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With interest I have been reading the discussion on ice dams and now have a much better idea of what I need to do to fix a home I own in Summit County Colorado. Ice has built up on the roof consistently for the years I have owned the home having become so large that it took three days and $1500 worth of labor to clear.
My plan is to seal wall penetrations into the attic, add sofit vents and increase the ceiling insulation where possible.
Additionally the cathedral ceiling is insulated but also has some blocking of the 2 inch air channel between the insulation and roof deck. I am not certain about what I can do to fix this problem other than removing the sheet rock and installing new high density insulation and an air barrier. Any suggestions?
The structure has a ridge vent which I am not certain is working adequately. I am considering added additional louvered wall vents into the attic space to ensure that the attic space stays as cold as possible.
Is this too much venting of the the attic?
How would I calculate the amount of venting I would need?
What is the best position for the louvered wall vents?
The builder of this home is one of those people that give the profession a really bad image, and even though it is a new structure refuse to do anything without an enormous fight. Therefore, I am on my own fixing this problem.
Any help would be much appreciated.
DT
Replies
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Thanks Fred,
I have reposted my message as the Ice Dams thread has developed into somewhat of a meaningless collection of comments rather than a useful discussion.
I do appreciate you taking the time to provide a response.
DT
*As Hilton would have said (if he had thought of it),the three most important things to consider when dealing with ice damming are ventilation, ventilation, and ventilation. It is almost impossible to have too much ventilation and still have a roof to keep the rain and snow out.The standard around here (Central Alberta) is 1 in 300 and I see no reason why that would be any different in your area. That is one square foot for every three hundred square feet of attic area.The first place for you to start is to add either standard roof (mushroom style) vents or wall (gable end)vents or both. Either type should be installed as high as practicle on the roof or gable as the case may be.The eave ventilation is very important as it allows the flow of air through the attic (by convection) and I would ensure there is sufficient at that location.I would be hard pressed to recommend the removal of your drywall to either remove the blocking or change the insulation type. Try the other locations first(although I am unsure of your roof design) and you may find the results satisfactory.I have often wondered about the efficiency of ridge vents as they only offer small openings to the exterior which appear to be capable of quite easily becoming plugged with either frost, ice, or snow. The other thing to look at, is did the contractor leave a gap at the top of the sheathing through which the ridge vent can breathe? Or is the ridge vent merely an ornament tacked on top of a nice tight sheating joint? Stranger things have happened.Good luck, and I would like to hear how you make out!
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D. Toftness, Vennco, et al. First. I could not find your post which Fred said he had copied to Ice Dams 101. Second, Vennco, who is this Hilton you mentioned? Third. Vennco's response is another example of why it takes a lot of pages (about 75) to explain what is wrong with most (99%) attic ventilation devices. Fourth. The answer to ice dams is NOT :-] ventilation, ventilation, ventilation. It is sealing/insulation, sealing/insulation sealing/insulation,sealing/insulation.Having said that am I saying that ventilation cannot help? NO. To save time please see Chapter23 Attic Ventilation in my book, _Complete_Building_Construction_ 4th Edition, published by Macmillan.
I have seen millions of dollars of damage caused by.... little or no attic ventilation? NO. Caused by leaky ceilings below the attic--the attic floor--and worsened by little or no attic ventilation.You cannot jam a 2x12 rafters full of insulation,cover them with wallboard, fill the ceiling with recessed light fixtures, ceiling fans,HVAC ductwork, plumbing and not have troubles.In one condominium subdivision all 7 building's roofs had to be replaced in 4 years because of this condition. There was no way for the accumulating moisture to escape.Had there been some attic ventilation this might not have happened. Notice that I said this "might"not have happened. It depends largely on what attic ventilation devicesd were used.
One cannot live in the snow belt and seeing all the ice dams not wonder what is going on. One sees ice dams on houses with ventilated attics, on metal roofs, on roof eaves covered with heat tapes, on attic vented according to code, and even on roofs with ridge and sofit vents.One cannot help but ask, if attic ventilation is the answer why is it not working on all these houses.
Almost 40 years ago a researcher named H.C. Hinrichs proved in a real house attic that 99 percent of the attic ventilating devices available did not work. He also siad the 1/150 and 1/1300 ratios, Vennco's standards--were inadequate. The title of his research report is "Comparative Study of the Effectiveness of Fixed Ventilating louvers"published by ASHRAE in _Transactions_ Volume 68,1962, page 404.You can order a copy of this paper from ASHRAE by calling Customer Service at 800--5-ASHRAE (in USA only).My chapter on attic ventilation is a layman's version of Hinrich's research, not that Hinrichs's paper is that technical.
The standard that Vennco refers to:1/1300, or 1 square foot for each 300 square feet of attic area, translates to LESS THAN !/2 SQUARE INCH PER SQUARE FOOT of attic area...some standard.
Gable-end louvered vents work only when the wind blows directly into the vent.The air flow pattern is over the attic floor.See Figure 23-1 in my book.the air flow through eaves vents is over the attic floor where it does not belomg. Indeed when the wind is parallel to the ridge the air flow from the soffit vents is considerably reduced, see figure 23-4.
As for ridge vents, recent (1995) research at University of Illinois reinforced what years and years of prior reseach shows: ridge vents without an external baffle do not work. Nor do all combinations of ridge and soffit vents work. And the right ridge vent with the wrong soffit vents wont work.
Finally, why do building codes call for attic ventilation? To rid the attic of leaking warm moist air that can cause ice dams and moisture damage to the wood framing.But suppose you reduce, lessen, control, retard the warm moist air from getting into the attic space is attic ventilation necessary? If there is nothing to ventilate why the attic vents? Hope this helps a bit. GeneL.
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With interest I have been reading the discussion on ice dams and now have a much better idea of what I need to do to fix a home I own in Summit County Colorado. Ice has built up on the roof consistently for the years I have owned the home having become so large that it took three days and $1500 worth of labor to clear.
My plan is to seal wall penetrations into the attic, add sofit vents and increase the ceiling insulation where possible.
Additionally the cathedral ceiling is insulated but also has some blocking of the 2 inch air channel between the insulation and roof deck. I am not certain about what I can do to fix this problem other than removing the sheet rock and installing new high density insulation and an air barrier. Any suggestions?
The structure has a ridge vent which I am not certain is working adequately. I am considering added additional louvered wall vents into the attic space to ensure that the attic space stays as cold as possible.
Is this too much venting of the the attic?
How would I calculate the amount of venting I would need?
What is the best position for the louvered wall vents?
The builder of this home is one of those people that give the profession a really bad image, and even though it is a new structure refuse to do anything without an enormous fight. Therefore, I am on my own fixing this problem.
Any help would be much appreciated.
DT