Insulating around flue at roof

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Chrisg

Member
Sep 6, 2007
76
NEK VT
I installed a full simpson class a pipe system last year that I am finally getting ready to build the chase around. My question is what do I use to insulate around the pipe right where it exits the roof. I understand there is 2" clearance to combustibles is there a product that could be packed around the very top to stop the heated air that will be trapped in the full length chase from escaping and creating ice on the roof at this area?
I did not have a chase around the pipe last year and had a ton of ice build up below the flue. We got a lot of snow last year and it was a constant battle getting the snow raked off before the ice built up too much.
Here is a pic of the outside I will try to get one up of the inside. The inside is large finished closet/storage area that is very easy to work in.

IMG_0672.jpg

(The pipe is plumb,I don't know why it looks so askew in this pic)
Any suggestions would be a big help. Thanks Chris
 
I have the same chimney with a similar pitch roof and get no ice buildup. The floor of the attic is very well insulated but I have nothing directly under the roof deck and have significant ventilation. Maybe it is a ventilation issue?
 
Isn't the pipe already insulated between the two layers of pipe?
Not sure how say maybe 4 to 6 inches of additional insulation 2 to 3 inches thick around the pipe 20' up would hurt much. I think after running 6 cords thru the wood furnace that this pipe is venting and only coming up with a hand full of creo at the end of the season,not sure I would even call it typical creo more like fly ash, that a chimney fire would be an issue. I think poorly seasoned wood and improper burning practices play more into a chimney fire scenario.
Thanks Chris
 
Good idea I think I will check to see what they say. Maybe they have a product specific to this situation.
Thanks Chris
 
Chrisg said:
Isn't the pipe already insulated between the two layers of pipe?
Not sure how say maybe 4 to 6 inches of additional insulation 2 to 3 inches thick around the pipe 20' up would hurt much. I think after running 6 cords thru the wood furnace that this pipe is venting and only coming up with a hand full of creo at the end of the season,not sure I would even call it typical creo more like fly ash, that a chimney fire would be an issue. I think poorly seasoned wood and improper burning practices play more into a chimney fire scenario.
Thanks Chris
Click to expand...
Chris,
as an installer of duravent for a long time,

you can insulate the chaise walls, but will need to leave off insulating directly up to the pipe.
if air is flowing out of your attic thru the flashing, add an interior sheet metal firestop below the flashing inside the attic. screw and glue firestop to roof sheeting, and seal tight to pipe with high temp silicone, to allow for expansion/contraction

now that the chimney is in, a std firestop will be a trick to install!
you can make your own from 2 pieces of sheet metal
Dave
 
That sounds like a good plan of attack and that is probably what I will do.
I am curious if this would lead to condensation on the underside of that firestop/custom fabbed pc?
Maybe I am over thinking as it is basically wide open to the underside of roof flashing pc and there does not seem to be any condensation issue there. I did check for that all last winter because of the icing issue and it was always bone dry.
Thoughts. Thanks Chris
 
The outside of the chimney will still get warm/hot. Insulation within the Class A simply slows the flow of heat from inside to out. It can't prevent it and when fired continuously for months there will be heat on the pipe. Not the same temps as the inside of course since the outside of the pipe can lose heat almost as fast as it gets it from the inside of the flue.

When I've had a good hot fire going for a long time I can see the heat waves coming out of the chimney cap but also can see the heat waves from the side of the chimney.

The clearance to combustibles is 2" from that pipe. Perhaps Simpson is OK with non-combustible insulation in the area that you want.
 
Solarandwood sorry missed your post, good points about venting however the area in question is all new finished space with soffit,ridge and full length proper vent between insulation and roof deck. I did interrupt the one bay where the chimney penetrates the roof but I think the air can still circulate thru the proper vent.
But you know as I type this I scrolled down to review the tread and noticed the ridge cap is screwed down tight to the shingles the other side is a dormer(spl) addition with metal roofing.
I think I will get some of that mesh vent and unscrew that side and slip that in to provide for better air flow on that side. When we did the addition we ripped an opening down the lenght of that ridge ,screened over it and I figured that would be enough air flow out the metal side. Hope that made sense.
Good point none the less. This is exactly why this forum is such a great place.
Thanks Chris
 
Chrisg said:
I did interrupt the one bay where the chimney penetrates the roof but I think the air can still circulate thru the proper vent.
Click to expand...

