Hi Fellas! I’m curious as to how concrete overlay is added to floors with wood underlay. I’ve been in buildings (medium quality hotels, for example) where they have added/poured a layer of concrete over the sub-floor to reduce noise transmission, etc. However, I always thought that concrete in direct contact with wood was a no-no. How is this done?
We’re looking at having a custom-built house constructed and would really like to attenuate the noise that transfers between floors. In a dream world I’d be using precast slabs (Coreslab, for example) but the cost is too prohibitive. Do you have to re-design for stair risers if you build the floor up, say 1 1/2″, for example? Do you add fibremesh to the concrete or will it crack if it’s sitting on wood? How do you pour something like this? Before the framing is done? Do you crib out openings for duct runs, etc.? Do you form around heat register openings? In commercial applications, like hotels, the HVAC is generally an all-in-one window unit or heating is done via hot water. We would be using a centrally-located forced air furnace. How do you get level & smooth floors in these applications?
If anyone has done this before I’d love to know how they did it. And if there is a web-site that explains this, I’d really like to know if one exists. Thanks to all.
Cheers!
Ken
“They don’t build ’em like they used to” And as my Dad always added… “Thank God!”
Replies
Gypcrete is used sometimes, as is lightweight concrete. If you framed first, then added the 1 or 1-1/2" layer of concrete, you would effectively lose your sill plates.
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Read the details in the links here:
http://forums.taunton.com/tp-breaktime/messages?msg=75285.3
Thanks, but I'm talking about concrete thick enough to install hydronic heat piping in. It would have to be, I imagine, at least 2" thick? Short of pouring concrete in pans (Commercial-style) I thought that there were residential applications for concrete on wood floors.
I'm sure that someone here has seen it done. Maybe I'm not describing it correctly. Anyway, thanks for the link.
Cheers,
Ken
"They don't build 'em like they used to" And as my Dad always added... "Thank God!"
Concrete slabs on wood framing is quite common, and with the surge in hydronic heating systems and the heat/cooling moderating it provides there will probably be more of it instead of less.
We've added concrete floors in two story residential buildings, primarily for the hydronic heating benefits and it works great, although the extra costs are somewhat high.
There is nothing in dry concrete that damages wood, despite the wives tails. Concrete products are used all the time as floor levelers, in tile work, counter tops, etc.
However, wood doesn't like wet concrete since it acts just like a big sponge. That's why everyone says to not let concrete that is in contact with the damp ground contact untreated wood.
The UBC 2004 will allow nonpressure treated wood to be used as sills in direct contact with a slab if the slab has a moisture barrier membrane under it. Likewise, UBC is fine with elevated slabs on wood framing without a moisture barrier if it's a normal thickness slab.
As you surmised, vent openings and other penetrations in the slab are carefully thought out and allowed for before the concrete is poured. A concrete slab does not have to extend under the walls however, and it's probably better if it doesn't since it complicates running all the mechanicals that are usually snaked down the walls and through the floor framing.
The catch in all of this is the additional cost of the floor framing to hold all the additional weight. In smaller houses with short joist lengths this is not a big deal, but in floorplans with large open spaces it can quickly tripple the floor framing costs--or worse.
If done well it's a great custom feature. Done badly, it's an expensive mistake.
Good building.
"The UBC 2004"Where did you find this.I can't find any reference to a UBC after 97.
I messed up IRC 2004 with UBC 1997. :-)
Many thanks to all. It just that it feels great to go into a building with solid floors and not have to hear the click-click-click of heels or a dog's toe nails running over your head as you recline in your La-Z-Boy chair. When my wife and I have stayed at some of the more "basic" B & B's it's often been a source of irritation to hear every little sound transmitted through the floors. However, I guess that other using pre-cast slabs or poured floors, this is a problem that has plaqued builders and homeowners since we started building with wood.Cheers,
Ken"They don't build 'em like they used to" And as my Dad always added... "Thank God!"
There is another approach to concrete that's widely used
elsewhere but not in the United States, and that is the
use of AAC planks as underlayment.Most people here think of AAC or hebels as being blocks,
but actually it makes a superb panel, both for exterior
cladding and for floor underlayment. Cost is about $2 s.f.,
and you lay it over your 3/4 inch plywood subfloor, screwing
down with self tapping screws. Alternatively, if you have timberframe or something else with
a little more bearing surface than 2x lumber (such as steel) you
can use the AAC panel as the subfloor itself.Advantages: lightweight, extremely effective soundproofing, very
good insulative qualities, fire proofing. You just screw down your
Rau Panel or other simila RFH panel to the hebel, then finish floor over it.There are a few manufacturers in the United States, but I don't
know anything about them.Some good pictures of the process here:http://www.hebelaustralia.com.au/hebel/view.asp?contenttype=HEBEL-GENERALCONTENT&catalog_name=HEBEL&category_id=Homes-Hebel-Flooring&category_name=Homes%2DHebel+Flooring&topItem_name=Homeowners&sub_item=Hebel+Flooring
"However, I always thought that concrete in direct contact with wood was a no-no."
Why?
Now concrete that is in direct contact with moisture, ie: earth, can conduct that moisture.
But where would the moisture come from for an elevated slab.
GWN,
I agree with most of the responses above. Here's some more.
Your total thickness of concrete or gypcrete will be 1 1/2". You pour this after drying in, before building non-structural partitions. Install all bottom plates for the partitions and pour over them. Install wood blocks where you will need to penetrate the floor later for plumbing or wiring. Install your sheet metal and fill the openings with 2" foam, well taped into the metal. Plan on cutting your new slab to control random cracking.
Talk to a finisher about the mix. Cure it wet as long as you can.
