How to prevent ice dams
Q. About six or seven years ago I added another new layer of insulation in my attic. The good news is that my oil usage went down by several hundred gallons a year.
The bad news is I've been getting ice dams ever since and just discovered that some of the vertical trim boards along the edge of the roof are rotting. I'm assuming the reason for the rot is due to not enough, but some heat still escaping through the attic resulting in the ice and that it must be melting into the boards and rotting them out. The edges of the roof, which was replaced about 10 years ago, have edge vents. To ultimately solve this problem what do you suggest?
One thought I have had is to pull the insulation back from the edges of the attic leaving a bigger gap at the edges. This would allow more heat to escape and melt what is above. Thank you for any help you can provide.
A. It's surprising you didn't experience ice dams before with the lower level of insulation. Ice dams form when the snow cover on a roof melts because the attic's temperature remains above freezing. When the melting snow reaches cold areas of the roof, such as its eaves, it freezes and ice builds up to where it can cause further melting snow to back up under the shingles and leak inside the building.
I am not clear about what you call the "vertical" trim boards along the edge of the roof. Unless I am missing something, the only vertical trim boards I can think of are the corner boards at each corner of the house walls. Or are you calling "vertical" the fascia boards fastened to the bottom of the rafters and onto which gutters are installed? If so, they would be referred to as "on edge" as opposed to "flat."
The fascia boards are more likely to be rotting from another cause: Roof water following surface tension along the metal drip edge and getting into the fascia boards joints (boards that were most likely installed "raw," unprimed) over a long period of time as is too often the case. They can be replaced with one of the PVC boards that are now the favorite.
Since you are getting ice dams, it means that, even though you added insulation, there is still enough heat in the attic to melt the snow cover. If the ice dams are evenly spread across the entire roof, there may still be warm, moist air convecting into the attic from the conditioned space.
If the ice dams are more locally found at the eaves below skylights and chimneys, there isn't much you can do about the skylights, but the accessible parts of chimneys in the attic may be insulated.
You mention vents at the edge of the roof; I am assuming you mean you have soffit vents in the roof overhangs, and I hope that they are continuous across the entire soffits.
But do you also have a ridge vent at the peak of the roof? If so, you must make sure the soffit vents are not blocked by the added insulation in order to ensure that there is an uninterrupted air flow between the soffit and the ridge vents. This air flow is helpful in keeping the roof sheathing cooler and in dissipating any moisture in the air that may convect from the living spaces.
To accomplish this, there should be baffles at the bottom of each rafter space where the rafters meet the walls, and it is best if these baffles have a vertical leg that protects the end of the fiberglass insulation from any air currents that would reduce its effectiveness. The baffles should be such that they span the entire width of each rafter space and leave a space of at least 1½ inches for air circulation.
The eventual solution to the elimination of ice dams is to determine the source(s) of the heat loss into the attic, which is most likely convection (recessed light fixtures, bath fans, etc.), by getting an energy audit.
Q. Did you write the editorial for the Daily Herald about a product to use after you sand the bottom of your garage door? (It was a type of rust inhibitor.) You named it specifically in this column.
Of course I cut out the column and cannot for the life of me remember where I put it! Please let me know what this product would be as we are looking to do this.
A. Sorry, but it is not I who mentioned this product. If it is referring to a rust inhibitor, it must apply to a metal garage door.
There are a number of rust inhibitor products and you should be able to find one in a paint, hardware or big box store. But it seems to me that a better solution is to paint the bottom of the door with an exterior paint that contains a rust inhibitor.
Q. I'm glad you're back answering questions in the Daily Herald. My husband and I recently had a high-efficiency furnace installed in our home and are having issues with the cold-air return system. First was a loud whistling, which we solved somewhat by removing the grates to allow greater air flow. But so far we haven't found any replacement grates that will allow more air to enter than the old ones. Any thoughts where we could buy some?
The second, more-important issue is the amount of dust being pulled through the system to the furnace filter, probably because the volume of air being returned is larger and faster moving. We have an electronic air filtering system that was getting clogged frequently, so for the time being we have turned it off and installed a large paper filter. After three weeks, we need to replace that filter. This could get expensive over the winter.
When we removed the cold-air vent covers, we could see a thick lining of dust along the ducts. The air return system consists mainly of rigid metal with some flexible plastic tubing in the attic. Would duct cleaning be called for? I have heard that it can be a waste of money and can cause more problems than it solves. If you think it would be helpful, are there any specific methods of duct cleaning you would recommend? Knowing that would help us narrow down contractors.
If you don't think cleaning by a contractor is a good idea, is there anything we can do to reduce the amount of dust reaching the furnace filter?
A. There are decorative grilles that have larger openings, which should eliminate the whistling. Look up the selection of grilles at:www.signaturehardware.com and click on Hardware, click on Registers and scroll down until you reach wall registers. There are several registers with wider openings than the ones you removed may have had.
But you may want to ask your HVAC contractor if he or she would recommend reducing the speed of the fan as a solution.
Too bad you are not still using your electronic filter. The fact that it clogged frequently is telling you that it is very effective. It simply means more frequent cleaning.
It sounds as if a duct cleaning is in order; be sure to select an experienced firm by asking for references. Ask for the names of several customers who had work done in the last six months, and call them.
• Henri de Marne, a former remodeling contractor turned columnist and consultant, is the author of "About the House with Henri de Marne" (Upper Access Publishing). He continues to take questions from readers for this column and his website, www.henridemarne.com. Email questions to aboutthehouse@gmavt.net.