whether and how to insulate this chimney exit?

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cobscookie

New Member
Oct 15, 2022
8
Maine
I hired someone to install a wood stove with a manufactured chimney, which exits to the outdoors through a cathedral ceiling with a metal roof. Attached photos show the view from the interior after the chimney installation, before connecting the stove. My question: should I insulate this opening, and if so how?

My installer says absolutely not. He says that the space between the ceiling and the roof needs to be open to allow heat to escape from the chimney and "The little space, especially once the interior trim plate is covering the opening around the chimney pipe, will not be cooling down the home to any degree. Filling that void with insulation may create a situation that heats up the framing around it."

Looking up into the 14 x 18 opening (6" deep) you can see the bottom of the metal roofing, the wings on the roof support, the tin-snipped opening in the flashing, and above that the sloped walls of the flashing itself (it looks like daylight because the storm collar is sealed with clear silicone). My arm fits through the gap around the chimney in some spots. I see the argument for leaving air space in the void, but I strongly think I need to at least put an inch or two of Rockwool, SUSI, or similar perhaps on the flat at the top of the opening against that metal roofing/chimney flashing, to keep the rising heat in the room from conducting straight out through the metal--a situation that I imagine will be especially noticeable in the wee hours of a winter morning when the fire is down to coals and the outside temp is 10 degrees.

Even better IMO, but perhaps overkill, would be to create a retrofit sheet metal air barrier to go below the insulation, still leaving 4-5 inches of void below the sheet metal.

My installer does not approve of SUSI and says Rockwool is only fire resistant but not fireproof enough to go up against the chimney. I would welcome getting some clarity about whether I'm too paranoid about heat loss through the roof. Thanks.
IMG_3246.jpg IMG_3251.jpg IMG_3252.jpg
 

begreen

Mooderator
Staff member
Nov 18, 2005
98,097
South Puget Sound, WA
This is determined by the chimney pipe manufacturer. Some sell there own approved insulation which may be mineral wool or ceramic wool.
 

cobscookie

New Member
Oct 15, 2022
8
Maine
Thank you. I hadn't thought about asking the manufacturer directly! I contacted Selkirk and they replied that their insulation (SUSI) can only be used in tandem with their Attic Insulation Shield, the Cathedral Support Box or Wall Thimble, which I don't have. They reiterated that the air space clearance requirement for their chimney is 2” and "having more than 2” is fine, but is not necessary, and sometimes more is not better. If you have 4” – 5” of open space around the chimney as it’s exiting the room / roof, then that’s more space through which warm air can escape." My current plan is to fill the void by gluing in a batt of Rockwool (with Rockwool's fireproof glue), leaving a hole in the batt that's sized for 2" clearance for the chimney pipe.

[[ETA: It will prob end up being more like four pieces of Rockwool (one for each corner) rather than a rectangle with a hole in it, since the framing comes to within 2" of the pipe on the top, bottom, and sides.]]
 
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Eman85

Minister of Fire
Oct 10, 2022
510
E TN
What is holding that chimney up there? I've installed chimneys in a cathedral ceiling and the use a support box. That looks like they used an axe to cut the hole! With a box all you need is a small trim piece around it to cover the edge of the sheetrock. Then the ceiling insulation can go right against the box as the chimney is in it.
 
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cobscookie

New Member
Oct 15, 2022
8
Maine
Hi Eman85--to answer your question, a little history about that chase: There was a Metalbestos wood stove chimney exiting through that opening from 1988-2012, through a shingled roof, while I lived there (heating full-time with wood). That chimney must have had the roof support at that time, b/c there was no support box at the ceiling, just a flush trim plate (you can see the round shadow where it was). I never actually saw what the chase looked like at that point. I rented the space to a tenant from 2012 until last year, and for that person I replaced the wood stove with a Hearthstone direct vent gas heater, for which the installer used a cathedral support box. Since then I've put a metal roof over the shingled roof. Now I am moving back in and going back to wood heat. I had a hard time finding a local installer who would deal with the metal roof. The installer I hired took out the DV support box (which was too small for 8" insulated pipe) and used a roof support kit to hang the Selkirk chimney. I'm not sure whether he did that (instead of installing another support box) from lack of experience or lack of planning or pure preference. If you were so inclined, I'd be grateful if you might take a look at the exterior and tell me if *that* looks OK or if you have any caveats. (Note, I am waiting for the rain cap, which he forgot to order 😏)

IMG_3260.jpg
 

Eman85

Minister of Fire
Oct 10, 2022
510
E TN
I installed my cathedral ceiling support, from Selkirk when I had a shingle roof. Then we roofed over with metal and used a flashing boot over the metal roof. I like the flashing that was used on yours.
 