If you are thinking of doing this for sound control, you're on the wrong road. If you have a warm air heating system, the reduction of sound transmission through the ducting should be your objective. Until you can do something about that sound path, chasing sound reduction objectives with an expensive slab is a waste of money.
The general rule of no contact between concrete and wood is real and reasonable. In addition to what has been mentioned above, that concrete will wick moisture from the ground for quite a long way, wood in contact with curing concrete will be damaged by a process called preferential dessication. The curing concrete will draw water from the wood with enough force to damage the cell structure of the contacted wood, leaving it more vulnerable to rot. This damage is quite superficial and microscopic, but it can lead to big trouble with rot that is extensive and invisible until very serious.
After the concrete is cured, it's just another rock, unless it's damp.
Ron
I have a suspended concrete floor for my garage - its 4 inches thick. Since we live on a hill, all the houses here have have them (sitting in ther room under it rghit now)
12 inch joists - I have seen both 2x12 and engineered joists on 12 inch centers. Perpendicular glulam beams about every 12 feet. Also, quite a bit of blocking. 3/4 PT plywood over the joists, then they pour 4 inches over it.
They are building a house next door right now, if I can get pictures, I'll post them.
Excellent idea. Do you have any idea what the cost per sq ft was for this type of design? You mentioned that a lot of blocking was required - where are your duct runs, etc.? Did they have to be located elsewhere, say in a wall cavities, or are you heating with something other than forced air? And, yes, if you have some pictures I'd love to see them.
Cheers,
Ken"They don't build 'em like they used to" And as my Dad always added... "Thank God!"
I also have a suspended garage floor. Poured in place over tempoary plywood held in place with steel joist. The only permanate support is one steel beam for a 24x24ft floor.But that was done in 79.If I was doing it now I would certainly look at using ICF for the decking. And they have chases molded in them for utilities. FHB has an article on such a floor about 2-3 years ago.That one also required tempoary bracing, but I think that I have seen references to ones that are self supporting.
We have a suspended slab floor poured over wood. Ours in 1.5" of concrete with radiant in the slab. We covered the wood with plastic before placing the tubes and pouring. All joists etc. were beefed up to carry the weight.
Jill
Bill,
ICF for decking? I don't understand.
Could you be thinking of something like a Hambro floor system?
http://www.hambrosystems.com/
Ron
Yes for DECKING.http://www.quadlock.com/products/quad-deck.htmhttp://www.polysteel.com/litedeck.htmhttp://www.insul-deck.org/http://www.amvicsystem.com/amdeck.aspxhttp://www.litedeck.com/
Thanks for all the links, BillHartmann. That's exactly what we're looking for! And lo and behold, one of the homes profiled on the Insul-Deck site is not more than 15 miles from where we live. I'll be contacting the builder to see how exacting the building process was, etc. Many thanks!Cheers,
Ken"They don't build 'em like they used to" And as my Dad always added... "Thank God!"
them make another product like concrete but its a epoxy type mix, with a latex base. so it would not affect the wood and would be lighter than concrete.
Brownbagg, could you give me some more information to try and locate the source of the material you mentioned? Do you have any idea how much more expensive this stuff is than lightweight concrete. I am looking at possibly putting a thin concrete roof on a steel framed building and this stuff, if not prohibitively expensive, sounds interesting. Thanks
Bill,
That's all new to me and very interesting. Thank you.
Ron
I only have one thought to add that I don't think has been addressed - Design loading. Adding concrete adds dead load to the structure. The floor system and beams have to be designed for the added load. Going from memory, I think 1.5" of lightweight concrete adds 12.5 PSF to a floor system. It can make a significant difference in joist and beam spans. Not a big deal, as long as it's addressed in the design stage.
Organized people are just to lazy to look for things.
I lived in a 70's-era fourplex that had a concrete covered second floor. The floor had 10# masquerading as 15# felt on the plywood deck, and used a double bottom plate to make up for the difference in height.
Now, it meant that all the flooring attached the same (since the first floor was s-o-g). But, since it was unreinforced concrete (likely set with a 9-10" slump, too), it reacted poorly to building movement over the years. I could hear it every time when the upstairs neighbors stepped on an edge of "busted loose" slab (it did not help that one batch of u/s neighbors seemed to be training bably elephants in acrobatics).
If I were doing it now, I'd certainly take advantage of the improvements in concrete technology, like microfibre mesh. I'd also look into finding the right "mix" using flyash and other admixtures, too. I'd separate the floors with copious expansion/control joints, too. That is, if I could not go with concrete plank construction instead.
Through the course of this thread I lost track a little of whether you were just looking to cut noise down, or install hydronic as well, but here's my thoughts.
If you decide to pour concrete there is a light weight product that is typically used when installing radiant systems, this helps with the structural issues, but anything like this should only be done in consultation with an engineer. Other than that many others have posted good comments, and I would say if you do concrete absolutley install radiant, it's a great source of heat.
If you're not installing radiant then the concrete maybe overkill, and there are other products for reducing noise transmission, such as products like Regupol, which is a rubber mat that goes under finish flooring to Resilient channel for the ceiling drywall below. Also check out some Ownes Conrning noise abatment products.
http://www.owenscorning.com/quietzone/quietzone.asp
Yes, it's primarily to reduce noise transmission, but I figured since you're topping it anyway why not warm it up with some infloor heating? I'm getting some pretty good ideas here and I will follow-up on some of them. Plus, I'm going to call an archy that I know and ask him some questions. However, that generally means over-engineering and "form over function" and by the time that's all been examined it's back to plywood on joists. Thanks to all for your input.Cheers,
Ken"They don't build 'em like they used to" And as my Dad always added... "Thank God!"