Attic chimney vent needs more insulation+vents?

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DALE SR 3

Member
Feb 5, 2009
37
S.E. MICHIGAN
Since we got our Montecito fireplace we have gotten ice dams from snow melting off the roof around the roof chase and area near the chimney vent in attic. I would like to further insulate the insulated double wall vent by surrounding the chimney with a fence to keep insulation away from the chimney at required distance then wrap 6" of insulaltion on the fencing. We are securing the insulation with chicken wire to 2x4's. The area of concern is outlined in green in the photo.

My concern is the uninsulated chase sitting on the roof, will that area get too hot inside the walls. Should I put a vent near the top of the chase to let out the heat. I know it is desireable to have a warm chimney but I do not want the uninsulated boards and vinyl siding of the chase to be affected by excessive heat.
Or even add a vent to the bottom out to the soffit area for intake of cold air.

Attic vent 0989: area in green to be insulated with 6" of insulation
chase install: shows interior of roof chase
House rear shows finished chase and excessively tall chimney that installers put in, they did not have right pipe lengths!
 

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LLigetfa

Minister of Fire
Nov 9, 2008
7,360
NW Ontario
See where the short radiation shield stops? I would extend the radiation shield right up to the top of the chase. It will keep more heat in the chimney and less heat radiating into the attic. It could improve the draft with the chimney being kept warmer, reduce creosote buildup, and would also give you an additional margin of protection should you have a chimney fire.
 

begreen

Mooderator
Staff member
Nov 18, 2005
96,253
South Puget Sound, WA
This confuses me. Wouldn't a hotter chase cause even more snowmelt leading to the ice dam problem? I would think you would want the chase box walls to be insulated and cooler to reduce snow melt. Or install some roof heating tape over the doorway?
 

LLigetfa

Minister of Fire
Nov 9, 2008
7,360
NW Ontario
How would adding a radiation shield cause a hotter chase? I would think the opposite. It would stop the heat radiating out and provide the needed protection to insulate if the shield alone isn't enough. One purpose of the shield is to insure the insulation is kept away from the heat and keep radiated heat away from nearby combustibles. Remember, your average insulation is not considered to be non-combustible.
 

begreen

Mooderator
Staff member
Nov 18, 2005
96,253
South Puget Sound, WA
I was thinking that if the class A is kept hotter, it will radiate more heat in the unheated chase up on the roof.
 

LLigetfa

Minister of Fire
Nov 9, 2008
7,360
NW Ontario
Air is an effective insulator and the primary ingredient in most insulation. AFAIK, it (air) is the only brand of insulation that is permitted to occupy the 2" space around a class A chimney. The 2" air space is essentially insulation and the "shield" part of the radiation shield will shield the chase from "radiant" heat. Of course, if it proves not to be adequate, it can also serve as a code compliant stand-off for other brands of insulation.
 

Renovation

New Member
Oct 26, 2010
1,087
SW MI near Saugatuck
BeGreen said:
This confuses me. Wouldn't a hotter chase cause even more snowmelt leading to the ice dam problem? I would think you would want the chase box walls to be insulated and cooler to reduce snow melt. Or install some roof heating tape over the doorway?

That's what I'm thinking too.

I suggest Dale do essentially what he is thinking--build an insulated chase around the chimney in the attic, and continue the insulation inside the chase above the roof, and then vent the whole thing at the top with slots under an overhanging chimney cap. Of course, make sure that nothing but fittings come within 2" of the chimney. I'd also wrap a vapor barrier (like pvc sheet) around the attic chase to improve insulation.

That will keep the roof and chase cool, stopping the meltoff. And it will keep the chimney hotter improving draft. HTH, and good luck.
 

DALE SR 3

Member
Feb 5, 2009
37
S.E. MICHIGAN
When chase was being built I asked the contractors several times if the rooftop chase should be insulated, they said no they never insulate them. They also did not mount it very good so I had to retrofit that before they even finished the job. Now as usual I find out I have to find a way to insulate the chase with the vent pipe installed.

I am able to reach up inside the chase from below nearly half way up and that way insulation would at least be above any snow line. For insulation I plan to use Roxul.
This way I will cover the joint at at the roof and critical low level of the rooftop chase and also the attic space. I can't afford to redo the chase.

The roof trusses are 24"oc and the vertical 2x4's and the fencing will keep the insulation well away from the vent pipe.

There is wrap under the vinyl siding of chase, at least they did that correct.

