Dehumidifier probably unnecessary in empty condo
Q. My condo in Florida is not occupied in the summer. It is 1,000 square feet, and I keep the air conditioner at 82, to keep the humidity down, but it still is pretty expensive. I was thinking of putting in a dehumidifier instead. Does that make sense? The condo is on the top floor of a large seven-story building. Also, how can I tell if I have ice dams (in my house in Boston, not Florida)?
RALPH DESMOND, Jamaica Plain
A. A dehumidifier might be just as expensive, but I wonder if you need either to keep the humidity down, even in Florida. Your building must be pretty tight and insulated, and there is little breathing, washing, or cooking in the unit to create water vapor or humidity when no one is around, so you can experiment next summer without either an air conditioner or a dehumidifier.
As for ice dams, they are caused by a warm roof and the only way to tell if you have them is if water leaks into attic or house. Other signs are heavy icicles on the eaves, and quick loss of snow on the roof. If you have ice dams and no leaks, it is probably because you have an ice and water shield on the low part of the roof, which prevents water from backing up and leaking through shingles and shield.
Q. The white cedar shingles on my house on Cape Cod were treated with bleaching oil, and when they got rather tired looking after many years, I painted the house. Not much later, the paint peeled. I plan to reshingle. Can I shingle over the old shingles?
BOB WHALEN,
Cotuit
A. You at least learned your lesson, and will swear not to paint or put anything on the new white cedar shingles. They will weather very nicely to that Cape Cod silver, especially on the Cape. Yes, you can put new shingles over the old. The installers might put something under it like Tyvek or thin insulation, but no matter what they do, you will have to put a molding around the window and door frames to allow the new shingles to butt up against something instead of ending up in midair.
Q. I have found water coming up through some of my hardwood floors, and in two places the oak is rotting. The hardwood is on a plywood subfloor set on joists sitting on the concrete slab floor. There is no insulation between the joists. What is causing that water seepage and how can I replace the decayed areas?
CAL RAMSDELL,
Hyde Park
A. The water is not coming up through the floor but rather is water vapor in the house that condenses into water when it hits the cool floor. If it stays wet too long, decay will occur. One cure is to dehumidify the house, or in summer use central a/c, which is also a dehumidifier.
You must also remove the rotting boards; that is not easy because they are tongued and grooved, but if you start at one border of the room and remove the boards, up to the rotted area, it will be easier. You can cut the boards with the decay, and re-use all that are not decayed. Buy new boards to replace the rotted ones, unfinished oak or prefinished oak by the bundle. Make sure the new boards are the same width and thickness of the old.
An important part of the work is to take off the old boards very carefully because you can re-use them.
Q. The roofer put in a ridge vent in my house when he redid the roof, but he said he could not put in soffit vents because the roof overhang, which contains the soffit, did not end at the roofline but below it. Consequently, there is not enough ventilation in the attic, especially low ventilation. There are vents in the very peak of the gable but they are small. The previous owner cut two small holes in the gable for exhaust fans but they really don’t seem to be in the right places to be effective. It gets mortally hot up there in summer. Any ideas?
PETER HUNT,
Maynard
A. It’s the heat you have to consider. The ventilation industry says that with a ridge vent and proper-sized soffit vents the attic temp will be no higher than 10 degrees above the outdoor air. So, your goal is to install some low vents in each gable, the triangular-shaped ends of the roof. Picture the A-shaped gable, and cut vents in each of the two lowest angles, as close to the floor as possible. Make them 16 by 16 inches, and put them in both gables. That is four vents. Sounds weird, but they will give you the ventilation you need. This idea is not new. Look around your neighborhood; you may find some Cape Cod style houses that have small windows at the low angles of the gables. They vent the crawl space behind the knee walls on the second floor, not the attic, but they do the same thing as soffit vents.
Globe Handyman on Call Peter Hotton is also in the g section on Thursdays. He is available 1-6 p.m. Tuesdays to answer questions on house repair. Call 617-929-2930. Hotton also chats online about house matters 2-3 p.m. Thursdays. To participate, go to www.Boston.com. Hotton’s e-mail is photton@globe.com 
