Palo Alto roofs on the peninsula north-west of San Jose

Why do the flat sections need a drain check here?

A flat section drains to its outlets, and a pool that stays after rain loads the membrane and stresses the seams at its edge. The drain is cleared and tested in the same visit, and the level around it is checked.

The parapet and curb flashings are checked for lift, since they carry the membrane up the wall and are the commonest route for water into the house.

Palo Alto's older houses also carry chimneys that have been repointed more than once, and each repointing can leave a seam that water finds. The technician checks the mortar along the chimney and the flashing at the roof line together.

How does the bay air affect the flashings?

Damp bay air keeps the metal of a flashing wet after each rain and holds the moisture against its joints. The technician checks the fixings and the cut edges first, and replaces any piece that has corroded.

The metal and the sealant are named on the scope, with the reason for each choice.

What do the storms show on an older roof?

A long storm finds the joints that were fine in a light rain, and the valleys and vent flashings are the first places to be checked. The trace follows the wet framing from the stain back to the entry point.

The gutter outlets are checked for a discharge at the wall and carried clear of the foundation where that is needed.

How is a roof's penetration sealed on the peninsula?

A vent pipe or a chimney on a peninsula roof takes the damp air and the wind from more than one side. The flashing is lapped so water runs over each joint, and the sealant is chosen for the metal it closes.

The penetration is tested with water after the work, and the result is recorded with the date and the position of the test.

What is the role of the parapet on a peninsula building?

A parapet on a building with a flat section carries the membrane up the wall and is capped to shed the water down both faces. On the peninsula the cap and the joints are checked for lift and for sealant that has cracked in the damp.

The parapet is re-capped where the joints have failed, and its flashing is re-made where the membrane meets the wall. The work is recorded on the scope.

The technician notes the faces that take the damp most, so the next visit can check them first.