Home / Chimney Academy / Roof Replacement and Your Chimney
Roof Replacement and Your Chimney
A new roof and an old chimney meet at the flashing, and that junction is where many later leaks begin. The order of the work, and who is responsible for which part, matters more than most homeowners expect. A little coordination before the shingles come off can save a second visit and a disputed leak.
The short answer: Have the chimney inspected before the roof is replaced, so masonry, crown and cap repairs are done first or planned alongside it. Chimney flashing should be renewed with the new roof, not reused, and the roofer and the chimney contractor need to agree on who handles which layer.
Why the roof and chimney are one system
A chimney passes through the roof, so every roofing job has to deal with it. The roof sheds water down and away. The chimney stands in the way. The flashing is the metal that bridges the two so water runs around the chimney instead of into the house.
If the flashing is installed well, nobody thinks about it for decades. If it is rushed, reused, or sealed with a bead of caulk alone, a leak can show up at the next heavy rain or wind-driven storm. Roofers are usually paid and scheduled around the roof. Chimney masonry is a different trade, and the joint between them is easy to fall through the cracks.
This guide explains the sequence and the vocabulary so you can ask the right questions. It does not replace a roofer’s scope or a building code review. For local requirements, ask your municipal construction office or building department.
What the flashing actually consists of
Chimney flashing is normally two layers that work together. Base flashing sits on the roof surface and turns up against the chimney. Counterflashing is set into the masonry and laps down over the base flashing, so water that runs down the brick lands on the metal and is carried onto the roof.
A Brick Industry Association brief on flashing chimneys gives dimensions for this arrangement. Base flashing at the roof is described as extending at least 4 inches along the roof and 4 inches up the chimney face, with counterflashing lapping the base by at least 3 inches. The brief also states that flashing which does not extend fully into the wall is “little better than no flashing at all”. Those numbers come from a masonry industry document, not a local code, so use them as an idea of the proportions, not as a requirement for your house.
The same source covers materials. Copper and Type 304 stainless steel of a minimum thickness are described as suitable, galvanized steel is not recommended because thicker zinc coatings can crack when folded, and aluminum should not be used because alkalis in fresh mortar attack it. For a deeper tour, see chimney flashing repair and roof leaks.
Wide chimneys and the cricket question
On a wide chimney, water collects behind it on the uphill side like a dam. A cricket, also called a saddle, is a small peaked structure that diverts water around the chimney. A Brick Industry Association technical note on residential chimneys says a cricket is typically used when the chimney is more than 30 inches wide parallel to the ridgeline. Again, that is a design guideline from the masonry industry. Local code and the roofer’s judgment decide what your roof needs.
If your chimney is wide and has no cricket, a roof replacement is the cheapest time to raise the question, since the roofing is already open. Your roofer or chimney contractor can tell you whether one makes sense.
A sensible order of work
- Inspect the chimney before the roofing contract is signed. A chimney inspection checks the crown, cap, mortar joints, and the existing flashing. If the flashing was installed into a mortar joint that is crumbling, the new metal will be set into weak material.
- Decide who owns each repair. Masonry repair, crown work and cap replacement belong to a chimney contractor. Roofing and often the base flashing belong to the roofer. Counterflashing set into brick sits on the line between them, so agree in writing who is doing it.
- Do masonry work first when it affects the flashing. Repointing joints where counterflashing will be set, or repairing the upper courses, goes better before the roof is finished. Otherwise the roof crew may need to return.
- Remove old flashing, do not bury it. The roofer strips the old base flashing as the roof comes off. Reusing the counterflashing in old mortar joints is a common shortcut, and it is worth asking about.
- Install the new base flashing as the shingles go on, in layers that overlap in the direction water flows, with the lower pieces going first.
- Set the counterflashing into cleaned joints and seal it as the product requires.
- Check the finished work, from the ground and the attic, after the first heavy rain.
The timeline above is a general sequence. Your job may differ, particularly when there is a factory-built chimney with a metal storm collar, a stucco chase, or siding around the base.
Questions worth asking the roofer
- Will the chimney flashing be replaced with new material, or reused?
- What metal will it be, and is it compatible with the cap and chase cover?
- Will the counterflashing be set into the brick, or will sealant alone hold it?
- If a cricket is needed, who builds and flashes it?
- If I have chimney masonry repairs pending, how will you coordinate with that contractor?
- What happens if a leak shows up at the chimney after the job?
A good answer is specific. A vague one (“we’ll seal it up”) is a signal to ask for the detail in writing. Compare quotes by scope, not only total, with the help of understanding a chimney repair quote.
During and after the roofing job
Roof work puts weight, vibration and sometimes loose debris around the chimney. Tell your chimney contractor if a roofing crew has been working beside a masonry chimney with loose mortar or a lean. A chimney that already has a gap or a lean should be evaluated first, see a leaning chimney or gap between chimney and house.
Afterward, look at the following:
- Water stains on the ceiling or wall near the chimney after a storm.
- Debris or sealant smears on the cap, crown or brick, which a roofer may have left.
- Loose or bent metal at the chimney base visible from the ground.
- Any pieces falling into the fireplace. That is covered in mortar, brick or tile pieces falling into your fireplace.
If you plan to use the fireplace soon, a chimney cleaning and inspection after construction work is reasonable, since roofing debris, nails or granules can end up in unexpected places. A cap that was removed for the roof should be confirmed back in place before you light a fire.
When to call a chimney professional
Call before the roofer starts if the chimney has crumbling mortar, a cracked crown, a rusty cap or chase cover, or an older flashing detail you do not understand. Call after the job if you see a leak, a loose cap, or damaged brick. AM Chimney Sweep provides chimney repair, crown repair, masonry repointing and cap and chase cover work across New Jersey, and explains findings and options before any work begins.
This guide cannot say what your flashing needs or whether your roofer’s plan is right. It gives you a sequence and a list of questions so the roof and the chimney are treated as the connected system they are.
Frequently asked questions
Should chimney flashing be replaced when the roof is replaced?
In general, yes, since the shingles around the chimney are being removed anyway. Ask the roofer whether the flashing will be new and what it will be made of.
Who should install the counterflashing?
Either a roofer or a chimney contractor can, as long as the work is agreed in advance. What matters is that it is set into the masonry properly rather than only sealed.
Do I need the chimney inspected before a roof replacement?
It is a good idea, because weak mortar or a damaged crown affects how the flashing is attached and can cause leaks later.
Is caulk enough for chimney flashing?
Sealant alone is not a substitute for properly lapped metal flashing. It is a supplement, and it ages.
Related reading
Sources
- Brick Industry Association, Flashing Chimneys: base and counterflashing layers, laps, materials and common failures
- Brick Industry Association, Technical Note 19B: Residential Chimneys: flashing requirements in most codes and when a cricket is typically used
Want a professional to look at your chimney?
Book a visit, or call and tell us what you are seeing.