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begreen

Mooderator
Staff member
Nov 18, 2005
98,097
South Puget Sound, WA
Hi Eman85--to answer your question, a little history about that chase: There was a Metalbestos wood stove chimney exiting through that opening from 1988-2012, through a shingled roof, while I lived there (heating full-time with wood). That chimney must have had the roof support at that time, b/c there was no support box at the ceiling, just a flush trim plate (you can see the round shadow where it was). I never actually saw what the chase looked like at that point. I rented the space to a tenant from 2012 until last year, and for that person I replaced the wood stove with a Hearthstone direct vent gas heater, for which the installer used a cathedral support box. Since then I've put a metal roof over the shingled roof. Now I am moving back in and going back to wood heat. I had a hard time finding a local installer who would deal with the metal roof. The installer I hired took out the DV support box (which was too small for 8" insulated pipe) and used a roof support kit to hang the Selkirk chimney. I'm not sure whether he did that (instead of installing another support box) from lack of experience or lack of planning or pure preference. If you were so inclined, I'd be grateful if you might take a look at the exterior and tell me if *that* looks OK or if you have any caveats. (Note, I am waiting for the rain cap, which he forgot to order 😏)

View attachment 300972
Looks like the upper edge of the flashing is properly tucked in under the metal roof. I like to see a bead of silicone on that upper seam (but not on the bottom). It shouldn't be heavily goobered, but a bead a the top will help prevent bees from going up the channel and migh stop wind driven rain if blowing against the seam.
 
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lofarabia

New Member
Oct 10, 2022
8
Minnesota
Thank you. I hadn't thought about asking the manufacturer directly! I contacted Selkirk and they replied that their insulation (SUSI) can only be used in tandem with their Attic Insulation Shield, the Cathedral Support Box or Wall Thimble, which I don't have. They reiterated that the air space clearance requirement for their chimney is 2” and "having more than 2” is fine, but is not necessary, and sometimes more is not better. If you have 4” – 5” of open space around the chimney as it’s exiting the room / roof, then that’s more space through which warm air can escape." My current plan is to fill the void by gluing in a batt of Rockwool (with Rockwool's fireproof glue), leaving a hole in the batt that's sized for 2" clearance for the chimney pipe.

[[ETA: It will prob end up being more like four pieces of Rockwool (one for each corner) rather than a rectangle with a hole in it, since the framing comes to within 2" of the pipe on the top, bottom, and sides.]]
Hello I am pretty sure the 2 inches is for combustibles, not air space.I questioned insulating the cathedral ceiling support also,(check out you tube video ) I called Supervent and they said, yes In cold climates that is what the SUSI is for. The guy on the video used Perlite. I used 2000+ degree Johns manville Sound and fire block and insulated the whole chase.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
31,154
central pa
Hello I am pretty sure the 2 inches is for combustibles, not air space.I questioned insulating the cathedral ceiling support also,(check out you tube video ) I called Supervent and they said, yes In cold climates that is what the SUSI is for. The guy on the video used Perlite. I used 2000+ degree Johns manville Sound and fire block and insulated the whole chase.

No the 2" is for what ever the manufacturer specified. Many specify air space. Some provide an insulation kit
 
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lofarabia

New Member
Oct 10, 2022
8
Minnesota
No the 2" is for what ever the manufacturer specified. Many specify air space. Some provide an insulation kit
Yes... in the Supervent literature the Cathedral ceiling support (CCS) as well as the Attic insulation shield (AIS) states they are installed to maintain the 2 inch requirement from combustibles.
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
31,154
central pa
Yes... in the Supervent literature the Cathedral ceiling support (CCS) as well as the Attic insulation shield (AIS) states they are installed to maintain the 2 inch requirement from combustibles.
Yes. You can do whatever you want outside that box. But anything going in it needs to be approved by the manufacturer.
 

