Pick your flashing by roof pitch, not by pipe brand. A chimney pipe roof flashing has a fixed cone angle, so a flat-roof flashing will not sit down on a 9/12 roof and a steep-pitch flashing will not seal on a low one. Measure the pitch first, then match the flashing to it and the collar to your pipe diameter.
Which flashing fits your roof?
There are three pitch bands, each made in 6 inch and 8 inch to match your chimney pipe. Find your roof in the left column and the flashing is decided.
| Your roof | Flashing that fits |
|---|---|
| Flat, or almost flat | Flat roof flashing with storm collar |
| Shallow to standard, 1/12 up to 6/12 | 1/12 to 6/12 pitch roof flashing with storm collar |
| Steep, 7/12 up to 12/12 | 7/12 to 12/12 pitch roof flashing with storm collar |
The flashing is part of a through-the-roof chimney kit, so it arrives matched to the pipe rather than ordered on its own. If you are not sure which band your roof falls in, send us the measurement and we will confirm it.
Not sure of your pitch?
Pitch is the rise in inches over 12 inches of horizontal run, so a roof that climbs 6 inches across a 12 inch run is a 6/12. You can measure it from inside the attic with a level and a tape, without going up on the roof. The step by step method is in how to measure the pitch of a roof.
If your reading lands right on a band edge, take the band that covers the steeper angle. A flashing can flex down onto a shallower roof more easily than it can lift onto a steeper one.
What is the flashing around a chimney called, and what else do you need?
Three separate parts do three separate jobs at a roof penetration, and people often think of one when the job needs all three.
- Roof flashing. The metal base plate with a cone in the middle. It sits on the roof deck, laps under the covering on the uphill side, and carries water around the pipe. This is the part that must match your pitch.
- Storm collar. A narrow band that clamps around the pipe just above the flashing cone and is sealed with a bead of high temperature silicone. Without it, rain runs down the outside of the pipe and straight into the top of the cone.
- Roof radiation shield. A separate part that keeps the required air space where the pipe passes the roof framing. It is not a weather part and it does not replace the flashing.
All three belong to the same through-the-roof set. Ordering them as a matched kit is what stops one of the three being missed.
What does a storm collar do?
A storm collar stops rain tracking down the outside of the pipe and into the flashing cone. The flashing handles water arriving on the roof surface. The collar handles water arriving down the pipe itself, which is the leak most people only discover in the first heavy storm after the install. It is the smallest part at the penetration and the one that prevents a repair inside the ceiling. The pipe it clamps to is rated for 1000 degrees F continuous use, so the bead that seals it has to be a high temperature silicone rather than an ordinary exterior caulk.
What are chimney flashings and storm collars made from?
Ours are stainless steel, the same material family as the Class A chimney pipe they seal against. That matters at a roof penetration for two reasons. The part sits in standing water and snow for the life of the roof, and it is clamped to a pipe rated for 1000 degrees F continuous use, so it goes through a heating and cooling cycle every time the stove is lit. Aluminum and painted steel flashings sold for masonry chimneys are not built for that duty on a hot round pipe.
How do you install a storm collar on chimney pipe?
The collar goes on after the flashing, clamping around the pipe just above the flashing cone, and it is sealed along its top edge where it meets the pipe. Slide it down the pipe until it sits above the cone with a small gap, draw the clamp band tight, then run a continuous bead of high temperature silicone around the joint between the top of the collar and the pipe wall. The bead is what makes it watertight. The clamp only holds it in place. Torque figures and any product specific steps come from the instructions supplied with your parts.
What sealant is used on a storm collar and a flashing?
A high temperature silicone is used at the storm collar, and a high temperature roofing sealant is used where a flashing base is bedded onto a metal panel. Ordinary exterior caulk is the wrong product in both places, because the pipe and the metal around it move as the system heats and cools and a low temperature sealant hardens and cracks. Use the sealant named in the instructions that come with your parts, and apply it to a clean, dry surface.
How do you seal around a chimney pipe on the roof?
