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Ice Damming ~ Solutions for this Situation …

Jake Rabe | Posted in Energy Efficiency and Durability on

Some time back I’ve asked a question about my ice damming issue and received some good advice but had difficulty with local contractors; unskilled or untrustworthy. With time ticking and panic in my heart i went ahead and just got my roof resheeted (steel) but at least got all my soffit vents opened, ridge vent installed and the steel sheets installed with 1″ to 2″ strapping. Ice Damming still occurs, if not worse, and so i’m back for an updated solution to my existing situation.

To recap. I own an older home (1920s) with a low slope attic in Southern Ontario, Canada. The roof measures 30 ft length x 25 ft width. The roof has new steel roofing in place (ice & water shield, moisture membrane, strapping, steel sheets). I cant resolve the ice damming issue externally and so the solution must be from within.

The attic makes use of cellulose. I had a crew come out 3 years ago to add more. All rafters have had the soffit ends opened to allow air in and a ridge vent to complement it. From within the attic, from ridge to drywall, the height is about 40″. Of course as one moves toward the eaves the attic height gets smaller — there is no raised heel and so I’d say the height is about 4″, the distance from the drywall to the roof sheathing. So from 4″ to 40″ of usable space from eave to ridge. If the ceiling joist is about 4″ tall then there seems to be a total 10″ cellulose along the centre. I cant say for certain if the cellulose is spread out evenly but it is significantly less toward the eaves, of course. Digging through the attic cellulose i do not see a vapour barrier.

With the above restrictions what is the best i can do to eliminate ice damming? From what i’m reading the R-value should be R49+ in the attic. I would prefer NOT to rip down the bedroom ceilings. I was considering crawling in and affixing Rigid Foam to the top of all rafters starting from as deep as i can go from the eaves to all the way up to about 10″ from the ridge and then topping up the entire attic with more cellulose all the way up to where the rigid foam ends (10″ from the ridge). I cant do too much about the eaves. Of course between each rafter would be baffles all the way up to where the rigid foam ends.

Thanks for any tips.

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Replies

  1. Joshua Elliott | | #1

    Jake,

    Do you have any can lights or other large penetrations between the top floor and the attic that could be letting warm moist air into the attic?

    Could you link to the earlier discussions?

    Joshua

  2. Jake Rabe | | #2

    Hi Joshua.

    Yes i do in fact have 5x 5" insulated ceiling can lights penetrating the ceiling into the attic. They all are using 4.5w LED bulbs. These were a new addition this season.

    My old discussion:

    https://www.greenbuildingadvisor.com/community/forum/gba-pro-help/98433/ice-damming-low-slope-roof-resolvable-or-hopeless

    Thanks

  3. GBA Editor
    Martin Holladay | | #3

    Jake,
    I re-read some of the old thread. In that thread, in Comment #14, I wrote, "Installing rigid foam on the exterior side of the roof sheathing -- the thicker, the better -- is always the best approach, as I advised you in Comment #1."

    The usual reasons that people shun this excellent advice is, "I like my roofing, and I can't implement that solution until I install new roofing."

    But in your case, you just installed new roofing. So why didn't you take my advice and install thick rigid foam above the roof sheathing, in conjunction with your new roofing project?

    As you probably know, you have an air leakage problem. Adding recessed can lights was nuts, especially in light of the fact that you spent many hours on GBA asking questions about ice dams.

    It's hard to give advice when you willfully ignore it.

  4. Jake Rabe | | #4

    I definitely appreciated the advice Martin. The problem, as stated, was limited time and experienced installers. Also the aesthetics and additional work (some said removal of all gutters) needed for installing the rigid foam on the roof. The can lights were installed in the room bc there was no lights at all in this very short ceiling (about 6'3" height).

    Again much appreciated, though. I have a pretty good idea now on how to handle my circumstances. Will keep y'all posted once implemented.

  5. GBA Editor
    Martin Holladay | | #5

    Jake,
    I'm sorry that my response was short. I wish you the best of luck.

    I'm a big believer in solving ice dam problems by installing exterior foam, and I know that homeowners have to wait for a re-roofing job -- a chance that only comes around every 20 or 25 years. It breaks my heart to see brand new roofing installed without rigid foam on a house with ice dams.

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