R-30? R-38? R-49? What the numbers mean, what Florida code requires, how many inches that is, and how to measure what you have — without a contractor.
Nothing confuses homeowners faster than R-values. You'll read R-30 in one place, R-38 in another, R-49 on a blog written for Minnesota, and then a contractor says "we'll bring it up to code" without saying what that is.
Here's the plain version for South Florida.
R-value is resistance to heat flow. Higher is better. It adds up — R-11 of old insulation plus R-19 of new is R-30. Each type of insulation has an R-value per inch, so you can convert between the number on the quote and the depth in your attic.
| Material | R per inch | Inches for R-30 | Inches for R-38 |
|---|---|---|---|
| Blown fiberglass (CertainTeed InsulSafe SP) | ~2.9 | ~10½" | ~13–14½" |
| Blown cellulose | ~3.5 (settles) | ~9" (more after settling) | ~11½" |
| Fiberglass batts | ~3.1 | ~10" | ~12" |
| Open-cell spray foam (roof deck) | ~3.6 | Different approach — see below |
The Florida Building Code energy provisions for our climate zone set the ceiling minimum at R-30 for new construction and additions. That's the number. Not R-49 — that's for climate zones where the problem is keeping heat in through a six-month winter. Our problem is nine months of heat coming down, and R-30 with a sealed ceiling handles it.
R-38 is a legitimate upgrade. It's about three more inches of material and it buys you a bit more comfort on the worst afternoons and a little less AC runtime. We offer it as an option. We don't push it, because the step from R-13 to R-30 is where almost all the benefit lives; the step from R-30 to R-38 is nice-to-have.
Homes built before the early 2000s were typically insulated to R-19 or less — and twenty years of settling, humidity and foot traffic has taken that down to R-11 or R-13. That's 4–6 inches of grey, compressed fiberglass. If you can see the tops of your ceiling joists from the hatch, you're in this group.
Homes built 2005–2015 are often R-30 on paper but installed unevenly — 14 inches near the hatch where the installer stood, 6 inches at the far eaves where he didn't walk.
Open the hatch. Push the tape straight down through the insulation to the drywall at three or four spots you can reach — near the hatch, and as far toward an outside wall as you can see. Note the depth and the color. Fluffy pink, white or yellow is fiberglass. Grey, dense, newspaper-looking is cellulose.
Under 10 inches of fiberglass or 9 inches of cellulose: you're below R-30.
Under 6 inches: you're below R-19 and this is costing you money every month.
Big difference between spots: uneven install; the thin spots are where the heat comes through.
Can I just add R-30 on top of what's there and get R-43?
Yes, if what's there is dry and clean — R-values add. Here's how to tell if yours can be topped. But past R-38 you're paying for inches that barely move the needle in our climate.
What about spray foam on the roof deck instead?
A different approach: the attic becomes part of the conditioned space. It works, it's expensive, and in an existing home it changes how your HVAC and roof ventilation behave — it needs a full-system design, not a quote from the hatch. For most retrofits, blown fiberglass to R-30 plus air sealing gets you nearly all of the benefit at a fraction of the cost.
Does more insulation help if my ceiling leaks air?
Much less than it should. Air moving through the ceiling carries heat and humidity straight past the insulation. That's why air sealing comes first on every job we do — and why a quote that doesn't mention it is leaving the biggest win on the table.
How do I know the contractor installed what he quoted?
Three ways: depth markers stapled across the attic that you can read from the hatch, completion photos of those markers, and the bag count against the manufacturer's coverage chart. Ask for all three. If a company can't provide them, they can't prove the R-value.
Our free inspection measures depth at multiple points, photographs the attic, and tells you exactly where you are against code — in inches, not jargon. Book it here or call (561) 375-5720.
Owner, Prime Attic Solutions. 15+ years in South Florida attics. Still does every inspection himself.
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