Quick Question on concrete slab isolation.

Hi Def · Post by **Hi Def** » Tue Apr 13, 2004 7:03 pm

Hello everyone. Thanks to everyone for providing such valuable knowledge on this forum. Well the ground is thawing and it's about time to get my concrete poured.

While looking through Mr. Sayers' designed studios, The Carriage House in Texas caught my eye. As far as I can see, it looks like the concrete slab is the only floor. Doesn't look like they are using floated floors at all! (may be too early to tell based on the 2 updates)

Anyway, my question is...What kind of isolation performance differences would there be between having truely floated and isolated floors verses using the concrete slab as THE ONLY floor in the building? Isolation both between the room inside as well as isolation from the outside. What kind of STC - Db are we talking here?

Many thanks in advance and once again, thank you for the great resource!

M

Sen · Post by **Sen** » Tue Apr 13, 2004 8:54 pm

Hi Hidef

,
Floating the floors would (if floated correctly) significantly improve your low frequency transmission loss between the rooms. Concrete still does "carry" the bass from one room to another. I am not sure what the actual figures of improvement would be, but it would be worth doing I believe. Do a search on "floating" and you might find a useful thread in which Steve (Knightfly) explains the process of choosing the right material to float your floors on. I believe I read it at this forum.

good luck with your construction

Post by **Aaronw** » Wed Apr 14, 2004 1:23 am

Take a look at this one. It shows the isolated slabs...

http://www.johnlsayers.com/Studio/Mainpage/MP-Egan.htm

Hi Def · Post by **Hi Def** » Wed Apr 14, 2004 6:38 pm

Thanks guys for such a speedy reply! I spoke with my concrete guy today and we'll be having a meeting on thursday regarding the slab. Which leads me to my next question...

Would it be possible to pour the new slab in sections that correspond to my wall layout? You know, so there's actually a space in the concrete between the rooms. Basicall what Mr. Egan did in his studio but not pouring a new slab over an existing one. Hopefully I'm not confusing you too bad. I'm starting to confuse me!

The only way that the floors would be coupled to each other would be through the steel reinforcement bars in the concrete. My concrete guy seemed to think it was possible but needed to see my layout first.

Reason I'm asking all these crazy questions is I'd like to save that money that I would've originally spent on the floated floors and use it on more construction/acoustics stuff.

Thanks again everyone. Your help is always much appreciated.

M

knightfly · Post by **knightfly** » Thu Apr 15, 2004 9:37 am

I don't have any hard facts on this at the moment, but generally if you leave the rebar connecting between sections of concrete it will flank through the steel, and likely almost as much as if there were solid concrete.

If you're looking for maximum isolation between rooms AND to the outside, but still tight for money, I would float just the tracking room (if that's where drums and bass will be tracked live) - that gives you most of the isolation of fully floated rooms (for setting mics, etc) as well as better outside isolation for the loudest instruments - drums can reach 120 dB at times, where SANE people limit mix volumes to 85-90 dB (except for "wow" factors occasionally)

Hope that helps... Steve

rod gervais · Post by **rod gervais** » Thu Apr 15, 2004 10:36 pm

Def,

Do not run the reinforcing through the slab sections. What you want to do is haunch the slab at the edges to about 12" thick with a 12" wide base - (this effectively creates a footing with the slab to carry the wall) and completely isolate the slabs from one another. HAve your concrete contractor put 2 #4 bar at the bottom of the haunch and make sure to marry the bottom of the haunch back to the slab with a 45 degree slope - not a 90 degree corner.

Maintain a 1" seperation between the slabs through the use of a styrofoam spacer and then caulk the final joint.

No need for floated floors using this system.

Rod

knightfly · Post by **knightfly** » Fri Apr 16, 2004 12:57 am

Def, Rod's method is more expensive than a single slab but 'way cheaper than separately floated floors, with as good isolation between rooms and nearly as good outside isolation (probably not measurable difference) - however, make sure if you do Rod's method that you watch the pour like a hawk, and don't let ANYTHING happen to bridge between sections (like sloppy cleanup or pour methods) - and DEFINITELY not continuous rebar... Steve

Hi Def · Post by **Hi Def** » Fri Apr 16, 2004 1:19 am

Wow you guys rock! I'm having a a little trouble understanding exactly what Rod is describing. I will copy this post and show it to the concrete guy tonight and see if he knows whats going on with it!

