Questions and answers about how to build or inspect a wood-framed chimney chase.

This article series describes wood-enclosed metal chimneys, how a chimney chase should be constructed, and how those structures can be inspected for leaks, damage, or unsafe conditions.

Q&A about Wood Framed Chimney Chases Surrounding Metal & Insulated Metal Flues

These questions and answers about wood-frame chimney chase construction and safety were posted originally at CHIMNEY CHASE CONSTRUCTION - be sure to review that article.

On 2018-11-09 by (mod) - what to do about a prefab fireplace / chimney that's leaking

Rob

It's unclear just what sort of leak you are describing: flue gases, inadequate combustion air, what?

I don't assume the chimney needs to be replaced; but you should have it inspected by a certified chimney sweep who can tell you what's wrong and what repairs (or possibly re-lining if it's an older masonry flue) is needed.

Watch out: Meanwhile to be safe don't use the gas log fireplace and leave fuel to it shut OFF.

And be sure you have working smoke and CO detectors properly located and tested.

On 2018-11-09 by Rob

I have a prefab fireplace with gas logs. I recently discovered it is leaking. I am not sure how long this has been happening.

I replace the chase cover and it is still leaking the same as before. The chimney is on the side of the house. Any suggestions for how i could find out where the leak is coming from without replacing the entire chimney? Thanks for any help

On 2018-09-25 by (mod) -

Most likely you want to remove rodent infested insulation as it's unsanitary and a potential health hazard.

Before reinsulating which might require partial disassembly to provide access, you want to be sure that the design of the chimney Chase and its insulation and any fire blocking required therein will meet local fire and safety codes.

On 2018-09-25 by David

I recently discovered that there were mice or another rodent have been in the chimney chase and eaten through, knocked off and otherwise damaged the fiberglass insulation that was there. It's a two story house. What am I to do? What are my options

On 2017-08-02 by Thanh Truong

Hello,
I have a brick chimney about 2'x2'. After exit the roof ridge, it raises up about 3.5'. The crown portion is about 1.5'. This crown is cracked and the mortar is no longer holding bricks

. I would like to remove this crown (1.5') and replace it with wood frame. I then wrap all of them (3.5') with either metal or vinyl siding. This will help flashing the chimney at the roof. Will this cause any issue?
Thank you

On 2017-03-23 by (mod) -

No, Todd I don't think that's a common construction method. However I think that the drywall may have been put where you found it as a fire barrier. You should consider that and you should discuss with your local building inspector what she considers safe for the type of Chimney that you are enclosing.

On 2017-03-23 by Todd

Started to replace old cedar wood planks on side of chimney chase and found 25+ year old Sheetrock is this common ? Sheetrock in bad shape due to age ! And can I go back with exterior grade plywood or is Sheetrock required ?

On 2016-11-13 by (mod) -

Joe,

Before cutting any openings in a chimney chase I would review the fire blocking requirements likely to be specified by your local building inspector.

On 2016-11-13 by joseph dorsett sr

Good day,
I am building a 2 x 4 enclosure covered with 5/8" fire rated sheetrock around a selkirk supervent double wall chimney, running through a living space on the second floor just below the attic.All joints (3) are fastened with bolted joint rings and spacing codes meet regulations. The only reason I can find for the closure is to prevent someone or something from hitting the chimney causing it to part consequently causing a fire. With the closure in place I don't see how this is possible.

Question: can you install grills in the sheetrock to recover the heat comming off the chimney, which will also prevent the interor of the enclosure from geting to warm/hot?

Thank you
Joe d

On 2016-11-09 by (mod) - Check the UL Listing of the product you are thinking of using

Jon:

Where a mutli-wall metal chimney has corroded, you might find, as I have, that an exact replacement (such as a simple two-walled metal flue with just air as insulation) is no longer considered safe nor code-approved for a wood fireplace chimney. Neither may be a single-wall flexible stainless chimney re-liner.

Check the UL Listing of the product you are thinking of using, as well as checking with care the manufacturer's product description of its intended use.

For example you wouldn't use a single-wall flexible stainless product designed to *re-line* an existing masonry chimney flue when what's needed is an actual fireproof, insulated, multi-wall metal chimney.

