Water leaks in winter?
Water leaking in around windows in winter is usually a sign of ice buildup on the edge of a home's roof: The ice prevents melting snow from running off, and the water leaks through the roof, down into the home's infrastructure.
An ice dam may be to blame
Ice dams come in spells. Some years we'll see none, then, one winter week after prolonged temperatures in the 20s, they'll break out like the mumps.
Ice dams generally form when your home's heat escapes into the attic and warms the roof. This melts snow on the roof, and the water freezes on the eaves�which are are colder because there's no warm attic under them.
Though there are some short-term fixes you can try, the best way to prevent ice dams is to make sure your attic is properly insulated, ventilated, and sealed against heat from below.
The right insulation, in the right amount, properly placed on your attic floor will help keep your home's heat in the living area and out of the attic.
Proper ventilation will keep your attic and roof cool. Because heat rises, exhaust vents high up typically let out warm air, drawing in cool air from intake vents down low.
Your attic might be sufficiently ventilated but the vents simply need cleaning.
Sealing an attic against infiltrating warm air means making sure it isn't being heated by leaky heating ducts, improperly vented bathroom fans, recessed lighting fixtures and the like.
Good roofing is another consideration, and a waterproof membrane under shingles near the eaves can help keep water out. The links at left can tell you more.