Getting ice dams after polyurethane insulation, is it normal?
Mike
7 years ago
last modified: 7 years ago
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How to insulate a conditioned attic after framer mistake
Comments (44)It's helpful to know the code requirements and unfortunate that the builder was not familiar with them and did not follow the contract documents. Your builder and architect should have already presented you with all of the possible alternatives. One alternative should be to remove the non-complying work and building the roof as required by law and the contract. Section 9.19. Roof Spaces 9.19.1. Venting 9.19.1.1. Required Venting (1) Except where it can be shown to be unnecessary, where insulation is installed between a ceiling and the underside of the roof sheathing, a space shall be provided between the insulation and the sheathing, and vents shall be installed to permit the movement of air from the space to the exterior. 9.19.1.2. Vent Requirements (1) Except as provided in Sentence (2), the unobstructed vent area shall be not less than 1/300 of the insulated ceiling area. (2) Where the roof slope is less than 1 in 6 or in roofs that are constructed with roof joists, the unobstructed vent area shall be not less than 1/150 of the insulated ceiling area. (3) Required vents are permitted to be roof type, eave type, gable-end type or any combination of them, and shall be distributed, (a) uniformly on opposite sides of the building, (b) with not less than 25% of the required openings located at the top of the space, and (c) with not less than 25% of the required openings located at the bottom of the space. (4) Except where each roof joist space referred to in Sentence (2) is separately vented, roof joist spaces shall be interconnected by installing purlins not less than 38 mm by 38 mm on the top of the roof joists. (5) Vents shall comply with CAN3-A93-M, âÂÂNatural Airflow Ventilators for BuildingsâÂÂ. 9.19.1.3. Clearances (1) Except as provided in Sentence (2), where venting is provided to a roof joist space, not less than 63 mm of space shall be provided between the top of the insulation and the underside of the roof sheathing. (2) Where venting is provided at the junction of sloped roofs and exterior walls and where preformed baffles are used to contain the insulation, the baffles shall, (a) provide an unobstructed air space between the insulation and the underside of the roof sheathing, that is, (i) not less than 25 mm in dimension, and (ii) of sufficient cross area to meet the attic or roof space venting requirements of Article 9.19.1.2., and (b) extend vertically not less than 50 mm above the top of the insulation. (3) Ceiling insulation shall be installed in a manner that will not restrict a free flow of air through roof vents or through any portion of the attic or roof space. 9.19.1.4. Mansard or Gambrel Roof (1) The lower portion of a mansard or gambrel style roof need not be ventilated. (2) The upper portion of roofs described in Sentence (1) shall be ventilated in conformance with the requirements in Articles 9.19.1.1. to 9.19.1.3....See MoreIce Dams on Flat Roof
Comments (3)It's not clear to me how ice dams form on a flat roof. It must have some sort of pitch so a "dam" forms on the downslope side and prevents the water from runing off. Otherwise your problem is that a puddle forms in the low point in the center and leaks through (although I'd expect this to happen during/after significant rains also). Lastly your roof slopes back towards the main roof and leaks at the intersection. If you have "dams" that are actually blocking runoff, one suggestion is to fill a nylon stocking with ice melt pellets and rest it across the dam. The ice melt will slowly eat its way through the dam to the base roof and let the runoff out. If the sunroom below (and the cavity in the ceiling) is truly unheated then I can't see the insulation doing much for you. yopu actually want to vent that space so then underside is as cold as the top. Shoveling the roof sounds like the best short term corrective action you could take. Sheet roofing on flat roofs is supposed to be tight enough to withstand some ponding, but there still needs to be some slope (using crickets) and a drain mechanism. Pictures might add some clarification. Hope that helps....See MoreGetting ice dams after polyurethane insulation, is it normal?
Comments (6)Are the ice dams above the areas free of spray insulation? If so, the lack of insulation caused the heat from the building to form the ice dams. Adding the insulation to areas that already have ice dams will not remove the ice dams, only melting the ice from above(warmer weather or physically melting) will remove the dams. But, once the spray insulation is installed, new ice dams should not happen. Ice dams usually occur with incomplete insulation/venting problems. Warm air from inside the building melts the bottom layer of snow on a roof, which flows down the roof surface to a colder section which freezes at the eaves/edges of the roof. That builds up over time to cause unwanted ice buildup. Freezing rain causes buildups of ice that looks similar, but covers everything, not just eaves/roof edges. There will be a layer of ice on the entire roof, trees, power lines, plants, everything. Icicles form with normal thaw/freeze cycles during the day/night when the sun heat begins to melt the top layer of snow on a roof, which flows down and freezes as the water drips off the edge of the roof. Incorrectly insulated/vented attic spaces can create a combination of ice dams and icicle buildup. Different situations that can seem similar. The solution is to determine if the building is correctly insulated and ventilated. In your situation, freezing rain seems to have caused the problem, unless it happened on the yet to be sprayed areas....See MoreIce Dams on new construction ?
Comments (23)Thanks all. To answer a few questions: - The attic (3rd above-ground level of house) is conditioned and finished (my office, my wife's craft room) - The dormers are real. You can walk in to them. - There is no vapor barrier. Primary insulation throughout for walls and underside of roof deck is closed cell spray foam (which should act as vapor barrier?). - Walls are 3.5" so R-21 (plus 2" blown fiberglass). Underside of roof deck is R-49. - The only batt insulation is in interior walls for what minimal sound reduction that provides. - The exterior wall cavities were filled out with blown fiberglass (between closed cell foam and drywall). This was to alleviate my concern that the 2" of stud projecting beyond the 3.5" thick foam would act as a cold sink and make the already bad thermal bridging that much worse. - There is no way that I know of to see in to the vent pans (insulation stops). A blower door test after insulation and just prior to sheetrock was 1.8 @ ACH50 which was disappointing. For anyone interested there are numerous photos here: http://bamasotan.us And here: https://www.instagram.com/bamasotan/...See MoreMike
7 years agolast modified: 7 years agoSaltiDawg
7 years agoMike
7 years agoSaltiDawg
7 years agolast modified: 7 years agoroof35
7 years agoMike
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