Turning a Screened Lanai Into a Sunroom in Florida.

What Actually Changes in a Conversion

Converting a screened lanai to a sunroom is not a glass-swap. A screened lanai is a covered, screened patio engineered to a single light job: holding aluminum framing and insect screen against wind. The moment you replace screen with glass walls, you add weight, you turn the openings into wind-loaded surfaces, and you change what the FBC expects the structure and its foundation to carry. The room is re-rated from the slab up.

That re-rating runs through one document: AAMA/NSA 2100, the national sunroom specification the Florida Building Code adopts by reference. It sorts every glazed patio room into five categories by how it is enclosed and conditioned, and the category you land in dictates the structural, energy, and wind requirements. Picking the category is the first real decision, because Category V — the only one that becomes living space — triggers the heaviest scope.

Screen and glass are not the same load case

Screen lets wind pass through; glass stops it and transfers the pressure into the frame, the connections, and ultimately the slab edge. A wall that was fine as screen can be undersized the day it becomes glass.

Why the category decides the budget of work

Categories I through III need no heating or cooling and stay nonhabitable. Category IV is conditioned but thermally isolated. Category V is conditioned and open to the house, which is what makes it habitable — and what makes it the most involved build.

The AAMA Category Ladder

AAMA/NSA 2100 defines five sunroom categories. Where your lanai lands on this ladder controls the framing, the glazing, the energy code path, and whether an appraiser can ever count the room as finished area.

Categories I to III: still a patio room

A screen room (Category I) and a glazed-but-unheated porch (Categories II and III) stay nonhabitable and unconditioned. They are pleasant three-season spaces, but no appraiser will add them to your finished area, because they are not climate-controlled by the home.

Category IV: conditioned, still not living area

Category IV adds a separate heating or cooling source but stays thermally isolated from the house. It is comfortable year-round, yet because it is partitioned off and on its own system, it remains nonhabitable under the standard and does not count toward gross living area.

Category V: the one that becomes a room

Category V is a sunroom that is heated and cooled by the home system and open to the main structure. It is the only category the specification calls habitable and conditioned — and therefore the only conversion that turns a lanai into true interior square footage.

Will the Existing Slab Hold a Sunroom

Sometimes, but it must be verified, not assumed. A lanai sits on a slab-on-grade — concrete poured directly on the soil. That slab was sized to carry foot traffic and a light aluminum screen cage, not glazed walls bearing a re-rated roof. Before any panel is ordered, the slab is checked for thickness, edge detail, flatness, and cracking.

What gets inspected first

A project director looks at the slab the way the code does — as the bottom of a load path that now has to carry more.

• Edge thickness. A field slab is often 4 in; a load-bearing wall wants a thickened, reinforced edge beneath it.
• Flatness and slope. Lanai slabs are pitched to drain; a sunroom floor and glass base need a flatter, controlled plane.
• Cracking and settlement. Active cracks or a settled corner are resolved before glazing locks the geometry in place.
• Moisture. The slab now sits under a conditioned room, so vapor from the soil has to be managed, not vented to open air as before.

If the slab passes on thickness and edge, the conversion may reuse it; if it does not, the edge is cut and a footing is added before framing starts. Either way, the answer comes from inspection, not optimism.

Why a lanai slab drains, and why that matters now

A screened lanai slab is intentionally sloped so rain blows through the screen and runs off. A conditioned sunroom floor wants a flatter, controlled plane and a managed slab edge, so that built-in pitch becomes something the conversion has to correct rather than inherit.

Do You Need a New Footing to Glass It In

Usually yes for a Category IV or V build, because the FBC requires a complete load path — every load from the roof and the new glazed walls must travel continuously down to the foundation. Glass walls and a re-rated roof are heavier and wind-loaded, and a thin field-slab edge is rarely a footing.

What a sunroom footing has to do

Carry vertical load

The footing supports the new walls and the roof above them. AAMA/NSA 2100 allows a load-bearing wall in any sunroom category to sit on a concrete foundation at least 12 in wide over a continuous footing.

Resist uplift and overturning

In Florida, wind tries to lift and rack the room. The footing and its anchors hold the structure down against the design wind pressures.

Tie into the slab

A new thickened-edge footing is doweled into the existing slab so the old and new concrete act together rather than separating under load.

How crews typically resolve a thin edge

The footing decision is made on the slab, by the engineer of record sizing the load path — which is exactly the work a home addition crew does on any new conditioned space, scaled to a lanai footprint.

Does Enclosing a Lanai Add Square Footage

Only if the finished room meets the appraisal standard, not just the building code. Square footage that counts toward value is gross living area (GLA), measured under ANSI Z765. A glassed-in lanai earns GLA only when it is finished, climate-controlled, and connected to the house the way a Category V sunroom is.

The three tests an appraiser applies

1. Heated and cooled by the primary system. A wall AC unit or space heater does not qualify; the room must be on the home HVAC.
2. Accessible from inside. You must reach it without going outdoors, which is the practical meaning of "open to the main structure."
3. Permanent and tall enough. Finished walls and ceiling, with a ceiling height of at least 7 ft over the counted area.

Meet all three and the lanai becomes living area an appraiser can add to the home; miss any one and it is documented separately as a patio room with contributory value only. That single distinction is why category choice is a financial decision, not just a comfort one.

The table is the whole money question on one line: the same glass walls add value only when the room reaches Category V.

The Permit Path and the Steps

A lanai conversion is permitted work everywhere in Florida, and the heart of the submittal is a wind-rated, category-specific design. Inside the HVHZ — Miami-Dade and Broward counties — the glazing carries an extra requirement that shapes the whole package.

None of these steps are optional shortcuts; each is a checkpoint the building department signs off, and skipping the engineering is how a conversion fails its inspection or its next windstorm. A sunroom remodeling team sequences all five so the slab work and the glazing arrive in the right order.

Flooring the New Sunroom

A converted sunroom is now climate-controlled, but it still sees more sun, glass-edge condensation, and temperature swing than the home interior, so the floor is chosen for that reality. The slab is the same one the structural work just qualified, which means it is ready for a bonded finish.

What holds up best over a sunroom slab

Why a Category V room still reads as a sun-exposed space

Even on the home HVAC, a sunroom is mostly glass, so it gains and loses heat faster and takes more direct ultraviolet light than an interior room. That is why a UV-stable, dimensionally calm finish outperforms a reactive one here, despite the room now counting as living area.

• Porcelain tile. Low water absorption and UV-stable color make it the default for a sun-flooded, slab-on-grade room.
• Rigid-core vinyl. Waterproof and dimensionally tougher than wood, though darker planks can warm under direct afternoon glass.
• Natural stone. Sealed and slip-rated, it suits a higher-end Category V room that reads as interior space.

Whatever the finish, it goes over a slab that has already been moisture-checked as part of the conversion, so the flooring and the foundation work share one inspection trail. Our crews set the tile floor in the finished sunroom once the structure passes, closing the loop from slab to living area.