Yet another floating floor question

Hi - my plan is to float a timber floor over an existing concrete floor. NOTE - this is an existing & operating studio - its a freestanding building. I am NOT floating the floor to improve sound isolation - I am floating the floor for one reason only - concrete is cold n ugly, timber is warm & sexy & I wouldn't mind a bit of sound reflection off the timber (although there will be rugs going down to warm it up physically & visually). So this is pretty much 100% asthetics. My plan is to construct a monoplane floor out of 100 by 45 mm Red alert (laminated beam floor joists). So no bearers, just joists layed out at 400mm centres - then fixed with 'noggins' between the joists - all on the same horizontal plane. Then fix tongue & groove cypress pine flooring, secret nailed onto the joists..very tight floor. My question is - what to put between the joists & the concrete - if anything? Remembering that I'm not particularly in need of further sound isolation. I know most people here would use some kind of 'puck', neoprene pad or whatever to seat the joists onto. Is there any need to do this in my case? I have no moisture issues coming up from the concrete, or anywhere else that I can see. But I thought is would be wise to lay black plastic down under the joists all the same....thoughts? Ah also - just between the joists...wasn't quite sure what to lay to stop standing waves under the floor & the floor itself resonating? Rockwool? Thanks in advance! Robbie

Hi Robbie. Please read the forum rules for posting (click here). You seem to be missing a couple of things! :) It doesn't matter "why" you do what you are planning, it will still act the same as any other light-weight floor over a cavity: as a drum head. Like it or not, that's what you will be creating. Any time you put a membrane over a cavity, it becomes a resonant system, regardless of your intentions or the reasons behind it. It will resonate at a frequency given by the surface density of the floor, and the depth of the cavity. In order for that frequency to be low enough to not cause issues with your room, you need a large amount of mass, and a deep cavity. If the floor is light weight (just a couple of layers of plywood, for example, or hardwood planks, or suchlike) and the depth is small (just a few centimeters) then the resonance will be up where you don't want it. That will do several things to your room, such as reducing isolation around the resonant frequency, and also acting as an un-damped panel trap, which will absorb that frequency (and its harmonics) out of your room. If your issue is just "cold feet" ( :) ), then the best solution would probably be some good thick laminate flooring on top of a good thick thermally isolating underlay pad.

Remembering that I'm not particularly in need of further sound isolation.

The way you describe it, you would not get an increase in isolation, but rather a reduction in isolation.

wasn't quite sure what to lay to stop standing waves under the floor & the floor itself resonating? Rockwool?

You can't stop standing waves: all you can do is damp them. Since they are modal in nature, and are due to the dimensions of the cavity, it is impossible to get rid of them. The only thing you can do is to damp them as much as possible. But that still won't solve the problems created by a light-weight floating floor. - Stuart -

Thanks for your reply, I'm taking that on. Ok - so I'll have to post some more details, and keep reading....but meanwhile, could someone please point me toward finding out how to mathematically calculate what the floor's resonant frequency would actually be? I'm searching madly.... And if anyone has great idea on how to 'cover' a concrete floor with a timber surface, for asthetic purposes, rather than build a chamber every foot with joists, I'd love some inspiration! Thanks Rob

Soundman2020 wrote:

If your issue is just "cold feet" ( :) ), then the best solution would probably be some good thick laminate flooring on top of a good thick thermally isolating underlay pad.

out of curiosity Stuart, would you describe 14mm thick bamboo laminate boards as 'Good' and 'Thick'? and also a 2mm underlay/vapour barrier as 'Thick'? That's the product I'm researching for my build.

out of curiosity Stuart, would you describe 14mm thick bamboo laminate boards as 'Good' and 'Thick'?

14mm laminate is pretty thick, yeah! Most laminate these days seems to be 8mm (cheap) or 10 mm (good). But I've never seen true laminate flooring made from bamboo: It is normally made from tightly engineered wood with a high quality and very tough photo-laminate, and the planks just "click" together. Are yours actually made of bamboo, or just have a bamboo look to them?

and also a 2mm underlay/vapour barrier as 'Thick'?

