What Are South Florida Houses Made Of? Concrete Block vs Wood Frame

Knock on an exterior wall in most South Florida neighborhoods and it sounds like a rock. That is not an accident. Builders here have leaned on concrete block for generations because it stands up to wind, it does not rot in the humidity, and termites cannot eat it.

This blog is called Building Blocks for that reason. If you own a home here, there is a good chance its walls are made of them, and that affects almost every remodeling decision you make.

What CBS actually means

CBS stands for concrete block and stucco. You will see it on listings, appraisals and insurance forms. The wall itself is built from hollow concrete masonry units, the gray blocks most people picture, stacked with mortar and finished with stucco on the outside.

A block wall on its own is heavy but not especially strong against sideways force. What makes a South Florida CBS house work is what happens inside and on top of the blocks:

• Filled cells. At corners, beside windows and doors, and at regular spacing along the wall, steel rebar runs vertically through the hollow cells, which are then filled solid with concrete.
• The tie beam. A continuous concrete beam with steel inside runs along the top of the walls, tying them together like a belt.
• Lintels. Reinforced concrete beams span over every window and door opening.
• Roof connections. Metal straps cast into the tie beam wrap over each roof truss so the roof cannot peel off in a storm.
• The slab. Most homes sit on a concrete slab with thickened edges that act as the footing.

Put together, the slab, the reinforced cells, the tie beam and the straps make a continuous load path. Wind pushing up on the roof gets passed down through the straps, the beam and the steel into the foundation. Break that chain anywhere and the house is only as strong as the weakest link.

Why the rules got stricter after Hurricane Andrew

Hurricane Andrew hit south Miami-Dade in August 1992 and exposed how many homes had weak roof connections, poorly attached sheathing and openings that failed once the wind got inside. The response was a tougher local code, and eventually the statewide Florida Building Code, which took effect in 2002.

Miami-Dade and Broward kept the strictest rules for themselves. They are the only two counties in the High-Velocity Hurricane Zone, which has its own testing and product approval requirements. We cover that in its own article on what the High-Velocity Hurricane Zone means for your project.

The practical takeaway: a house built before the early 1990s and a house built in the last twenty years can look identical from the street and perform very differently in a storm. The difference is mostly hidden in the connections.

Where wood frame still shows up

Wood frame is not banned here. It is common in a few places:

• Second floors. A lot of two-story homes have a block first floor and a wood-framed second floor.
• Additions. Some additions are framed in wood and tied to the existing block house.
• Interior walls. Partitions inside a CBS house are usually wood or metal studs.
• Newer construction. Some builders frame entire homes in wood. Like everything else here, it has to be engineered for the local wind loads, with sheathing, nailing and hold-downs to match.

Wood frame does have two local enemies: moisture and termites, including the subterranean kind that thrive in South Florida. Good flashing, treated lumber where required and a termite protection plan matter more here than in most of the country.

Block vs wood frame at a glance

What a block house means when you remodel

Owning a CBS home changes the math on a few common projects.

Moving or adding windows and doors

You cannot just cut a hole in a block wall. A new or wider opening needs a lintel above it and reinforced cells on each side, designed by an engineer and inspected. Making an existing opening smaller is easier, but the infill still has to be tied in properly. If you are replacing windows anyway, that is the time to fix an awkward opening.

Electrical and plumbing on exterior walls

Interior faces of block walls are usually covered with furring strips and drywall, which leaves a small gap. New outlets and wiring either use that gap or need channels cut into the block. It is doable, just slower than a wood wall, so budget for it.

Taking out an interior wall

Interior walls in a CBS house are often non-structural, but not always. Some older homes have block bearing walls down the middle, and some roof trusses bear on interior walls. An engineer should look before anything comes down. Our article on whether a project needs a permit covers why wall removal always does.

Building up

A second story on a block house is possible, but the existing foundation, walls and tie beam have to be checked for the new load. That engineering review should come before you pay for full architectural drawings. See our home additions page for how we approach it.

How to find out what your house is made of

• Check the property appraiser's record for your address. It usually lists construction type and year built.
• Look in the garage or attic. Exposed block, a tie beam and strap ties are easy to spot.
• Ask for a wind mitigation inspection report if you have one. It documents roof-to-wall connections and opening protection.
• Pull the permit history for the property to see what was added and when.

The bottom line

Concrete block is the backbone of South Florida housing for good reasons, and wood frame has its place too. What matters most is not the material but the connections: the steel in the cells, the tie beam, the straps and the openings. If you are planning a remodel, an addition or a new build, tell us about the house and we will tell you what its construction means for your plans.