There is not much an overhang at top so I plan to use something like maybe 2 -(3" or 4")intake vents with hoods, like a dryer vent without the flapper near the top.
So I do NOT need intake cooling vents at the bottom also, great?

Thanks for confirming my plans. The attic is too hot to work in during the summer and cold at this time, but least coats in winter protect us from the dreaded itch of insulation
 

Renovation

New Member
Oct 26, 2010
1,087
SW MI near Saugatuck
DALE SR 3 said:
When chase was being built I asked the contractors several times if the rooftop chase should be insulated, they said no they never insulate them.

And the check is cashed before you notice anything's wrong. First your cabin, and now this. Well, that can be par for the course. At least you know better now.

I am able to reach up inside the chase from below nearly half way up and that way insulation would at least be above any snow line. For insulation I plan to use Roxul.
This way I will cover the joint at at the roof and critical low level of the rooftop chase and also the attic space. I can't afford to redo the chase.

Sounds like a plan. As a reminder, keep insulation, even if non-combustible, 2" from the flue. Insulation contact can cause hot spots and flue failure if you ever have a chimney fire.

There is not much an overhang at top so I plan to use something like maybe 2 -(3" or 4")intake vents with hoods, like a dryer vent without the flapper near the top.

No red flags from me. Oh, and I meant wrap a vapor barrier around the the chase that you're constructing inside your attic, for a little extra insulation.


So I do NOT need intake cooling vents at the bottom also, great?

I don't know of any requirement for vents for cooling Class A chimney pipe--the 2" airspace is the only requirement that I know of. I suggest the vents for basic construction hygiene--to ventilate trapped moisture, etc. I think what you propose is sufficient. I hope others will confirm or correct.

Thanks for confirming my plans.

You're welcome. Don't just take my word for it, but it sounds right to me. Anyone?

The attic is too hot to work in during the summer and cold at this time, but least coats in winter protect us from the dreaded itch of insulation

Yeah, I know all about that. I fixed my 3' tall attic for about two weeks in the middle of the summer. The neighbor kid I hired to help has never forgiven me and still exhibits signs of PTSS. I suggest a filter mask, if even a cheap one. Airborne glass fragments do not make your lungs happy. HTH, and good luck!
 

DALE SR 3

Member
Feb 5, 2009
37
S.E. MICHIGAN
Snow is on the way and snow is on the roof already. Since I already have a injured back I do not need to slide off the roof, so the vents on chase will have to wait, hopefully I can at least get the insulation in soon. I would guess the insulation would be at least 6-8" away from the flue at minimum. The vapor barrier should go on the outside of the insulation right? That would be more flammable than the insulation.

Sorry in advance for the rant but my blood boils everytime someone asks or mentions fireplace installation. Our family has had 3 screwups and one general screwup contractor screwup while installing 2 fireplaces.

Installers on my fireplace did a HORRIBLE job, I had to watch them and tell them how to do the stuff or it would NOT have passed code in any way. Plus their mistakes delayed install by 6 months. They damaged walls, ceiling and overcharged me, that galvanized pipe in photo, they charged me the same as a Stainless pipe until city questioned compatibility of it. I could have saved $100's + in purchasing the galvanized clad stainless interior chimney system except for the top part of chimney. But they said it looked better,but in our situation, the whole system is behind a wall or in attic, we do NOT see any pipes. Then to install the fireplace instead of sliding unit in from the front they yanked out a newly installed wall I paid for. I then had to rebuild the wall a second time, the wood was damaged beyond reuse because of mulltinailing and splits.
The guys who did the chase and wall, I have never seen so many nails in the end of a 2x4 that were bent over. Or so many 2x4's that were split by those multi nailed boards to form a wall. My 3 yr old niece could nail a better board than those guys.

I noticed the ice problem on roof last Winter, which was the first winter we had fireplace burning wood. People may say why have you waited so long to fix it now.
1. Can't fix in summer when attic is hot
2 Biggest holdback is my back which was re-injured so I am extremely limited in motion like crawling around in an attic or up and down a ladder or just standing.


Then comes the problems at cabin where we have more incompetant installers. I spoke to my Dad last night and he said all the installers came out for pre inspection and said," no problem using existing 90 degree elbows and chimney" First guy then breaks chimney and interior ceramic collar, the second guy fixes the chimney and collar and charges us. Now we have to run a new chimney and have someone install it I am not capable of doing it and nobody else in family can either.

