Wood trusses vs. Concrete vs. Other Options? for 2nd floor
We are going to be starting to build a townhouse/duplex in South Florida sometime in the next 6 months or so and are working through some of the design decisions. One of them involves whether or not to use wood trusses or concrete for the second floor. Besides the obvious differences in overall sound dampening and strength, I’m trying to get a better idea of what the cost difference would be. Is concrete 2x the cost? 3x the cost of wood trusses? Is there something in between (pre-formed concrete?) that would provide a similar benefit without the full cost of pouring concrete?
I’m still a novice here and I’m sure I’m being very simplistic but I’m just trying to get some clarification on the options so I can look into the cost vs. benefit in more detail.
Replies
A big difference is that concrete weighs more and requires a stronger structure to support it.
ICFs
Quad lock makes a foam forming system for structural concrete floors and roofs that works with their wall forms. Not a good DIY project. Google quadlock (I can't seem to be able to paste).
None of this is going to be DIY. We have a GC that will be handling all of the subcontracting but we need to choose the design and strucural elements and this is one that we are going back on forth on.
Thanks for this, I'll take a look at it. From a cost perspective, does it run between what wood trusses would cost versus poured concrete?
From a cost standpoint, look at any apartment building or motel under construction of 4 or fewer floors. Odds are very good it will be wood frame all the way, because it's so much cheaper. This in spite of the advantages of concrete in terms of fire resistance and noise.
Seriously. Do you just make this stuff up or did you read it somewhere once? I'm a Florida General Contractor and in 40 years have never seen a wood floor in any multi story building besides a house.
I've watched two large motels (one 3-story, one 5) and a large apartment building (perhaps 50-100 units) go up in the past year, just on my drive between home and town. All wood frame. And we have some pretty strick building codes here. (Though keep in mind that we don't get many hurricanes in Minnesota.)
Your speculation about wood frame structures has nothing to do with this post at all which is about a CBS duplex in Florida.
Yeah, I didn't catch the fact that Steam's location is coastal Florida the first time through. That certainly weights things in favor of concrete.
But my point is that if you look very far inland you will find that concrete is rarely used in apartment/motel type construction anymore, presumably due to the cost difference (and because nothing is built to last a lifetime anymore).
You may want to look into wood frame construction that incorporates light(er) weight gypcrete poured floors. This can give you additional fire resistance between levels and a material density that can reduce noise transmission between floors. Other aspects (longevity, storm resistance, etc) aside, my guess is that detailing your wood frame construction for redections in sound transmission (use of Roxul, acoustical drywall channel, offset framing, resiliant sealants, etc.) will give you a bigger bang for your buck over poured structural concrete floor systems. Precast concrete can be more cost effective than cast in place if you have higher than average architectural and engineering costs and specialized construction services are incorporated into your budget; particuarly if you design a considerable amount of redundancy into your structural elements.
How many dwelling units will you be designing for... and what is the total height of your proposed structure?
Total height of the structure is 25' with two floors and a third floor terrace (open, no roof). There will be two units side, by side. The entire footprint of the building will be approximately 50' x 58' with each unit approximately 25' wide and 58' deep (connected).
We live in a towhnouse currently with similar footprint that I believe is poured concrete on the second floor. It feels very solid and considerably I'm a heavy walker, we don't hear anyone when they are walking around upstairs. My wife is concerned that with wood trusses, it's going to be louder and the floor will have a "bounce" to it that we don't have currently.
I'm not necessarily looking for what's cheapest. While our business partner is looking to flip their unit, we are going to be living in ours so while we are looking at it from a different point of view, I also know that this is not going to be our dream home and we will most likely be selling in the next 5-6 years so the economics still need to work.
In south Florida your floor will typically be wood trusses. Not to say it couldn't be concrete but it would be very unusual for a single family home or 2 story duplex. Atypical concrete floor here in a commercial multi story buiding would be prestressed planks over poured concrete walls with another slab poured on top of the prestressed planks. Formed and poured concrete floors would be more often found on expensive beach front house.
Thanks for the response. Specifically, the build is going to be in the Coconut Grove/Coral Gables area of Miami where townhouses and duplexes have become very prevalent over the past 10 years or so. Due to the lot size (typically 50x100) or in our case, slightly larger at 65x113, many developers are buying up the lots, knocking down the 50's/60's era bungalows and building a 2-unit townhouse/duplex on the property. These are selling for anywhere from $750k-$975k depending on the area. That being said, does that change your answer as the values are considerably higher than a normal suburban home located in other areas of Miami (i.e. Doral, Kendall, South Miami, etc.)?
We have noticed that a lot of the new builds are either concrete 2nd floor or wood trusses with a layer of concrete over the plywood (at least that's what I think it is).
Yes, that changes the equation. Since you're in Dade County, and I believe in the 170 mph zone, concrete floors may be your only option. If price was no consideration I'd go concrete even if it wasn't required. If it's a common floor in that area the price difference may not be that bad.