There are two seals to get right, not one: the flashing base against the roof covering, and the storm collar against the pipe. The base laps under the covering on the uphill side and over it on the downhill side, so water runs across the flange and away rather than under it. The collar closes the gap between the pipe and the top of the cone. Getting one right and skipping the other is the usual reason a new penetration still leaks.
Round chimney pipe, not a masonry chimney
Search results for chimney flashing mix two different jobs, and the parts are not interchangeable. If you have a brick or block chimney, you need step flashing, counter flashing and possibly a cricket, cut and woven into the roof covering course by course. That is roofing work and we do not supply those parts. If you have a round metal chimney pipe coming through the roof, which is what a Class A insulated system uses, you need a one piece cone flashing sized to the pipe. Everything on this page is the second kind.
Metal, tile and shingle roofs
The flashing is chosen by pitch and that does not change with the roof covering. What changes is how it is bedded and fastened. On a ribbed or standing seam metal panel the base is bedded in high temperature roofing sealant along the uphill and side edges and fastened with gasketed screws, with the downhill edge lapping over the panel so water sheds outward. Full detail is in wood stove chimney through a metal roof. For clay or concrete tile, where the covering is rigid and cannot be dressed down onto the base, see installing a chimney pipe through a tiled roof.
How far does the pipe have to clear the roof?
The flashing sets where the pipe leaves the roof. Code sets how far it carries on above that point, and getting it wrong means buying pipe twice.
The 3-2-10 rule (NFPA 211 / IRC R1003.9) requires that a chimney extend at least 3 feet above the highest point where it passes through the roof, AND at least 2 feet higher than any portion of the building, structure, or obstruction within a 10-foot horizontal radius.
Measure the 10 foot radius before you order. A ridge, a dormer or a neighboring wall inside that circle raises the termination height, and the extra length is often one more pipe section plus a brace.
Which clearance applies where the pipe passes the framing?
The flashing is a weather part. The air space through the roof structure is a fire safety requirement and it is set by the pipe listing.
Class A insulated chimney pipe, when UL 103 HT-listed for wood-burning, maintains a minimum of 2 inches clearance to combustibles per the standard listing. Always verify the exact clearance specified by the manufacturer's UL listing for the specific product.
That air space is held open by the roof radiation shield, not by the flashing, which is why the two belong to the same through-the-roof set. Our Class A insulated chimney pipe is double-wall insulated stainless steel rated for 1000 degrees F continuous use, and it carries a 100% replacement warranty for the first 15 years and 50% of the original price after that, for as long as the original buyer owns the system, when it is installed in accordance with the instructions supplied with it.
Can you fit it yourself, and how do you know it is right?
Fitting a flashing and collar is within reach of a competent DIY installer, provided the roof itself can be worked on safely and the pipe below is already correct. The parts bolt together and the sequence is short. What is not a DIY judgement call is whether the penetration keeps the 2 inch clearance the pipe listing requires and whether the termination meets the height rule above, because both are fire safety requirements rather than preferences. If either is in doubt, have the install checked before the first fire.
Three signs the job is right, all checkable from the ground or a ladder:
- The flashing base disappears under the roof covering on the uphill side and laps over it on the downhill side.
- The storm collar sits above the cone with a continuous silicone bead at its top edge and no gap you can see daylight through.
- After the first heavy rain there is no staining on the ceiling around the pipe. Staining after a dry install almost always means the collar, not the flashing.
How do you work out what to order?
- Measure your roof pitch from inside the attic, using the method in how to measure the pitch of a roof. Write down the rise over 12.
- Confirm your chimney pipe inner diameter, 6 inch or 8 inch. It is stamped on the pipe or listed on your original order.
- Measure the 10 foot radius around the penetration and work out the termination height against the 3-2-10 rule.
- Send us those three numbers. We will specify the flashing, the collar, the radiation shield and the pipe lengths as one matched set.
That last step is the free flue design service, and it exists so you are not assembling a roof penetration part by part and hoping the pieces meet. Send the pitch, the pipe diameter and a photo of the roof area, and we build the list.
Need More Information?
Review the frequently asked questions, browse the installation guides, or use the free flue-design service if you would rather have the penetration specified for you. You can also call 888-834-0880.
