Home repair: The perfect conditions for heating a driveway
Q. I live in Illinois and am going to replace my driveway with concrete. I would like it to be heated, but my husband says that heating a driveway in freezing temps could cause cracking or other problems. Can you confirm or tell me what drawbacks there are to heated driveways aside from the high cost?
A. If the driveway is reinforced with No. 4 rebars, 12 inches on center both ways, and the concrete is poured over a good stone bed and is 3,500 to 4,000 psi and air-entrained, you should not have any problems, whether it is heated or not. There should be frequent control joints or scoring to allow for expansion and contraction. If scoring is chosen, the grooves should be sealed with Sikaflex or an equivalent joint sealer. So be sure that you select the most experienced concrete contractor in your area.
If you have a boiler and a hydronic-heating system to heat your house, you will need a separate zone, and the system will need antifreeze, which will reduce its efficiency. If you have a warm-air system, you will need a water-heating appliance — a small boiler or water heater — to feed the hot water to the concrete (it will need to have antifreeze). When heavy snows are expected, you should start the heated water flowing early to warm the concrete ahead of time to keep up with the snowfall or you will still need to have it plowed or shoveled.
Q. I read your column about the Pittsburgh homeowner moving his radiators. In your response, you mentioned installing a reflective shield behind the radiator. What exactly would this reflective shield be made of? Where would you get it? Would it be just the size of the radiator itself?
A. It can be made of copper (most expensive), aluminum or sheet metal. You can buy the metal to make the shields in some hardware or big-box stores or a metal shop. The shields need only to be the size of the radiators.
Q. We are replacing four boards on the Charlotte, Vt., Grange Hall and would like your comments on a finish that will last longest. Built around 1870, the hall had been used for about 80 years as a school until the Charlotte Grange purchased the building. We want to keep the boards as close to original as possible. Attached is a photograph of the building with boards removed from each of the four sides at the top of the cupola, and one of the decaying boards. Each board is 10 feet long, one full inch thick and 17.5 inches wide. There is also a 4-foot-by-3-inch piece attached at the top of the boards. Cutting out wood for the full thickness made the decorations in each board.
When I checked with one of our woodworking neighbors to make sure that the boards were white pine, he gave us four dry boards of the correct length. I have made the cutouts and am about ready to finish the boards. They are at the top of a high building and can only be repainted using a lift. We have several recommendations, but I would like an expert opinion.
What finish do you recommend and what glue, if any, should be used to attach the 4-foot-by-3-inch piece on top? I would never have considered white pine, but it is a native wood from which wide boards can be cut and doesn’t warp too much. The boards are only attached to the four-sided roof by 2-by-2 pieces at each corner that were toe-nailed through the roof with long galvanized nails. There were also two 2-by-2s going horizontally from boards and were nailed into the roof. Each of the boards was raised one inch above the roof by the 2-by-2 pieces in each corner. All rain had to run through this one-inch gap, and the snow must have stayed all winter!
Attachment of the boards seems marginal for wind loads, so we will try to tie the boards to the roof more securely and decide on how to minimize water damage when attaching to the roof. We currently don’t know what structure is under the roof in the area of the overhang, but we’ll find out this summer. — Charlotte, Vt.
A. Because you are thinking of improving the attachment of these four large boards, please consider having steel brackets made up that would be screwed to the roof sheathing through a waterproof gasket of the type used by people who install roof antennae. The bottom of the brackets would be bent up to form vertical posts to which the boards would be bolted. A horizontal brace between the vertical leg and the piece attached to the roof would greatly strengthen and stiffen the assembly against strong winds, but is not necessary if the steel is thick enough. The brackets could be made of stainless steel or painted with three to four coats of metal paint. Apply two coats of metal primer and two coats of a metal paint that is durable, such as Hammerite. This would allow the boards to be mounted higher off the roof to allow a better runoff, and it would hardly be noticeable from the ground.
To fasten the 4-foot-by-3-inch boards to the top of the large ones, coat the entire surface of the small boards with Sikaflex-1a — a sealant, adhesive and long-lasting caulking compound. Bed the small boards onto the large ones and, assuming that the small boards are also one full inch thick, pre-drill three holes (one near each end and one in the center) in both boards to apply 5-inch-long TimberLok-type screws (you can get them at Lowe’s). This will ensure that the adhesive is firmly squeezed to prevent any open spaces between the two boards and keep the small boards from warping. Once you have done this, screw a pressure-treated deck board (5/4 inches by 6 inches) to both boards as a backup to strengthen the whole assembly. For a long-lasting paint job, sand the boards to roughen them enough to remove any mill glaze (the polishing often resulting from planning operations that prevents paint from sticking). Apply two coats of an acrylic primer such as Benjamin Moore Fresh Start, followed by two coats of Benjamin Moore Aura. Make sure that all the cutouts are also fully sanded and painted. Hopefully, this will last a long time and resist the vagaries of Vermont’s weather.
