Replies

1. 
   csnow | Nov 19, 2003 05:34pm | #1

   Do you have an attic, or is this a cathedral ceiling?

1. 
   user-1149688 | Nov 19, 2003 07:37pm | #4

   Cathedral ceiling, wood framed chase open from basement to roof.  Framing contractor came back (at my request) a couple of years after it was built to increase the insulation around the inside of the chase.  Light snow shows heat loss through the roof in a triangle from bottom corner to the peak (about 4 ft) and along ridge (about 8 ft).  Think if I could vent along outside of chase at roofline (without allowing either snow or rain in) that would be better than increasing venting at ridge....?

1. 
   csnow | Nov 19, 2003 08:13pm | #5

   Doubt ventilation is the problem.  Probably have an air leak.

   Is the flue sealed at the ceiling plane?  Code generally requires a 2 inch clearance to combustibles.  A careful installer will seal this gap airtight with sheetmetal and a high temperature sealant.  Insulating or sealing the chase at anyplace but the ceiling plane is not likely to be effective.

   If it is normally in use, another possibility to consider is that your flue is radiating enough heat to melt snow.

1. 
   user-1149688 | Nov 19, 2003 09:01pm | #6

   Chase is only sealed at the top -- per code, I believe.  Includes two wood stove pipes (not normally in use), gas furnace and water heater vents.  Entire length would be heated since it's open from bottom to top.  Sides well insulated from top down to well below the ceiling height.  Stands about 3 feet above roofline at the peak and probably 4 1/2 feet on low side, so I doubt it could radiate through the sides or down from the top....

   My thought is that heat is somehow escaping from the living space or the chase into the roof trusses in the area where the ceiling meets the chase.  Vapor barrier breaks there at the chase.

   Roof otherwise in good shape at 18+ years, so I hate to start tearing it off around the chase to try to find the source of my problem.  My inclination is to assume it is an air leak and find a way to vent it so that it doesn't continue to melt snow and cause ice dams.

1. 
   Piffin | Nov 19, 2003 09:45pm | #7

   Near as I can tell, you have a number of problems leading to this symptom.

   Adding extra venting in the attic or at the ridge is not the solution in this case, because it will merely puill more heated, saturated air into that attic space at the point where the ice damns happen and make them worse.

   There should be a firestop spacer at each floor and the ceiling.

   There should be insulation and firestop rock at all the verticle walls surronding the chase.

   Without these, you have a torch channel carrying the most dangerous air in the house. ANY fire starting in or near there will accelerate and be dangerous before you know that it exists.

   With both of the above, the airflow should be limited enough to prevemnt the attic problem you have.

   It sounds like your only firestop scaper is at the bottom level.

   Since hge had tpo comne back to add insulation, I am going to presume (knowing that I could be wrong) that the firewalls are inadequate and have Broken seals someplace and that there may still be a spot or two that is less than well insulated, knowing how hard it can be to get to some of that stuff for anyone other than an eel.

   firestopp spacers can have fire caulk added but that doesn't always stay permanent when thermal expansion stretches the joint.

   .

   Excellence is its own reward!

2. 
   user-1149688 | Nov 19, 2003 10:26pm | #8

   Please re-read my posts.  There is no attic -- vaulted ceiling throughout (24 inch trusses with fibreglas batts all above vapor barrier).  Chase has good insulation on sides as well as firestop gypsum board. 

   House happens to be a front to back split level.  Bottom of chase starts at ceiling of basement (above floor level at front of house, at floor level at back of house).  It passes through no floors (except right at the base).  Code requires that the bottom of the chase be left open (I assume to be able to detect a problem with any of the metal chimney pipes).

   If I can somehow vent the ceiling space adjacent to the exterior of the chase without allowing rain or snow into the area, I believe I will solve the ice damming (damning!) problem..... 

3. 
   Piffin | Nov 19, 2003 11:18pm | #9

   If you open that space, you are openning a window to such air straight from basement to the sky then.

   I am not familiar with that code. Every stovepipe manufacturer I know of recommends and sells a support backage that acts as a firestop spacer as well for the base of the chase. that is where the problem is. Are you saying that the chase vents into the cathedral ceiling space without going to the top? That should not be. There should be insulation and firestop between the chase and the roof insulation area wheather you call it cathedral or attic. Fire and drafts should be prevented from going there. The fact that you have this problems says that those drafts are going there. If drat can travel that way so can fire spread. It shou;ld be found and stopped not only for heating efficiency, but for safety also.

   Sorry if I haven't quite understood your description clearly, but you have the advantage of seeing what I can only visualize in my minds eye..

   Excellence is its own reward!

2. 
   DavidThomas | Nov 19, 2003 05:51pm | #2

   Seems that either a fan(s) in the eaves pushing air into the effected bays or a power vent tied into the top of those bays would move a bunch more air than natural convection and keep down the temps under the sheathing.

   Could you insulate around the chimney chase somehow? Or would that involve intensive ripping and shredding of your roof?

   If ripping and shredding up your roof is in the cards, you could lay down some Water & Ice membrane, maybe two courses, in the effected area. Then reshingle that area. How many more years do the current shingles have in them?

   David Thomas   Overlooking Cook Inlet in Kenai, Alaska
3. 
   hammer1 | Nov 19, 2003 07:24pm | #3

   The flow from the soffit is critical. Generally we use propa vent to keep this flow open. The chimney chase should be closed to prevent it from becoming a chimney during a fire. We use heavy gauge metal attached to the framing and up tight to the masonry. With the open flow closed off you may have to address indoor air quality and supply. You are not super insulated if there is a big hole going to the attic.