Replacing Your Roof? Plan the Chimney Too

Why the roof job is the right moment

During a roof replacement the old roofing around the chimney comes off, the decking is exposed, and the roof is staged for safe work. That is the easiest time to see the condition of the chimney where it meets the roof, to replace rotted decking around it, and to install new flashing properly. Once new shingles are down, any chimney repair that disturbs the flashing risks damaging a brand-new roof.

Masonry repairs that drop mortar and debris, such as rebuilding the top of a chimney, are also better done before the new roof goes on, not after.

How chimney flashing works

Flashing is the sheet metal that seals the joint between the chimney and the roof. A typical system has several parts:

• Base flashing at the low side of the chimney, lapped over the shingles below.
• Step flashing along the sides, one L-shaped piece woven into each course of shingles.
• Cricket or saddle on the high side, a small peaked structure that diverts water around a wide chimney.
• Counterflashing (cap flashing) attached to the chimney and lapped down over the step and base flashing.

One flashing manufacturer's instructions describe the key principle: the base and step pieces are fastened to the roof only, and the counterflashing is fastened to the chimney only, so the roof and chimney can move independently without tearing the seal. A municipal flashing detail we reviewed shows counterflashing set into the mortar joints of the chimney. See chimney flashing repair.

Does your chimney need a cricket?

Water running down the roof hits the high side of the chimney and pools there unless it is diverted. Masonry trade guidance recommends a cricket for chimneys wider than 30 inches, and building codes generally call for one behind wider chimneys. Your town's construction office can confirm what applies. If your chimney is wide and has no cricket, a roof replacement is the natural time to add one, since it is built into the roof framing and covered with roofing or metal.

Who does what

There is no single rule for who does each part. The important thing is that someone owns each piece and the order is clear. Counterflashing that is only caulked to the face of the brick, rather than set into the mortar or a cut reglet, is a common source of repeat leaks.

What to check before the roofer arrives

• Crown. Cracks or a missing overhang. See crown coating vs. rebuild.
• Cap. Missing, rusted or loose caps let rain and animals into the flue.
• Masonry above the roof. Open joints, spalled brick, or a leaning stack. See repair or rebuild.
• Old flashing and signs of past leaks. Staining on decking, rafters, or ceilings near the chimney, checked from the attic when safe and accessible.
• The flue. If the chimney is still used, a camera look inside, when the flue allows, can show whether relining should be planned while access is easy.

A practical sequence

1. Chimney inspectionWeeks before the roof date, so findings and any repairs can be scheduled.
2. Masonry, crown and cap workCompleted before the roofer reaches the chimney area.
3. Roof tear-off and decking repairRotted wood around the chimney is replaced.
4. Flashing and cricketInstalled with the new roofing.
5. CounterflashingSet into the chimney and lapped over the roof flashing.
6. CheckA final look at the joint between roof and chimney.

Questions to ask your roofer

• Will the old chimney flashing be removed and replaced, or reused?
• Who installs the counterflashing, and how is it attached to the masonry?
• Will a cricket be added if the chimney is wide and does not have one?
• What happens if rotted decking or rafters are found around the chimney?
• How will the chimney area be protected if masonry work is still underway?

Share the chimney findings and photos with the roofer so both trades are working from the same information. Many leaks blamed on a new roof turn out to be gaps at the hand-off between the two.

Signs the joint is not right after the job

Watch the ceiling and attic near the chimney during the first heavy rains after a new roof. Staining, drips, or damp insulation near the chimney suggest the flashing, counterflashing, or the chimney itself is letting water in. Not every leak near a chimney comes from flashing; a cracked crown or porous brick can send water down inside the masonry. See why is my chimney leaking? When the source is not clear, controlled water testing can help isolate it.

Permits and unused chimneys

A roof replacement sometimes prompts the question of whether an unused chimney should come down below the roofline. That is a bigger decision involving framing and possibly permits. See should you remove an unused chimney?

In New Jersey, the state's code guidance lists repair or replacement of roof covering on detached one- and two-family homes as ordinary maintenance. Structural masonry and other chimney work may be treated differently, and towns apply the rules locally. Check with your local construction office for your project.

Next step

Planning a new roof? Request a chimney assessment ahead of the roofer, and a team member will contact you to confirm a time. Findings come with photos so you and your roofer can plan together. See our flashing repair and crown repair services.

Questions homeowners ask

Sources

1. Moheco UniFlash chimney flashing installation instructions
2. City of Saint Paul, MN: Chimney flashing detail
3. Masonry Magazine (MCAA): Masonry Chimney Checklist for Weather Resistance
4. NJ Department of Community Affairs: Significant Changes to Minor Work and Ordinary Maintenance (2018)
5. Brick Industry Association, Technical Note 46: Maintenance of Brick Masonry

This guide is general information. It can't diagnose a specific chimney; an inspection can.