ICF vs CBS vs Wood-Frame in South Florida

5 years ago

Hello, my wife and I are building our first home. Our lot is on a salt-water canal (not sure if this matters for this discussion). We just started working with an architect and are still in the design phase. The home is going to be two-stories and between 3000-3500 living square feet with roughly 2000 of it on the first floor. 4000-4500 total square feet for the home when you count garage, lanai, etc.

The standard construction in our area is Concrete Block System (CBS) on first-floor and wood-frame on second-floor.

I have researched Concrete Block System (CBS) vs ICF vs wood-frame for hours and hours. I have gotten a lot of conflicting info from contractors and other forums/sites. Please help me put these questions to rest. Here goes:

- Is it possible to have CBS on first-story and ICF on second-story? Would this even make sense to do? Or if you go ICF, go ICF all the way.

- Is ICF more impact resistant to hurricanes than CBS? By how much? Max wind mph tested? I've heard 200 mph.

- Is it possible my architect can't design an ICF home? He said that it was very uncommon in this area and could cost significantly more to build. He didn't entirely dismiss it but seemed to think it was a bad idea.

- How big of a job would it be for another architect to change my guy's CAD from CBS to ICF prior to building? Are there floor plan design considerations I should be conscious of?

- How much better of an R-value will ICF have vs CBS? I've seen the comparisons to wood-frame but not CBS. I was told the following: "The most energy loss is through glass surfaces, then the roof/ceiling, then the walls. Therefore, the most payback by far is to invest into energy efficient glazing (double or triple) and extra insulation in the ceiling." Is this true?

- Sounds like termites can nest in the foam and they should be pre-treated. Concrete obviously not. How long does that treatment last? Can it be treated a second-time years later? Termites are a big deal here.

- How much is the cost differential between CBS vs ICF vs wood-frame? First-floor will be CBS or ICF, regardless. Wood-frame only a possibility on second-story. I know it depends on a lot of specifics---but ballpark or a range?

- Does our selection of exterior wall have an effect on our floor system? In other words, should the ceiling of first story / floor of second story be concrete/wood/or what? I was told the way to go was a concrete plank for less sound transmission but could cause HVAC difficulties (no space for ducts so extra soffits needed). Would this screw up my R-value in the home?

Thank you so much for any advice that you all can provide.

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jln333
5 years ago
So many questions that it might be too much for posters.

Triple glazing in south florida would be ridiculous. Low SHGC (solar heat gain coef.) is what you want.

I can't see why a floor system would effect the R value. R value is not really a big concern. Look at your outside temp right now. I am guessing it is within 10 degrees of the desired inside temp. Florida is not about temp extremes. It is downright cold in the summer and hot in the winter. It is about solar gain and humidity. AZ is hot in the summer. I just looked and depending on where in South Fl you are, we are the same up here in Raleigh - we are warmer than Miami but cooler than Ft. Lauderdale but either way 1-2 degrees diff in July.

Humidity is about infiltration rather than R value. ICFs are great for infiltration but I suspect CBS is too.

Your codes will require a hurricane resistant structure. At some point the big one causes flooding and wind is less of the problem. Going forward, flooding is a bigger concern and the wind probably won't change much. What you often see is people who have seen wood structures blow down and they conclude that concrete is better. It is harder to build concrete inadequate for a hurricane but Fl code is pretty strict. Are you in Dade/Broward? Salt water canal and So Fl to me means within 5 miles of the coast. You have the strictest codes in the world.

I built on NC coast 5 years ago and at some point, you just conclude that it doesn't make sense to build a great structure when the entire barrier island gets wiped off the map. Probably different where you are in Florida but you should probably consider than your area my be different in 50 or 100 years and the house may be gone regardless of how well you build it.
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ICF vs CBS vs Wood-Frame in South Florida

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jln333

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