Los Altos roofs on the foothill side of the valley

Why does the attic hold moisture on the foothill side?

On a clear night the foothill air cools quickly, and the underside of the roof cools with it. Warm, moist air rising from the house meets the cold boards and condenses there, and the boards stay damp into the morning.

The technician reads the attic on a cool morning and again in the afternoon. The moisture, the staining and the temperature are recorded at each time, so the cause is seen rather than guessed.

How are the vents balanced on these houses?

The intake at the eave and the exhaust at the ridge are checked as a pair. A blocked intake or a missing exhaust leaves the air still and the moisture in place, and both are corrected.

A bathroom or kitchen duct that vents into the attic is redirected outside. The duct is sealed and checked for a sag where water can collect.

What does the covering look like after the cool nights?

The covering on the sunny faces still wears from the sun, and the shaded faces can hold damp for longer. The technician checks each face for granule loss, moss and staining, and notes any change from the last visit.

The flashings are checked for lift, since the daily cycle of cool and warm moves the metal and the sealant.

How are the older houses' chimneys read?

Older chimneys on the foothill side are often masonry with a cap that has cracked. The cap sheds the water off the top of the flue, and a cracked cap lets the rain down the inside of the chimney and into the attic.

The technician checks the cap, the mortar and the flashing at the roof line, and repoints or re-caps where needed. The record notes the state of each chimney.

Why are the vent flashings checked on a foothill-side house?

Vent flashings on the foothill side take the cool and the damp together, and the sealant at their joints cracks in the swing of temperature. A cracked joint lets the damp reach the framing around the pipe.

The technician checks each vent from the ladder and the attic, and re-makes any flashing that has lifted or lost its seal. The record names each vent.

Owners on the foothill side are advised to keep the vents clear through the cool months, since the attic is the part of the house most affected by the swing in temperature.