In my OPINION UL or CSA listed flexible stainless chimney liners are suitable for re-lining an existing masonry chimney flue, and are most-useful where the chimney includes bends or offsets that would make inserting a solid smooth-walled chimney relining kit difficult.

But I also think that despite warranty claims, a flexible liner probably has a shorter life-expectancy than a heavier-gauge smooth-wall metal flue liner.

On 2016-11-09 by (mod) - Can I use the flex-stainless-still products to replace the double-wall-steel liner.

Richard:

I am way too scared of a house fire to say, based on e-text, that building wood (hence combustible) "chimney" to extend / repair a brick chimney is safe and OK. You are likely to set the house afire.

However there are alternative ways to extend a chimney top including a wood chase (properly constructed) around an insulated, multi-wall, fire-rated metal chimney flue.

On 2016-11-09 by Jon

My wood-framed fireplace has a 25-years old double wall steel liner that is corroded. Can I use the flex-stainless-still products to replace the double-wall-steel liner.

On 2016-10-03 17:32:32.807117 by Richard

I have a brick chimney that had some damage on the top. I'm thinking about replacing the top part of the chimney with a wood chase, so it's half wood half brick. The primary reason to use wood is to save some money. The existing flue is 8 by 8 clay. Is it possible to build a wood chase with the same 8 by 8 clay that connects to the bottom half? If not, is it possible to connect the metal flue used in the wood chase to the 8 by 8 clay flue in the bottom half?

On 2016-07-22 by (mod) - I had a chimney fire in the top 6 ft of my stainless chimney

Craig:

Watch out: The bad news is that probably anyone you talk with about this, if they have any sense at all (I have only a little sense), is not going to promise you that the chimney is safe (from fire or fatal CO poisoning) if you do any sort of home-made or patch job at all.

Best would be to remove and replace any damaged or questionable chimney sections of the chimney.

It might be possible to do this from the top, lifting, replacing, reinserting - avoiding having to wreck the stone veneer on your chimney chase. Be careful: you don't want a house fire.

On 2016-07-21 by craig oliver

apparently I had a chimney fire in the top 6 ft of my stainless chimney. The sweep found a small hole in a joint. The manufacturer was Marco and out of business. Can this be repaired with some type of cement or a stainless sleeve? I don't want to remove the stone veneer and replace the entire chimney.

On 2015-12-31 by (mod) - It is possible that the defect is only in the application of the brick veneer,

Joe:

It is possible that the defect is only in the application of the brick veneer, but because ANY movement in a chimney system can open up gaps and present fire or fatal carbon monoxide hazards, I'd ask for an expert inspection promptly;

From your question I can't know if the veneer cracks are due to improper veneer application or due to movement in the framed structure; either could cause cracking.

On 2015-12-31 y Joe W - vertical cracks in brick veneer on chimney

I recently had a brick chimney replaced with a wood chase covered with brick veneer.

One month after it was installed vertical cracks started to appear running through more than 10 rows of brick at the corners. We have not had any weather below 40 degrees yet. What could cause the cracks so soon after construction?

On 2015-10-04 by jim dungate

How much of a concrete footing is required for a 2 story chase?

On 2015-09-04 by (mod) -

Chances are the old chimney needs to be removed entirely and a new masonry chimney built from foundation up through the roof line. You would not simply enclose the existing structure with brick.

On 2015-09-03 by lily

my home was built 20 years ago and at that time the chimney was enclosed with wood. What problems might we incur if we try to now change it to be enclosed by bricks?

On 2015-09-03 by (mod) -

Yes. Please see https://inspectapedia.com/chimneys/Chimney_Flashing_Leaks.php for details.

The top of the step flashing must be sealed by some means such as counter flashing.

On 2015-09-03 by don

my builder installed step flashing between the chimney and roof. do i need more than that?

Question:

(July 17, 2012) Anonymous said:
So it is not standard or code to insulate the chimney chase below the roof line? Mine had some rotted siding and when I was tearing the old wood off there was fiberglass insulation from the ground floor to the roofline fire stop.

Reply:

Anon,

right, since the chimney chase carries an insulated metal flue rated for "zero" clearance, possibly actually requiring an inch or more of airspace, and because the chase is outside the building, it's not normally insulated;

But a rot problem would better be blamed on construction or flashing errors that allowed leaks into the chase. I agree that once wet, insulation in such a space slows drying and increases damage, but it's the leak that caused the trouble.

