The Fairy Tale… Once Upon a Time
When I was a young boy, one of my favorite stories was the one about the big bad wolf and the three little pigs in which “Big Bad Wolf” tries to destroy the pigs’ homes so he could have a nice meal. The wolf easily blew down the house made of straw and had no problems mowing over the home made from sticks. When the wolf attempted to destroy the house made from bricks, he was unsuccessful and could not blow it down even with all of his huffing and puffing. The pigs in the brick home lived happily ever after.
Now for the Reality…
We would all agree that a straw home would not be a good choice in Florida. While the wolf was able to blow down the house made from sticks (wood) this was in the good ol’ days before building science and engineered wood framing techniques. The brick home that was spared was just a brick home. Brick is non structural and simply a face on the exterior that supports no weight other than its own. (A roof does not attach, nor does it “bear” or weigh on brick)
Most of Florida’s residential exteriors are built using one of two structural methods. One method is engineered frame wood construction and the other method is concrete block construction or CMU construction (short for concrete masonry unit).
Engineered Wood Frame Construction
The exterior walls are constructed with 2 x 4 or 2 x 6 dimensional lumber. The lumber member is spaced between 12″ and 16″ on center and is determined by the engineer using required building codes. The wall is anchored from the bottom of the wall at the slab to the top of the wall. The wall sits on a pressure treated 2×4 on top of a weather barrier that sits on the concrete slab itself.
Structural engineers design a new home for wind loads, sheer value, up lift and hold down protection. Rods, cables, clips and other hardware are incorporated into the design. The use of fasteners and nail spacing and patterns are also part of the design.
On both wood frame and CMU construction, the same wood roof trusses/rafters, sheeting and interior lumber walls are used. In the case of CMU homes, the second floor is usually built in wood frame for cost savings.
The exterior of the wall has OSB or plywood as sheeting with a certain nailing pattern applied to penetrate the wood studs for maximum strength and rigidity.
Concrete Block Construction (CMU)
CMUs are cement blocks made from a mold in a factory. Typically a residential exterior wall made from CMUs measures 8″ x 8″ x 16″ and is 80 % hollow.
The CMUs are laid on top of the slab in an interlocking staggered method and the wall is raised to its desired height. Mortar holds each block in place.
Once the CMU wall is constructed, some of the hollow block cells are filled with concrete in the cells that hold vertical rebar. The top of the wall consists of a “poured in place” concrete lintel that ties everything together.
People wonder why Florida has a combination of both wood frame and concrete block homes. The northern part of the state as well as the panhandle and some central Florida areas are mainly built in wood frame. The other areas in the state generally build CMU homes even though the majority of homes with a second floor are constructed out of engineered wood frame construction.
In my opinion, either method is acceptable because both methods meet all current building codes which require the structure to withstand 120 mph winds. Some people prefer CMU because they think they will be safer in a hurricane. It is true that the exterior walls in a CMU home are more durable than a wood frame home, but just because a CMU home might have some exterior walls still standing after a hurricane, doesn’t mean the home wouldn’t be missing a roof, windows and doors, rendering it a total loss. Of course, the best idea for all of us is to leave town if a “Cat 4” hurricane (winds over 131 mph) is about to strike and let the our homeowner insurance folks sort out the details later.
Pros and Cons about Block (CMU) vs Wood Frame
Concrete Block (CMU)
- Better sound proofing
- Durability during a hurricane
- A “simple box” one-story home could be less expensive that wood frame. (Not always the case with more intense design, angles and varying wall heights.)
- Some say CMU has a better fire rating however the roof and interior walls are still wood frame.
- Better protection from termites. This is true but most builders on all homes now provide termite colony elimination systems that ward off termites and provide very sizable insurance bonds if termites strike.
- Not as energy efficient as a wood framed home
- Possible dampness in areas of the walls that can be trapped within
- Higher cost on larger, high-end homes due to more complicated design elements
- The block size dimension is wider that a 2 x 4 or 2 x 6 thus robbing a couple of inches from a room located on an exterior wall area.
- Harder to rout mechanical rough-ins such as electrical and plumbing or retro-fitting wiring
Engineered Wood Frame
- Meets building code wind requirements just like CMU homes
- Much more energy efficient due to having deep wall cavities for various types of insulation
- Allows greater freedom in design for multiple wall heights, angles, curves and other detail at an affordable level
- Improved moisture protection due to advancements in house wrapping products in the last several years
I am comfortable with both methods of construction, but prefer wood frame mainly due to the ability to maximize energy efficiency. Insurance cost is similar these days in both methods. Like most trade industry associations, the masonry association may be at odds with the wood frame industry and each will have opinions that one is better that the other. When you build your Florida home, you should feel at ease with either of the two methods described here because your builder will have a reason as to why they specialize in one or the other….or both.
So, who’s afraid of the Big Bad Wolf? You shouldn’t be.