Eman85

Minister of Fire
Oct 10, 2022
510
E TN
I was just looking at your pics again. I would be concerned about the bare metal roof you can see. Metal will have condensation from any temperature differential if there is any moisture. I'd be concerned it would drip from the back of the metal.
 
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GrumpyDad

Minister of Fire
Feb 23, 2022
767
Champion, PA
I hired someone to install a wood stove with a manufactured chimney, which exits to the outdoors through a cathedral ceiling with a metal roof. Attached photos show the view from the interior after the chimney installation, before connecting the stove. My question: should I insulate this opening, and if so how?

My installer says absolutely not. He says that the space between the ceiling and the roof needs to be open to allow heat to escape from the chimney and "The little space, especially once the interior trim plate is covering the opening around the chimney pipe, will not be cooling down the home to any degree. Filling that void with insulation may create a situation that heats up the framing around it."

Looking up into the 14 x 18 opening (6" deep) you can see the bottom of the metal roofing, the wings on the roof support, the tin-snipped opening in the flashing, and above that the sloped walls of the flashing itself (it looks like daylight because the storm collar is sealed with clear silicone). My arm fits through the gap around the chimney in some spots. I see the argument for leaving air space in the void, but I strongly think I need to at least put an inch or two of Rockwool, SUSI, or similar perhaps on the flat at the top of the opening against that metal roofing/chimney flashing, to keep the rising heat in the room from conducting straight out through the metal--a situation that I imagine will be especially noticeable in the wee hours of a winter morning when the fire is down to coals and the outside temp is 10 degrees.

Even better IMO, but perhaps overkill, would be to create a retrofit sheet metal air barrier to go below the insulation, still leaving 4-5 inches of void below the sheet metal.

My installer does not approve of SUSI and says Rockwool is only fire resistant but not fireproof enough to go up against the chimney. I would welcome getting some clarity about whether I'm too paranoid about heat loss through the roof. Thanks.
View attachment 300627 View attachment 300628 View attachment 300629
My chimney doesnt seem to get very warm, and i dont understand how condensation can be predicted but I would expect that there would be some specification by your chimney pipe manufacturer as to what to do. (leave a 2" gap) or use rockwool etc. If there is a requirement for a gap, dont insulate and expect the insulation to stay in place. I can show you a before and after picture of when I insulated a new expansion , walls and ceilings, and what it looked like a month later. Even having stapled the craft paper in place. It expands, it shifts. So you will need a cavity support sytem to allow for insulation while not having anything touch if manufacturer states such.
BTW your options are limited now, because I see your picture was taken BEFORE the roof flashing was installed else I doubt I would see that much light on the sides where the hole was cut for the chimney.
Hopefully the ceiling support looks good now in that spot where the old one was.
My only gripe with the install (and Im NOT a pro), so there may be issues that the pros see, but for me, it's the silicon on the storm collar. I absolutely do not trust silicon anymore. Nor sir. Maybe GE if I dont really care what Im sealing (like a pull cart where the bolts hold the poly cart to the wheel assembly below). I used solar 900, and it literally rained 20 minutes after my install. Hard. I went up and looked at the install and not a drip on the pipe. I then went back up a couple hours later on the roof and it looked like I had just layed down my sealant. As a test, I adhered two pieces of wood on the very edge with this stuff and stuck it out in the rain, then tried to pull it apart. It was very soft but held up nicely. A few weeks later it was much more firm, but felt like a perma structure that was never letting go of the wood and was never splitting and would never get harder than that. To avoid going up the roof to inspect, Im leaving this piece of wood outside in the elements to inspect, but man am I sold on this stuff. Its like owning a rubber factory in a tube whereas you can make any size/shape of something you want and need out of rubber.
 

