Why Windows Fog or Drip on Damp Coastal Mornings

Ten minutes with a towel costs nothing, and a replacement glass unit costs real money, so the first job is telling which fog is which. Moisture on a window in Carlsbad, CA falls into three places, the inside face, the outside face, or between the panes, as the notes at window installation carlsbad earth liberation front describe. Each one has a different cause and a different fix.

Fog on the inside face

Condensation forms when a glass surface is colder than the dew point of the air touching it. On a new, tight vinyl window the inside face often beads up in winter because the house is holding moisture, not because the window is defective. Showers, cooking and laundry drying indoors supply the water. Beading on the glass alone does not mean the window leaks. The frame can be dry and sound while the glass sweats.

Moisture between the panes

Fog or droplets trapped between the panes of insulated glass mean the edge seal has failed. The air space is no longer sealed, and the moisture is inside the unit where no towel can reach. Wiping the glass fixes nothing. The glass unit has to be replaced. Measure the unit thickness and the sight size before ordering, and check the sash for rot or warping while it is out.

Outside the glass on damp mornings

Under the marine layer, the outside of an efficient double pane unit can fog over at dawn. The outer pane stays cool because very little heat leaks through from the house, so this is a sign the glass insulates well. Low emissivity coatings reduce heat flow through the glass, which can make exterior condensation more frequent. It clears once the sun warms the pane, and it needs no repair.

Water standing in a slider track

Weep holes in sliding window sills drain water outward. When they clog with sand or debris, water pools in the track and can spill inside during a heavy rain. Sand is a constant near the lagoons and the beach. Clear each hole with a plastic probe or a puff of compressed air, then pour a cup of water down the track and watch it leave through the outside. If it still sits, the hole is not open yet.

Cutting the load on the glass

Bath fans, kitchen range hoods and dehumidifiers lower indoor humidity and reduce interior condensation. Run the bath fan during the shower and for a while after, and use the hood whenever a pot is boiling. Warm edge spacers keep the glass edge warmer than older metal spacers, which reduces condensation along the bottom of the glass, so it is worth specifying them on any new order. Water left sitting on a sill is what feeds mold, so wipe it up. The new window does not cause mold by itself.