Question:

(Oct 24, 2012) grant said:
does the chimney flue need to be completely enclosed in the attic?

Reply:

Grant, no, assuming you mean e closing a fire rated insuated metal chimney, but fire clearances must be respected.

Question:

(Dec 26, 2012) Paul said:
We are planning on installing a wood stove on the ground floor of a two story home and running the stove pipe straight up. I want to get as much heat as I can from the chimney pipe on the second floor. The chimney pipe will be in a corner of the room and I would like the other two sides to have large wall vents to allow heat into the room. Does the chimney pipe have to be completely enclosed by sheetrock?

Reply:

(Dec 28, 2012) Steve said:
Paul,

It all depends on the type of vent pipe you are using and their clearance to combustibles rating. For Instance.. HT 103 chimney pipe for wood hardly gives off any ambient heat at all

(Jan 6, 2013) Paul said:
The chimney pipe requires two inches clearance. Although there may not be much heat, it still seems like a waste to fully enclose it in sheetrock.

Question:

(Jan 11, 2013) Anonymous said:
where could melted snow run down a wood framed vinyl sided chimney chase?

Reply:

Typically from a leaky chimney crown or top. Potentially elsewhere if the chase was not properly constructed, flashed, or sided.

Question:

(Jan 26, 2013) Dennis said:
Hi ,
we need to know cost price for repair wood chimney planks with cement planks
separately from job protecting leakage between bottom of chimney and roof
connection

What it cost usually ??We would need about 34 cement planks
Thanks

(Jan 27, 2013) Greg said:
We have a wood framed chimney chase and a gas insert. We want to raise the fireplace so we can install a hearth for seating. It is currently just a bit above the floor level. We are going to be tearing this area apart. How difficult is it going to be to raise the level. I am thinking it might be simple and only require re-trimming the metal flue after raising are re-supporitng the insert. Any comments would be appreciated

(Feb 7, 2013) Celeste said:
I've been having problems for almost 2 years now with a leaking (severely rusted) 28 - 30 year old chimney Pan.

The strata council in my complex after having a chimney mason inspect it (the chimney chase has no masonary, it is framed & stucco) has now deemed it my fault because I removed a WOOD burning zero clearence fireplace box from my second story townhouse (the home inspector condemned & said it can't be used).

I had the Chimney professionally capped off but left the chimney in tacked to avoid issues with the three other chimneys coming out of that same box. Now I need to have my own instection done... What is the best route to take & who would be qualified to assess my situation, not only the actual leak but the possible water damage etc. that has occured over the past 2 years?

(Nov 2, 2014) Virgil said:
My problem is that I have a 64 inch wide wood farmed fireplace enclosur that broadsides the roof and a valley about three inches in from one side.

That means that water coming down the roof has to travel horizontally for about 60 inches. Water leaks at the fascia board on both sides. Adding a saddle would cause a dead end at the valley. The solution seems rather complex.

Question:

(Nov 4, 2014) Robert A Wilson ll said:
I've been a sweep for 34 yrs. Finding in my area prefab fireplace double wall chimneys coming apart in condos build in the early 80's.

At that time there was no codes or inspections. Am now blamed for latest find. The owner thinks I damaged her chimney with my 8" poly brush. Do you know of any information to support my case? I believe lack of support straps inside chase is the real reason for pipe collapse and separation. I have given up cleaning metal flues over 2 stories now. thank you robert

Reply:

I agree Robert. Sometimes the solution is a very large saddle (cricket) or even roof mods. At the very least, use absolutely bulletproof flashing and detailing to minimize the leak risk.

Question:

(Nov 13, 2014) paul said:
Having a 2nd floor split system HVAC unit replaced. Contractor wants to run new refrigerant lines inside of the chimney chase from the crawl space to the attic. Is this allowed? Won't it ruin any fireblocking?

Reply:

Paul

I would NOT do what is suggested for several reasons if the chimney is or is ever likely to be in use.

If the chimney has been abandoned and if fire sealant is used at penetrations that might be ok.

