Sandstone chimney, slate roofing and copper chimney flashing.

Installing copper flashing on a sandstone chimney is basically the same as most other chimney flashing installations. The problem many roofers have is fitting the flashing to the uneven stone and irregular mortar joints of the chimney. The following illustrations show the steps taken to re flash a currently leaking sandstone chimney. This is not a do it yourself project. Nor should it be attempted by any hack with a ladder and pickup truck. The main goal is to install a leak free flashing system that will last as long as the slate roofing shingles.

Working on a chimney with a slate roof, doing chimney repairs or installing flashing, requires experience and often some specialized equiptment and tools. This chimney is situated at the peak of a steep random size slate roof. Hook ladders and adjustable slaters roof brackets and planks are required to do the work.

 

Previous chimney repairs and flashing.

The original copper flashing had been re done about 8-10 yrs before. This picture shows the front chimney apron flashing and the corner of the side counter flashing. The apron is a one piece flashing that is secured to the roof and the face of the chimney. The problem with this type of one piece flashing is that the roof and chimney move separately from each other. The copper flashing also expands and contracts with the daily heating and cooling causing movement. If the flashing is secured at both points eventually the seal at the chimney will crack and lead to water leakage. You can see in this photo that the caulking has begun to crack between the flashing and the stone.

Slate roof ridge peak flashing.

The point where the chimney meets the roof ridge is also leaking at the flashing joint. You can also see signs of previous chimney repair at the mortar joint above the counter flashing. There  have also been repairs made to the slate roof.

Soil stack flashing repairs and side chimney flashing.

The one piece side counter flashing joint caulking is cracked and leaking. The lead soil stack flashing to the left is worn and has been repaired a few times by smearing tar around the top flange. It is also possible to see a slate nail at the bottom edge of the flashing.

Chimney leak at lower corner.

After removing the slate next to the chimney, I found that the apron flashing was not extended far enough past the corner, covering the lower slate joint and nail. And that the roof step flashing tin did not extend down past the corner of the chimney to cover the lower slate and apron. Another roof leak.

New copper apron flashing.

After cleaning the roof deck and installing new heavy tar paper underlayment, the new copper apron flashing and side step tins are installed. The side counter flashing had been left in place to minimize possible leakage due to rain, the step tins being slid underneath. The front of the apron flashing is held in place by two copper strips first fastened to the roof before installing the flashing. The front flashing is not a problem to install here because the masons ran the brick up past the roofline on this part of the chimney leaving a flat surface to work with.

New copper apron counter flashing installed.

After the old mortar/flashing joints are cleaned thoroughly of old tar, the new apron counter flashing is installed. The new copper flashing is held temporarily with lead wedges before new mortar is applied. This is the way the original roofers fastened the flashings. There were remnants of the original lead left in the mortar joint as the last workers did not take the time to clean the joint thoroughly.

New side copper flashing.

Individual counter flashing pieces are installed into the mortar joint and held in place by lead wedges. The separate copper pieces will minimize the effects of expansion and contracton, preventing buckling of the metal and loosening of the flashing joint.

New lead soil stack flashing.

A new lead soil stack flashing is fabricated in the shop to match the pitch of the slate roof. The new flashing covers the old pipe completely, eliminating the need for any sealant around the pipe.

New mortar at flashing joint.

New mortar that closely matchs the original chimney mortar is pointed into the flashing joints. The mortar is a mix of lime and sand with a small amount of cement to help the curing process.

The finished chimney flashing.

The finished sandstone chimney with new copper flashing. Copper apron sub and counter flashing with copper step tins woven into the slate. And new mortar at the flashing joints. The side counter flashing has been wrapped around the front of the chimney and soldered to the front apron counter flashing. The step tins are fitted at the corners and soldered to the apron. The copper apron is soldered securely to the copper strips fastened to the roof under the apron.
You will notice that the side counter flashing runs parallel to the roof instead of following the stone joints in a stepped fashion. The original flashing installers had hand chiseled a groove, or raggle, into the stone at that angle instead of using the mortar joints. They had also chipped some of the stone that protruded below that groove to make for a flatter surface to install their flashing against. I am not sure wether they were unsure or incapable of fitting the flashing to the rough stone in the traditional manner, or just thought it might look better this way.

With this new copper flashing installation and some repairs to the slate roof and chimney, this roof should be trouble free for quite a long time.

Dennis M. Crookshanks Construction Inc.
Slate and Copper Roof Restoration
Northeast Ohio