Nearly every house in Lake Wales is concrete block, and in the older streets around downtown it is block with furring strips, a sheet of drywall, and air. People usually find this out when they open a wall for a bathroom remodel and discover there was never anything in there. The question that follows is a fair one: can you insulate a block wall after the fact, and is it worth doing?
A bare block wall is worth about R‑1 to R‑2
Concrete is good at a lot of things and bad at slowing heat. A standard hollow 8‑inch block runs somewhere around R‑1 to R‑2 depending on the aggregate, and stucco outside and drywall inside only nudge that up a little. What block does have is mass — it takes heat up slowly and gives it back slowly, which is why a block house holds out for a while after sunset and then radiates warmth into the room at nine at night.
That mass is the reason the code treats block differently. The 2023 Florida Building Code, Energy Conservation asks for an R‑38 ceiling in climate zone 2, which is where Polk County sits — but for a mass wall in the same zone the prescriptive target is only about R‑6, or R‑4 if the insulation is continuous. That is not an oversight. A wall gets a fraction of the solar load a roof deck takes, and the mass does some of the work on its own. It is also the single best argument for doing your attic before your walls.
The three ways to add insulation to block
From the inside, where retrofit work almost always happens, there are three realistic routes:
- Into the existing furring space. If the drywall is already off, the 3/4‑inch to 1‑inch gap behind it will take closed‑cell spray foam, which runs roughly R‑6 to R‑7 per inch. You will not reach a big number in that space, but you air seal the wall at the same time, which matters more than the label suggests.
- A new furred or framed wall. Build out to 2 or 3 inches and you have room for real depth — foam board, closed‑cell foam, or a framed cavity filled with blown-in insulation. You lose an inch or two of room, and you are re‑running any outlets in that wall.
- Core‑fill injection. Foam or beads injected into the hollow cells through drilled holes. It is a real product and it does add R‑value, but read the claims carefully: the block's own webs still bridge straight through from outside to inside every eight inches or so, so the finished wall performs well below the number quoted for the material in the core.
Where the moisture rule bites
Block is a reservoir. Driven rain gets into stucco, stucco cracks, and the wall holds water a while before drying out in both directions. An impermeable layer tight against the inside face takes one of those directions away. Done well — closed‑cell foam, fully adhered, exterior in good repair — that is a sound assembly used across Florida every day. Done over an active leak, or behind a stucco crack nobody fixed, it hides the problem instead of solving it.
So the order is not negotiable: fix the water first, then insulate. If a wall has been wet, anything soft inside it comes out before anything new goes in — the same rule we apply to insulation removal in an attic, for the same reason.
When wall insulation is clearly worth it
Most of the time it is not the first dollar. It becomes the right dollar when the wall is already open, or about to be:
- A gut renovation, or one room being taken back to block anyway
- Drywall coming off after a leak or storm repair
- A garage, lanai or Florida room being converted to conditioned space — that is new construction in the eyes of the code, and it gets insulated properly
- A long west‑facing wall on an unshaded lot, which takes the worst of the afternoon
Lake Wales sits high on the Ridge, and the elevation does not buy you a cooler afternoon. A west wall here takes the same sun as everywhere else in Polk County.
Rebates: what exists here, and what does not
This one saves a disappointment. Duke Energy's Florida Home Energy Improvement rebates cover attic insulation, duct testing and repair, HVAC, energy‑efficient windows and heat‑pump water heaters. There is no wall insulation measure. The attic rebate also carries conditions worth knowing before you plan around it: a free Duke Home Energy Check within the past 24 months or before the work, the recommendation coming out of that audit, an existing attic averaging R‑19 or less, a contractor from Duke's prequalified list, and no manufactured homes. On a co‑op, ask what they currently run.
On the federal side, do not budget around the old credit. The Energy Efficient Home Improvement Credit under section 25C ended on 31 December 2025.
What we would look at in a Lake Wales house
We start in the attic, because the code agrees with the arithmetic — R‑38 against roughly R‑6 tells you which surface the heat comes through. Then ducts and the ceiling plane. Then, if a wall is open or coming open, we insulate it properly while the access is free, rather than talk you into opening one that is closed. If the windows in that wall are original single‑pane aluminum, window replacement usually does more for the room than anything behind the drywall.
One timing note: the 8th Edition of the Florida Building Code is in force today, with the 9th Edition taking effect at the end of December 2026. Planning a conversion or an addition? Ask which edition your permit will be reviewed under.