lofarabia

New Member
Oct 10, 2022
8
Minnesota
My chimney doesnt seem to get very warm, and i dont understand how condensation can be predicted but I would expect that there would be some specification by your chimney pipe manufacturer as to what to do. (leave a 2" gap) or use rockwool etc. If there is a requirement for a gap, dont insulate and expect the insulation to stay in place. I can show you a before and after picture of when I insulated a new expansion , walls and ceilings, and what it looked like a month later. Even having stapled the craft paper in place. It expands, it shifts. So you will need a cavity support sytem to allow for insulation while not having anything touch if manufacturer states such.
BTW your options are limited now, because I see your picture was taken BEFORE the roof flashing was installed else I doubt I would see that much light on the sides where the hole was cut for the chimney.
Hopefully the ceiling support looks good now in that spot where the old one was.
My only gripe with the install (and Im NOT a pro), so there may be issues that the pros see, but for me, it's the silicon on the storm collar. I absolutely do not trust silicon anymore. Nor sir. Maybe GE if I dont really care what Im sealing (like a pull cart where the bolts hold the poly cart to the wheel assembly below). I used solar 900, and it literally rained 20 minutes after my install. Hard. I went up and looked at the install and not a drip on the pipe. I then went back up a couple hours later on the roof and it looked like I had just layed down my sealant. As a test, I adhered two pieces of wood on the very edge with this stuff and stuck it out in the rain, then tried to pull it apart. It was very soft but held up nicely. A few weeks later it was much more firm, but felt like a perma structure that was never letting go of the wood and was never splitting and would never get harder than that. To avoid going up the roof to inspect, Im leaving this piece of wood outside in the elements to inspect, but man am I sold on this stuff. Its like owning a rubber factory in a tube whereas you can make any size/shape of something you want and need out of rubber.
Wow! that was done by a "professional"? I know Selkirk Products use their own SUSI product... it is mineral wood...I cant believe it is some special formulation. It is made from volcanic rock, must be the same stuff inside the chimney pipe. It is rated over 2100 degrees and Supervent chimney is 1000 degree . The problem is in their manuals they say not to have "any insulation inside the air clearance space " then on the next page the say you can use JUSI in the cathedral ceiling support and attic insulation shield. They say follow separate instruction provided in the package when installing the JUSI. The only thing I can find is for SUSI not JUSI they must have changed the acronym. Their tech data is terrible! Look at the install instructions I attached, they call it JUSI and SUSI and tell you to wrap the chimney and stuff the extra in the corners of the box...

Selkirk Universal Shielding Insulation - SUSI - 200001​

Optional insulation for use with the Support Box, Attic Insulation Shield and Insulated Wall Thimble. The SUSI protects building material against radiant heat from the chimney and helps maintain temperatures within the chimney system. Engineered for safety, MetalBest, also known as MetalBestos, chimneys are packed with one inch of premium fiber insulation, ensuring a 100% fill. This superior insulation maintains higher...




More Inf

Selkirk Universal Shielding Insulation - SUSI - 200001​





Selkirk Universal Shielding Insulation - SUSI - 200001
Made in the USA

SKU: NLE5SE_SUSI
MPN: 200001
$46.86



  • Optional insulation for use with the Support Box, Attic Insulation Shield and Insulated Wall Thimble. The SUSI protects building material against radiant heat from the chimney and helps maintain temperatures within the chimney system. Engineered for safety, MetalBest, also known as MetalBestos, chimneys are packed with one inch of premium fiber insulation, ensuring a 100% fill. This superior insulation maintains higher...


 

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  • Universal_Shielding_Insulation_(SUSI_JUSI)_U1_US.pdf
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GrumpyDad

Minister of Fire
Feb 23, 2022
767
Champion, PA
Hello I am pretty sure the 2 inches is for combustibles, not air space.I questioned insulating the cathedral ceiling support also,(check out you tube video ) I called Supervent and they said, yes In cold climates that is what the SUSI is for. The guy on the video used Perlite. I used 2000+ degree Johns manville Sound and fire block and insulated the whole chase.

im curious why a ceiling support box was used with whatever that thing is below it.
I also hate seeing screws be used on flashing because they dont pry they bite and hold, and then the heads round out when you need to get them out 10 years from now, or just snap off.
 
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cobscookie

New Member
Oct 15, 2022
8
Maine
Thanks for these replies! I didn't get email notifications and didn't realize this conversation had been continuing. I am most grateful. I will read through more carefully when I have time and reply where appropriate.

