How to Repair a Leaky Chimney – Part 6

How to Repair a Leaky Chimney – the roofers install new step flashing and HardiPlank lap siding to complete the repair.

This project is continued from Part 5.

View of the ice and water shield, new step flashing and shingles as the roofer works his way around the chimney corner.

Chimney Leak: Ice & Water Shield, Step Flashing and Shingles

HardiPlank Lap Siding – Chimney Installation

I bought several 12 foot x 8.25 inch x 5/16 inch HardiPlank® primed boards in the Cedarmill© style to replace those removed from the chimney. The new siding boards were cut using the old boards as a pattern, but 1 inch shorter on the bottom slope to provide the required clearance above the roof surface.

Sawing new HardiPlank® Cedarmill© Lap Siding

I used my Bosch circular saw with a Dewalt diamond masonry blade to saw the HardiPlanks. At only 5/16 inch thick, the 12 foot HardiPlanks are very flexible and it would take several saw horses to support the boards. So instead of using saw horses, I set the saw blade to about 3/4 inch depth and laid the siding on 2x4s for support and ground clearance. The blade cut the HardiPlanks very quickly, but made a huge amounts of dust. I held my breath while sawing then walked away for the dust to clear.

A new set of boards ready to be installed on west side of the chimney. Instead of nails, the siding was fastened with corrosion resistant bugle head wood screws. The roofers were kind enough to install the siding for me while I sawed the boards.

New HardiPlank Lap Siding for the Chimney

The corner board seams and screw heads were caulked with more of the BASF Sonolastic® NP 1™. The lapped bottoms of the HardiPlanks are NOT caulked (per the HardiPlank installation instructions) because it needs to breathe. Also, the HardiPlanks are installed with the required 1 inch clearance above the roof.

Leaky Chimney Repair: New Shingles, Step Fashing and Siding

The inset image in the above photo shows the corner board and step flashing detail so there’s nothing to obstruct the flow of water or catch tree debris at the narrow roof valley exit.

The chimney looks great after the HardiPlank is painted with a coat of Sherwin Williams Duration® exterior latex paint. I took care to paint the bottom edges of the HardiPlank above the roof and the plank end at the chimney corner.

Leaky Chimney Repair: Coat of Sherwin Williams Duration Paint

Here’s the west side of the chimney before painting:

New HardiPlank Siding and Shingles on West Side of Chimney

And after painting:

Chimney after Painting

I liked how the new GAF ELK Timberline® Natural Shadow™ shingles blended well with the discontinued Atlas Chalet Weathered Shake shingles.

Chimney Step Flashing Inspection

There were rust stains on the old step flashing, but the roofer said it was cosmetic and found no rust holes. I looked at each piece of the old step flashing and found it to be in generally good condition with no holes, except where it was nailed to the roof as required. The step flashing was therefore not the cause of the chimney leak.

Leaky Chimney: Old Step Flashing

Toilet Paper Tell-Tales

There’s been no roof leaks since the chimney repair with ice and water shield, new flashing, shingles and siding despite several more thunderstorms. I placed some toilet paper tell-tales inside the chimney box at the corner where it had been leaking and will be checking after hard rains for a while to be certain the leak is fixed.

Attic Leak – Toilet Paper Tell Tales

Leaky Chimney Repair Cost

My repair cost wasn’t that much since I did a significant amount of work myself:

  • Setup the ladders and roof brackets
  • Removed the damaged HardiPlank siding
  • Bought the GAF ELK shingles, HardiPlank siding, Sonolastic NP 1 caulk and Sherwin Williams paint
  • Measured and sawed the HardiPlank siding

The cost for repairing the leaky chimney was:

  • $200 for the roofer’s labor
    The roofer supplied the Owens Corning ice & water shield and step flashing. He also installed the HardiPlank (20 minutes work) and caulked the chimney.
  • $26.95 for one pack of GAF ELK shingles purchased at Home Depot
  • $18.57 for three HardiPlank Cedarmill boards @ $6.19 each at Home Depot
  • $3.80 for a tube of NP 1 caulk
  • $35.99 for a gallon of Sherwin Williams Duration paint (purchased on sale)
  • I already had the tools, ladders, brackets, 2×6 step board and screws, so there was no direct cost for these items.

The total out of pocket expense of $285.31 for the leaky chimney repair. Not bad! If I had hired a roofer to do the entire job soup-to-nuts I could see the job costing me $500 to $750.

Hope this saves you some money!

Roof Replacement

A year after fixing the leaky chimney, the entire roof was replaced due to hail damage. I had the roofing contractor remove the HardiPlank siding from all four sides of the chimney to wrap it in ice & water shield, followed by new step flashing and HardiPlank siding to guarantee the chimney would be leak free. You can read about that project here.

Bob Jackson

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