(Nov 13, 2014) paul said:
I could not find any IRC codes that say don't run a refrigerant line in a chimney chase other than the fire blocking issue.

Reply:

Paul:

Re no code prohibition for refrigerant lines in chimneys: in my OPINION there are so many possible variations in SNAFUS in construction that building codes do not and cannot list every thing NOT to do. Rather codes list more general guidelines including "follow the manufacturer's instructions". Probably a chimney chase - if we're speaking accurately - is less worrisome than running refigerant piping in an actual chimney where heat from combustion gases could ruin the piping and overheat refrigerant.

Question:

(Nov 17, 2014) Chris said:
I am installing a wood stove and because of the pitch of the roof I decided I need a false chase due to the exposé 10 foot piping. . Do you do this (its a stone/siding house) or could you refer me to someone in Cincinnati. Thanks.
Cnneus@gmail.com

(Dec 20, 2014) Keith said:
I have a minor draft at my fireplace. Blows back in the room enough to make it unusable. It is an insert with a 22 degree offset. I have covered the chimney to see if it is down draft not the problem. I have also covered the outside air intake not the problem. Help!

Reply:

Keith I don't think we could find a draft by e-texting. A careful on-site inspection by a fireplace mason or installer or possibly an experienced home inspector may be of some use.

Or you could try some smoke testing. You could perhaps also do the test in reverse: fans blowing into the home to pressureize it and smoke released in and around the fireplace, spotting smoke appearing outdoors.

See inspectapedia.com/Energy/Air_Leak_Heat_Loss_Tools.php#Leaks5 for smoke test suggestions

See inspectapedia.com/Energy/Air_Leak_Heat_Loss_Tools.php for examples of detecting air leaks

See inspectapedia.com/Energy/Smoke_Pencils_Testers.php for sources of smoke testers

Question:

(Feb 16, 2015) Brian said:
I have a 3 story house that had its chimney destroyed by an earthquake.

The chimney serviced first and second floor fireplaces traveling up the inside of the house and transitioning to the outside as it passed through the third stories mansurd roof. From the first floor to the mansurd roof the existing chase where the brick chimney used to be is fairly wide and deep, however, it narrows where it passes through the mansurd roof.

At this point the new internal dimension of the wood framed replacement chimney is only 24 inches wide by about 18 inches deep. This section is about 8 feet long before entering a 5 foot tall metal sleeve/cap that sits above the roof line. I need to pass a 8" class A metal flue through (10" outside dimension) along with a 6" B vent.

That totals 16 5/8" of flue leaving 6 3/8 " of space left for clearance between combustibles and the two pipes.

Even though I can achieve 2" clearance between the chases plywood walls and metal flues, I am more than a little worried about applying these clearance criteria to 8 feet of plywood surface that the city would like to have fireblocked. It would seem to me that I would be creating an oven made of plywood. Do I have a problem?

Reply:

Yes.

I would 1. ask for details of what the city wants you to do

and 2. check with a design professional

Question: is there a fire-retardant paint to use inside of a chimney chase?

(June 6, 2015) Anonymous said:

I just replaced my chimney siding (T11) after 7 years since the new roof was installed. The usual cause due to rain rot around the edging. I noticed the discarded T11 where the side facing the flu appeared to be painted with some form of (possibly) fire resistant paint or it could just be discoloration from the Heat.

Is there a paint available? The new job is tight as skin. Let me know if I needed some type of interior coating.

You can send me a reply via my email tomhaeussner@yahoo.com

Reply:

Anon:

In a properly constructed chimney chase with the proper-rated and type of chimney installed there should never be enough heat emitted to char the interior surface of the T111 siding. I would ask for an inspection by a certified chimney sweep to be sure your chimney is the proper type and properly installed. The risk is a house fire.

If your chimney is venting a UL listed appliance you do not need and should not require any type of insulating or fireproofing coating on the interior of the chimney chase, though some writers such as my friends over at the JLC (Journal of Light Construction) like putting a fire-resistant covering inside of a chase (keep those clearance distances though).

To build a fire-retardant chimney chase one might use FIRE RETARDANT PLYWOOD and sure one could try spraying a fire-retardant coating, but those are not common practices.

Codes allow a maximum of 90 degF temperature rise above ambient inside the the chimney chase - well below the combustion or pyrolysis point for plywood.