I was just looking at your pics again. I would be concerned about the bare metal roof you can see. Metal will have condensation from any temperature differential if there is any moisture. I'd be concerned it would drip from the back of the metal.
Thanks for the additional comment. I have been seriously wondering about the bare metal for that reason as well.
 

cobscookie

New Member
Oct 15, 2022
8
Maine
My chimney doesnt seem to get very warm, and i dont understand how condensation can be predicted but I would expect that there would be some specification by your chimney pipe manufacturer as to what to do. (leave a 2" gap) or use rockwool etc. If there is a requirement for a gap, dont insulate and expect the insulation to stay in place. I can show you a before and after picture of when I insulated a new expansion , walls and ceilings, and what it looked like a month later. Even having stapled the craft paper in place. It expands, it shifts. So you will need a cavity support sytem to allow for insulation while not having anything touch if manufacturer states such.
BTW your options are limited now, because I see your picture was taken BEFORE the roof flashing was installed else I doubt I would see that much light on the sides where the hole was cut for the chimney.
Hopefully the ceiling support looks good now in that spot where the old one was.
My only gripe with the install (and Im NOT a pro), so there may be issues that the pros see, but for me, it's the silicon on the storm collar. I absolutely do not trust silicon anymore. Nor sir. Maybe GE if I dont really care what Im sealing (like a pull cart where the bolts hold the poly cart to the wheel assembly below). I used solar 900, and it literally rained 20 minutes after my install. Hard. I went up and looked at the install and not a drip on the pipe. I then went back up a couple hours later on the roof and it looked like I had just layed down my sealant. As a test, I adhered two pieces of wood on the very edge with this stuff and stuck it out in the rain, then tried to pull it apart. It was very soft but held up nicely. A few weeks later it was much more firm, but felt like a perma structure that was never letting go of the wood and was never splitting and would never get harder than that. To avoid going up the roof to inspect, Im leaving this piece of wood outside in the elements to inspect, but man am I sold on this stuff. Its like owning a rubber factory in a tube whereas you can make any size/shape of something you want and need out of rubber.
My concern about condensation isn't about heat from the chimney but rather the warm air from the room filling that void--and condensation happening on the bottom of the metal roof because of that (as the warm air convects straight out through the metal roof and the flashing). I use wood heat exclusively and full-time November through March, when nights often go below 0* and nice days are in the 20s. The air at the ceiling is easily 100* when the room is 70-75.

The light you're seeing is looking up through the roof cutout at the installed flashing--the pic was taken after the installer left. So nope the ceiling support doesn't look good :-/ Next step will be to add the rest of the stove pipe, add a trim plate, and put the stove in place. I'm still trying to find a trim plate that works with my 8/12 pitch ceiling without leaving any gap around the pipe.

Interesting info about the silicon. I'm content with the exterior (except I'll ask the installer to add a bead of something along the upper seam of the flashing, per BeGreen's advice). We've had a couple of torrential rain storms (3-4") since the install, and everything under the flashing is staying completely dry. I can keep an eye on it while I'm sitting at the supper table :)
 
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cobscookie

New Member
Oct 15, 2022
8
Maine
Wow! that was done by a "professional"? I know Selkirk Products use their own SUSI product... it is mineral wood...I cant believe it is some special formulation. It is made from volcanic rock, must be the same stuff inside the chimney pipe. It is rated over 2100 degrees and Supervent chimney is 1000 degree . The problem is in their manuals they say not to have "any insulation inside the air clearance space " then on the next page the say you can use JUSI in the cathedral ceiling support and attic insulation shield. They say follow separate instruction provided in the package when installing the JUSI. The only thing I can find is for SUSI not JUSI they must have changed the acronym. Their tech data is terrible! Look at the install instructions I attached, they call it JUSI and SUSI and tell you to wrap the chimney and stuff the extra in the corners of the box...

Selkirk Universal Shielding Insulation - SUSI - 200001​

Optional insulation for use with the Support Box, Attic Insulation Shield and Insulated Wall Thimble. The SUSI protects building material against radiant heat from the chimney and helps maintain temperatures within the chimney system. Engineered for safety, MetalBest, also known as MetalBestos, chimneys are packed with one inch of premium fiber insulation, ensuring a 100% fill. This superior insulation maintains higher...




