Ice Dam

When the weather starts to warm, ice dams can form on the roof causing leaks and ice.
An ice dam is a ridge of ice that forms at the edge of a roof and prevents melting snow (water) from draining off the roof. The water that backs up behind the dam can leak into a home and cause damage to walls, ceilings, insulation, and other areas.

What causes ice dams?
There is a complex interaction among the amount of heat loss from a house, snow cover, and outside temperatures that leads to ice dam formation. For ice dams to form there must be snow on the roof, and, at the same time, higher portions of the roof's outside surface must be above 32° F while lower surfaces are below 32°F. For a portion of the roof to be below 32°F, outside temperatures must also be below 32°F. When we say temperatures above or below 32°F, we are talking about average temperature over sustained periods of time.
The snow on a roof surface that is above 32°F will melt. As water flows down the roof it reaches the portion of the roof that is below 32°F and freezes.

The dam grows as it is fed by the melting snow above it, but it will limit itself to the portions of the roof that are on the average below 32°F. So the water above backs up behind the ice dam and remains a liquid. This water finds cracks and openings in the exterior roof covering and flows into the attic space. From the attic it could flow into exterior walls or through the ceiling insulation and stain the ceiling finish.

Some steps to help prevent ice dams:
First, make the ceiling air tight so no warm, moist air can flow from the house into the attic space.
After sealing air leakage paths between the house and attic space, consider increasing the ceiling insulation to cut down on heat loss by conduction.
Roof ventilation can help maintain uniform roof temperatures, but if the long-term actions described here are done effectively, then only small amounts of roof ventilation are needed to maintain uniform roof surface temperatures. If heat transfer has been reduced substantially, then snow will build up on the roof and cover natural roof ventilation systems, reducing attic ventilation rates. Natural attic ventilation systems are needed to dry the attic space and remove heat buildup during the summer. Power fans are not recommended.

Condensation on new windows

Water forming on new windows is because one of several things is happening. The temperature of the inner glass surface is at or below the dew point for the amount of humidity in your inside air. The humidity of your indoor air is quite possibly much higher now with your new windows because the air leaks around your old windows were eliminated once the new windows were installed.
Several conditions can increase condensation problems. If you close drapes over windows, this can cause the glass temperature and the temperature of the air between the drape and the glass to become cooler, making condensation more likely. If the thermostat setting is dropped substantially at night, this will cause an increase in relative humidity and may increase condensation. This condensation should vanish once the temperature rises in the morning.
The best way to deal with condensation on high-quality, double-glazed windows is to reduce indoor relative humidity to no more the 40 percent. You can do this by using kitchen or bath exhaust fans until condensation disappears. The fans will be more effective if you open a window elsewhere in the house to provide replacement air. Be sure that the fans you use exhaust to the outside, instead of going to the attic or just recirculating air within the house.