What we know is we can not trust installers.
 

begreen

Mooderator
Staff member
Nov 18, 2005
96,253
South Puget Sound, WA
I'd leave the attic alone and just insulate the chase.
 

DALE SR 3

Member
Feb 5, 2009
37
S.E. MICHIGAN
We have plenty of insulation in attic and plenty of unblocked soffitt vents plus the ridge vents, so I would guess the attic temps would be fairly close to outside air temp.
At the top of the chimney insulation barrier that is around the chimney I got a reading of 150 degrees in contact with chimney(double walled). The farther away from chimney vent it would be colder but 1 foot down from peak of roof and 1 foot away from the chimney I placed a thermometer in the attic. The outside temperature is 18 degrees the temperature on thermometer 1 ft down from the peak is 38 degrees.

Insulating just the rooftop chase will do nothing for the attic, I have to isolate the chimney from the cold attic space.
 

Renovation

New Member
Oct 26, 2010
1,087
SW MI near Saugatuck
DALE SR 3 said:
Snow is on the way and snow is on the roof already. Since I already have a injured back I do not need to slide off the roof, so the vents on chase will have to wait, hopefully I can at least get the insulation in soon. I would guess the insulation would be at least 6-8" away from the flue at minimum. The vapor barrier should go on the outside of the insulation right? That would be more flammable than the insulation.

Well, actually the vapor barrier usually goes on the warm side of the insulation (in this case the chimney side) so that moisture in the insulation can vent out, rather then condensing on the cool side. Your insulation isn't hidden in a wall, so I don't think condensation will be much of a problem, and it will be easier and yes, slightly safer to put it on the outside.

EDIT: Hmmm, now that I think of it, I'm torn, because moisture could get in there and condense on the vapor barrier. So I guess I would put it on the inside. The ideal solution would be to use a foil barrier or foil backed insulation, but you're well beyond the required clearance, so I personally wouldn't worry about it. Others can chime in if they disagree.
 

DALE SR 3

Member
Feb 5, 2009
37
S.E. MICHIGAN
RenovationGeorge said:
DALE SR 3 said:
Snow is on the way and snow is on the roof already. Since I already have a injured back I do not need to slide off the roof, so the vents on chase will have to wait, hopefully I can at least get the insulation in soon. I would guess the insulation would be at least 6-8" away from the flue at minimum. The vapor barrier should go on the outside of the insulation right? That would be more flammable than the insulation.

Well, actually the vapor barrier usually goes on the warm side of the insulation (in this case the chimney side) so that moisture in the insulation can vent out, rather then condensing on the cool side. Your insulation isn't hidden in a wall, so I don't think condensation will be much of a problem, and it will be easier and yes, slightly safer to put it on the outside.

EDIT: Hmmm, now that I think of it, I'm torn, because moisture could get in there and condense on the vapor barrier. So I guess I would put it on the inside. The ideal solution would be to use a foil barrier or foil backed insulation, but you're well beyond the required clearance, so I personally wouldn't worry about it. Others can chime in if they disagree.

I am still concerned about the fire rating of a vapor barrier such as plastic melting or paper burning even with more than enough clearance, I have found fire retardant plastics but they are very expensive and for large rolls. How about the the stuff found at Lowe's or Home depot: Reflectix 4' x 25' R-3.7 Double Reflective Foil Insulation
The specs say it is Class A/Class 1 Fire Rating. the left over stuff I can then use on my ducts or something. Then I could put it on inside of insulation and use foil tape to tape the edges together.
 

Renovation

New Member
Oct 26, 2010
1,087
SW MI near Saugatuck
DALE SR 3 said:
I am still concerned about the fire rating of a vapor barrier such as plastic melting or paper burning even with more than enough clearance, I have found fire retardant plastics but they are very expensive and for large rolls. How about the the stuff found at Lowe's or Home depot: Reflectix 4' x 25' R-3.7 Double Reflective Foil Insulation
The specs say it is Class A/Class 1 Fire Rating. the left over stuff I can then use on my ducts or something. Then I could put it on inside of insulation and use foil tape to tape the edges together.

I think your concern is good, and your solution too. Going beyond the minimum is a fine thing, and doing it right is a good way to ease your mind after all the substandard work that was done before. Maybe it's over kill, but that's a lot better than wrong. I do the same thing with my place--every time I opened a wall or checked a fixture it was wrong, and putting it right and maybe then some is how I keep my sanity.
 
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