A greater fire risk in chimney chases might occur if birds or squirrels can get into the chase where it's a lovely place for nesting.

Do check that the chimney chase has the code required fire blocking.

[Readers with masonry chimneys will want to take a look at Chapter 10 of the 2003 (or later) IRC: Chimneys and Fireplaces.]

Question: ok to run pipes through the chimney chase?

22 July 2015 Tom Brackett said:
Can I run my sewer pipe thru the fire place chase

Reply:

Tom:

I doubt your local code officials will permit running a sewer line through a chimney chase. There are issues with fire blocking and clearances to combustibles.

Useful Wood Chimney Chase & Cap & Shroud References & Codes

• Stephen Werner General Manager Chimney King, op cit, personal communication 3/26/2013 w/attachments:
  • CHIMNEY KING INSTALLATION INSTRUCTIONS FOR CHIMNEY CROWN, [PDF]
  • Purdie, Roger K., "CHIMNEY FIRE SAFETY BULLETIN", Vista Fire Protection District, 2001, report of house fire related to the home's metal chimney. Contains advice for chimney * fire safety & sketches of approved and not-code-approved metal chimney tops, caps & crowns. [PDF]
  • See also CHIMNEY SHROUD FIRE - technical article contribution by Mr. Werner
• Residential Masonry Fireplace and Chimney Handbook, James E. Amrhein, S.E., MIA, Masonry Institute of America, 2d. Ed., 1995, ISBN 0-940116-29-4. The MIA is in Los Angeles, CA 213-388-0472. This manual reflects the 1994 Uniform Building Code, Energy Conservation Requirements of California, and the U.S. Department of Housing and Urban Development - HUD. The complete UBC is available from the International Conference of Building Officials (ICBO), Whittier CA 310-699-0541.
• National Chimney Sweep Guild - Yellow Pages of Suppliers
• International Residential Code IRC R100.11 - Fireplace Clearance:
  International Residential Code was recently amended:
  
  R1001.11 Fireplace clearance. Combustible material shall have a clearance of not less than 2 inches (51 mm) from the front faces and sides of masonry fireplaces and not less than 4 inches (102 mm) from the back faces of masonry fireplaces. The air space shall not be filled, except to provide fire blocking in accordance with Section R1003.12.
  
  Exceptions:

  1. Masonry fireplaces listed and labeled for use in contact with combustibles in accordance with UL 127, and installed in accordance with the manufacturer's installation instructions, are permitted to have combustible material in contact with their exterior surfaces.

  2. Combustible materials, including framing, wood siding, flooring and trim, shall be permitted to abut the sides and hearth extensions, but not the backs, of masonry fireplaces, in accordance with FIGURE R1003.12, provided such combustible materials are a minimum of 12 inches (306 mm) from the inside surface of the nearest firebox lining.

  3. Exposed combustible mantels or trim may be placed directly on the masonry fireplace front surrounding the fireplace opening provided such combustible materials shall not be placed within 6 inches (153 mm) of a fireplace opening. Combustible material within 12 inches (305 mm) of the fireplace opening shall not project more than 1/8 inch (3.2 mm) for each 1-inch (25 mm) distance from such opening

• NFPA 211 - Standards for Chimneys & Fireplaces, NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2006 Edition (older editions and standards are found at the same bookstore), NFPA #211-3.1 1988 - Specific to chimneys, fireplaces, vents and solid fuel burning appliances.
  • NFPA 211 - 3-1.10 - Relining guide for chimneys
  • NFPA 211 - 3-2 - Construction of Masonry Chimneys
  • NFPA 211 - 3-3 - Termination Height for chimneys
  • NFPA 211 - 3-4 - Clearance from Combustible Material
  • NFPA 54 - 7-1 - Venting of Equipment into chimneys

...

Continue reading at CHIMNEY CHASE CONSTRUCTION or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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• CHIMNEY CHASE FIRE
• CHIMNEY SHROUDS
• CONCEALED SPACE FIRE CODES
• FIRE STOPPING in BUILDINGS
• FIREPLACE INSPECTION PRE-FAB
• CHIMNEY INSPECTION DIAGNOSIS REPAIR - home
• CHIMNEY STAINS & LEAKS

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