Moisture visible on home's roof points to vulnerable areas

Q. I have a Cape Cod house in New Hampshire. I have been here one year, and after this nasty winter I had ice dam issues in the front. I notice every morning there is a strong demarcation line from the dew.

This ice dam was along the same line. Is this an issue with the insulation in the flat part of the attic or along the roof slant? I've attached a picture of the house in the morning. I am having the roof in the back replaced so the roof vent hasn't been installed yet.

A. The photo you sent shows several interesting patterns. The shingles in the upper part of the roof are dry, indicating that the existing gable louvers are adequately ventilating the small attic area above the ceiling because it is so small. Large attics are not usually well-ventilated by gable vents, as the air entering the vents falls to the floor before rising again to exhaust at the other end of the attic.

The sizable damp area visible one third of the way down the roof is at the vulnerable section of the roof where the collar ties are fastened to the rafters. This is a difficult area to insulate properly. The insulation is too often bent over to account for the thickness of the collar ties, as the framing changes from the flat ceiling to the sloping rafters. This leaves a triangular uninsulated space.

The insulation batts or blankets installed between the collar ties should be cut to fit tightly against what should be baffles set between the rafters to allow ventilation from soffits to ridge.

The rafter insulation should be totally independent and installed tightly against the rafter baffles and the end of the insulation between the collar ties on the flat ceiling.

The improperly installed insulation allows uncontrolled heat loss to melt the snow in that vulnerable band, and an ice dam can form. Over time, the shingles have deteriorated enough to absorb moisture, and they do not dry as fast as the unaffected ones.

There is a lighter, secondary line about one-third of the way up from the eaves, which is where knee wall studs are attached to the rafters. Because wood is not as effective an insulator as fiberglass, the snow melts faster above it, resulting in a similar situation where the shingles are absorbing moisture.

The photo also shows that the rafter bays are well insulated, but it also shows the heat loss through the rafters themselves with the same effect on the shingles. Looking at the picture, you can see the outline of the rafters as vertical damp areas.

It looks as if there is no space for soffit vents, so installing a ridge vent is not going to be helpful. However, an alternative to soffit venting would be to use a product such as DCI's SmartVent, which is installed under the shingles at the eaves. Yet considering that the gable vents seem to be doing a good job, perhaps you should leave well enough alone.

There also seem to be vents in the knee wall space on the front of the house, with insulation between the knee wall studs, which is why there are fewer signs of moisture absorption on the lower part of the roof.

One way to improve the insulation of the roof and eliminate the rafter ghost lines while addressing the insulation "holidays" is to add a minimum of 1-inch-thick XPS rigid insulation on top of the roof sheathing when the shingles are replaced.

You could start with the back roof since you plan on replacing it, and do the front whenever you are ready.

You may also want to consider a cold roof, which would eliminate all your problems. On the bare sheathing, have a non-asphalt-based roofing paper stapled and 2-inch-thick XPS rigid insulation installed. Next come 2-inch-by-3-inch "sleepers" set on edge with long screws driven into the rafters through the rigid insulation. New sheathing follows, and new paper and shingles.

If you plan on staying in the house for a long time, the energy savings and the increased longevity of the shingles will help pay for the additional cost of the cold roof.

Q. Thank you for your response last month regarding water seeping into our 1852 stone church's basement during heavy rains.

We will follow through with your suggestions: Check the grade around the church, plant a ground cover, set concrete pavers flush with finish grade at the drip line of the roof and check the sump pump capacity. I will inform you of the results once the suggestions are implemented over time.

Do you believe it best to remove the wallpapered blue board (with plastic sheeting under everything) and merely paint the walls to avoid problems if a fire develops? Perhaps it does nothing to prevent the development of mold.

A. Thank you for the follow-up. Please let me know if the water problem has been solved.

Regarding the wallcovering, you should keep it, as it provides insulation for the bathrooms. To make the wallpaper-covered rigid foam insulation (the blue board) fire-retardant, you can simply have the insulation covered with 5/8-inch fire code drywall. Paint it with your choice of latex paint.

Q. I thoroughly enjoy reading your column every Sunday in the Daily Herald in suburban Chicago. This may not be the most important question you have ever received, but it really bothers me.

I live in a three-unit condo on the second floor (my garage and entry door are on the ground floor). My problem is that many times this summer, I have come home to find several houseflies buzzing around the sidelights by the entry door. It doesn't happen every day and seems to occur more a day or two after we have had some rain.

The house is sealed up during the day and the air conditioner is on a setback, so the house is cool when I get home. I can't figure out where the flies are coming from. It's not like they are coming in from an open window or door.

This past weekend, I was away from the house till midafternoon and opened up a couple of windows when I came back (a cold front came in, so I didn't really need the A/C). About two hours later, I looked at the open windows (they are screened), and sure enough, there were a half-dozen flies on the inside of each of the screens or buzzing nearby.

The house is pretty clean - there are no garbage cans full of rotting garbage or anything and I have no pets. As far as I can tell, the windows and doors are fairly well sealed. I'm not sure what is going on or how to prevent it. Any thoughts or suggestions?

A. Flies can get in through the smallest cracks, so it is not surprising that you are bothered by them. They may come in around the window screens, but they may also get in through joints with walls and windows and doors, or other aspects of the construction of your condo.

It is probably going to be impossible to find out where they get in and to seal their entrance points. And it is likely that, as cold weather approaches, you will find a different type of fly inside - cluster flies looking for a warm winter home. Cluster flies are not "dirty" flies in the sense that they are not disease carriers, but they are a royal nuisance.

The best way to handle them is to vacuum them up.

Q. I have a question regarding dog urine damage to hardwood floors. I recently removed some carpeting and discovered that my terrier has been urinating in two spots for what appears to be a while. The urine soaked through the carpets and there are black stains on the floorboards. I assume this is some sort of mildew. What can I do to remove it, or can it be removed? Would sanding and refinishing get rid of this?

A. The urine has penetrated deeply into the hardwood floor. The best way to remove the dark stains is to do so with a solution of oxalic acid - a very potent bleaching agent, but also very corrosive.

You can buy oxalic acid crystals in paint stores. You'll need very little to treat the two spots. Mix the crystals in hot water to saturation (when there are still some unabsorbed crystals in the water).

Do not use any metal containers or tools; use glass or plastic. Wear skin and eye protection, and old clothes.

Apply the solution to the dark stains with a small brush, and allow it to do its work. You may need more than one application.

Once you are satisfied with the results, wipe off the residue with a cloth dampened with white vinegar.

The hardwood boards may now be of a lighter color than the rest of the floor. You may have to do some refinishing.

• Henri de Marne was a remodeling contractor in Washington, D.C., for many years, and is now a consultant. His book, "About the House," is available at www.upperaccess.com. His website is www.henridemarne.com. Email questions to henridemarne@gmavt.net, or mail First Aid for the Ailing House, Universal Uclick, 1130 Walnut St., Kansas City, MO 64106.

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