More Inf

Selkirk Universal Shielding Insulation - SUSI - 200001​





Selkirk Universal Shielding Insulation - SUSI - 200001
Made in the USA

SKU: NLE5SE_SUSI
MPN: 200001
$46.86



  • Optional insulation for use with the Support Box, Attic Insulation Shield and Insulated Wall Thimble. The SUSI protects building material against radiant heat from the chimney and helps maintain temperatures within the chimney system. Engineered for safety, MetalBest, also known as MetalBestos, chimneys are packed with one inch of premium fiber insulation, ensuring a 100% fill. This superior insulation maintains higher...


The data really is opaque. Is that tech sheet recent? The only thing I see that might be a date is 020821 on page 1, which would suggest it's from 2021. Thanks for attaching. I might contact Selkirk again to ask about that wrap on page 3 and see if some other tech gives me some other info.

I just found a thread here ( https://www.hearth.com/talk/threads/rock-wool-against-a-manufactured-chimney.188079/ ) saying that SUSI is ceramic wool, not mineral wool. I wonder if SUSI is less dense, and lets the chimney breathe more. As I understand it, the importance of air space clearances isn't just to do with the combustibility of the surrounding material but also has to do with maintaining the integrity and function of the chimney itself.
 

cobscookie

New Member
Oct 15, 2022
8
Maine
I have really appreciated this conversation and have yet another question: Any thoughts on cutting a piece of 10" single-wall stove pipe down to 5.5-6" tall, and slipping it over the 8" class A stove pipe, then insulating around that sleeve? Is there an issue I'm not seeing? Thank you!
 
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I have been going around and around the same issue with my DuraTech chimney from DuraVent company, and have appreciated all the posts here. After doing a conscientious job of insulating my roof (spray foam), I can't bear having the equivalent of an open window blasting cold air into the house. Though, just as certainly, I don't want to create a fire-safety hazard!

DuraTech Installation Instructions seem to conditionally support insulating the clearance-to-combustibles space in the roof bay. HOWEVER company tech support seemed to conflict with that - he said insulation is allowed only in their support boxes because they have tested them.

Lest anyone should care or have a comment, here are my looong notes as I was trying to figure it out. Sections from the Installation Instructions https://duravent.wpengine.com/wp-co...Install-Instructions_DuraTech_06-28-21_V3.pdf are copied here, bolds are my own emphasis and [my notes are inserted in brackets]

[page 4] NON-COMBUSTIBLE INSULATIONS
Non-combustible insulation is tested and approved through UL for use within the clearance to combustibles distance between a passthrough leading to the exterior of a building, and only as described in these instructions [sections copied below]. The non-combustible insulation used must be listed / compliant with ASTM E136/ULC S114 as non-combustible, have a melting temperature above 2000°F/1100°C, be water resistant with low moisture absorption and be acceptable to the AHJ. Acceptable insulations include those made from stone (aka “rockwool” or “mineral wool” insulations [Roxul Comfortbatt meets the standard]).

[page 9] 3-A. When installing a Support Box into a roof, non-combustible insulation adhering to the specifications on page 4 may be added to prevent cold/outside air intrusion and limit condensation on the surface of the Support Box. Cut the insulation into squares as shown in Figure 9a, or wrap the pipe with an insulation blanket and fill in the corners as shown in Figure 9b. Do not compress the insulation more than 25% or you may adversely affect the thermal resistance of the insulation. Non-combustible insulation is allowed up to the top edge of the Support Box, but not go past the edge where it can fall out or come in direct contact with combustible materials.

[page 11] 9. Spray Foam Insulation Shield: A Spray Foam Insulation Shield is necessary whenever spray foam is used to insulate the roof rafters. Install the Spray Foam Insulation Shield in the same way as a Support Box [Section 3, Cathedral Ceiling section*], however only 1 screw or nail per side is needed. The Spray Foam Insulation Shield may be insulated with non-combustible insulation as specified [I ASSUME meaning "may be insulated in the clearance-to-combustibles... as specified for the Support Box in section 3-A & Fig 9a or 9b." will try to attach file].

[*We will be spray foaming the rafter bay and have installed round heavy gauge sheet metal shield for 2” clearance to combustibles around Duratech pipe in rafter bay from roof to more than 5” lower than finished ceiling.]