Hey Rod, with you being from CT, do you know this method to still work in the frigid temperatures of the north? I'm in WI and, much like CT, the ground freezes solid up here during the winters. Would the constant freezing and thawing have any effects on your method as far as stability? Would the concrete slabs drift apart after time? I know the frost just buckles the roads like crazy up here! Sorry for my ignorance...I know nothing about concrete work!

Once again, you all are such a great help. It is truely appreciated!

M

rod gervais · Post by **rod gervais** » Fri Apr 16, 2004 4:40 am

Hi Def wrote:Wow you guys rock! I'm having a a little trouble understanding exactly what Rod is describing. I will copy this post and show it to the concrete guy tonight and see if he knows whats going on with it!"

If he doesn't understand it (although he should - it's pretty standard practice) have him give me a call - you can reach me at 860-209-6852

Hey Rod, with you being from CT, do you know this method to still work in the frigid temperatures of the north? I'm in WI and, much like CT, the ground freezes solid up here during the winters. Would the constant freezing and thawing have any effects on your method as far as stability? Would the concrete slabs drift apart after time? I know the frost just buckles the roads like crazy up here! Sorry for my ignorance...I know nothing about concrete work!

When you do this you should be installing at least 1" of foam insulation from the top of the slab down (2 to 4' depending on your local codes). Not only will this help to keep your heating costs down - it will also stop frost from entering the area and create the isolation seperation you want from the outside world.

Good luck,

Rod

giles117 · Post by **giles117** » Fri Apr 16, 2004 10:09 pm

Rod, here is one for you. What kind of code violations are there (if any) if I chose to cut a separation in my concrete basement floor and put in that expansion joint stuff between the sections??? I know I am in Michigan but I am curious to your knowledge as codes can be similar.

Or is this an all around BAD idea

Thanks

Bryan Giles

rod gervais · Post by **rod gervais** » Sat Apr 17, 2004 3:03 am

giles117 wrote:Rod, here is one for you. What kind of code violations are there (if any) if I chose to cut a separation in my concrete basement floor and put in that expansion joint stuff between the sections??? I know I am in Michigan but I am curious to your knowledge as codes can be similar.

Or is this an all around BAD idea

Thanks

Bryan Giles

Bryan,

The biggest issue with pouring a slab and then sawcutting it to create isolation is that the slab itself is not really intended to carry any bearing walls - so if you are building a true room within a room (i.e. the ceiling for each room is bearing on the individual wall panels) then the floor should not be carrying the weight.

However - even in the case of a uncut slab - there should still be a haunch under the wall locations.

If the walls are NOT bearing - then there is no issue.

In as much as the slab assembly itself is generally non-structural in nature - sawcutting and isolating areas of slab should not be a code violation. But then again - if you are pouring a new slab - there is no reason to sawcut. Just pour isolated slabs -

I am curious to the reason for the question.

Rod

giles117 · Post by **giles117** » Sat Apr 17, 2004 4:26 am

TRhnaks rod. No the walls will not be load bearing. I am gonna keep the joists there and just at as needed. I envision cutting the slab as needed and cutting around the wall edges to iso the slab from the basement walls.

My Goal is to eliminate the need to float a floor and loose 5" or so of ceiling height.

Now for the fun part, getting a concrete cutter down there. LOL. Price will ultimately determine which way i go of course.

Thanks bud

Bryan Giles

Hi Def · Post by **Hi Def** » Mon Apr 19, 2004 11:48 am

Just wanted to say thanks to everyone who helped on my concrete questions. Ya'll were a huge help. After weighing the benefits and costs, I've decided to go with an artificial floor system. It seems to work better and will allow for the concrete to be much stronger. Plus, I can modify my plans if need be. Thanks again guys, you were of tremendous help!

M