Insulation Installation in South San Francisco, CA

Local Context

A Buri Buri Attic Was Insulated to the Rules of the Year It Was Framed

Most of South San Francisco was framed in one long tract wave, from the Buri Buri and Winston Manor blocks through the Westborough hillside that filled in behind them. Attics from those decades were insulated to standards California has raised repeatedly since, and many have never been touched. Title 24 now sets minimum R-values well above what was normal then, so an attic can be fully insulated by the rules it was built under and clearly thin by today's.

The local climate changes what the upgrade buys you. Marine air through the San Bruno Gap holds summer down, so nobody here is insulating an attic to fight air-conditioning load. Almost all of the benefit lands in the long cool winter, when the heat runs for months at a stretch. What owners usually notice first is not the utility bill. It is that the room over the garage and the north-facing bedrooms stop being noticeably colder than the rest of the house.

Sequence matters more than product choice. New insulation goes in after air sealing and after exclusion, never before. Gaps at recessed light housings, plumbing penetrations, HVAC chases and top plates send conditioned air straight into the attic, and blowing material over them buries the problem instead of fixing it. In the hillside neighborhoods there is a second reason to sequence it properly: one open roof rat entry turns brand-new insulation into brand-new nesting material within a season. Borate-treated cellulose adds pest resistance that fiberglass does not have.