Screen Shot 2022-11-06 at 12.41.01 AM.png
 

begreen

Mooderator
Staff member
Nov 18, 2005
98,097
South Puget Sound, WA
I have really appreciated this conversation and have yet another question: Any thoughts on cutting a piece of 10" single-wall stove pipe down to 5.5-6" tall, and slipping it over the 8" class A stove pipe, then insulating around that sleeve? Is there an issue I'm not seeing? Thank you!
It would have to be 12" with non-combustible spacers to ensure an even 2" spacing.
 
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I have really appreciated this conversation and have yet another question: Any thoughts on cutting a piece of 10" single-wall stove pipe down to 5.5-6" tall, and slipping it over the 8" class A stove pipe, then insulating around that sleeve? Is there an issue I'm not seeing? Thank you!
I used 12" diameter heavy gauge sheet metal and used 1/4 carriage bolts - 2 1/2" to maintain 2" clearance space (it took lots of them to keep it from going out-of-round): smooth head butts to the insulated chimney pipe, 1" washer + nut on the inside and 1" washer + lock washers+ nut outside the pipe. I will pop rivet the shield together. See photos, though given all the reflection, not sure if it is clear

Because my DuraTech pipe instructions indicate that I can insulate that clearance space (unless I'm misunderstanding), I am using a 2" batt of Roxul. Though I'm still awkwardly working out how to get it all together, in a tight space with only 2 hands keeping the insulation nice and even. But I'm gaining - temporarily holding it on the pipe with a sheet metal screw at the top and a strap around the bottom.

If I was starting all over again, I would ring the spacers at the same height at the bottom so I wouldn't have so much trouble working the insulation in around them.

Screen Shot 2022-11-06 at 5.56.17 PM.png Screen Shot 2022-11-06 at 5.56.31 PM.png
 

cobscookie

New Member
Oct 15, 2022
8
Maine
I used 12" diameter heavy gauge sheet metal and used 1/4 carriage bolts - 2 1/2" to maintain 2" clearance space (it took lots of them to keep it from going out-of-round): smooth head butts to the insulated chimney pipe, 1" washer + nut on the inside and 1" washer + lock washers+ nut outside the pipe. I will pop rivet the shield together. See photos, though given all the reflection, not sure if it is clear

Because my DuraTech pipe instructions indicate that I can insulate that clearance space (unless I'm misunderstanding), I am using a 2" batt of Roxul. Though I'm still awkwardly working out how to get it all together, in a tight space with only 2 hands keeping the insulation nice and even. But I'm gaining - temporarily holding it on the pipe with a sheet metal screw at the top and a strap around the bottom.

If I was starting all over again, I would ring the spacers at the same height at the bottom so I wouldn't have so much trouble working the insulation in around them.

View attachment 302178 View attachment 302179
These photos and the rest of the details are SO helpful--exactly what I've been trying to envision, and I think this is what I will do. Thank you very much.

I will be insulating only *around* the metal sleeve (filling the corners of the rafter bay) but not inside it. I got the same caution that you did from company tech support, along the lines of "insulation is allowed only in the company-manufactured support boxes, because those have been through Underwriters Labs testing (UL 103)," which I find summarized online as follows: https://jeremiasinc.com/fileadmin/u.../ul_summaries/Jeremias_Inc_UL_103_Summary.pdf

My amateur interpretation is that although the Roxul isn't combustible, if there's any kind of severe thermoshock in the insulated portion of the pipe (for instance, a burnoff of creosote that has collected in the chimney near the roof line) it might conduct enough heat from the chimney pipe to damage a homemade sleeve? (And you wouldn't be able to inspect for that, once it's surrounded with spray foam.)

However: in the course of trying to sort out my current dilemma I've had several people who heat exclusively with wood-- (1) the owner of an Ace hardware store (Selkirk dealer), (2) an instructor at the local trade school, and (3) a neighbor who is a volunteer firefighter--all tell me that they have simply had pink fiberglass insulation filling that roof void directly around the class-A chimneys in their homes for decades. For liability purposes, the company specs certainly represent safety overkill. But personally, I know I'll sleep better at night if I stick to the specs!