decoupled wooden floor

hello all, Long time lurker here. Grate site and forum, I have learnt so much ever since i discovered it, thanks! I am currently converting a shed at the bottom of my garden into a mixing/recording room. The existing structure is a rectangular timber (4x2) sub structure sitting on 8 concrete blocks which in turn sit on top of 8 concrete footings. On top of this rectangular base frame the existing shed walls are built. I'm adding mas between the studs and building a proper door frame and door with seals, and plan to build decoupled stud celing and walls inside. My big question however regards the floor. As i understand it, the earth is good at damping, as is sand, and sand is easy to level, so my thoughts thus far are to lay a damp proof membrane, extend the existing 2x4 frame downwards sandwhiching the membrane with the earth. Then lay and tamp some sand on top of the mr membrane, inside the shed. I then plan to lay boards on top of this sand to create a decoupled floor upon which my inner walls can be constructed. (boards will be a layer of 18mm ply, chip and then mdf all loose tongued at joints) Does this sound reasonable, or am i barking up the wrong tree? Any input would be grately appreciated by both me and my wallet! (before i spend money doing something stupid!) Many thanks in advance for any help you can offer tom ugli

Hi, Tom, and welcome! Personally, I think it would be just as easy to pour a concrete slab, and leave it like that. Probably not much more expensive, either. IMHO - Stuart -

Thankyou for the quick reply and the welcome! Would the there be an enormous acoustic benefit from pouring a slab when compared next to the wall construction which will be 1osb and 2 drywall 100mm air gap 2 drywall. We were hoping to steer clear of pouring a slab if we could. My predicament is that the boards are free because they come in as cover boards at work, and generally go straight in the skip!!! I know what a waste! I would seriousely reccomend that anyone making anything like Helm Holtz resonators or anything really requiring sheet material find a local joiner's shop and nip down and ask for off cuts because we throw so much away that'd find a million uses in many home studio projects! cheers, tom

Hey, Tom. I'm sure you'll find PLENTY of uses for free boards in the acoustic treatment of your room! Especially if you decide to go with John's slot wall design: Those are all boards... :) You can still lay wooden flooring if you want, but the advantage of a concrete slab is that it makes a great acoustic floor just like it is, nothing else needed. Anything you put on top of it means that you have less room height, and height is your friend, for acoustics. Besides, dealing with sand isn't fun: it has to be dry sand, carefully leveled, and well contained. But if you add a bit of cement power and some water to it, then it behaves a lot better. :) Seriously, some folks here have done sand-filled floors, but personally I don't think I'd want the hassle. Pouring concrete is so much easier, and gives you a great surface that you can use exactly as it is. - Stuart -

You're swaying me i must admit! :) To put my mind wanderings to rest, do you think there is a vast difference between these two methods in terms of the isolation levels i would achieve? perhaps it's off to wickes for some ballast and cement at the weekend!

Agreed on the concrete floor. If you were to pursue the wood floor (people did that for hundreds if not thousands of years), you will want to put in some moisture barrier and interlock the boards, panels so they are stable. You would not use this to support an inner isolation wall because it's likely a building code violation.

To put my mind wanderings to rest, do you think there is a vast difference between these two methods in terms of the isolation levels i would achieve?

Probably not much in it, in terms of isolation. The overall mass would be similar (ballpark), and they would both be damped by the entire planet. Of course, that's assuming you can get the sand to stay level, not settle, and not leave voids under the wood... :) Plus, like Glenn said. with concrete you can stand your walls on it without a hassle, but not with wood-on-sand... Convinced yet ? :) But I'd say don't start laying any concrete until you have a total plan well worked out! You can so useful stuff with concrete, such as embed cable ducts and wall anchors in it, and shape it, and pour it in sections to improve isolation (separate for walls/floor, and especially if you have two rooms). Get your entire plan together first, before you pour. - Stuart -

cheers for the input chaps!