the tallest flue.
  4. Clean debris from crown with brush.
  5. Fit a masonry bit to your power drill that is 1/8 inch smaller in diameter than screws.
  6. Drill pilot holes in crown in alignment with holes in cap.
  7. Run a wavy bead of caulk around the crown’s edge.
  8. Place the cap on the crown with holes lined up with pilot holes.
  9. Attach tightly with screws.
  10. Confirm that installation is secure on all sides.

Tools & Materials

  • Tape measure
  • Ladder
  • Screwdriver
  • Power drill with masonry bit
  • Brush with stiff bristles
  • Caulking gun

Chimney Cap Inspection by PJ Fitzpatrick

Any cracking and peeling of your chimney flashing will eventually cause a leak that can penetrate your roof. If you noticed any flashing problems when following the steps for how to install a chimney cap, call PJ Fitzpatrick. We can inspect and repair your roof and chimney. Contact us for an estimate today.

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