2mm underlay doesn't sound like enough, especially if your floor is very cold. Normal underlay is at least 1/8" (3mm) which is 50% thicker than the stuff you mention. I have also seen 5mm, but you should check with the manufacturer or your laminate to make sure you can use that. Some underlay has a moisture barrier built in, and some also has a "metalized" surface, to help with thermal insulation. I have never tried it myself, but some people recommend using a thick layer of cork glued to the subfloor. But whatever you choose to do, call the manufacturer of the actual laminate to make sure it is OK. You don't want an underlay that is either too hard or too soft, as both can lead to cracking and other issues as you walk on it. --

could someone please point me toward finding out how to mathematically calculate what the floor's resonant frequency would actually be? I'm searching madly....

Assuming that the solid outer floor is much more massive than the light-weight inner floor, and also well damped (concrete slab on grade fits that bill), then the simplified version of the equation can be used: Fmsm = 60 / ( SQRT (m * d)), where "m" is the surface density in kg/m2, and d is the depth of the cavity, in meters. If not, then you need the full version of the equation: Fmsm = 60*( SQRT ((m1 + m2) / (m1 * m2 * d ))) Both of those assume standard atmospheric conditions. If you want the version for absolutely any situation, it is:

And if anyone has great idea on how to 'cover' a concrete floor with a timber surface, for asthetic purposes, rather than build a chamber every foot with joists, I'd love some inspiration!

As above: laminate flooring is by far the easiest and most effective way to do it. OK, so maybe that's not really "timber", but modern laminates do a damn good job of looking like timber, and they do a pretty good job of isolating cold too, if done right. Another good option is proper parquet flooring, which can be laid directly on concrete. Other good alternatives to wood are ceramic tiles (but cold!) and linoleum (cheaper, also looks good, but not as good at thermal isolation as laminate. - Stuart -

Hi Stuart, The flooring that Steve is referring to (and has turned me onto), is reconstituted bamboo. It is then stained various colours for different tastes, applications etc. it clips together like other laminate products, and floats on top of an underlay/vapour barrier, which I assume could be matched to suit the application. See what you think: Product: Solid prefinished strand woven click lock Bamboo flooring Colour: Carbonised (coffee colour ) or Natural (blonde colour) Size: 14mm x 130mm x 1850mm Bamboo flooring: · The hardest and most environmentally friendly flooring · Premium A – grade flooring, the best quality in Australia · Best price in Australia · 14mm thick (not 10mm as other sellers are offering) · Prefinished with 9 coats of German polyurethane · Manufactured with German technology and precision Prefinished Strand woven click lock bamboo flooring · Strand woven bamboo flooring is the most eco-friendly and renewable source of material · Strand woven bamboo flooring is cheaper than traditional hardwood flooring · Strand woven bamboo flooring is cheaper than other types of sustainable flooring. · Strand woven bamboo flooring quality is at least equal to any other alternative flooring · Strand woven bamboo flooring has a Janka hardness greater than oak, ash, cherry and most other hardwood floors. · Strand woven bamboo flooring has a gentle grain and a natural appearance · Strand woven bamboo flooring is ideal for those people suffering from allergies and asthma. · Strand woven bamboo flooring is the healthiest flooring alternative on the market. · Strand woven bamboo flooring prevent dust mites, is antibacterial, antimicrobial and anti-fungal. UB Trading Pty Ltd · We sell only the best quality bamboo flooring, harvested and manufactured in an environmentally friendly and socially responsible way. · We sell only 14mm thick strand woven bamboo flooring offering much better strength than the 10mm thick flooring on offer. · We sell click lock system which is the easiest system to install, ideal for D.I.Y installation. · We sell our bamboo flooring at the best prices available on the market, there is no other supplier offering this product at a better price. · We sell bamboo flooring manufactured with the most up to date German technology available to ensure quality and precision · We offer prefinished bamboo flooring with 9 coats of German polyurethane · We offer 10 year warranty on our bamboo flooring · We offer installation services, or we can offer installation tips / advise. I've dropped the tongue n groove/joists concept completely.. So thanks for your input on that! Would be very interested to hear your thoughts on the bamboo floating floor! Cheers Robbie

Sounds like it should work fine! Seems to be the same general concept as ordinary laminated flooring, and acoustically it should work the same, since the top surface is hard, solid, reflective, etc. As long as there are no air cavities in the underlay, then you'd be fine with that stuff. - Stuart -