I assume the icing is in the area directly adjacent to the flashing? Is the interruption of the bay below the chimney? To keep the chimney flashing cool, you need a nice clear shot from the soffit vent to it. Does snow cover the bottom of your chimney flashing? Can you put your hand on it while you have a good burn going?
 
NOTHING WITHIN 2" OF THE PIPE non combustible insulation will conduct heat to the combustibles- nothing around the pipe- like the stickers and the install guide said.
 
I assume the icing is in the area directly adjacent to the flashing? The roof will be void of snow below the chimney to about three feet above the eave edge.

Is the interruption of the bay below the chimney? Not sure what your saying, the construction is old school minimal tru 2x6 2 ft oc( I know it aint much but it works and is what was there for 50+yrs) so by saying bay I meant the 2ftoc framed section that runs from eave to ridge.

To keep the chimney flashing cool, you need a nice clear shot from the soffit vent to it. Does snow cover the bottom of your chimney flashing? No. It melts off relatively fast

Can you put your hand on it while you have a good burn going? Yes if you mean the exterior roof flashing pc. But it is warm, enough to melt the snow.

My opinion is when I look at the inside of this area,which I have done alot lately, as it is now I see it as a hole in the roof that heat is just dumping out of with a thin pc of metal as the only insulation to speak of. I believe a well constructed chase with the firestop/fabbed filler at the top will go a long way to keep the heat from pouring out. I think the heat also finds its way up and down the underside of the roof in this bay which is probably a major cause of the snow melt.The snow only seems to melt in the area directly above and below the chimney there was never a problem before the chimney in this area and everywhere else on the roof has no melting issue.
Thanks again this is all great info. Chris
 
Chrisg said:
I assume the icing is in the area directly adjacent to the flashing? The roof will be void of snow below the chimney to about three feet above the eave edge.

Is the interruption of the bay below the chimney? Not sure what your saying, the construction is old school minimal tru 2x6 2 ft oc( I know it aint much but it works and is what was there for 50+yrs) so by saying bay I meant the 2ftoc framed section that runs from eave to ridge.

To keep the chimney flashing cool, you need a nice clear shot from the soffit vent to it. Does snow cover the bottom of your chimney flashing? No. It melts off relatively fast

Can you put your hand on it while you have a good burn going? Yes if you mean the exterior roof flashing pc. But it is warm, enough to melt the snow.

My opinion is when I look at the inside of this area,which I have done alot lately, as it is now I see it as a hole in the roof that heat is just dumping out of with a thin pc of metal as the only insulation to speak of. I believe a well constructed chase with the firestop/fabbed filler at the top will go a long way to keep the heat from pouring out. I think the heat also finds its way up and down the underside of the roof in this bay which is probably a major cause of the snow melt.The snow only seems to melt in the area directly above and below the chimney there was never a problem before the chimney in this area and everywhere else on the roof has no melting issue.
Thanks again this is all great info. Chris
Click to expand...

I have roughly the same pitch and penetrate halfway up the roof similar to yours. I burn 24/7 and the snowpack covers the base of the flashing just like the rest of the roof. The snow gets almost up to the storm collar before I notice any difference. I have no chase through the attic space. I did design generous ventilation into this house as I have had to deal with ice damming in every house I've owned. Given how much roof deck you are heating, my guess is that your need additional ventilation from the soffit to the chimney. BTW, any chance you are near the Kingdom Trails? My wife and I have been up there a few times to ride and loved it.
 
Yes I also think the venting is an issue in the area of the chimeny. Wanted to add when I rehabed the upstairs we were limited by the rafters 2x6 for insulation thickness so I also added 2" foil faced foam, foil taped all the joints strapped it for an air space and rocked over that to bump up the Rvalue. Like I said earlier never had a problem before the chimny install.
Your talking about the Mnt bike trails in Burke we are about 15 mins away. I bet it is muddy right now the rain just wont stop.
Chris
 
Chrisg said:
Your talking about the Mnt bike trails in Burke we are about 15 mins away. I bet it is muddy right now the rain just wont stop.
Chris
Click to expand...

Nice, I'm jealous. Unfortunately, the conditions aren't what is keeping us from getting back up there. We haven't been up since the addition of kids and the current house endeavor. Good luck with your ventilation. You may find that just popping the soffit cover off and cutting a bigger hole gets you there.
 
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