San Diego Roof Insulation Calculator
Tell us your roof type and square footage. We'll return the exact insulation layers we would install, the total R-value they reach, and an installed cost range for San Diego County.
Your roof
Coastal San Diego, narrow temperature swing, cooling-driven design. Prescriptive targets: R-38 at a vented attic floor, R-30 continuous above the deck.
No cavity to insulate, so the thermal barrier goes above the deck. This is the assembly we build on San Diego homes that get brutally hot in summer.
Use the roof surface for above-deck work, or the ceiling footprint for attic insulation. Typical San Diego home: 1,200–2,800 sq ft.
Scope we include on this assembly
- Tear-off of existing membrane to bare framing/deck
- Polyiso thermal barrier directly above the living space
- New plywood deck + Polyglass SA V underlayment
- Torch-down or cool-roof cap sheet, all flashings replaced
Recommended Build-Up
R-30total · 4.9" thick
Title 24 target for this assembly in climate zone 7: R-30. Meets target.
Layer 1
Polyiso rigid insulation board (2 layers, staggered)
R-24
4"
Two 2" layers with staggered, taped joints to kill thermal bridging.
Layer 2
Peel & stick SA underlayment + cool-roof cap sheet
R-3
0.25"
Self-adhered vapor/air control layer under a reflective cap for solar-heat rejection.
Layer 3
New structural plywood deck over insulation
R-3
0.63"
5/8" CDX re-nailed through the boards into framing, giving a solid roofing substrate.
Installed Range
$12,400 – $18,700
For 1,800 sq ft, materials and labor included.
- Climate zone 7 target is R-30 — this build-up already exceeds it, so no extra thickness is required.
Get your exact insulation plan
A senior estimator confirms rafter depth, ventilation and deck condition, then puts the R-value in writing.
Free • No Obligation
Get Your San Diego Estimate
Sent directly to sales@californiafirstroofing.com — response within 15 minutes during business hours.
FAQ — Roof Insulation in San Diego
How much insulation does a San Diego roof need?
Title 24 guidance for San Diego County (climate zones 7 and 10) lands around R-38 at a vented attic floor and roughly R-30 continuous above the deck when there is no attic. Our estimator targets those numbers by assembly.
What if my house has no attic space?
Insulation goes above the roof deck instead. We tear off to the framing, install two staggered layers of polyiso rigid board, add a new plywood deck, then Polyglass SA V peel-and-stick underlayment and a cool-roof cap sheet.
Can insulation be added during a re-roof?
Yes, and it is the cheapest time to do it. The deck is already exposed, so above-deck polyiso, radiant barrier, ventilation upgrades and attic top-ups all get done in the same permit and mobilization.
Is this estimate exact?
It is a real planning range based on 2026 San Diego material and labor rates. Final R-value and price depend on rafter depth, deck condition, ventilation and access, which a licensed estimator confirms on-site for free.
Planning a full replacement? See re-roofing or run the roof cost calculator.