Q. When we renovated our house in 2003, we removed the roof from the chimney west, creating a shed dormer over our stairway and gable dormers out front, back (shown in the first photo) and to the west. I cross-bordered the rafters and laid rafter vent with cross pieces at each bore hole, hoping the soffit vents would allow cold air to draw through them and to the ridge vent.
All insulation is 12 inches and is covered from the inside with 5 mil poly. The gable in the first photo has a flat ceiling (it is our master bath) with an exhaust fan in it. The front gable and first eight feet of the ridge for the back gable — as well as the gable end — are full cathedrals. We have recessed lighting (rated for insulation) in the shed dormer and in the ceilings of the tiled shower and bedroom.
Obviously, we are getting heat loss that is causing this significant ice damming. Interestingly to me is that the front gable (last two photos) has no snow loss, while the other roofs do. Our builder suggested removing the top three courses of shingles and cutting back the sheathing to expose and remove all the fiberglass insulation and replacing it with dense-pack cellulose. He also suggested that we seal off the soffit vents, which would create a cold roof. If I read your latest piece accurately, you suggested the same. My concern is that there will be condensation and we will then have a mold and reduced-insulation problem.
Our original plan was to do work only on the shed-dormer roof, and I had thought we would just build a cold roof atop the existing roof. With all the other ice damming, we decided we should tackle the whole problem. We can’t afford to pull the whole roof and lay a cold roof. Do you have any thoughts on this problem? Anything you might be able to add would be welcome.
A. Assuming that the chimney is operational, this would account for the ice dams seen in photos two and five. If you have access to the attic, you may want to wrap fiberglass insulation loosely around the chimney, held in place with string. Whatever ventilation you achieved is not enough to overcome the heat loss from the chimney, which is causing the snowmelt.
Even recessed lights rated for insulated ceilings can allow a considerable amount of warm air to convect into the attic, adding to the problem. The front gable retains its snow cover because there is no heat loss from the chimney or can lights.
Removing the fiberglass insulation and replacing it with dense-pack cellulose and closing off the soffit vents will result in a hot roof, not a cold roof. This is not likely to solve the problem, even though dense-pack cellulose will stop any air movement that can occur through fiberglass, as the chimney and can lights are still there, causing the heat loss. Even dense-pack cellulose can allow moisture through and result in condensation on the cold sheathing. The best solution is to replace the fiberglass with closed-cell polyurethane foam (at a high cost) to provide an air and moisture barrier, but the entire rafter cavities will have to be filled with the foam to prevent the heat from the chimney from melting the snow as much as it does now (there will still be some melting).
Less expensive solutions worth trying would be to insulate the chimney in the attic, seal around the can lights with polyurethane caulking if you do not want to get rid of them, and keep the ventilation. You can build a cold roof over the existing by removing the shingles, adding sleepers over the sheathing, new plywood, new felt and new shingles — an expensive job. If the eaves of your various roof planes are covered with an ice- and water-protective membrane, this should prevent any leakage into the house. But it will not do anything to lessen the ice dams and the damage they cause to shingles.
IMPORTANT INFORMATION: The thinking on removing ice from concrete is changing as technology and research bring new information. Years ago, we used rock salt (sodium chloride), which worked fine but had temperature limitations and was known to damage concrete surfaces. So we were advised to use calcium chloride, which was purported to be less damaging to concrete surfaces. Now, this is all upside down as research has demonstrated that calcium chloride actually interacts with hardened cement paste in concrete, resulting in expansive cracking, increased permeability and a significant loss in compressive strength. This chemical attack was not seen with sodium-chloride brines. So the tables have turned.
But we need to be aware that sodium-chloride brine, used more and more on roads to clear them of snow and ice, does penetrate deeper into the pores of the concrete and, when it reaches reinforcing steel, will accelerate the rusting process. Sodium-chloride crystals or brine do not have the same long-lasting effect as calcium chloride, which also works at a much lower temperature. One way to protect concrete surfaces is to coat them with siloxane or silane sealants, which you can buy in masonry-supply houses. Special additives, such as coal fly ash and ground, granulated blast-furnace slag, can be added to the concrete mix to make it resistant to these chemical attacks. It may be that these additives will become standard on all mixes in cold regions. Meanwhile, we have to decide whether or not we want to use any of these de-icers, knowing that they are likely to cause damage and shorten the life of our concrete driveways.
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 e-mail at henridemarne@gmavt.net.
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