Proper roof flashing installation around a chimney is essential for preventing water leaks and protecting your home from structural damage. Flashing acts as a barrier that directs water away from the chimney and onto the roof, keeping your home dry and safe. Installing roof flashing might seem intimidating, but with the right tools, materials, and step-by-step guidance, it’s a manageable DIY project for experienced homeowners or a helpful reference before hiring a professional. Here’s a comprehensive guide on how to install roof flashing around a chimney.
Step-by-Step Instructions for Installing Chimney Flashing
Step 1: Prepare the Roof Surface
Safety first: ensure your ladder is secure, and use proper fall protection. Remove any shingles around the base of the chimney where the flashing will be installed. Clean the area of debris, old roofing cement, or deteriorated flashing. A clean, dry surface ensures proper adhesion and prevents leaks.
Step 2: Install Step Flashing on the Sides
Step flashing is installed along the sides of the chimney where the roof meets the masonry.
- Start at the bottom of the chimney on one side.
- Slide the first piece of step flashing under the first course of shingles and against the chimney. The vertical edge should lie flat against the chimney wall.
- Nail the flashing in place using galvanized roofing nails. Place nails about 6–8 inches apart, ensuring they’re secure but not overdriven.
- Cover the step flashing with the next course of shingles.
- Continue installing step flashing up the side of the chimney, alternating with each shingle course, until you reach the top.
Step 3: Install Step Flashing on the Back Side
Repeat the same process for the back side of the chimney, starting at the bottom and working up. Make sure the pieces overlap correctly with the shingle courses to ensure water flows away from the chimney.
Step 4: Install Counter Flashing
Counter flashing is installed over the step flashing and embedded slightly into the chimney masonry. This creates a waterproof seal.
- Measure and cut pieces of counter flashing to cover the step flashing completely.
- Use a hammer and chisel to cut small grooves into the chimney mortar joints. Slide the top edge of the counter flashing into these grooves.
- Secure the counter flashing with masonry nails or roofing cement, depending on your material choice. Make sure seams are tight and edges are sealed to prevent water intrusion.
Step 5: Apply Roofing Cement or Sealant
To reinforce the waterproofing, apply a thin layer of roofing cement or high-quality sealant where the counter flashing meets the chimney and around any nail heads. Smooth the sealant with a putty knife to ensure full coverage without gaps.
Step 6: Inspect and Replace Shingles
Check that all shingles are correctly aligned and that flashing pieces are properly seated. Replace any shingles removed during preparation, ensuring they overlap the step flashing correctly. Use roofing nails and sealant as necessary to secure them in place.
Step 7: Final Check
Examine the entire installation for gaps, exposed nails, or improperly seated flashing. Use a chalk line to check alignment if needed. Proper installation should create a continuous barrier directing water from the roof and chimney joint safely onto the roof surface.
