Almost every Brandon homeowner who calls us about a hot upstairs or a climbing power bill asks the same thing in the first five minutes: how much insulation am I supposed to have up there? It is a fair question, and one you can check yourself with a tape measure and ten minutes. Here is the number the code uses, what it looks like in inches, and how to tell if your attic is short.
The number Florida's code uses
Florida sets its own energy code, and it splits the state into two climate zones. Under the 2023 Florida Building Code, Energy Conservation (8th Edition), ceilings — including ceilings with an attic above them — are built to R‑30 in Climate Zone 1 and R‑38 in Climate Zone 2. Zone 1 is only three counties: Broward, Miami‑Dade and Monroe. Every other county in the state, Hillsborough and Polk included, sits in Zone 2.
So the figure that applies to a Brandon house is R‑38.
One caveat, because it gets misread constantly: that code number governs new construction and additions. Nobody is going to require you to re‑insulate a house built in 1994. It is a benchmark, not a citation — but a useful one, because it tells you what a builder would have to install in your house if it went up today, and plenty of homes around Brandon were built when the number was lower.
What R‑38 looks like in inches
R‑value is a measure of resistance to heat flow, not a depth, so the inches depend entirely on what the material is. Using the settled values the U.S. Department of Energy publishes through its Building America Solution Center:
- Loose‑fill fiberglass — roughly R‑2.2 to R‑2.7 per inch, so roughly 14 to 17 inches to reach R‑38.
- Loose‑fill cellulose — roughly R‑3.2 to R‑3.8 per inch, so roughly 10 to 12 inches to reach R‑38.
- Rock wool — roughly R‑3.0 to R‑3.3 per inch, or roughly 11.5 to 13 inches.
Those are ranges on purpose. Density, how evenly the material was blown and settling all move the real number — loose‑fill cellulose is expected to settle in the region of 10 to 20 percent over its life, while fiberglass settles far less. Anyone quoting an exact inch figure without getting in your attic first is guessing.
The ten-minute check you can do yourself
Open the attic hatch, take a flashlight and a tape measure, and look at three things.
First, can you see the ceiling joists? In most Brandon homes the joists or truss bottoms are nominal 2x4s or 2x6s, so they sit somewhere around three and a half to five and a half inches deep. If the tops of the joists are showing above the insulation, you are almost certainly well under R‑38 — probably under R‑19.
Second, measure in several places. Depth near the hatch is often the deepest spot, because it is the easiest place to blow. Check the far corners and over the eaves — eight inches in the middle and two at the edges is common.
Third, look at the condition, not just the depth. Grey matted fiberglass, dark streaked staining, rodent tunnels or anything damp means depth is the wrong thing to be measuring. Insulation that has been wet does not recover its R‑value when it dries.
Why the energy people recommend more than code
Code is a floor, not a target. ENERGY STAR's own retrofit guidance for existing homes recommends adding up to R‑49 in Zone 2 when the attic starts out uninsulated, and up to R‑38 of new material when there are already three or four inches up there. That is deliberately above the code minimum, because the extra depth is cheap at the point you already have a crew and a blowing machine in the driveway.
In practice the first R‑19 you add does far more work than the last. Going from nearly nothing to R‑30 is a change you can feel; R‑38 to R‑49 is a slower return. We will tell you which side of that line your attic is on.
Depth alone will not fix a leaky ceiling
This is the part the inches do not capture. Insulation slows heat moving through a surface. It does very little about hot, humid air moving around it — up a wiring chase, around recessed lights, past a bath fan, over the wall top plates. Pile loose fill over gaps like those and you get an attic that measures correctly and still loses in August.
Which is why on any blown-in insulation job we seal the ceiling plane first and add depth second. If the air handler and ductwork live up in the heat, that changes the conversation again, and spray foam at the roofline is often the more honest recommendation than more inches on the attic floor.
When adding on top is the wrong call
Topping over existing insulation is usually fine and usually cheapest. It is the wrong call when the old material is wet, compressed flat, contaminated by rodents, or so uneven that new fill just hides the problem. Then it has to come out first — our page on insulation removal covers what that involves. Covering a bad layer buys a worse attic and a bigger bill later.
What we would do in your attic
We measure depth in several spots, identify the existing material, check its condition, look at where your ducts and air handler sit, and check whether the eaves are blocked. Then we tell you the number you are at and the number we would take you to, with the reasoning for both. Sometimes that is a straightforward top‑up to R‑38. Sometimes it is removal first. Occasionally it is: your attic is fine, the problem is elsewhere.