Protective membrane prevents ice dams

Q. We have a 60-year-old brick Cape Cod that was built with no soffits. As a result, we experience occasional ice dams, but even more troubling is condensation in the attic that has led to water buildup and staining on the drop ceiling panels in our upstairs bedrooms.

We’ve heard differing opinions on an attic fan with a thermostat and humidistat. Does an attic fan create too much air circulation? Do you have any suggestions for how to alleviate this problem?

A. Ice dams occur because snow cover melts from the bottom of the roof and runs until it reaches a cold area, which causes it to freeze. As it builds up, further snowmelt backs up behind the dam, which keeps growing as new water freezes. At some point, new water creeps under the shingles instead of freezing and finds a joint in the underlying felt (if any was used). Water then leaks into the attic, wets the insulation and can damage interior surfaces.

The way to eliminate ice dams is to prevent heat loss from the conditioned spaces. Heat loss occurs when the attic floor is inadequately insulated and warm, moist air convects through cracks and crevices into the attic, resulting in condensation on cold surfaces. Ventilation is often a help, but it is not always necessary if other conditions are right.

Attic fans are not the answer. They generally increase the draw of conditioned air, thus adding to the cost of energy; this is also so in the summer.

If ice dams cannot be controlled, an ice- and water-protective membrane can be installed at the eaves on bare sheathing and covered with shingles. These membranes self-seal around nails and prevent water from penetrating the structure.

Condensation on cold attic parts can be eliminated only if convection of conditioned air is eliminated. I suggest that you consider an energy audit, which will detect the paths that heat and moist air are taking into your attic. Check with your utility providers (electricity, gas or oil) to see if they offer the service or can lead you to those providing it.

Q. We would appreciate your help with this mystery. We have had problems with crusty rings in the toilets of our almost 20-year-old house for the last several years, despite a water softening system. We tested our water several times and do not have hard water coming through this system or directly from our well. Can you think of anything else that might contribute to our problem?

A. A water softener changes calcium ions into sodium ions, but this does not change the dissolved solids, which are responsible for the toilet bowl rings.

Your best option is to have a water specialist evaluate your system.

Q. I would like to insulate my garage so I can do woodworking in winter. I have had installed an insulated garage door, two electrical circuits and an electric heater with a dedicated circuit. The walls are concrete block, and they are so cold the heater cannot warm the area. It is a one-car garage, 12-by-23 feet, with about 7-foot-high walls. The ceiling is not insulated, just drywalled. I want to insulate just two of the walls: the 12-foot wall at the front, which is below grade, and a 23-foot wall that is almost all above grade. How do I insulate those two walls and finish them correctly?

A. I assume you also plan to insulate the ceiling, but why would you insulate only two walls?

To insulate the concrete block walls that are above grade, clean the surfaces and apply 2-inch-thick rigid insulation using an appropriate adhesive — StyroBond or polyurethane caulking. If you choose polyiso rigid insulation or any other aluminum-covered insulation, adhesive will not work because the foil is likely to peel off. An alternative is to fasten furring strips to the blocks with masonry nails or construction adhesive, tack the insulation to it and screw drywall over the insulation.

Be careful insulating the parts of the walls that are below grade. If the soil against the walls is clay, as opposed to coarse and well-draining soil, it could push in the walls as it freezes. Under such circumstances, you should insulate only from the top to 3 feet below grade to allow some heat loss to prevent freezing. Keep in mind that the soil offers some protection.

Q. I am remodeling a one-car garage connected to the house. Two sides are connected and are insulated, one side is not insulated, and the other side is the actual garage door. The plan is to take out the garage door and frame a wall from the slab up. The frost wall is approximately 9 inches above the slab on the uninsulated side, and on the back wall and other sidewall, the height of the slab varies from about 7.25 inches to 8.5 inches. Since the owner wants to raise the floor to the level of the existing interior floor, I plan to put down 2-by-8-inch joists, attaching the band joists to the existing frost wall with shot-in nails where needed. There is a drain in the concrete floor that connects to a footing drain. I plan to plug this drain with concrete or spray foam.

The questions I have are these:

Should I put down a 6-mil vapor barrier over the concrete before I build the joist system for the floor? (The plan is to have the joists, 16 inches on center, ¾-inch plywood and carpet.)

How would I insulate this floor? Would it be better to use 2-inch foam board (the blue stuff) and layer it? Should I use foam board with foil backing or just plain? If I do use foam board, I would cut the board to fit between the joists, since there would not be enough height to lay down even 1-inch foam board over the whole concrete floor before building the floor joist system.

Or would it be better to use fiberglass insulation in the floor system? If fiberglass is used, would the vapor barrier be on top of the joists or next to the concrete floor under the joists? Do you know of any better way to insulate this floor system?

There will be electric baseboard heat with its own thermostat. I will insulate the garage ceiling itself rather than the roof rafters above the garage ceiling. Is it best to use faced insulation for the ceiling or unfaced?

A. I would lay 6-mil plastic on the slab to prevent moisture from the slab, which may not have much of a stone base under it. In addition to fastening a pressure-treated band joist to the frost wall, consider using pressure-treated legs to support the band joists just in case the fasteners loosen over time. I would also suggest you use pressure-treated joists.

The safest way to insulate the floor under these potentially troublesome areas would be to nail furring strips to the sides of the joists at whatever depth you decide to insulate and to layer the XPS on top of the strips, alternating the joints and caulking the perimeter of the foam at each board and every layer. Two layers of 2-inch XPS should be sufficient, so the strips should be set 4 inches below the top of the joists. No need for polyiso.

To make it easier for you and to reduce waste of the foam, consider using 24-inch-on-center floor framing, which you can do with ¾-inch plywood.

If the new room is not going to generate moisture (no plumbing and not an excessive number of water-loving plants), you can insulate the ceiling with foil-faced or kraft-faced fiberglass, but it is always safer to use unfaced fiberglass and staple on a 6-mil plastic vapor retarder/air barrier.

Q. I enjoy reading your column every week. I have a gas fireplace surrounded by brick. My house is about 20 years old now, and the brick looks dull to me. I’ve tried cleaning it, but is there anything to use on the brick that would give it a shine?

A. Once you have the bricks cleaned as you like, you can apply a masonry sealer, which you should buy in a masonry supply or construction supply store. If you do not have one nearby, contact A.H. Harris Construction Supplies (www.ahharris.com), which has several stores along the East Coast. Be sure to specify that you want a sealer with a shine.

Strange things happen: This comes from a reader with a most interesting story: “This memo is in regard to … the subject of bathroom odors. I would like to add my two cents’ worth.

“A few years ago we started having this problem, too, and I just could not figure it out (full trap, used often, etc.). Then I realized my son was using a different soap (Irish Spring) from mom and dad (Zest), so I had him stop using that brand, and the smell disappeared. I wonder if it depends on the type of fats used to make the different soaps?

“Thanks for letting me ‘vent’ my opinion.”

What a fabulous story! One for the record! Thank you for sharing it.

Ÿ Henri de Marne was a remodeling contractor in Washington, D.C., for many years, and is now a consultant. Write to him in care of the Daily Herald, P.O. Box 280, Arlington Heights, IL 60006, or via email at henridemarne@gmavt.net.

© 2012, United Feature Syndicate Inc.